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Histogram of C(Z, W j ) classified by positive and negative values as well as > and < 1 (a). Also shown is a histogram classified by quadrant (b). Both illustrate anoverall preference for C(Z, W j ) > 0 with increasing discharge and also illustrating an increasing preference for positive values of C(Z, W j ) > 1 up until 283.2 m 3 s −1 after which it declines. Colors represent bin centered values.
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This paper demonstrates a relatively new method of analysis for stage dependent patterns in meter-scale resolution river DEMs, termed geomorphic covariance structures (GCSs). A GCS is a univariate and/or bivariate spatial relationship amongst or between variables along a pathway in a river corridor. Variables assessed can be flow independent measur...
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Citations
Geometric modeling of river channel topography is a method of design synthesis wherein specific 2D geometric elements of river topography, such as the bed profile, cross sectional shape, and channel planform contours, are expressed mathematically in isolation and then combined to produce a 3D heightmap. We utilized the geometric modeling framework to synthesize channel terrains that reveal flow‐form‐function linkages to investigate what roles variability in bed roughness, thalweg elevation and channel width play in defining hydraulic and ecohydraulic conditions of a channel reach from baseflow to bankfull discharge. To achieve a robust inquiry for a range of settings, this study developed four distinct synthetic channel terrain models for each of 3 stream reaches of different channel types in the South Fork Eel River in northern coastal California, USA. To test the process‐based effects of these diverse terrain synthesis options, we compared the resulting hydraulic patterns and preferred habitat availability for fry/juvenile steelhead trout and coho salmon over a range of discharges. Among thalweg bed undulation, width variation and bed roughness, we found thalweg bed undulation was the key factor affecting the channel ecohydraulic response at baseflow condition. Furthermore, at bankfull, thalweg bed elevation has the largest effect in high‐order mainstem streams identified by gravel‐cobble, high width‐to‐depth ratio, riffle‐pool sequences, width variation in intermediate confined channels with gravel‐cobble, high width‐to‐depth ratio with expansions/contractions, and bed roughness in low‐order streams with low width‐to‐depth ratio, high‐gradient, cobble‐boulder and step‐pool/cascade.
The extent and timing of many river ecosystem functions is controlled by the interplay of streamflow dynamics with the river corridor shape and structure. However, most river management studies evaluate the role of either flow or form without regard to their dynamic interactions. This study develops an integrated modeling approach to assess changes in ecosystem functions resulting from different river flow and form configurations. Moreover, it investigates the role of temporal variability in such flow-form-function tradeoffs. The use of synthetic, archetypal channel forms in lieu of high-resolution topographic data reduces time and financial requirements, overcomes site-specific topographic features, and allows for evaluation of any morphological structure of interest. In an application to California's Mediterranean-montane streams, the interacting roles of channel form, water year type, and hydrologic impairment were evaluated across a suite of ecosystem functions related to hydrogeomorphic processes and aquatic habitat. Channel form acted as the dominant control on hydrogeomorphic processes, while water year type controlled salmonid habitat functions. Streamflow alteration for hydropower increased redd dewatering risk and altered aquatic habitat availability. Study results highlight critical tradeoffs in ecosystem function performance and emphasize the significance of spatiotemporal diversity of flow and form at multiple scales for maintaining river ecosystem integrity. The proposed approach is broadly applicable and extensible to other systems and ecosystem functions, where findings can be used to inform river management and design testing.
Geomorphometry, the science of quantitative land-surface analysis, has become a flourishing interdisciplinary subject, with applications in numerous fields. The interdisciplinarity of geomorphometry is its greatest strength and also one of its major challenges. Gaps are still present between the process focussed fields (e.g. soil science, glaciology, volcanology) and the technical domain (such as computer science, statistics …) where approaches and theories are developed. Thus, interesting geomorphometric applications struggle to jump between process-specific disciplines, but also struggle to take advantage of advances in computer science and technology. This special issue is therefore focused on facilitating cross-fertilization between disciplines, and highlighting novel technical developments and innovative applications of geomorphometry to various Earth-surface processes. The issue collects a variety of contributions which fall into two main categories: Perspectives and Research, further divided into “Research and innovative techniques” and “Research and innovative applications”. It showcases potentially exciting developments and tools which are the building blocks for the next step-change in the field.
