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Incorporating subsurface-flow mechanism into geomorphology-based IUH modeling
Abstract
Surface- and subsurface-runoff processes on hillslopes are quite different in nature; nevertheless, the geomorphological instantaneous unit hydrograph (GIUH) simulates runoff using only the surface-flow mechanism. In this study, the GIUH model was revised to consider both the surface- and subsurface-flow processes. Kinematic-wave approximation was used to estimate the mean value of the travel-time probability distributions for runoff in surface-flow regions and channels, and Darcy's law was adopted to estimate the runoff travel time in subsurface-flow regions. Based on the linear system assumption, the hydrologic response of a watershed is the superposition of the hydrologic responses resulting from the surface flow and subsurface flow of the watershed. The IUH can adequately reflect the variation of surface-flow roughness and hydraulic conductivity. An example watershed was selected to test the capability of the revised model. The simulated hydrographs obtained using the original and revised models were basically in good agreement with the observed hydrographs. However, significant improvement of the simulation was found in the recession limb of the simulated hydrograph because flood recession was dominated by the subsurface-flow process.
... The slope variations directly affect the water speed travel (in advance and recession), the hypsometric curve, the hydrographs, the flood peak times, the soil erosion, and consequently the runoff estimates and the flow design that support the waterworks safety. At the sub-basin scale, the effects of slopes on hillsides and channels propagate in surface and subsurface runoff [21,28,87,88]. ...
... Achieving the highest accuracy in quantifying the watershed area is vital since it influences the estimates of most theoretical hydrological models. Wooding [93] and Lee [87] referred to the direct influence of the area in hydrological investigations. Similarly, dos Santos and Fewtrell expressed that the discrepancies in the watershed area impact simulations for estimating rainwater and sediment distribution. ...
... Variations imply that the number of sub-basins is different in each scenario, including the geomorphometric characteristics of each one. In investigations of non-urban watersheds where the unit of analysis is the sub-basin for estimates of water travel times (e.g., [21,28,29,87,88,94]), it is logical that the results are affected by the DEM resolution and also for the algorithms of the hydrological processing used. Similarly, the unit base for estimations in urban flood assessment studies is the sub-basin [37,95]. ...
Hydrological cycle research requires a detailed analysis of the involved parameters to understand watershed behavior comprehensively. In recent decades, both Geographic Information Systems (GIS) and Digital Elevation Models (DEMs) were implemented and took a substantial role in watershed geomorphological parameterization; however, the variability of these instruments remains a challenge, together with high-resolution DEMs being unavailable, requiring digital processing to improve resolution. This research aims to merge DEMs and evaluate GIS geoprocessing algorithms to determine drainage networks and the geomorphological parametrization of a semiarid watershed. DEMs with resolutions of 1.5, 5, 12.5, and 30 m, the Jenson/Domingue (J/D) and Wang/Liu (W/L) fill algorithms; and D8, D, KRA, and MFD flow routing algorithms were used. One of the research findings proved that the divergences of the drainage networks are mainly attributed to filling algorithms and not flow routing algorithms; the shifts between the networks obtained in the processes reach horizontal distances up to 300 m. Since the water movement within the watershed depends on geomorphological characteristics, it is suggested that DEM-based hydrological studies specify both the resolution and the algorithms used in the parametrization to validate the rigidity of the research, improving estimate areas of high hydrological risk.
... The concept of partial contributing area (PCA) was proposed to approximately delineate the saturated region having a high groundwater table within a watershed, on which surface runoff generates immediately after receiving precipitation. To introduce the subsurfaceflow mechanism in a geomorphology-based IUH model, Lee and Chang (2005) proposed an interesting issue, utilizing the ratio of PCA to separate the watershed area into the surface-and subsurface-runoff zones. In their method, kinematic-wave approximation was adopted to estimate the probability distributions of travel time for surface runoff and channel flow in saturated areas; Darcy's law was used to calculate the travel time of subsurface flow in hillside fields. ...
... where P E (τ) is the effective precipitation intensity at the time step τ; u(P E , t − τ) is the instantaneous unit hydrograph depending on the timevarying effective precipitation intensity. As shown in Fig. 1, by assuming that a watershed has a dendritic stream network with Ω order and its entire drainage area can be separated into the unsaturated subsurfaceflow region (in upper slopes) and saturated surface-flow region (near streams), the IUH at a designated location can be calculated by Lee and Chang (2005) ...
... where η denotes the soil porosity; K u denotes the hydraulic conductivity of upper soil; L subi and S subi denote the mean length and slope of the ithorder subsurface-flow region respectively. In this study, the mean length of the ith-order surface-flow region is assumed as (Lee and Chang, 2005) L suri = R PCA (t)⋅L subi (9) Green and Ampt (1911) applied Darcy's law to establish a simple model for simulating water infiltration into a homogeneous soil with uniform initial moisture content. Mein and Larson (1973) extended the Green and Ampt model to estimate the time when surface ponding begins under steady rainfall conditions. ...
... In recent years, the digital elevation dataset and all types of hydrological tools with open source are becoming easier to acquire; this prompts the extensive utilization of hydrological models or associated routing systems [13][14][15][16][17][18][19][20][21][22][23]. As a result, hydrologists are not only concerned about the extraction of topographic characteristics from a watershed, but also the influences of using different flow direction methods on the surface runoff simulation. ...
... The R 2 coefficients for the above two regression equations are 0.817 and 0.7943 respectively, this demonstrates that approximately 80 percent of DT can be described by the variance of flow dispersion area (AD) according to these two regression models shown in Equations (17) and (18). ...
... The R 2 coefficients for the above two regression equations are 0.817 and 0.7943 respectively, this demonstrates that approximately 80 percent of DT can be described by the variance of flow dispersion area (A D ) according to these two regression models shown in Equations (17) and (18). ...
Different approaches for flow-direction determination have been continuously proposed to perform a more realistic simulation of surface runoff, yet the diversity of the existing methods causes significant differences in the extractions of geomorphic parameters as well as the results of rainfall-runoff simulations. In this study, the three most widely used flow-direction methods were separately applied in hydrological models to thoroughly investigate their effects on the simulation output. The results show that the drainage area is a significant factor that affects not only the flow-collecting ability but also the time to peak discharge; however, the definition and calculation of the drainage area become different when the consideration of multiple flow directions is involved in a terrain analysis. This study adopted two area indexes, flow concentration area and flow dispersion area, to understand their consequences in the aspects of the flow volume of simulated hydrograph and the delay of time to peak discharge. The multiple-flow-direction methods show the later time to flow peak and less amount of outflow volume in comparison with the single flow-direction method. By merely extracting two area indexes, a transformation approach is suggested to predict hydrograph shape and to quantify the extent of hydrograph deviations induced by using different flow-direction methods.
... It integrates numerous watershed geomorphologic factors for the derivation of instantaneous unit hydrographs (IUHs) under different effective rainfall conditions without the need for flow discharge observations Yen and Lee 1997). Lee and Chang (2005) extended the framework of the KW-GIUH model to further integrate the subsurface-flow mechanism. In recent years, the KW-GIUH model has been successfully implemented for rainfall-runoff simulation (Shadeed et al. 2007;Lee et al. 2008;Cao et al. 2010) and other applications (Wang and Tung 2006;Lee et al. 2009;Lee and Yang 2010;Arekhi et al. 2011). ...
... Because the rapid runoff response is sensitive to the initial moisture conditions of a watershed (Da Ros and Borga 1997;Norbiato et al. 2008;Berthet et al. 2009), the current precipitation index (CPI) was applied in this study to quantify the soil moisture status and to recommend an initial infiltration rate for determining the effective rainfall. In addition, the KW-GIUH model in Lee and Chang (2005) employed a constant partial contributing area (PCA) ratio throughout the entire storm duration to separate direct runoff into surfaceflow and subsurface-flow components. Although using a constant PCA ratio is convenient for model operation, it is difficult to give an adequate estimation for the PCA ratio before the occurrence of the storm. ...
... For a raindrop falling in the upper region of a watershed with unsaturated soil, it will infiltrate into the soil and move to the stream network as subsurface flow. Furthermore, a travel-time probability density function is used in the KW-GIUH model to describe the time required for a raindrop to adopt a specified flow path (Lee and Chang 2005). ...
Typhoons and heavy storms frequently cause severe inundation in Taiwan. For early flood warning purposes, a real-time flood forecasting system was acknowledged as a pivotal tool and developed in this study. The system integrates four parts: (1) a gray-based rainfall prediction model, (2) the antecedent hydrological condition estimation method, (3) a deterministic runoff model, and (4) a runoff updating algorithm. The developed system was applied to the Hsia-Yun watershed in Taiwan. The time-invariant parameters, which characterize terrain features, were calibrated in advance. Additionally the time-variant parameters were modeled to change with temporal hydrological condition of the watershed. The gray theory was performed to predict the rainfall intensity in the next 1–3 h, which thus enables the runoff model to forecast incoming runoff in the next 1–3 h. By consulting the real-time feedback flow observation, a runoff updating algorithm was adopted and was helpful in improving the performance of the simulated hydrographs. In real-time application, the system can be initiated or terminated by detecting if the cumulative rainfall depth is larger or less than a predefined threshold value. The idea of the developed system has recently been constructed with a visual interface for real-time flood forecasting by authorities. The overall results confirm that the developed system is competent to forecast flash floods.
... It integrates numerous watershed geomorphologic factors for the derivation of instantaneous unit hydrographs (IUHs) under different effective rainfall conditions without the need for flow discharge observations Yen and Lee 1997). Lee and Chang (2005) extended the framework of the KW-GIUH model to further integrate the subsurface-flow mechanism. In recent years, the KW-GIUH model has been successfully implemented for rainfall-runoff simulation (Shadeed et al. 2007;Lee et al. 2008;Cao et al. 2010) and other applications (Wang and Tung 2006;Lee et al. 2009;Lee and Yang 2010;Arekhi et al. 2011). ...
... Because the rapid runoff response is sensitive to the initial moisture conditions of a watershed (Da Ros and Borga 1997;Norbiato et al. 2008;Berthet et al. 2009), the current precipitation index (CPI) was applied in this study to quantify the soil moisture status and to recommend an initial infiltration rate for determining the effective rainfall. In addition, the KW-GIUH model in Lee and Chang (2005) employed a constant partial contributing area (PCA) ratio throughout the entire storm duration to separate direct runoff into surfaceflow and subsurface-flow components. Although using a constant PCA ratio is convenient for model operation, it is difficult to give an adequate estimation for the PCA ratio before the occurrence of the storm. ...
... For a raindrop falling in the upper region of a watershed with unsaturated soil, it will infiltrate into the soil and move to the stream network as subsurface flow. Furthermore, a travel-time probability density function is used in the KW-GIUH model to describe the time required for a raindrop to adopt a specified flow path (Lee and Chang 2005). ...
Due to the steep topography and concentrated rainfall intensity, tremendous disasters frequently occur in Taiwan. If accurate information about future rainfall and floods could be provided to the work of disaster prevention and mitigation, the loss of life and property would be reduced. Therefore, Taiwan Typhoon and Flood Research Institute, which belonged to the National Applied Research Laboratories, cooperates with academic and research institutions to perform Taiwan Cooperative Precipitation Ensemble Forecast Experiment (TAPEX) for providing typhoon rainfall forecasts to disaster prevention agencies. However, at present time, 1- to 6-h ahead rainfall forecasts from TAPEX are with highly uncertainty. It is necessary to improve the accuracy of rainfall forecasts provided by TAPEX for hydrologic forecasting. In this study, we first adopted a rainfall characteristic analog methodology to yield the improved 1- to 6-h ahead rainfall forecasts. Then, these rainfall forecasts are used as inputs to a geomorphology-based rainfall-runoff model combined with an updating scheme to generate the 1- to 6-h ahead flow forecasts. These real-time rainfall and runoff forecasting techniques are actually applied to the Cho-Shui River basin. For rainfall forecasting, the results show that by applying the rainfall characteristic analog methodology on the 1- to 6-h ahead rainfall forecasts from TAPEX, the forecasting uncertainty is reduced and the performance is improved. As to runoff forecasting, the geomorphology-based rainfall-runoff model combined with an updating scheme is applied to the Pao-Shih Bridge, the Lung-Men Bridge, and the Yen-Ping Bridge watersheds in the Cho-Shui River basin. The results indicate that the rainfall-runoff model can provide reasonable hydrograph forecasting, and both the forecasted and recorded hydrographs are in good agreement in the study watersheds. It is therefore considered promising to apply the proposed real-time rainfall and runoff forecasting techniques for accurate rainfall and runoff forecasts to disaster prevention agencies to reduce the loss of life and property.
... Nash 1957;Rodriguez-Iturbe and Valdes 1979;Gupta et al. 1980;Lee and Yen 1997;Hsieh and Wang 1999). A geomorphological instantaneous unit hydrograph (GIUH) model has been applied to consider both the SF and SSF processes by Lee and Chang (2005). This model is based on the travel-time probability distribution for runoff in SF and SSF regions and streams. ...
... This model is based on the travel-time probability distribution for runoff in SF and SSF regions and streams. Recently, Sabzevari et al. (2013a) revised the GIUH model already presented by Lee and Chang (2005). The GIUH model was employed to predict the SFs and the SFs in the Kasilian catchment, Iran; however, they did not take the hillslope geometry into account. ...
... The influence of excess rainfall on response time as well as on the IUH has been verified by many researchers. Lee and Chang (2005) used the equation T 0 ¼ fL=K s S to calculate the SSF travel time. Recharge rate was not incorporated in this equation and has no effect upon any other parameter. ...
Dividing a catchment to subcatchment or hillslope scales allows for better scrutiny of the changes in spatial distribution of rainfall, soil attributes and plant cover across the catchment. An instantaneous unit hydrograph model is suggested for simulating runoff hydrographs for complex hillslopes. This model is able to estimate surface and subsurface flows of the catchment based on the Dunne-Black mechanism. For this purpose, a saturation model is used to separate the saturated and unsaturated zones in complex hillslopes. The profile curvatures (concave, straight and convex) and plan shapes (convergent, parallel and divergent) of complex hillslopes are considered, in order to compute the travel time of surface and subsurface flows. The model was used for prediction of the direct runoff hydrograph and subsurface flow hydrograph of Walnut Gulch No. 125 catchment in Arizona (USA). Based on results, the geometry of hillslopes can change the peak of the direct runoff hydrograph up to two-fold, either higher or lower. The divergent hillslopes show higher peaks in comparison with the parallel and convergent hillslopes. The highest and lowest peak flows correspond to divergent-concave and convergent-straight hillslopes, respectively.
... Nash 1957;Rodriguez-Iturbe and Valdes 1979;Gupta et al. 1980;Lee and Yen 1997;Hsieh and Wang 1999). A geomorphological instantaneous unit hydrograph (GIUH) model has been applied to consider both the SF and SSF processes by Lee and Chang (2005). This model is based on the travel-time probability distribution for runoff in SF and SSF regions and streams. ...
... This model is based on the travel-time probability distribution for runoff in SF and SSF regions and streams. Recently, Sabzevari et al. (2013a) revised the GIUH model already presented by Lee and Chang (2005). The GIUH model was employed to predict the SFs and the SFs in the Kasilian catchment, Iran; however, they did not take the hillslope geometry into account. ...
... The influence of excess rainfall on response time as well as on the IUH has been verified by many researchers. Lee and Chang (2005) used the equation T 0 ¼ fL=K s S to calculate the SSF travel time. Recharge rate was not incorporated in this equation and has no effect upon any other parameter. ...
Dividing a catchment to subcatchment or hillslope scales allows for better scrutiny of the changes in spatial distribution of rainfall, soil attributes and plant cover across the catchment. An instantaneous unit hydrograph model is suggested for simulating runoff hydrographs for complex hillslopes. This model is able to estimate surface and subsurface flows of the catchment based on the Dunne-Black mechanism. For this purpose, a saturation model is used to separate the saturated and unsaturated zones in complex hillslopes. The profile curvatures (concave, straight and convex) and plan shapes (convergent, parallel and divergent) of complex hillslopes are considered, in order to compute the travel time of surface and subsurface flows. The model was used for prediction of the direct runoff hydrograph and subsurface flow hydrograph of Walnut Gulch No. 125 catchment in Arizona (USA). Based on results, the geometry of hillslopes can change the peak of the direct runoff hydrograph up to two-fold, either higher or lower. The divergent hillslopes show higher peaks in comparison with the parallel and convergent hillslopes. The highest and lowest peak flows correspond to divergent-concave and convergent-straight hillslopes, respectively.
... They have been proposed to estimate floods for ungauged streams by using the information obtainable from topographic maps or remote sensing possibly linked with the 82 Geographic Information Systems (GIS) and Digital Elevation Models (DEM) (Snell and Sivapalan, 1994;Jain et al., 2000;and Hall et al., 2001). Lee and Chang (2005) reviewed the development of GIUH approach and concluded that the significant advance in research on the topographic runoff approaches was the development of the geomorphologic instantaneous unit hydrograph model (GIUH) proposed by Rodriguez-Iturbe and Valdes (1979). During the last two decades, the use of catchment geomorphologic characteristics in runoff simulations has received a great deal of attention from hydrologists (e.g. ...
... Overland flow over a permeable soil surface can occur when the rainfall rate is greater than the infiltration capacity or when surface saturation exists in regions near the stream (Lee and Chang, 2005). ...
... The second part of equation (25) (Lee and Chang, 2005) The distribution function bound is set to be from 0 to 2 k x T because the definition of the mean travel time. Substituting in the previous equation, the IUH can be expressed analytically as: The coefficients are determined by comparing coefficients in partial fractions after applying the Laplace transformation. ...
... Recently, the GIUH model has been applied to consider both the surface and the subsurface flow processes by Lee and Chang (2005). This model is based on the travel time probability distributions for run-off in surface flow and subsurface flow regions and channels. ...
... Dunne and Black, 1970;Dunne, 1978;Mosely, 1979;Eshleman et al., 1993;Fujieda et al., 1997). Lee and Chang (2005) developed a GIUH model based on the Dunne-Black mechanism to predict hydrographs of catchment subsurface flow. The main point in their method was the separation of saturated and unsaturated zones in the overlands. ...
... The surface and subsurface flows were considered in the saturated zone and the whole overland, respectively. The travel time equation for the subsurface flow used by Lee and Chang (2005) depends on soil porosity, the soil hydraulic conductivity, and the length and slope of the hillslope, and it is independent of the rainfall recharge rate into the soil and soil thickness. They have applied no systematic theory to separate the saturated zone from the unsaturated zone, considering the saturated zone length (SZL) is a constant percentage of the overland length (i.e. ...
Flood estimation in ungauged catchments is one of the important points in designing hydraulic structures. In this paper, the geomorphological instantane-ous unit hydrograph (GIUH) model previously suggested by Lee and Chang to estimate the surface and subsurface hydrographs of catchments was extended. To improve the model, a new equation was presented based on the Dunne–Black mechanism for separating the overland into saturated and unsaturated zones. Two new factors, soil thickness and rainfall recharge rate, were taken into account in calculations of the saturation zone length, and the travel times of surface and subsurface flows. The effect of saturation upon subsurface flow travel time was regarded in the GIUH model. The convolution equation for the estimation of the direct run-off hydrograph (DRH) was improved according to the response of subsurface flow to rainfall recharge, and the response of surface flow to excess rainfall. The final model was employed to predict the surface and subsurface flows in the Kasilian catchment. The performance of the GIUH was found to be more effective, as reflected in lower root mean square error (1.24 m 3 /s) and relative mean absolute error (0.07). The average error was 8.78% to estimate the flood peak. In general, the efficiency of the model in the esti-mation of DRH was assessed as proper.
... Although complex process-based models may be useful in research, models used for management decisions should be simple and with few data requirements (Grayson et al., 1992). Consequently, instead of constructing a fully-distributed model, Lee and Chang (2005) developed a semi-distributed model for realtime flood forecasting in a computationally efficient way. They incorporated subsurface-flow mechanism with the partial contributing area ratio into a kinematic-wave-based geomorphologic instantaneous unit hydrograph model (KW-GIUH), and the spatial patterns of partial contributing area were then determined by using a topographic-index threshold (Chang and Lee, 2008), but the temporal variation of PCA regions during a storm was not clearly mentioned. ...
... In considering computational efficiency, a semidistributed model was developed. The framework of the model was based on the KW-GIUH model proposed by Lee and Chang (2005) and it was further modified for the purpose of present study. The time-varying PCA ratio was estimated according to the hourly current precipitation index (CPI) (Smakhtin and Masse, 2000), and then an exponential transformation was adopted to correlate the CPI and the PCA ratio of the watershed during storms. ...
... Instead, a semi-distributed model for computational efficiency was adopted in the present study. The framework of the model was based on the kinematic-wave-based geomorphologic instantaneous unit hydrograph model (KW-GIUH; Lee and Chang, 2005) and further modified to include a time-varying PCA function. ...
... This paper presents one of the scenarios of such a development, the model of geomorphological instantaneous unit hydrograph, based on the kinematic wave equation (KW-GIUH). It was developed by К. Т. Lee and collaborators [7][8][9][10] and is used in calculating and forecasting floods in Taiwan. It is anticipate that this model assumes the influence of the basin's geomorphology, vegetation cover, soil characteristics and intensity of atmospheric precipitation on runoff-formation. ...
... The probability P x i x j of the transition x i → x j is determined by the formula: , (7) where N i, j stands for the number of i-th order streams falling into the j-th order streams. The probability P oA i is calculated by the formula , (8) where A is the catchment area at the closing site. ...
... Usually, the width of the river increases proportionately with an increase in its order. Based on this assumption, for calculating B i the following linear dependence was suggested [7,8]: ...
We examine the concept, the structure and the main algorithms of the model for a geomorphological instantaneous unit hydrograph based on the kinematic wave equation. The model has been developed and is successfully implemented in calculations and forecasts of rain-induced floods on Taiwan. We present the results from its comparative testing on small catchments of Taiwan and Russia (Primorski Krai) made to verify the validity of the model in the region with substantially differing conditions. The limitations of the model and the prospects of its perfection are discussed.
... The purpose of this study is to introduce this new approach by combining a series of synthetic and real-case experiments as recently supported by the hydrological community (e.g., Lee and Chang, 2005;Sulis et al., 2010;Kim et al., 2012;Clark et al., 2015). It is beyond the scope of this study to test the JULES model using the single column experiment under several different combinations of factors. ...
... The use of synthetic experiments to test a new model is a common approach (e.g.,Kim et al., 2012;Lee and Chang, 2005;Sulis et al., 2010;Clark et al., 2015) that allows to control better the variables and the forcing. In this work, we reproduce the same synthetic cases used inRahman et al. (2019) and inKollet et al. (2017) in order to compare the new JULES-GFB model with a widely used hydrological model (ParFlow), used as benchmark in this work. ...
... In recent years, the IUH model has been generalized with the aim of considering both surface and subsurface flow processes. Lee and Chang (2005) developed a GIUH model following the Dunne-Black mechanism, where the main point was the separation of saturated and unsaturated zones in the hillslopes according to the topographic wetness index (TWI). Sabzevari et al. (2010) investigated the saturation rate of complex hillslopes by considering the effects of their shape and geometry. ...
... In conclusion, the direct runoff seems more likely to be seen as a combination between the surface and subsurface flow processes. In the following, this approach is adopted, starting from the theory of Lee and Chang (2005) and making the hypothesis that the gross rainfall can be divided in two parts. The excess rainfall, that is responsible for the "fast" response of the watershed, and the infiltration, that is responsible for the "slow" response of the watershed. ...
Rainfall–runoff modelling has always been of great importance in hydrology. Recently, the Event-Based Approach for Small and Ungauged Basins (EBA4SUB) model, based on the instantaneous unit hydrograph (IUH) formulation, was released. The EBA4SUB model was originally developed considering only the surface flow, and in this work it has been generalized considering also the subsurface flow. The aim is to make EBA4SUB applicable both for Hortonian and/or for Dunne-Black mechanisms, proposing the so-called Generalized EBA4SUB model (GEBA4SUB). Here, GEBA4SUB and EBA4SUB are compared at the event scale, using observed rainfall–runoff events, and in estimating design discharge, using extreme value observations. In both cases, the results suggest that GEBA4SUB could outperform EBA4SUB, with improvements from 15% to over 100%.
... The geomorphologic instantaneous unit hydrograph (GIUH) model currently has a huge number of applications in the estimation of the surface runoff of ungauged catchments (Sabzevari 2017;Sahoo 2006;Kumar et al. 2007;Ghavidelfar et al. 2011). Lee and Chang (2005) developed the GIUH model for the prediction of subsurface runoff of an ungauged catchment, in which the kinematic wave approximation was used to estimate the mean value of the travel-time probability distributions for runoff in surface-flow regions and channels, and Darcy's law was adopted to estimate the runoff travel time in subsurface-flow regions. ...
... where t c is the time taken for the subsurface water to reach the designated downstream point from the designated upstream point (Lee and Chang 2005;Sabzevari et al. 2010;Aryal et al. 2005). ...
Prediction of subsurface flow (SF) in hillslopes is more complicated than prediction of surface flow; hence, a simple and practical SF model would interest hydrogeologists. For the first time, the time-area method is employed to estimate the SF of hillslopes. The locations of the isochrone curves for complex hillslopes were determined using SF travel-time equations. Some equations were developed to delineate the isochrones and the subsurface time area (STA). The analytic equations suggested by the characteristics method of solving a hillslope-storage kinematic wave were used for validation of the STA method results in complex hillslopes. The average values of the coefficient of efficiency (CE), correlation coefficient (R), error of peak flow (EPF) and root-mean-square error (RMSE) of the STA method for the nine defined hillslopes are, respectively, 0.96, 0.96, 1.35, and 0.076. To further verify the results, a laboratory rainfall simulator with sandy loam soil was employed, which was conditioned under artificial rainfall intensities of 31.7, 4.6 and 63.46 mm/hr, and slopes of 3°, 6° and 9°. The STA model results were compared with those of a laboratory model of subsurface flow. The average values of CE, R, EPF and RMSE of the STA method for the nine events are, respectively, 0.81, 0.85, 0.98, and 0.017, which are regarded as good values. For the final evaluation of the STA model, the subsurface flow rates obtained from the Richards’ equation using HYDRUS were also used. The proposed STA model has good agreement with the results of the laboratory and HYDRUS models.
... They also used the ANNbased geomorphologic model developed by [22] for surface and subsurface flow simulation in Heng-Chi watershed in Taiwan [23]. The results of this model were also compared with ones obtained using GIUH model developed by [24] based on kinematic-wave approximation and Darcy's law. The authors suggested that the ANN model showed better performance than GIUH model in terms of time to peak and peak flow estimation. ...
... ., x˝} with total number of N(w s ), P(w s ) is the probability of the surface flow adopting path w s . The probability of P(w s ) is defined by [24] as follows: ...
In spite of the efficiency of the Artificial Neural Networks (ANNs) for modeling nonlinear and complicated rainfall-runoff (R-R) process, they suffer from some drawbacks. Support Vector Regression (SVR) model has appeared to be a powerful alternative to reduce some of these drawbacks while retaining many strengths of ANNs. In this paper, to form a new rainfall-runoff model called SVR-GANN, a SVR model is combined with a geomorphologic-based ANN model. The GANN is a three-layer perceptron model, in which the number of hidden neurons is equal to the number of possible flow paths within a watershed and the connection weights between hidden layer and output layer are specified by flow path probabilities which are not updated during the training process. The capabilities of the proposed SVR-GANN model in simulating the daily runoff is investigated in a case study of three sub-basins located in a semi-arid region in Iran. The results of the proposed model are compared with those of ANN-based back propagation algorithm (ANN-BP), traditional SVR, ANN-based genetic algorithm (ANN-GA), adaptive neuro-fuzzy inference system (ANFIS), and GANN from the standpoints of parsimony, equifinality, robustness, reliability, computational time, simulation of hydrograph ordinates (peak flow, time to peak, and runoff volume) and also saving the main statistics of the observed data. The results show that prediction accuracy of the SVR-GANN model is usually better than those of ANN-based models and the proposed model can be applied as a promising, reliable, and robust prediction tool for rainfall-runoff modeling.
... For large catchments, however, soil properties and land cover become very important in addition to geomorphological and climatic conditions. There are recent attempts (e.g., Lee and Chang 2005;Babaali et al. 2021) to incorporate subsurface flow into a GIUH model so that the effects of land cover and soil properties on infiltration is reflected in the developed hydrographs. ...
Runoff data is crucial for development of water resources. Runoff data is however rarely available for ungauged catchments, especially in developing countries. Geomorphological instantaneous unit hydrographs (GIUH) models can be used for predicting runoff in poorly gauged catchments, but a challenge with these models is estimating the dynamic velocity parameter. In this study, three GIUH models were developed based on estimation of flow velocity using calibration of Manning’s n (GIUH-cal), peak discharge (GIUH-pq) and 30-min rain intensity (GIUH-I30). The objectives of this study were to (a) assess suitability of a GIUH model for simulating runoff in Gule catchment, northern Ethiopia and (b) evaluate performance of three velocity parameter estimation methods in simulating runoff using GIUH models. Runoff hydrographs of the GIUH models matched well with observed hygrographs for most rain events. The GIUH-cal model had the best performance, 18 out of 20 rain events resulting in Nash–Sutcliffe model efficiency (NSE) values of 0.53 to 0.95. The GIUH-pq and GIUH-I30 models performed satisfactorily with 12 of the 20 rain events resulting in NSE values greater than 0.50. Overall, the GIUH models underestimated peak discharge compared to observed data. The GIUH models were moderately sensitive to changes in flow velocity. Peak discharge and time to peak discharge were highly sensitive to changes in flow velocity. The developed GIUH models could be used for simulating flood hydrographs of the Gule catchment. Particularly, the GIUH-I30 model will be very useful for estimating direct surface runoff in the absence of streamflow data.
... This geomorphological information is used in GIUH models (e.g. Gupta et al. 1980;Rodriguez-Iturbe et al. 1982a, b;Yen and Lee 1997;Lee and Chang 2005;Sahoo et al. 2006;Sabzevari et al. 2013;Sabzevari and Noroozpour 2014;Chen et al. 2019). The GIUH model was suggested by Rodríguez-Iturbe and Valdes (1979) and Gupta et al. (1980). ...
Estimation of rainfall-runoff model parameters in ungauged catchments is of significant importance. The Nash geomorphological instantaneous unit hydrograph (NGIUH) model is widely used to predict runoff in ungauged catchments. The NGIUH model parameters are estimated based on the stream network delineation of the catchment to obtain the stream-order-law ratios. Different methods have been presented to delineate stream networks of catchments based on topographic maps and satellite images using remote sensing (RS) and geographic information system (GIS). In this study, the fractal dimension of the stream network (D) and the fractal dimension of the main river (d) were calculated by wavelet image processing of the stream network images. Shearlet transform was applied to compute the bifurcation ratio (RB). New equations were proposed to estimate the NGIUH parameters based on the fractal analysis of the river network and main river length. The proposed approach was evaluated by computing the flood hydrographs in three catchments of Kasilian, Galazchai and Heng-Chi. Based on results, coefficients of efficiency (CE) were 0.42 and 0.96. The errors in peak discharge estimation were in an acceptable range 0.93–12.91%.
... The purpose of this study is to introduce this new approach by combining a series of synthetic and real-case experiments as recently supported by the hydrological community (e.g., Lee and Chang, 2005;Sulis et al., 2010;Kim et al., 2012;Clark et al., 2015). It is beyond the scope of this study to test the JULES model using the single column experiment under several different combinations of factors. ...
Groundwater is an important component of the hydrological cycle with significant interactions with soil hydrological processes. Recent studies have demonstrated that incorporating groundwater hydrology in Land Surface Models (LSMs) considerably improves the prediction of the partitioning of water components (e.g., runoff and evapotranspiration) at the land surface. However, the Joint UK Land Environment Simulator (JULES), an LSM developed in the United Kingdom, does not yet have an explicit representation of groundwater. We propose an implementation of a simplified Groundwater Flow Boundary parameterization (JULES‐GFB) which replaces the original Free Drainage assumption in the default model (JULES‐FD). We tested the two approaches under a controlled environment for various soil types using two synthetic experiments: (1) single‐column, and (2) tilted‐V catchment, using a three‐dimensional hydrological model (ParFlow) as a benchmark for JULES’ performance. In addition, we applied our new JULES‐GFB model to a regional domain in the UK, where groundwater is the key element for runoff generation. In the single‐column infiltration experiment, JULES‐GFB showed improved soil moisture dynamics in comparison to JULES‐FD, for almost all soil types (except coarse soils) under a variety of initial water table depths. In the tilted‐V catchment experiment, JULES‐GFB successfully represented the dynamics and the magnitude of saturated and unsaturated storage against the benchmark. The lateral water flow produced by JULES‐GFB was about 50% of what was produced by the benchmark, while JULES‐FD completely ignores this process. In the regional domain application, the Kling‐Gupta efficiency (KGE) for the total runoff simulation showed an average improvement from 0.25 for JULES‐FD to 0.75 for JULES‐GFB. The mean bias of actual evapotranspiration relative to the Global Land Evaporation Amsterdam Model (GLEAM) product was improved from −0.22 mm day−1 to −0.01 mm day−1. Our new JULES‐GFB implementation provides an opportunity to better understand the interactions between the subsurface and land surface processes that are dominated by groundwater hydrology. This article is protected by copyright. All rights reserved.
... In 1940, Kirpich [35] deduced an empirical formula of the travel time t c (min) by using the hydrologic data record in six agriculture catchments: (20) where means the average slope of the drainage area and computed by: Three flood events in each catchment are selected to calculate the average i e and the corresponding v of each isolated flood event with the method (I). While in the method (II), it demonstrates that v is independent on the rainfall, but the geomorphologic characteristic value and the value of v is computed to be as a constant in every basin. ...
The geomorphologic instantaneous unit hydrograph (GIUH) is an applicable approach that simulates the runoff for the ungauged basins. The nash model is an efficient tool to derive the unit hydrograph (UH), which only requires two items, including the indices n and k. Theoretically, the GIUH method describes the process of a droplet flowing from which it falls on to the basin outlet, only covering the flow concentration process. The traditional technique for flood estimation using GIUH method always uses the effective rainfall, which is empirically obtained and scant of accuracy, and then calculates the convolution of the effective rainfall and GIUH. To improve the predictive capability of the GIUH model, the Xin’anjiang (XAJ) model, which is a conceptual model with clear physical meaning, is applied to simulate the runoff yielding and the slope flow concentration, integrating with the GIUH derived based on Nash model to compute the river network flow convergence, forming a modified GIUH model for flood simulation. The average flow velocity is the key to obtain the indices k, and two methods to calculate the flow velocity were compared in this study. 10 flood events in three catchments in Fujian, China are selected to calibrate the model, and six for validation. Four criteria, including the time-to-peak error, the relative peak flow error, the relative runoff depth error, and the Nash–Sutcliff efficiency coefficient are computed for the model performance evaluation. The observed runoff value and simulated series in validation stage is also presented in the scatter plots to analyze the fitting degree. The analysis results show the modified model with a convenient calculation and a high fitting and illustrates that the model is reliable for the flood estimation and has potential for practical flood forecasting.
... After that, the calibrated model parameters of the KW-GIUH model for the Shihmen Reservoir catchment were respectively set to be n 0 = 7 and n c = 0.04 in the present study. Two parameters were determined by a trial-and-error procedure (Lee and Chang, 2005;Lee et al. 2013). The U.S. Army Corps of Engineers has provided suggestions for overland roughness values corresponding to various vegetated surfaces (HEC, 1990), which are helpful in the model parameters calibrating processes, and referable channel roughness values for different channel conditions have proposed by Chow (1959). ...
This study proposes an integrated hydrometeorological system combining a fully physically based rainfall-runoff model (i.e., kinematic-wave-based geomorphologic instantaneous unit hydrograph model, KW-GIUH) with a numerical weather model (i.e., Taiwan cooperative precipitation ensemble forecast experiment, TAPEX) for performing hourly reservoir inflow forecasting patterns in the Shihmen Reservoir, in Northern Taiwan. If there is an accurate reservoir inflow with enough lead time, it could help reservoir operators to efficiently operate reservoirs in both dry and wet times of the year. Five historical typhoons, having severe impacts on the study reservoir, were used for model calibration, validation, and further application. For accurate reservoir inflow forecasting, it is necessary to understand a series of uncertainties that occur in this system. Therefore, the present study assessed the forecast uncertainty of the peak inflow and cumulative reservoir inflow on the basis of several TAPEX runs. Using the average forecasting result derived from all TAPEX runs could be less uncertain than randomly choosing a run's result. For example, the results for Typhoon Saola (2013) showed that the uncertainty in the cumulative reservoir inflow ranged −31.3% (first TAPEX run) to 27.0% (sixth run); otherwise, its average forecasting result was only −0.9%. On the basis of the analyzed typhoons, the proposed system can provide accurate forecasts of the magnitude and timing of the peak inflow when rainfall distribution is concentrated during typhoon events. The results demonstrated that the proposed hydrometeorological system can substantially represent reservoir inflow forecasting in the Shihmen Reservoir and provide valuable information for operating reservoirs. © 2018 International Association for Hydro-environment Engineering and Research, Asia Pacific Division
... (1)-(3). In recent years, the KW-GIUH model has been successfully implemented for rainfall-runoff simulation (Cao et al., 2010;Huang et al., 2016;Lee & Chang, 2005;Lee et al., 2008;Lee & Huang, 2013;Shadeed et al., 2007; and other applications (Arekhi et al., 2011;Lee et al., 2009;Wang & Tung, 2006). ...
A flow-sediment rating curve is used to describe the relation between flow discharge and suspended-sediment concentration for a specific location. Five types of flow-sediment rating curves - single-valued line, clockwise loop, counterclockwise loop, single-valued line plus loop, and figure eight - were found to rely on the flow and available sediment arriving at the measuring site. In this study, equations for flow and sediment travel time were derived according to soil, rainfall, and watershed geomorphologic characteristics. The hysteresis of the rating curve was related to the travel times by a series of numerical tests. Field data collected from the Goodwin Creek Experimental Watershed, Mississippi, United States were used to verify the proposed rating curve hysteresis analysis. The results indicate that when the flow travel time is more extended than the sediment travel time, the rating curve shows a clockwise loop. A counterclockwise loop in the rating curve shows that the flow travel time is less extended than the sediment travel time. If the flow travel time exceeds the sediment travel time in specific runoff states and is less than the sediment travel time in other runoff states, then a single line plus a loop rating curve or a figure-eight rating curve is observed. The criterion for the model parameters to obtain equalization of the flow and sediment travel times was derived, which can identify the type of flow-sediment rating curve in a specific watershed. © 2017 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research.
... Rodrigueze-Iturbe and Valdes (1979) developed geomorphologic IUH (GIUH) theory by combining a dynamic probability model with basin geomorphology. Unlike the previous IUH models (Clark 1945;Nash 1957;Dooge 1959;Singh 1962;Diskin 1964) being largely dependent on such conceptual elements as linear reservoir and linear channel GIUH theory attempts the physical explanations about the transformation process of rainfall into runoff, so that it could become one of the central themes in the field of hydrology and keeps on evolving through a lot of consecutive researches (Gupta et al. 1980;Kirshen and Bras 1983;Rosso 1984;Mesa and Mifflin 1986;van der Tak and Bras 1990;Rinaldo et al. 1991;Rinaldo et al. 1995;Gandolfi et al. 1999;Kumar 2002, 2004;Botter and Rinaldo 2003;D'odorico and Rigon 2003;Lee and Chang 2005;Di Lazzaro 2009). ...
This paper investigates positively skewed shape of instantaneous unit hydrograph (IUH), one of the universal features of hydrologic response function. An analytical expression of statistical moments for IUH is derived in the framework of width function based geomorphologic IUH (GIUH) theory being interpreted by the concept of hydrodynamic, geomorphologic and kinematic dispersion. Within the extent of a river basin there is a significant scale difference between hillslope and channel flow path length. Even though the former has much smaller length scale its variation coefficient tends to be higher and skewness coefficient has a different trend than the latter. Kinematic heterogeneity has larger influence on the shape of IUH rather than hydrodynamic heterogeneity. Furthermore, its combined effect with geomorphologic heterogeneity can be a major cause of skewing hydrologic response function. Through transformation of width function into GIUH statistical properties of hillslope and channel flow path length can be imprinted on the shape of hydrologic response function in the form of dimensionless statistics.
... In several studies, 2D and 3D fully distributed models have been used to simulate the spatial pattern of partial contributing area (Frankenberger et al., 1999;Ivanov et al., 2004). A semi-distributed model for real-time flood forecasting was developed by Lee and Chang (2005). They incorporated the partial contributing area concept, along with a subsurface flow mechanism into a kinematic-wave-based geomorphologic instantaneous unit hydrograph model. ...
This study assessed the capability of soil and water assessment tool (SWAT) to identify areas contributing to flow in the Gully Creek Watershed in Ontario. The SWAT model predicted the streamflow at the outlet of the watershed, with monthly and daily Nash-Sutcliffe efficiencies of 0.75 and 0.60 during the validation period. In addition to the daily streamflow data, the flow was also observed at 16 monitoring stations during 6 different events. The validated model was then used to simulate flow at the monitoring stations. The effect of watershed delineation on streamflow and events at 16 monitoring station were then examined by SWAT. The delineation of 99 subbasins, with highest efficiency was selected for the purpose of predicting the potential flow contributing areas with the model. Overall, the flow events were overestimated by SWAT. Temporal variations in the potential flow contributing areas during each event were then analyzed. Flow contributing areas during each event was predicted by the model first and the results showed a good agreement with available information. A current precipitation index was used to simulate the continuous change of soil water content during each rainstorm, and the modeling results of the individual events were used to explore the capability of the model to predict the temporal variation of flow contributing areas during each event. The results revealed that the SWAT model over-predicted the areas contributing flow for events with lower rainfall; while for the events with higher rainfall amount the model closely simulated the time-varying contributing area. The results of this study provide some insight into the possible capability of SWAT model to predict the temporal variations in potential contributing area, and therefore provide an important contribution to the modeling of runoff generation in watersheds, a vital aspect in the evaluation and planning of best management practices.
... Kinematic wave approximations have been commonly applied to understand or simulate hydrologic processes (Basha and Maalouf, 2005;Lee and Chang, 2005;Daniele and Marco, 2008;Mohammad, 2012;Maryam et al., 2015;Valipour et al., 2015), including the rapid subsurface flow response (Emily et al., 2009;Davies and Beven, 2012). However, some questions regarding this method must be discussed. ...
Velocity and celerity in hydrologic systems are controlled by different mechanisms. Efforts were made through joint sample collection and the use of hydrographs and tracers to understand the rapidity of the subsurface flow response to rainstorms on hourly time scales. Three deep subsurface flows during four natural rainstorm events were monitored. The results show that 1) deeper discharge was observed early in responding rainfall events and yielded a high hydrograph amplitude; 2) a ratio index, k, reflecting the dynamic change of the rainfall perturbation intensity in subsurface flow, might reveal inner causal relationships between the flow index and the tracer signal index. Most values of k were larger than 1 at the perturbation stage but approximated 1 at the no-perturbation stage; and 3) for statistical analysis of tracer signals in subsurface flows, the total standard deviation was 17.2, 11.9, 7.4 and 3.5 at perturbation stages and 4.4, 2.5, 1.1, and 0.95 at the non-perturbation stage for observed events. These events were 3 to 7 times higher in the former rather than the later, reflecting that the variation of tracer signals primarily occurred under rainfall perturbation. Thus, we affirmed that the dynamic features of rainfall have a key effect on rapid processes because, besides the gravity, mechanical waves originating from dynamic rainfall features are another driving factor for conversion between different types of rainfall mechanical energy. A conceptual model for pressure wave propagation was proposed, in which virtual subsurface flow processes in a heterogeneous vadose zone under rainfall are analogous to the water hammer phenomenon in complex conduit systems. Such an analogy can allow pressure in a shallow vadose to increase and decrease and directly influence the velocity and celerity of the flow reflecting a mechanism for rapid subsurface hydrologic response processes in the shallow vadose zone.
... Chang (2005) Kumar et al. (2004Kumar et al. ( , 2007 rendered the runoff estimation of ungauged catchments by applying 64 the GIUH-based Nash and Clark models. They used stream ratios to estimate Nash and Clark's 65 parameters. ...
Estimation of flood in ungauged catchments has great importance in the design of hydraulic structures. The geomorphologic instantaneous unit hydrograph (GIUH) technique uses geomorphologic parameters to estimate catchment runoff. In this research, regression equations were developed based on geometrical characteristics of nine catchments such as area, length and slope of the main river to estimate geomorphologic data of other catchments with no need for GIS and digital elevation model. These equations were used for verification of stream-order-law ratios as well as geomorphologic parameters corresponding to the Gagas, Heng-Chi and Kasilain catchments. In this study, the effect of stream-order-law ratios on the rate of runoff in Kasilian catchment was examined, and the sensitivity of each ratio was analyzed. The GIUH model was assessed in two cases of GIS-supported and GIS-unsupported. The mean errors of the regression equations in estimation of ratios RB, RL, RA, RS and RSO in three study catchments were 4.7 %, 23.5 %, 7.1 %, 41.3 %, and 22.9 %, respectively. The direct runoff hydrograph for the Heng-Chi and the Kasilian catchments were computed by GIUH model and compared with observed runoff. According to the results, the errors of peak discharge for four rainfall-runoff events in GIS-unsupported case were, on average, 10 % more than the error in the case of GIS-supported GIUH. The results of GIUH for the two cases are very close to each other. The mean coefficient of efficiency of the model was computed as 0.87.
... Furthermore, Gupta et al. (1980) generalized the RV-GIUH theory by the flow path concept of Strahler's stream order classification, and they proposed an enhanced model structure that is free from the theoretical restraints of the continuous semi-Markov process with respect to the travel time probability density functions of individual stream orders. Cheng (1982), van der Tak and Bras (1990), and Jin (1992) applied various probability density functions to derive a GIUH, while Kirshen and Bras (1982), Rinaldo et al. (1991), and Lee and Chang (2005) adopted hydrodynamic approaches to GIUH models. Rinaldo et al. (1991) focused especially on the shape of the IUH rather than the scale and analyzed the correlation between hydraulic and geomorphologic characteristics for more reliable (or accurate) simulation of hydrologic responses; they derived the GIUH model by using a diffusion-analogy methodology from the context of hydrodynamics and then suggested the analytical solution to the second statistical moment (i.e., GIUH variance). ...
This study presents a new method to estimate the Nash model parameters on the basis of the concept of geomorphologic dispersion stemming from spatial heterogeneity of flow paths within a catchment. The proposed method is formulated by including physically meaningful characteristic velocities for channel and hillslope and also takes account of the effect of complex interactions between channel and hillslope hydrological behaviors on catchment responses. We applied the proposed formulas to the Bocheong watershed, an experimental area established under the International Hydrological Programme (IHP) in Korea, with several storm events to assess the individual effect of channel and hillslope on hydrological responses in the study site. The characteristic velocities were estimated by topographic data based on a 20 x 20 m digital elevation model (DEM) from a 1:25000-scaled topographic map and statistical features of the historical events. We then calculated the Nash model parameters by substituting the estimated characteristic velocities into the new formulas proposed in this study. The sensitivity analysis results of the Nash model parameters and instantaneous unit hydrograph (IUH) shape of the characteristic velocities indicated that the scale parameter of the Nash model was more sensitive to the hillslope velocity than the channel velocity, whereas all of the Nash model parameters were determined by the relative difference between the hillslope and channel characteristic velocities. The rising limb of IUH and time to peak were dependent mainly on the channel velocity, whereas the recession limb of the IUH reacted very sensitively to the variation of the hillslope velocity. In addition, the skewness of the IUH varied with the ratio of characteristic velocities. Finally, the IUHs, estimated from regional analysis of the characteristic velocities, led to acceptable and constant hydrological responses for the catchment scale. If the improved regional analysis, modeled on hydrodynamic (or physical) approaches, is performed, the proposed formulas for the Nash model in this study can be a useful tool to simulate rainfall-runoff processes in ungauged basins. DOI: 10.1061/(ASCE)HE.1943-5584.0000371. (C) 2011 American Society of Civil Engineers.
... The primary idea describing the engineering of stream network and results of geomorphologic responses was derived and named geomorphologic instantaneous unit hydrograph (Karvonen et al., 1999). A mathematical method and its efficiency were proposed by (Lee and Chang, 2005) as a result of studying the northern Taiwan. The results shows since the run off primarily occurs in low portions of a watershed near streams of a precipitation run off model, only the surface run off is recognized as being inadequate. ...
... Some reports are available on successful application of this model and modified versions of the model in different climates and topographic conditions: e.g. United States (Yen and Lee, 1997; Lee and Huang, 2013), Taiwan (Yen and Lee and Chang, 2005;Lee and Huang, 2013), Palestine (Shadeed et al., 2007), Japan (Chiang et al., 2007), India (Kumar, 2008), Russia (Lee et al., 2009), andIran (Azizian andShokoohi, 2014). ...
This research addresses the effect of using digital elevation models (DEMs) derived from different sources on the results of a kinematic wave based GIUH model. DEMs from different sources exhibit data-resolution effects on the important derived geomorphological properties of watersheds used in rainfall–runoff modelling. Using DEMs derived from topography maps (TOPO DEM) and the SRTM DEM, it was illustrated that different threshold areas for stream network extraction affect GIUH model performance. The results show that the SRTM DEM gives higher values for sub-basin and channel slope as well as number of streams, than the TOPO DEM, while mean length of overland and channel flow is greater for the latter source. The results also indicate that peak flow and slope of the hydrograph rising limb obtained from the SRTM DEM at different threshold areas (ranging from 0.25% to 3%) are greater than that for the TOPO DEM. Investigating the effects of stream network delineation threshold area on the simulated peak flow shows that the maximum and minimum differences (12% and 1%) occur at the threshold areas of 0.5% and 1%, respectively, while for threshold areas higher than 2% the difference in peak flow of the two sources is limited to 10%. Based on the results of this research, it is deduced that the effects of data resolution and stream network delineation threshold areas on the geomorphological parameter values and the performance of GIUH-based models are significant and should be considered when using SRTM DEMs in ungauged watersheds.
... This could be partly attributed to the assumption of linearity in the rainfall-runoff transformation process particularly for the hilly watersheds in this study. The effect of subsurface flow component in runoff generation, not considered in this study, could also be significant in GIUH simulation for hilly watersheds (Lee and Chang 2005). ...
Hydrologic response of two fourth-order hilly watersheds of the Ramganga river basin in the central Himalayan region of India has been predicted in this study. Geomorphologic Instantaneous Unit Hydrograph (GIUH) was derived using two models: (i) Horton’s stream-order ratios based model (GIUH-I); and (ii) Nash’s two-parameter gamma distribution based conceptual model (GIUH-II). The travel times for the overland-flow and the stream-flow in Horton-Strahler stream ordering system of the watersheds were determined analytically and probabilistically for GIUH-I model; while a dynamic component (mean velocity of flow) was estimated for the GIUH-II model using two approaches: (a) as a function of effective rainfall intensity (GIUH-IIa); and (b) on the basis of time of concentration concept (GIUH-IIb). Based on eight single-peaked isolated storm events for each watershed, the statistical analysis and coefficient of efficiency showed better overall correlation between predicted and observed direct runoff hydrographs, particularly in terms of the magnitude and time of occurrence of peak runoff rate, by GIUH-IIb as compared to GIUH-I and -IIa models. Moreover, the GIUH-IIb has additional advantage (compared to GIUH-IIa) for being independent of the measured velocity of flow corresponding to the peak flow rate at the watershed outlet. Since, these models require no historical data of rainfall and runoff, they can be effectively used to predict direct runoff from ungauged hilly watersheds for water resources planning and management in the region.
... V-shaped subbasins(after LEE and CHANG 2005) Flow paths of the third-order watershed with Strahler stream-ordering system (after LEE and YEN 1997) V-shaped subbasins (cited fromLee and Chang [2005]) ...
Typhoon events occur frequently in Taiwan resulting in flood-related disasters. A well-operated reservoir can reduce the severity of a disaster. This study incorporates a genetic algorithm, a river hydraulic model, an artificial neural network and a simulation model of Tseng-Wen Reservoir to propose a real-time flooding operation model. The model includes two parts: an optimal flooding operation model (OFOM) and a reservoir inflow forecasting. Given an inflow condition, the OFOM is run based on the safety of the dam structure, reservoir flooding operation rule, and minimization of the downstream loss due to flood. A simple and robust model for reservoir inflow forecasting, which automatically chooses the most similar event from a typhoon event database as the future inflow, is developed. This study compares the model results with the real operations during Typhoons Sepat, Krosa, Kalmaegi, Fung-wong, Sinlaku, and Jangmi. This study compares the performances of the proposed model with the practical operation operated by the management center of Tseng-Wen Reservoir. The proposed model indicates shorter flooding duration in the downstream area. For example, the flood durations of the model output are 4 and 3 hours shorter during Typhoon Krosa and Sinlaku, respectively, than the practical operations.
... Overland flow over a permeable surface can occur when the rainfall intensity is greater than the infiltration capacity or when surface saturation exists in regions near the stream [16]. When a unit depth of excess rain falls uniformly and instantaneously onto a catchment, the unit excess rainfall is assumed to consist of a large number of independent, noninteracting raindrops. ...
Digital elevation model (DEM) resolution and the assigned threshold for river network delineation affect the results of rainfall-runoff models. In this study, the effects of these 2 issues on the extracted geomorphologic parameters of watersheds and the performance of a kinematic wave based model, called KW-GIUH, are investigated. The results show that by decreasing the DEM resolution at fixed thresholds, parameters such as subbasin mean slope and the number of streams decrease and the area of the ith order subbasins and the mean length of the overland flow increase. Moreover, the results indicate that the reduction of the DEM resolution at a fixed threshold causes the peak flow and hydrograph time base to decrease up to the cell size of 100 m and then, after experiencing a jump, again decrease with the increase of the cell size. According to the achieved results, above the threshold of 2%, the difference between the peak flows of different hydrographs at different resolutions is meaningful. The KW-GIUH sensitivity to DEM resolutions and thresholds is sharper in peak flow and then in hydrograph time base and time to peak. At a fixed threshold, the value of time to peak is independent of DEM resolution.
... 따라서 물리적으로 기초한 강우-유출 현상에 대한 해석 은 반드시 대상유역의 형태적 혹은 지형적 특성에 대한 객관적이고 신뢰성 있는 평가를 바탕으로 수행되어야 하며, 이에 대한 중요성은 수문학 혹은 지형학 분야를 통해 지속적으로 강조되고 있다(Rodríguez-Iturbe and Valdes, 1979 ). 이러한 개념에 충실한 대표적인 강우유출 모형으로는 통계역학적 접근법(Lienhard, 1964) 을 기반으로 한 지형학적 순간단위도(GIUH, Geomorphologic Instantaneous Unit Hydrograph) 모형을 들 수 있으며 이를 기반으로 한 모형들은 현재까지도 꾸준한 진화를 거듭해 오고 있다(Iturbe and Valdes, 1979; Gupta, et al., 1980; Rinaldo, et al., 1991; Lee and Chang, 2005). 이러한 일련의 연구들 중 Rinaldo, et al.(1991) 우 비교적 큰 격자 해상도를 적용하는 것은 큰 의미가 없을 것으로 판단되어 1:5,000 축척의 수치지형도 격자 해상도는 5, 10, 15, 20m를 적용하였다. ...
In this study, when interpreting leakage using the concept of geographical dispersion based on grid, to choose an appropriate spatial resolution, the statistical characteristics of drainage path length and the pattern of change of hydrodynamic parameters have been observed. Drainage path length has been calculated using an 8-direction algorithm from digital elevation model, from which the hydrodynamic parameters of the watershed were estimated. The scales of topographical map for this analysis are 1:5,000 and 1:25,000, appling grid sizes 5, 10, 15, 20 m and 20, 30, 50, 100, 150, 200 m, respectively. As results of this analysis, depending on the scale of stream networks, the statistical characteristics of drainage path length by spatial resolution and hydrodynamic parameters of the watershed have been changed. Based on the above results, when interpreting leakage using the concept of the geographical dispersion based on grid, in the case of 1:5,000 scale topographical map, a spatial resolution of 5 m will be better showing geographical and hydrodynamic characteristics to apply to the well developed stream network in basins, spatial resolution of 5~20 m to the less developed stream network in basins. And in the case of 1:25,000 scale topographical map, spatial resolution below 50 m is more desirable to show above two characteristics to apply to both cases.
... Jain et al. (2000), Jain and Sinha (2003), Sahoo et al. (2006) and Kumar et al. (2007) applied a GIS-supported GIUH approach for estimation of design flood. Lee and Chang (2005) incorporated a sub-surface flow mechanism into the GIUH approach. López et al. (2005) analysed UH models based on watershed geomorphology represented as a cascade of reservoirs. ...
This review paper critically examines one of the most popular flood hydrograph modelling techniques for ungauged basins, the synthetic unit hydrograph (SUH), and its recent developments and advances. For this purpose, the SUH models were first grouped into four main classes, as follows: (a) traditional or empirical models; (b) conceptual models; (c) probabilistic models; and (d) geomorphological models. It was found that the geomorphological class is the most useful and interesting, since it is able to employ topographic information, so limiting the role of the calibration parameters. This review is expected to be helpful to hydrologists, water managers and decision-makers searching for models to study the flood hydrograph, modelling techniques and related processes in ungauged basins. It was completed as the International Association of Hydrological Sciences (IAHS) Decade (2003–2012) on predictions in ungauged basins (PUB), drew to a close. Editor D. Koutsoyiannis; Associate editor S. GrimaldiCitation Singh, P.K., Mishra, S.K., and Jain, M.K., 2013. A review of the Synthetic Unit Hydrograph: from the empirical UH to advanced geomorphological methods. Hydrological Sciences Journal, 59 (2), 239–261.
... In the past, the Geomorphological Instantaneous Unit Hydrograph (GIUH) was used for simulating surface runoff (Rodriguez-Iturbe, 1979;Gupta et al., 1980;Rodriguez-Iturbe et al., 1982;Chutha and Dooge, 1990;Yen, 1997, 2005;Olivera and Maidment, 1999). Recently, the GIUH model has been applied to consider both the surface and subsurface flow processes (Lee and Chang, 2005). This method is based on travel time probability distributions for runoff in surface flow and subsurface flow regions and channels. ...
The travel time of subsurface flow in complex hill- slopes (hillslopes with different plan shape and profile curva- ture) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes ge- ometry (plan shape and profile curvature), soil properties and climate conditions. The saturation capacity of hillslopes af- fect the travel time of subsurface flow. The saturation ca- pacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hy- draulic conductivity, plan shape (convergent, parallel or di- vergent), hillslope length, profile curvature(concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all com- plex hillslopes was presented. This equation is a function of the saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numeri- cally by using the hillslope-storage kinematic wave equation for subsurface flow, so an analytical equation was presented for calculating the saturation zone length of the straight hill- slopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsur- face travel time , convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hill- slopes and their saturation capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on saturation zone extension were investigated.
Large errors in Quantitative Precipitation Estimates (QPE) tied to remote-sensing retrieval algorithms remain a challenge especially in complex terrain with fast hydrologic response. We propose a new framework to derive dynamic hydrologic corrections of rainfall in headwater basins that enforces water budget closure, and distributes transient rainfall corrections by Lagrangian backtracking along runoff trajectories constrained by realistic time-of-travel distributions. Downscaled QPE products (250 m resolution) are applied first as input to a distributed hydrologic model to predict runoff trajectories and the event hydrograph at the basin's outlet. Second, time-varying rainfall corrections are derived from the residuals between predicted and observed discharge at the outlet. Finally, the corrections are spatially distributed following the runoff trajectories backward (i.e. trajectories are used as streaklines originating at the basin's outlet). Because nonlinear interactions between rainfall, runoff and storage are transient, the corrections are applied recursively until the shape and volume of the predicted hydrograph are stable. The framework is applied to ground-based (e.g. Stage IV) and satellite-based remote-sensing QPEs (e.g. IMERG) associated with the 49 largest floods 2008–2018 in the Southern Appalachian Mountains, USA. The results show improvements in hydrograph prediction efficiency skill at 15 min timescale from −0.5 to 0.6 on average and up to 0.9 for warm season events, bounding event runoff volume errors with a mean of 3%, and reducing time to peak errors by half an hour on average. Corrected QPEs exhibit nearly perfect correlation and no bias at high elevation gauge locations. Uncertainty in the water budget closure at the event scale is less than the uncertainty in streamflow measurements. Error attribution shows strong organization of QPE corrections according to seasonal weather and rainfall regime, thus providing a path to generalization to ungauged mountain basins.
Separating surface flow (SF) from subsurface flow (SSF) based on direct runoff measurements in river gauges is an important issue in hydrology. In this study, we developed a simple and practical method, based on runoff coefficient (RC), for separating SF from SSF. RC depends mainly on soil texture, land use and land cover, but we also considered the effect of slope and rainfall intensity. We assessed our RC-based method for three different soil types by comparing the value obtained with laboratory rainfall simulator data. The correlation coefficient between observed and calculated data exceeded 0.93 and 0.63 when estimating SF and SSF, respectively. The method was then used to separate SF and SSF in two catchments (Heng-Chi and San-Hsia) in Northern Taiwan, and the results were compared with those produced by the geomorphological instantaneous unit hydrograph (GIUH) model. Test revealed that, if RC is calculated accurately, the proposed method can satisfactorily separate SF from SSF at catchment scale.
For many permeable catchments with proper plant cover, subsurface flows play a key role in generating surface runoff. In this regard, developing subsurface flow models is of great importance and requires further studies. In Dunne-Black mechanism, it is subsurface flow causing saturated zone in hillslopes and generating surface runoff. The Nash model is an instantaneous unit hydrograph (IUH) model commonly used to predict the surface runoff. In this study, the Nash model was applied to estimate subsurface flow hydrograph in the catchments. The parameters of the subsurface Nash IUH (SNIUH) model were determined by developing of the subsurface travel time equations with the concept of celerity. The efficiency of the SNIUH model was verified by two rainfall simulator laboratory models. The mean error of the peak subsurface flow estimation ranged from 6.7 to 11.21% for both laboratory models, which was acceptable. Ultimately, the SNIUH model was used to estimate the subsurface flow hydrograph in Heng-Chi and San-Hsia catchments in Taiwan, and the results were compared with results of the subsurface geomorphologic IUH (SGIUH) model. The coefficients of efficiency (CE) of SNIUH were higher than 0.9 in four events for both catchments and the subsurface peak error values were between 10 and 16%.
Heavy rainfalls and rain-induced floods regularly cause substantial damage in the Western Caucasus region. In this study, we assess the accuracy of heavy rainfall forecasting with ICON-Eu regional atmospheric model (developed by the weather service of Germany) and the possibility of its use as input data for rain flood prediction. The main conclusion is that the forecast accuracy is strongly determined by the nature of the rainfall in question (mainly convective or triggered by synoptic-scale processes) and the season of the year. The ICON-Eu model systematically underestimates (by 2-3 times) the precipitation amount in the warm season (April-September) and almost never reproduces local convective heavy rainfall events. Therefore, its forecasts for short-term prediction of summertime rain floods have low efficiency. On the other hand, in the cold season (October-March) the model adequately reproduces heavy precipitation events, with some underestimation of the maximum precipitation amount and overestimation of the coverage area. These forecasts can be used to improve the short-term prediction of flash floods on the rivers of the Black Sea coast of the Caucasus during the period from October to March. In addition, we have performed a detailed analysis of the heavy rainfall and a related flood event which occurred on August 17-18, 2019 by comparing hourly observed precipitation with ICON-Eu and Cosmo-Ru forecasts, as well as applying WRF simulation and rainfall-runoff modelling.
Due to the extreme weather, flood disasters occur frequently in recent years. It induces the changing of hydrological condition, flow and sediment transport mechanics, river bed slope, river bed degradation and river bed aggradation. However, bridge pier geometry and disposition, bank and river channel protection, and hydraulic works are the main factors affecting the erosional depth and river bed stabilization. Therefore, it is a vital issue to develop a system that can provide valuable and useful information for the estimation of bridge pier scour depth. This study apply interface operation system to develop and integrate rainfall runoff model, 1-D and 2-D hydraulic and sediment transport model, and calculation formulas of bridge pier scour depth. The purpose of this study is to develop an estimation system of bridge pier scour depth that is suitable for the hydraulic pattern simulation and sediment transport routing in the Zhuoshui River Basin. Numerical simulation models combined with interface operation on assessment system development of specific bridge pier scour depth is established. Therefore, it can be implemented to simulate the general scour and local scour depth at bridge piers. In this study, the historical events are adapted to calibrate and verify models that include rainfall runoff model, 1-D and 2-D hydraulic and sediment transport model, and calculation formulas of bridge pier scour depth. In addition, easy operation and integrated interface is developed in the system for the estimation of bridge pier scour depth. The system can supplies users for model verification by input and output through the interface. To achieve the forecast of the erosional depth on the bridge piers in the ZhuoShui River, the system can also be connected to the rainfall forecast system of Taiwan Typhoon and Flood Research Institute (TTFRI) and the tidal forecast of Central Weather Bureau (CWB) in the future. Additionally, the results can be provided references for the management unit of bridges, such as estimating the risk of bridge piers damage and the necessity of bridge closure. © 2018, Taiwan Agricultural Engineers Society. All rights reserved.
The relative contributions of overland-flow and stream-flow to the response process at the basin scale are evaluated in the present study. The moments of GIUH models were applied to the data of the Bocheong watershed in the Geum river basin in Korea in order to discuss the feasibility. The GIUH model derived in this study consists of the stream path and overland region. The characteristic velocities for the flows between two cases mentioned above make a clear distinction as expected and would have more physical meaning than the ones of the model by Rodriguez-Iturbe and Valdes(1979). The path lengths of overland for each stream order are nearly constant, whereas the case of stream is shown to grow larger according to the basin sizes. As a result, the overall basin response process was founded out to be greatly under the influence of the hydrodynamic behavior of overland, and its behavior is suggested to be further researched for catching the broader meanings.
This paper is aimed at the development and implementation of an ensemble flood forecasting system in Taiwan. This system features providing the ensemble flood forecasts with 3-hour lead time in a near real-time manner. Four sets of flood forecasts can be obtained at once for the ensemble analysis. A weighting method for ensemble average is proposed to improve the accuracy of the forecasting water levels in this study. The flood event caused by Typhoon Sinlaku in Tamsui River basin is taken as an illustrated example. Due to the flash flood characteristics, the ensemble forecast with 3-hour lead time does provide the officials more responding time for flood hazard mitigation. On the other hand, in order to help the authorities using decision support systems (DSS) effectively, a human-centered, open and virtually integrated platform for the use of heterogeneous DSSs is proposed. Via this virtual platform, the officials, experts and scholars at different locations can easily share their DDSs' information and communicate and discuss immediately. Finally, an application example associated with a flood event has been carried out to demonstrate the applicability of the proposed system and platform. The result shows that the real-time monitoring, the water-level forecasting, and the spatial geographic information are very crucial and can be obtained immediately in this application. Therefore, the potential usefulness and benefit of the systems and platforms has been recognized.
Since tremendous disasters frequently occur in Taiwan due to steep topography and concentrated rainfall intensity, flood forecasting during storm period is considered important for water resources engineering. The objective of this study is to develop a real-time flow forecasting model for river discharge estimation to improve disaster prevention ability. In this study, a grey model for rainfall forecasting based on previous hourly observed data was developed, and a geomorphology-based rainfall-runoff model combined with an updating function using real-time measured flow data were adopted to generate watershed runoff. The proposed flow forecasting model was applied to Heng-Chi and San-Hsia watersheds in northern Taiwan. The results indicated that the proposed model can provide reasonable hydrograph forecasting, and both the forecasted and recorded hydrographs were in good agreement in the study watersheds. It is therefore considered promising to apply the proposed method for flood warning to alleviate the loss of lives and property.
土石流預警在台灣是以有效累積雨量為基準，但在不同累積雨量下的土石流災害範
圍，卻少有學者討論。針對這個問題，本文以北市DF024 為例，用其警戒雨量500 毫米做為基
準，再選300 和700 毫米的累積雨量做影響範圍的比較。透過物部公式 (Monobe formula) 將累
積雨量轉換為降雨強度，並搭配合理化公式和流量歷線去估算集水區產生的總水量，再以土石
流平衡濃度公式推估土石流體積量。並經過現場調查，將料源分佈於崩坍地與河床崩積層，最
後採用DEBRIS-2D 去模擬土石流影響範圍。在北市DF024 的案例中發現，土石流影響範圍會
隨著累積雨量的增加而擴大，但最大土石堆積深度皆在3~3.5 公尺之間。透過此方法得到的土
石流影響範圍不只可以連結與累積雨量的關係，並且可提供相關單位一個修正警戒雨量或疏散
範圍決策的參考。
In conventional rainfall-runoff modeling, entire watershed was assumed to contribute surface runoff to the drainage network during rainstorm. However, field survey has shown that only the areas near channels or those areas with high groundwater level contribute surface flow. In this study, the time-varying soil moisture content in the study watershed was analyzed based on a current precipitation index (CPI). An exponential function was selected to describe the relationship between the CPI and the partial contributing area (PCA) during storm events. A kinematic-wave-based geomorphic instantaneous unit hydrograph model (KW-GIUH), which can consider PCA concept, was used to simulate watershed storm flow to evaluate the adequateness of the transform functions for the relationship between CPI and PCA. Hydrologic records from two watersheds, Wu-Tu and Tung-Tou in Taiwan were adopted to validate the proposed analytical procedure for storm runoff simulation. The time-varying CPI and PCA series were generated from hourly rainfall records, and the influences of the parameters in the transform function were detailed investigated. The results show that the KW-G1UH model coupled with the time-varying PCA provides good performances in runoff simulation. Moreover, the PCA ratio was found increasing from the beginning of the rainstorm and attaining to a maximum value at the occurrence of the peak discharge or the maximum rainfall intensity in the storm. Subsequently, the PCA ratio decreases gradually in accordance with the recession of the storm flow. The results of this study are expected to improve the reliability of the rainfall-runoff model parameters to provide a stable model for flood prediction during storms.
This paper presents the systematic approach to positively skewed shape of instantaneous unit hydrograph (IUH), that is one of the universal features of hydrologic response function. To this end an analytical expression of statistical moments for IUH is derived within the framework of geomorphologic instantaneous unit hydrograph (GIUH) theory and quantified according to the concept of hydrodynamic, geomorphologic and kinematic heterogeneity. There is a big scale difference between hillslope and channel flow path system. Although the former has the much smaller level of scale its variation coefficient tends to be higher and coefficient of skewness has the different trend than the latter. The shape of IUH is likely to be much more affected by kinematic heterogeneity rather than hydrodynamic heterogeneity and its combined effect with geomorphologic heterogeneity is the major cause of skewing hydrologic response function. Statistical features of hillslope and channel flow path can be transferred into hydrologic response function in the form of dimensionless statistics and their relative importance forms the general shape of hydrologic response function.
This study quantified directional properties of channel network and hill slope for a river basin by applying the von Mises distribution, also examined the relation between them. Ultimately, it was examined that whether the directional properties of channel network and hill slope have a certain relation, which might be considered to the rainfall-runoff modeling. From the results derived by analyzing the Naesung stream basin, the von Mises distribution was found well to explain the directional characteristics of directional properties of channel network. There was a clear relation between directional properties of channel network and hill slope. The higher-order streams also showed very obvious modal characteristics. The results derived in this study could be helpful to estimate more quantitatively the difference in the runoff response with respect to the directional properties of channel network and hill slope.
A unifying synthesis of the hydrologic response of a catchment to surface runoff is attempted by linking the instantaneous unit hydrograph (IUH) with the geomorphologic parameters of a basin. Equations of general character are derived which express the IUH as a function of Horton's numbers RA, RB, and RL; an internal scale parameter LΩ and a mean velocity of streamflow v. The IUH is time varying in character both throughout the storm and for different storms. This variability is accounted for by the variability in the mean streamflow velocity. The underlying unity in the nature of the geomorphologic structure is thus carried over to the great variety of hydrologic responses that occur in nature. An approach is initiated to the problem of hydrologic similarity.
This paper reviews the importance of large continuous openings
(macropores) on water flow in soils. The presence of macropores may lead
to spatial concentrations of water flow through unsaturated soil that
will not be described well by a Darcy approach to flow through porous
media. This has important implications for the rapid movement of solutes
and pollutants through soils. Difficulties in defining what constitutes
a macropore and the limitations of current nomenclature are reviewed.
The influence of macropores on infiltration and subsurface storm flow is
discussed on the basis of both experimental evidence and theoretical
studies. The limitations of models that treat macropores and matrix
porosity as separate flow domains is stressed. Little-understood areas
are discussed as promising lines for future research. In particular,
there is a need for a coherent theory of flow through structured soils
that would make the macropore domain concept redundant.
Geomorphology-based instantaneous unit hydrographs have been proposed by several engineers as a tool to produce runoff hydrographs from rainfall for ungauged watersheds. A difficulty in applying the geomorphology-based unit hydrographs is the determination of travel time that is actually a hydraulic problem. In this paper, kinematic-wave theory is used to analytically determine the travel times for overland and channel flows in a stream-ordering subbasin system. The resultant instantaneous unit hydrograph is a function of the time rate of water input (intensity of rainfall excess in application); hence the linearity restriction of the unit hydrograph theory is relaxed. In applying the instantaneous unit hydrographs for hydrograph simulation, the model deals with temporally nonuniform rainfall through convolution integration of the instantaneous unit hydrographs applied to the rainfall excess of varying intensities with time. The proposed model is tested by comparing the simulated and observed hydrographs of an example watershed for several rainstorms with good results. Sensitivity of surface runoff unit hydrographs to the model parameters is also investigated.
The greatest difficulty in applying the geomorphologic instantaneous unit hydrograph is the estimation of the time scale of the hydrologic response of a basin. We derive the time scale from the effective streamflow velocity of the highest-order stream and the spatial distribution of velocity throughout the stream network. The latter is described by a dimensionless geomorphologic function with a single-shape parameter. The proposed method is applied to some Italian basins.
Hydrologists have attempted to relate the hydrologic response of watersheds as runoff production from rainfall to watershed topographic structures for many years. The recently proposed geomorphologic instantaneous unit hydrograph (GIUH) method is perhaps the most promising development in this direction; if successful, it would allow the derivation of the unit hydrograph (UH) for ungauged or inadequately gauged watersheds without the need of observed runoff and rainfall data. In this method, the geomorphic ratios of the Horton-Strahler stream-ordering laws are incorporated in the GIUH model for UH generation. In view of the variety of project requirements and the different levels of topographic detail available from maps or geographic information systems (GISs), five different levels of geomorphic data are allowed for incorporation with a kinematic-wave and stream-law based instantaneous UH model. Testing of the model on two hilly watersheds in the eastern United States and two relatively flat-slope watersheds in Illinois are presented. Comparison between the simulated and observed hydrographs for a number of rainstorms indicate the potential of this model as a useful tool in watershed rainfall-runoff analysis.
TOPMODEL, a semi-distributed, topographically based hydrological model, was applied to simulate continuously the runoff hydrograph of a medium-sized (379 km2), humid tropical catchment. The objectives were to relate hydrological responses to runoff generation mechanisms operating in the catchment and to estimate the uncertainty associated with runoff prediction. Field observations indicated that water tables were not parallel to the surface topography, particularly at the start of the wet season. A reference topographic index λREF was therefore introduced into the TOPMODEL structure to increase the weighting of local storage deficits in upland areas. The model adaptation had the effect of deepening water tables with distance from the river channel. The generalized likelihood uncertainty estimation (GLUE) framework was used to assess the performance of the model with randomly selected parameter sets, and to set simulation confidence limits. The model simulated well the fast subsurface and overland flow events superimposed on the seasonal rise and fall of the baseflow. The top ranked parameter sets achieved modelling efficiencies of 0·943 and 0·849 in 1994 and 1995 respectively. The GLUE analysis showed that the exponential decay parameter m, controlling the baseflow and the local storage deficit, was the most sensitive parameter. There was increased uncertainty in the simulations of storm events during the early and late phases of the season, which was due to a combination of: errors in detecting the rainfall depths for convectional rainfall events; the treatment of rainfall as a catchment areal value; and, the strong seasonality in runoff response in the humid tropics. Copyright © 2002 John Wiley & Sons, Ltd.
A method is proposed for routing spatially distributed excess precipitation over a watershed to produce runoff at its outlet. The land surface is represented by a (raster) digital elevation model from which the stream network is derived. A routing response function is defined for each digital elevation model cell so that water movement from cell to cell can be convolved to give a response function along a flow path and responses from all cells can be summed to give the outlet hydrograph. An example application of analysis of runoff on Waller Creek in Austin, Texas, is presented.
During an experimental study of runoff producing mechanisms in a small drainage basin, the major portion of storm runoff was produced as overland flow on a small proportion of the watershed. Where the water table intersected the ground surface before and during a storm, water escaped from the soil surface and ran quickly to the stream at velocities 100 to 500 times those of the subsurface system. Direct precipitation onto the saturated area was another major contributor of storm flow. Storage of water within these source areas was small and travel times out of them were short. Runoff from them was largely controlled by rainfall intensity. These partial areas contributing quick runoff could expand or contract seasonally or during a storm. Their position and expansion can be related to geology, topography, soils, and rainfall characteristics. In the study basin, water that remained below the ground surface on its way to the main stream channel was a relatively minor contributor to the storm hydrograph. The response of subsurface flow to rainfall was heavily damped by storage and transmission within the soil. Measurements of water table elevation and runoff from experimental plots in another small watershed with different geologic conditions confirmed the results outlined above. Runoff records from a large number of small basins of the Sleepers River experimental watershed indicate the more general applicability of these findings.
The theory of the geomorphological unit hydrograph (GUH) is examined critically and it is shown that the inherent assumption that the operation of the drainage network may be modelled by a corresponding network of linear reservoirs so restricts the instantaneous unit hydrograph (IUH) shape that the effects of further restrictions, reflecting the constraints imposed by the geomorphological laws of the channel network, cannot easily be identified. Without such identification, the geomorphological unit hydrograph theory is untestable and must remain only a plausible hypothesis providing an indication of a two-parameter IUH whose shape and scale factors must still be related empirically to appropriate catchment characteristics.
The probability mass function of peak streamflow from a given catchment
is derived from the density functions for climatic and catchment
variables by using the functional relationships provided by the
kinematic wave method of hydrograph forecasting. The exceedance
probability for a flood peak of given magnitude is then related to the
annual exceedance recurrence interval of this flood. The resulting
theoretical flood frequency relation shows a changing form with change
in catchment and climate parameters and agrees well with observations
from three Connecticut catchments. It provides a theoretical basis for
estimating flood frequency in the absence of streamflow records and for
extrapolating empirical estimates based on short records. Because of the
explicit appearance of physically meaningful catchment parameters it
also allows quantitative estimates of the effect on flood frequency of
changes in average land use. The flood frequency relation for a given
catchment is averaged across the population of catchments of given size
to provide a theoretical regional flood frequency function that compares
favorably with observations of mean annual floods on 44 Connecticut
catchments.
A dynamical model is devised for a hydrologic system where unsaturated and saturated storage serve as the principal control on rainfall-runoff and where complex topography, drainage area, and variable depth of moisture penetration describe the flow geometry. The model is formed by direct integration of the local conservation equation with respect to the partial volumes occupied by unsaturated and saturated moisture storage, respectively. This yields an ``integral-balance'' model in just two state variables. The relationship of the dynamical model to field data in complex terrain is found through a joint probability density for terrain features. This serves as a ``volume'' weighting function to construct conditional averages for the state variables and fluxes over a specified range of terrain features. The scale of averaging could range from hillslopes to river basins. Two examples of the joint probability of terrain features (altitude and aspect) are demonstrated for Valley, Ridge, and Appalachian Plateau digital elevation models. The strategy of a dynamical model formed by conditional averages of state variables with respect to terrain features is proposed as a way of simplifying the dynamics while preserving the natural spatial and temporal scales contributing to runoff response. The parametric form of the storage-flux or constitutive relationships for the proposed model is determined from numerical experiments in a simple hillslope flow geometry. The results show that a competitive relation exists between unsaturated and saturated storage except for the lowest precipitation rates. Saturation overland flow is proposed to be a storage-feedback relation. Solutions to the integral-balance model are presented in terms of the phase portrait, which represents all possible solution trajectories in state-space. The timing and magnitude of peaks in the runoff hydrograph from pulse-type input events demonstrate quick flow from near-stream saturated storage, saturation overland flow including rejected rainfall (storage-feedback), and late-time infiltration from upslope subsurface flow.
A recurring problem in watershed hydrology is the identification of flow paths along which water is routed in both surface and subsurface environments. In particular, the question of whether storm flow is composed primarily of water flowing over the land surface (overland flow) or beneath the land surface (subsurface flow) is significant, because the former flow path provides for little soil contact, while the latter allows for extensive interaction with subsurface materials. The Reedy Creek watershed (45.1 km2) in the Virginia Coastal Plain has been the subject of field hydrogeological, hydrochemical, and hydrological studies since 1989. Results from chemical separation of six storm flow hydrographs indicate that saturation overland flow (including both direct precipitation onto and return flow to the surface) from saturated contributing areas is the dominant storm flow generation mechanism in the watershed; new water composed 11-38% of creek discharge at the hydrograph peaks, and maximum 24-hour rainfall intensity explained 96% of the total variation in the peak new water contribution among the six events. Estimates of new water-contributing areas determined from the chemical separations were found to vary as a function of antecedent conditions and were also found to be consistent with estimates of areas of likely surface saturation (e.g., perennial channels, open water, and riparian wetland areas) based on field observations and topographic maps.
The equations describing overland flow, in three nondimensional forms, are solved for the rising hydrograph by finite-difference integration of the characteristic equations utilizing a characteristic net. A dry channel was used as an initial condition; the upstream and downstream boundary conditions were zero inflow and critical depth (or no condition for supercritical flow), respectively. A series solution is derived for flow in Zone A, the domain of determinacy of the initial conditions along t = 0. When compared with previous numerical, analytic, and experimental results, the results show that in general there is no unique dimensionless rising hydrograph for overland flow, but that for most hydrologically significant cases the kinematic wave solution gives very accurate results. A single dimensionless parameter was found to be a suitable criterion for choice between the complete equations or the kinematic wave approximation.
A nonlinear mathematical model, starting with the integral of an infiltration capacity function, is developed to analytically equate the difference between rainfall and runoff to hydrologie variables. Only the three independent variables—storm rainfall, duration, and soil moisture—are used, and an equation is evolved in which the identity of the coefficients is kept intact and unusually good statistical control is maintained. The coefficients of the equation appear to be stable over a range of watershed sizes and conditions. The equation strongly indicates that runoff usually originates from a small, but relatively consistent, part of the watershed. The function can be manipulated to show a ‘function of apparent watershed infiltration capacity’ This function characterizes the infiltration capacity of that portion contributing to runoff, on the average, and should prove to be a useful infiltration capacity index with which watersheds can be compared. The equation itself provides insight into why in situ measurements of infiltration capacity seldom agree with the capacity determined from rainfall-runoff data. It also indicates why storm runoff frequently is not linear with respect to causative factors.
The importance of the subsurface response of watersheds has been vastly
underrated in most studies of watershed behavior, both in a quantitative
sense and in a generic sense. The mechanism of base flow generation and
the nature of watershed response in base flow dominant streams are
examined with a deterministic mathematical model that couples
three-dimensional, transient, saturated-unsaturated subsurface flow and
one-dimensional, gradually varied, unsteady channel flow. The channel
flow model uses the single step Lax-Wendroff explicit technique to solve
numerically the full shallow water equations. The subsurface flow model
uses the line successive overrelaxation technique to solve numerically
the Jacob-Richards diffusion equation. The results of the simulations on
a hypothetical basin suggest a wide variability in watershed response
under the influence of variations in rainfall properties, antecedent
moisture conditions, and saturated and unsaturated subsurface
hydrogeologic properties. This evidence for a wide range of watershed
response functions leads to the development of a healthy skepticism
toward black box rainfall-runoff correlations, the concept of basin
linearity, and the rationality of hydrograph separation.
Runoff simulation for rainfall events on hypothetical upstream source
areas, carried out with a deterministic mathematical model that couples
channel flow and saturated-unsaturated subsurface flow, provides
theoretical support for the runoff-generating mechanisms observed in the
field by Ragan and Dunne. The simulations show that there are stringent
limitations on the occurrence of subsurface storm flow as a
quantitatively significant runoff component. Only on convex hillslopes
that feed deeply incised channels, and then only when saturated soil
conductivities are very large, is subsurface storm flow a feasible
mechanism. On concave slopes with lower permeabilities, and on all
convex slopes, hydrographs are dominated by direct runoff through very
short overland flow paths from precipitation on transient near-channel
wetlands. On these wetlands surface saturation occurs from below because
of rising water tables that are fed by vertical infiltration rather than
by lateral subsurface flow. These conclusions, when coupled with field
observations that show classic Hortonian overland flow to be a rare
occurrence in vegetated humid environments, have implications in the
planning of field instrumentation networks, and in the designing of
hydrologic response models.
The instantaneous unit hydrograph is conceived as a random function of climate and geomorphology varying with the characteristics of the rainfall excess. The probability density functions of the peak and time to peak of the IUH are analytically derived as functions of the rainfall characteristics and the basin geomorphological parameters. The main characteristics of these pdf's are studied, and a new approach to hydrologic similarity is initiated under the concept of the geomorphoclimatic IUH. For a given set of geomorphologic characteristics and a particular intensity and duration of rainfall, the peak and time to peak of the IUH corresponding to those values can be easily estimated.
A 0.3028-ha watershed has been instrumented to monitor streamflow and subsurface flow through the soil mantle at a variety of topographic locations. The watershed is forested, with steep (35°) slopes and shallow (average 55 cm) soils on impermeable Old Man gravels. Data for a number of storms indicate that subsurface flow via ‘macropores’ (root channels, pipes) and seepage zones in the soil is the predominant mechanism of channel stormflow generation in storms with quickflows greater than about 1 mm. Subsurface flow from all parts of the watershed appears to contribute to stormflow even in very small storms (quickflow of the order of 3% of net precipitation). The saturated hydraulic conductivity of the soil matrix is not a limiting factor on the ability of subsurface flow to generate channel stormflow, because dye tracer experiments demonstrate that water may move through macropores (particularly root channels) at rates 2 orders of magnitude greater. However, subsurface flow from lower slope areas contributes to delayed flow; cessation of subsurface flow and Streamflow after a drought period is roughly coincident in time. In the study area it appears that streamflow is at almost all times dominated by subsurface flow and that runoff from partial and variable source areas contributes significant quantities of streamflow only during the rising limb of small (less than 1 mm of quickflow) flood hydrographs.
This paper builds on the analysis of Henderson and Wooding (1964) in comparing simplified models of subsurface stormflow for the case of a sloping soil mantle in which the hydraulic conductivity is constant throughout. It is shown that models based on a kinematic wave formulation may be good approximations for those based on the extended Dupuit-Forchheimier assumptions for values of the nondimensional parameter λ = 4i cos θ/(K sin2θ) less than about 0.75 in terms of predicting both water table profiles and subsurface stormflow hydrographs. By using this critical value of λ the range of values of slope angle and saturated hydraulic conductivity for which the kinematic approximation is valid can be specified. A comparison is made with slope angles and hydraulic conductivities at field sites where subsurface stormflow has been shown to be an important component of catchment storm response. It is concluded that the kinematic approximation may be useful for cases of practical interest.
The channel network and the overland flow regions in a river basin satisfy Horton's empirical geo-morphologic laws when ordered according to the Strahler ordering scheme. This setting is presently employed in a kinetic theoretic framework for obtaining an explicit mathematical representation for the instantaneous unit hydrograph (iuh) at the basin outlet. Two examples are developed which lead to explicit formulae for the iuh. These examples are formally analogous to the solutions that would result if a basin is represented in terms of linear reservoirs and channels, respectively, in series and in parallel. However, this analogy is only formal, and it does not carry through physically. All but one of the parameters appearing in the iuh formulae are obtained in terms of Horton's bifurcation ratio, stream length ratio, and stream area ratio. The one unknown parameter is obtained through specifying the basin mean lag time independently. Three basins from Illinois are selected to check the theoretical results with the observed direct surface runoff hydrographs. The theory provided excellent agreement for two basins with areas of the order of 1100 mi2 (1770 km2) but underestimates the peak flow for the smaller basin with 300-mi2 (483-km2) area. This relative lack of agreement for the smaller basin may be used to question the validity of the linearity assumption in the rainfall runoff transformation which is embedded in the above development.
This paper presents an integrated analysis of flow through earth dams in
which the entire porous domain is considered. The mathematical model
provides a finite difference solution to two- or three-dimensional
problems involving transient or steady state flow in the saturated and
unsaturated domains of nonhomogeneous, anisotropic dam sections. In
general, the water table is not a streamline; in many zoned cross
sections, a significant proportion of the stream tubes may take
unsaturated flow routes for some part of their traverse. In addition,
the position of the water table may be quite different from that
determined from the classic saturated-only analysis. Unsaturated flow
components take on greater importance in small dams rather than in
large, in dams with sloping cores and downstream filter blankets rather
than more homogeneous sections, and in the fine-grained, well-graded
soils common to internal cores rather than in the more permeable and
more uniform soils of the external sections. A simulation of the
transient initial advance problem shows that the rate of growth of the
saturated zone is highly dependent on the unsaturated properties of the
soils and on the initial moisture contents. In the early stages of
seepage following a rapid rise in the upstream reservoir level, inflow
rates into the dam may be as much as 100 times the steady state seepage
rate. Consideration of the unsaturated zone in the analysis of seepage
through earth dams involves added mathematical complexity and requires
data on unsaturated soil properties that are not commonly available.
A three-dimensional finite difference model has been developed for the treatment of saturated-unsaturated transient flow in small nonhomogeneous, anisotropic geologic basins. The uniqueness of the model lies in its inclusion of the unsaturated zone in a basin wide model that can also handle both confined and unconfined saturated aquifers, under both natural and developed conditions. The integrated equation of flow is solved by the line successive overrelaxation technique. The model allows any generalized region shape and any configuration of time variant boundary conditions. When applied to natural flow systems, the model provides quantitative hydrographs of surface infiltration, groundwater recharge, water table depth, and stream base flow. Results of simulations for hypothetical basins provide insight into the mechanisms involved in the development of perched water tables. The unsaturated basin response is identified as the controlling factor in determining the nature of the base flow hydrograph. Application of the model to developed basins allows one to simulate not only the manner in which groundwater withdrawals are transmitted through the aquifers, but also the changes in the rates of groundwater recharge and discharge induced by the withdrawals. For any proposed pumping pattern, it is possible to predict the maximum basin yield that can be sustained by a flow system in equilibrium with the recharge-discharge characteristics of the basin.
The buildup and decay of a laminar or turbulent flow over a sloping plane is treated by the kinematic-wave method, neglecting the slope of the water surface relative to the slope of the plane. The relationships developed show certain distinct differences from those postulated in the unit hydrograph method. liowever, a comparison of the results of calculations with published experimental measurements shows quite good agreement. The problem is extended to include the case of groundwater flow through a porous medium over- lying a sloping impermeable stratum, where water is supplied by infiltration from the ground surface above. liere the depth of water may be appreciable, so that the actual slope of the water surface influences the gravity flow significantly, leading to a nonlinear diffusion prob- lem. Solutions of this problem for the buildup and decay phases are compared with those obtained by the kinematic-wave method, and significant differences are noted for the latter phase. Further, the physical boundary condition at the upper edge of the slope changes at a critical precipitation rate, the depth of water being either finite or zero there depending upon whether the rate is greater than or less than the critical value. Flow over an impermeable surface. Consider an impermeable surface (Figure 1) which is of length L, slope S ------ sin O, and of unit width perpendicular to the plane of the diagram. We take the origin at A with the x axis along AB. Rain begins to fall at a rate Vo per unit area, where Vo is a constant. We shall examine the buildup of a two-dimensionM flow over the sur- face until a steady state is reached and the subsidence of the flow after the rain ceases. The continuity equation takes the form
A set of algebraic equations to determine the design discharge for highway culverts is proposed. The kinematic-wave theory and the concepts underlying the commonly used rational method are adopted to derive these design discharge equations. Various drainage basin configurations, among which are rectangular and converging catchments, cascades of planes and overland flow-channel flow systems are considered. Composite basins with nonuniform slopes, roughness properties and runoff coefficients are included. In order to employ the proposed equations, the rainfall intensity-duration relationships and the physical characteristics of the basin should be specified. Unlike empirical formulas used for the same purpose, the proposed equations are physically based. They can be employed for a variety of drainage situations within the limitations of the kinematic wave theory. A practical application section is included to show the use of the proposed equations.
In 1945, C. O. Clark proposed a method to develop synthetic unit hydrographs for the modeling of watershed rainfall response. His technique utilizes two components: a translation hydrograph and a linear reservoir routing. Clark's three parameters (the time of concentration T(C), a storage attenuation coefficient R, and a time-area histogram) can be estimated for gauged basins. For ungauged basins, T(C) and R are difficult to estimate. T(C) can be approximated by analyzing physical basin characteristics whereas both T(C) and R have been successfully estimated using parameter regionalization. Technologies for observing and managing spatially distributed watershed and rainfall information are constantly evolving. The improved availability of areally oriented data brings the challenge of integration of these data into hydrologic models. The Hydrologic Engineering Center (HEC) has developed the program ModClark to take a first step in this integration. ModClark is based conceptually on Clark's So-year-old method and uses next generation weather radar (NEXRAD) data. The ability of Clark's technique to accommodate the spatially distributed nature of rainfall and runoff illustrates the adaptability of Clark's original methodology. A demonstration of this adapted methodology is provided.
An instantaneous unit hydrograph (iuh) based on the theory of
topologically random networks (topological iuh) is evaluated in terms of
sets of basin characteristics and hydraulic parameters. Hydrographs were
computed using two linear routing methods for each of two drainage
basins in the southeastern United States and are the basis of comparison
for the topological iuh's. Elements in the sets of basin characteristics
for the topological iuh's are the number of first-order streams only,
(N), or the nuber of sources together with the number of channel links
in the topological diameter (N, D); the hydraulic parameters are values
of the celerity and diffusivity constant. Sensitivity analyses indicate
that the mean celerity of the internal links in the network is the
critical hydraulic parameter for determining the shape of the
topological iuh, while the diffusivity constant has minimal effect on
the topological iuh. Asymptotic results (source-only) indicate the
number of sources need not be large to approximate the topological iuh
with the Weibull probability density function.
Linear mathematical models describing stream or river outflow due to storm runoff do not explain several important observed features, such as the change in shape of the discharge hydrograph and the non-linear variation of peak discharge rate with variation of rainfall intensity.In the present paper, analytical solutions for a hydraulic model are obtained by the method of characteristics, firstly, for flow over a plane V-shaped catchment under a constant uniformly-distributed rainfall of finite duration, and secondly, for the stream outflow arising from the catchment discharge. The advantage of this simplified two-component model lies in the fact that only four parameters are involved; these comprise two dimensionless indices in the power-law equations of motion assumed for catchment and stream flow, a scale of (i) rainfall intensity or (ii) total rainfall or (iii) rainfall duration and a dimensionless parameter which represents a ratio of suitably-defined time constants for stream and catchment respectively.The calculated stream hydrograph – for either stage or discharge rate – is found to be a smooth curve which contains up to six discontinuities in curvature, the locations of these discontinuities, and hence the shape of the function, depending upon the values of the parameters noted above. It is noted that the rising part of the curve depends initially only upon the integral of the catchment outflow. In this region various segments of the curve exhibit power-law behavior, but this is, in fact, a consequence of assuming power-law depth-discharge relationships. For a similar reason, the falling part of the curve exhibits a power-law decay.This paper is the first in a series of three. Part II discusses model solutions for a steady rainfall of finite duration, which could be relevant to work with sprinkled plots. In Part III, the model is applied to three natural catchments. Additional problems arising from infiltration are discussed in Parts II and III.
The geomorphic instantaneous unit hydrograph (GIUH) may be one of the most successful methodologies for predicting flow characteristics in ungauged watersheds. However, one difficulty in applying the GIUH model is determination of travel time, and the other difficulty is the large amount of geomorphologic information required in the study watershed. Recently, using the kinematic-wave theory Lee and Yen (1997) have analytically determined the travel times for overland and channel flows in watersheds. The limitation of using an empirical velocity equation to estimate the runoff travel time for a specified watershed is then relaxed. To simplify the time-consuming work involved in geomorphic parameter measurement on topographic maps, the GIUH model is linked with geographic information systems to obtain geomorphic parameters from digital elevation models. In this paper, a case study performed for peak flow analysis in an ungauged watershed is presented. The geomorphic characteristics of the study watershed were analyzed using a digital elevation model and were used to construct the runoff simulation model. The design storm was then applied to the geomorphic runoff simulation model to obtain the design hydrograph. The analytical procedures proposed in this study can provide a convenient way for hydrologists to estimate hydrograph characteristics based on limited hydrologic information.
The Cunha Forest Hydrological Laboratory was established in the Serra do Mar, São Paulo, Brazil to achieve some understanding of the hydrological processes and the effects of forest cover on these processes in the headwater areas. Stream-gauging from two subtropical forest catchments (56.0 ha and 36.7 ha) covered with the Mata Atlântica commenced in 1982. Measurements of crown interception, surface runoff from a hillslope and estimation of soil water storage within the catchments quantified individual components of the hydrological processes. Ten years of field measurements and hydrograph analysis show that about 15% of annual rainfall is intercepted by the forest cover and returns directly to the atmosphere while 85% of the rainfall reaches the forest floor, where it infiltrates and remains in the soil to feed subsurface flow and baseflow or transpiration. Humid conditions obtain throughout the year and surface runoff is a rare occurrence on forested hillslopes. Stormflow is generated from wetland source areas adjacent to streams and from seepage from hillslopes. The total volume of stormflow is only 11% of annual rainfall. Fifty-nine % of annual rainfall is stored in the soil mantle and flows via subsurface routes to streams as baseflow throughout the year. This sustained flow of streams is one of the most important hydrological features and is controlled by such basin characteristics as the physical properties of the soil, the depth of the soil mantle and the vegetative cover. Soil evaporation and transpiration were estimated as 15% of annual rainfall by the water balance equation. Thus, the annual hydrological budget for the catchments is 70% streamflow and 30% evapotranspiration. Riparian areas are also places of stormflow production as well as of soil water and groundwater storage of water derived from hillslopes as interflow. An assessment of the area, depth of sediment and porosity of the riparian areas helps in understanding the runoff processes in low-order catchments in the Serra do Mar. ©1997 Elsevier Science B.V.
The instantaneous unit hydrograph (IUH) is derived as a function of the basin's geomorphological and physiographic characteristics. Inherent in the basin IUH is the response of the individual channels composing the basin. The response of the individual channels is derived by solving the continuity and momentum equations for the boundary conditions defined by the IUH. Both the effects of upstream and lateral inflow to the channels is taken into account in the derivation of the basin's IUH. The time to peak and peak response are used as a basis for comparison between the results produced by this model and those produced by a model where the channel's response is assumed to be an exponential distribution. The comparisons indicate that of the approach taken in this paper is indeed accurate, for example, the assumptions used do not invalidate the model, then the type of channel response used for the basin's IUH is significant, and future efforts must be directed towards parameter estimation.
In recent years hydrologists have subjected the various subsystems of the hydrologic cycle to intensive study, designed to discover the mechanisms of flow and to arrive at physical and mathematical descriptions of the flow processes. As a consequence, meaningful results are now available in the form of numerical solutions to mathematical boundary value problems for groundwater flow, unsaturated porous media flow, overland flow, and channel flow. These developments in physical hydrology, together with the tremendous advance in digital computer technology, should provide the impetus for a necessary redirection of research in hydrologic simulation. In this paper, a blueprint for the development of physically-based hydrologic response models is presented; the level of sophistication that can be achieved with presently available methodology is discussed; and areas for necessary future research are pinpointed.
The paper forms the first part of an introduction to the SHE, a physically-based, distributed, catchment modelling system produced jointly by the Danish Hydraulic Institute, the British Institute of Hydrology and SOGREAH (France) with the financial support of the Commission of the European Communities. The SHE developed from the perception that conventional rainfall/runoff models are inappropriate to many pressing hydrological problems, especially those related to the impact of man's activities on land-use change and water quality. Only through the use of models which have a physical basis and allow for spatial variations within a catchment can these problems be tackled. The physical basis and flexible operating structure of the SHE allows the model to use as many or as few data as are available and also to incorporate data on topography, vegetation and soil properties not normally included in catchment models. It does not require a lengthy hydrometeorological record for its calibration and its distributed nature enables the spatial variability in catchment inputs and outputs to be simulated. However, the large amount of data required by the model means that new operation methodologies must be evolved. Thus spatial scale effects or simply a lack of data may create significant uncertainties in the values of the catchment parameters used in a simulation. These uncertainties will give rise to corresponding uncertainties in the predictions. However, the SHE is able to quantify these uncertainties by carrying out sensitivity analyses for realistic ranges of the parameter values. Even when there is a lack of data, therefore, the SHE can act as a valuable “decision-support system”.
Numerical experiments are carried out to explore: (a) the relationship between the dimensionless third moment and the dimensionless second moment of the classical geomorphologic unit hydrograph; (b) the sensitivity of this shape indicator to the assumption in the GUH model relating the delay time in a stream segment to some power of the segment length; (c) the relationship between the parameters of the GUH and the geomorphic parameters of the catchment. In the paper, the geomorphologic unit hydrograph is formulated on a deterministic basis in contrast to the Markov and the statistical mechanics approaches.
The principles governing the application of the conceptual model
technique to river flow forecasting are discussed. The necessity for a
systematic approach to the development and testing of the model is
explained and some preliminary ideas suggested.
A geomorphologic kinematic-wave (GKW) model was developed for simulation of extreme floods from small alpine catchments. The GKW model couples the kinematic-wave theory and the geomorphologic representation of the catchment based on the Horton-Strahler ordering scheme. The model was tested on two small alpine catchments in Switzerland, and the agreement between simulated and observed floods was good. Care must however be taken with the computation of slope and roughness parameters. Copyright (C) 1999 John Wiley & Sons, Ltd.
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Engineering Hydrology
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Ponce, V.M., 1989. Engineering Hydrology. Prentice Hall Book
Co., Englewood Cliffs, NJ.
Evolution of Clark's unit graph method to spatially distributed runoff
- Kull
A geomorphologic kinematic-wave (GKW) model for estimation of floods from small alpine watersheds
- Berod