Lars Bengtsson

Lund University | LU · Division of Water Resources Engineering

Three consecutively complicated versions of description of the heat and moisture transfer processes in snowpack for a one-dimensional model of the atmosphere-soil interaction are considered. Results of simulation by means of these parametrizations are compared with each other and with observed data from the Valdai research station. The observed dat...

Urban water balances differ from their rural counterparts due to extreme spatial heterogeneity, water imported from outside catchment boundaries and changed flow paths (e.g., drainage pipes and impervious surfaces). Urban catchments are characterized by increased peak discharges and fast response times, each contributing to specific environmental p...

The hydrology of a cutover fen was studied from May to October in 1995 and 1996. Rainfall equivalent depths were measured every 15 min and stream runoff was continuously monitored. Water table depths were measured bi-weekly during 1995 and continuously during 1996. Storm runoff was separated into different components; rain falling directly into cha...

A field study on current structure and circulation characteristics in Lake Vendyurskoe, a small, shallow, icecovered lake in Karelia, Russia, is presented. The current velocity magnitudes were generally found to be small. The most pronounced currents had an oscillating character, with velocity amplitudes on the order of millimeters per second. The...

The movement of water in a large (3.5 m3) undisturbed sample of 22-year-old municipal solid waste has been modeled using a kinematic wave approximation for unsaturated infiltration and internal drainage. The model employs a two-parameter power expression as macroscopic flux law. The model parameters were determined and interpreted in terms of the i...

The physical and chemical changes of a waste mixture consist ing of mumcipal solid waste (MSW) and sewage sludge were investigated during the anaerobic waste stablilization phases of the mixture. The emphasis of this study was the behavior of heavy metals. The waste was deposited in a test cell in 1973. It was found that the waste mass decreased by...

Despite having the same snowmelt processes, snowpacks in urban environments experience a range of conditions different from those of rural areas. Melt is intensified at some sites due to greater radiative energy. Shading, however, can reduce radiation and melt at other sites. Changes to the radiation balance and snowpack processes have been investi...

Because of its simplicity the rational method is still frequently used in urban planning and design. In this paper using the time-area method and statistically derived design storms, the design peak flow is computed for urban basins of different complexity and compared with the design flow determined from the rational method. It is shown that the d...

The hydrological sensitivities to long-term climate change of a watershed in Eastern Canada were analysed using a deterministic watershed runoff model developed to simulate watershed acidification. This model was modified to study atmospheric change effects in the watershed. Water balance modelling techniques, modified for assessing climate effects...

Using water balance computations, the behavior of different kinds of lakes is discussed. Simple analytical expressions relating water level to hydrological conditions and lake bathymetry are given. The importance of knowing the river basin area when analyzing lake levels is stressed. A conceptual rainfall-runoff model including lake routing is used...

A field study on the temperature, salt content, and density regime in three shallow ice-covered Karelian lakes is presented. The measurements show that the heat content increases during the whole ice-covered period. At ice formation a weak stable stratification existed in the lakes, with average temperatures about 1°C. Thereafter, the stability of...

A field study was carried out in three small shallow ice-covered lakes to study heat and mass fluxes and their spatial and temporal variability. During the main part of the winter, the heat flux at the ice-water interface, being of the order 0.5-1 W m−2, was dominated by conduction from water to ice and did not show any significant variations in ti...

Vertical movement of snowmelt water through snowpacks is modelled by applying the kinematic wave theory. Analytical solutions are obtained for moisture flux, particle velocity, time history and velocity of meltwater front and total moisture content for a single melt event assuming that the melt rate is constant. These solutions are extended to the...

Movement of snowmelt water through a thin saturated layer at the infiltrating base of a snowpack is modelled by applying the kinematic wave theory. Analytical solutions are obtained for flow depth, velocity and discharge assuming that the rate of input to the saturated layer due to vertical percolation is constant. This assumption results in a line...

India has a territory of 328 million hectares, which receives an average annual rainfall of 120 cm; this is among the highest for a comparable geographical area in the world. Despite India's vast water resources, droughts and famines are a common occurrence in many parts of country. This paper briefly surveys India's river-basin systems, drought-pr...

A field study on the temperature, salt content, and density regime in three shallow ice-covered Karelian lakes is presented. The measurements show that the heat content increases during the whole ice-covered period. At icc formation a weak stablc stratification existed in the lakes, with average temperatures about 1°C. Thcreaftcr, the stability of...

During late winter (18 March–7 April 1994), temperature and current measurements were made in Lake Vendyurskoe, Russia, including three surveys at six cross sections of the lake. Also, the temperature profile evolution was registered with two thermistor chains at two stations (bottom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperat...

The results of any hydrological calculation are highly dependent on rainfall data used. The spatial variability of precipitation, that is very substantial even on very small catchments, can never be completely revealed by a network of gauges. Equally, the time variability and extremes, sampled in a set of data with limited duration, are seldom adeq...

A micro computer model was developed for routing chemical waste contamination through a small aquatic system. The capabilities of this simulation model include the following characteristics: a) It distributes contamination by advection and dispersion along the longitudinal axis of the system. b) It may be discretized into any number of segments (ve...

The effect on evaporation of the presence of biodegradation heat in an uncovered biocell under operational conditions is elucidated. The contribution of the heat of biodegradation was investigated by measuring the temperature gradient in the top layer of a landfill. The evaporation was calculated by combining the energy budget with an expression fo...

To achieve effective environmental control, it is important to develop methodologies for dealing with uncertainties in model simulation of pollution behaviour and effects. Several procedures have been proposed to quantify uncertainties in modelling studies. This paper utilizes the two methods that are widely applied, i.e. functional analysis and Mo...

The finite element model was successfully applied to predict the Pb-210 and total extractable fatty acid concentrations at different depths in two sediment cores from Lake Ontario by using different transport parameters. The transport parameters were computed from Pb-210 data. These parameters were used to simulate the total extractable fatty acid...

High hydrogen ion concentrations of runoff events were analyzed in terms of the probability distributions of frequency, duration, magnitude, and time of occurrence. Simple stochastic models were applied to the probability distributions of the annual frequency of high hydrogen ion concentration flows and their magnitudes. A consideration of the stat...

Mixing in ice covered lakes is caused by through-flow currents, oscillations of the ice cover and by convective currents induced by heat flow from the sediments or by solar radiation penetrating the ice. Mainly from studies in Swedish lakes, current velocities and mixing coefficients are quantified for the different processes generating water movem...

Temperature conditions and heat fluxes in ice covered lakes are discussed analyzing measurements in eight Swedish lakes. Heat fluxes from sediments and heat fluxes from water to ice are determined from temperature profiles. The contribution o f solar radiation is estimated from heat-budget calculations. It is found that the heat content o f most o...

Prediction and evaluation of pollution of the subsurface environment and planning remedial actions at existing sites may be useful for siting and designing new land-based waste treatment or disposal facilities. Most models used to make such predictions assume that the system behaves deterministically. A variety of factors, however, introduce uncert...

Water-related processes in landfills are discussed with emphasis on internal processes such as field capacity, moisture variation in time and space, and macropore flow. Runoff production and evaporation from landfills in Sweden of different age are investigated. It is clarified in what ways and for how long a closed municipal landfill differs from...

In small catchments, the response of headwater streams to precipitation is often very rapid but is rarely the same, i.e. the proportion of precipitation which appears quickly as streamflow under the storm hydrograph differs from storm to storm. The environmental tracer approach was applied to three rainfall events in 1991 in the forested Rudbâck ca...

Resuspension of inorganic sediments in a very shallow Swedish lake is studied using settling sediment traps and measurements of suspended matter. Theoretical aspects of resuspension dynamics is discussed emphasizing special shallow lake aspects. Bottom shear stress distribution is computed for different wind conditions.

The pathways of melt water from a subdrained agricultural basin in southern Finland were investigated using oxygen-18 as tracer and measuring subdrainage water and total basin runoff. The flow paths for the melt water to reach the subdrains were through cracks in the ploughed layer and through regular spaced vertical sand-gravel drains. As long as...

Snowmelt and runoff in urban areas in Luleå, north Sweden, are discussed and compared with rural conditions. The uneven snow distribution in cities is quantified. Energy fluxes at the snow surface in different environments are estimated. It is shown that, mainly because of increased absorbed radiative energy in the snow, the daily melt is about 10...

Analytical solutions for runoff caused by a moving rain storm of time-varying rain intensity from a complex drainage basin are derived assuming constant concentration times for the different systems within the basin. It is found that the runoff caused by a peaked rain intensity distribution is higher than that from a uniform distribution of the sam...

Meltwater, stream water, and subsurface water at different depths and locations within the basin were analyzed with respect to oxygen isotopes. The average fraction of event water in the stream was 0.22 during the melt period, and 0.15 during a 15 mm storm event in early May. The area contributing to runoff, following the traditional contributing a...

Sedimentation and redistribution of fine sediments in three Swedish lakes of different character have been investigated using settling sediment traps. The bottom shear stress from wind generated waves are calculated and the extension of erodable bottom area is related to wind conditions. Wave induced erosion and deposition during and after cessatio...

Two different rainfall-runoff models are applied to river basins in northern Sweden and Finland to study the effect of changed climate on peak flows. Hypothetical meteorological data series are constructed by increasing observed values by given amounts and fractions. In a Swedish moderately large basin snowmelt and daily precipitation were consider...

Hydrograph separation using oxygen-18 was undertaken during the snowmelt periods of 1985 and 1987 in a forested basin (0.69 km") in southern Finland. The degree of mixing of acid meltwater and neutral groundwater was estimated. Application of isotope techniques indicated that subsurface pre-event water is the major component of discharge even durin...

A kinematic approach is applied to compute moisture flux and particle velocities in the unsaturated zone. The computations are compared with observations of tracer marked meltwater particles. Groundwater flow is computed accounting for storage and assuming constant particle velocity. It is found that meltwater particles that reach the groundwater n...

The natural isotope oxygen-18 and artificially injected tritium are used for studying the percolation of soil water. Particle velocity, progression rate and soil moisture flux are distinguished from each other. Water particle velocities and seasonal groundwater recharge are determined in glacio-fluvial deposits and in till soils. In the glacio-fluv...

Dispersion studies in three ice-covered lakes are presented. One of the lakes has a large river through-flow. In the other two lakes, small seiche-induced currents are generated through wind action on the ice cover. Dispersion coefficients are computed from five dye experiments lasting from 1/2 day to 16 days. These coefficients are related to meas...

The relation between rain movement and areal reduction of rain intensity is investigated. An approach for calculating areal reduction factors from point hyetographs and storm speed is suggested. Very good agreement is found between moving storm derived areal reduction factors and reduction factors determined using a dense net of rain gauges. Moving...

The variability in ice conditions over a lake and between lakes is studied. The effect of snow and snow drift on ice growth is theoretically discussed and quantified. Heat flow from the lake water to the underside of the ice and melting from the upper surface are also discussed quantitatively. Observations of spatial variability in late February an...

The variability in ice conditions over a lake and between lakes is studied. The effect of snow and snow drift on ice growth is theoretically discussed and quantified. Heat flow from the lake water to the underside of the ice and melting from the upper surface are also discussed quantitatively. Observations of spatial variability in late February an...

A model for determining the interaction between the lakes in a lake system is derived. The continuity equations for all the lakes in a lake system are coupled through discharge equations based on measured resistance factors for the channels interconnecting the lakes. A resistance factor shown to be a unique function of the mean of the up- and down-...

ABSTRACT In runoff,models,snowmelt,is usually,determined by a degree-day,approach.,The computed,melt,of a par­ ticular day may be erroneous, but since peaks from groundwater flow are the result of several days' melt, runoff,peaks,are,accurately,estimated.,For small,basins where,overland,flow,occurs,and,considerable,streamflow variations over the da...

The variability in ice conditions over a lake and between lakes is studied. The effect of snow and snow drift on ice growth is theoretically discussed and quantified. Heat flow from the lake water to the underside of the ice and melting from the upper surface are also discussed quantitatively. -from Author

Six years' runoff data from Bensbyn Research Watershed (BRW) in northern Sweden is discussed. BRW is 1.6 km2, out of which 0.5 km2 is a large meadow and the remaining area consists of a dense coniferous forest. In the runoff analysis, runoff contribution from the meadow is separated from that from the forest. Peak flows are related to snowmelt from...

The influence of the Bay of Bothnia sea level on the water stages in a series of interconnected lakes near the city of Lulea in Sweden is studied. Future conditions as a consequence of land elevation and channel improvements are simulated using a mathematical model. It is found that due to landlift the lake system will be divided into two lake syst...

The hydraulics of meltwater percolation through a snowpack is analyzed in some detail. An implicit numerical model is used for determining the meltwater movement. The effect of freezing fronts of the free liquid water in the snowpack is evaluated. It is shown that even after a moderately cold night, it takes several hours of snowmelt before the sno...

The snowmelt runoff process from small basins is discussed. A differentiation is made between overland flow in the snowpack and groundwater flow induced by infiltrating meltwater. The effect of variations of the snowmelt intensity on streamflow is studied. It is shown that the runoff is high from the first day of snowmelt runoff if the streamflow i...

A method for including night-time refreezing of the top layer of a snowpack in the degree-day method for computing daily snowmelt rates is presented. It is found that during days of large diurnal temperature variations the daily melt is more determined by the day-time conditions than by the daily mean conditions. Applications are made to an open ar...

The daily variation of snowmelt generated run-off is discussed. The heat conduction in the snowcover and refreezing during cold nights are discussed. The refreezing phenomena significantly influences the saturation conditions in the top layer of the snowcover.-from Author

Possible evaporation rates from a snow surface with respect to available energy and vapour pressure deficit in the air are discussed. In literature reported measurements and measurements carried out at the University of Luleå are analysed. It is found that for northern areas the total amount of evaporation during the whole snow covered season amoun...

Possible evaporation rates from a snow surface with respect to available energy and vapour pressure deficit in the air are discussed. In literature reported measurements and measurements carried out at the University of Lulea are analysed. -from Author

In most lakes the wind is the most important flow generating mechanism. In this paper the problem of wind generated circulation - directly wind induced currents and seiches - in small lakes is reviewed. Many field observations are presented and discussed. In the thermocline and the hypolimnion forced seiche currents are shown to dominate the direct...

A new device (time-distance recorder; TD-recorder) is presented for the measurement of the relative movements of two echoes visualized by a two-dimensional real-time scanner. One of the real-time image lines is selected and the instant distance between two echoes, indicated by markers, is assessed on-line. The output analog signal passes through a...

The snowmelt at a point is estimated through a simplified energy budget. From the energy equation a degree-day method is derived. The rate of snowmelt is found as a constant multiplied by the temperature excess over an equilibrium temperature which depends on solar radiation. The snowmelt events in Kiruna (3 years) and Luleå (4 years) are analysed...

TRANSIENT AND STEADY-STATE MODELS FOR HOMOGENEOUS AND TWO LAYERED WATER MASSES ARE PRESENTED.THE STATIONARY MODELS HAVE BEEN ADAPTED TO LAKE VELEN.THE CORRESPONDENCE BETWEEN THEORETICAL AND MEASURED CURRENTS XAS GOOD.A TRANSPORT OF MOMENTUM PROBABLY TAKES PLACE ONLY WHERE THE THERMOCLINE TOUCHES THE BOTTOM.KNOWLEDGE OF THE TURBULENT MECHANISMS IS M...

Turbulent exchange coefficients are studied by field experiments and by mathematical models. The field experiments give a horizontal diffusivity of about 200 em'/s- The vertical exchange coefficient departs on the wind and is about 10 em'/s. Il has a maximum value a few metres below the surface and lends to fall to molecular values in the thermocli...