Channel dynamics and habitat development in a meandering, gravel bed river

Abstract

[1] We investigated how channel morphology, flow complexity, and habitat characteristics in a meandering gravel bed river evolved over time from a simple, reconfigured initial condition. Using a time series of topographic data, we measured rates of channel migration and morphologic change, documented patterns of sediment storage, and estimated rates of sediment supply. We constructed, calibrated, and validated hydrodynamic models to quantify how the evolving morphology influenced hydraulic conditions, flow complexity, and habitat suitability for Chinook salmon spawning and rearing. For a series of meander bends with constant curvature, similar bank materials, and an identical flow history, sediment supply and bar storage directly influenced channel migration rates. Habitat modeling indicated that the availability of Chinook salmon spawning habitat increased over time, whereas the majority of the reach continues to provide only low-to medium-quality rearing habitat for juvenile salmonids, primarily because of a lack of low-velocity refuge zones. However, other metrics of flow complexity indicate that areas of favorable flow conditions gradually expanded as point bars developed along the inner bank of each bend. These results indicate that although sediment supply can stimulate channel change and diversify river morphology, which acts to promote flow complexity and provide spawning habitat, these sediment-driven morphological changes might not create bioenergetically favorable habitat for juvenile salmonids.

Streamwise vortices destabilize swimming bluegill sunfish (Lepomis macrochirus)

“…Streamwise vorticity occurs in the wild both from anthropogenic pressures such as boats, energy turbines and other propellers and naturally from river confluences, meandering and interactions with obstacles in the river bed (Harrison et al, 2011;Roy et al, 2004;Smith et al, 2005). In the wild, streamwise vorticity might be more detrimental as it is not frequently constant or predictable.…”

Modeling the influence of flow on invertebrate drift across spatial scales using a 2D hydraulic model and a 1D population model

“…Transects were placed among the first three riffles and bend pools in the upper portion on the reach; see Fig. 1 in Harrison et al (2011) for exact locations. Velocity data were obtained with an acoustic Doppler velocimeter (ADV), which measured three-dimensional velocities for 60 s at a height above the bed equal to 40% of the local flow depth, approximating the depth-averaged velocity for an assumed logarithmic vertical profile, consistent with the hydrodynamic model.…”

“…In order to take advantage of existing hydraulic data sets, the MIKE21 FM model was calibrated and validated using a 2D flow model developed for the entire Robinson Reach, which included 10 bends of nearly uniform dimensions and curvature (see Harrison et al, 2011;Legleiter et al, 2011) for additional site description). Bed topography was surveyed across the active channel and roughly 10 m of the floodplain on either bank using a total station, with a mean cross section spacing of 7 m (20% of the channel width) and an average distance of 2 m between points along a transect.…”

Nitrate retention capacity of milldam-impacted legacy sediments and relict A horizon soils

“…Floodplains are known to be active N sinks that can support high N retention in sediments of adjacent water bodies (Forshay and Stanley, 2005;Kaushal et al, 2008b;Harrison et al, 2011). In contrast, legacy-sediment-rich fill terraces have been shown to dampen N removal pathways in the long-buried relict soils which they overlie, while also acting as potential sources of nitrate (NO − 3 ) to waterways (Weitzman et al, 2014).…”