Quantifying Flow-Dependent Changes in Subyearling Fall Chinook Salmon Rearing Habitat Using Two-Dimensional Spatially Explicit Modeling

Abstract

We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady‐state flows ranging from 1,416 to 11,328 m3/s. High‐resolution river channel bathymetry was used in conjunction with a two‐dimensional hydrodynamic model to estimate water velocities, depths, and lateral slopes throughout our 33‐km study area. To relate the probability of fish presence in nearshore habitats to measures of physical habitat, we developed a logistic regression model from point electrofishing data. We only considered variables that were compatible with a GIS and therefore excluded other variables known to be important to juvenile salmonids. Water velocity and lateral slope were the only two variables included in our final model. The amount of available rearing habitat generally decreased as flow increased, with the greatest decreases occurring between 1,416 and 4,814 m3/s. When river discharges were between 3,682 and 7,080 m3/s, flow fluctuations of 566 m3/s produced the smallest change in available rearing area (from −6.3% to +6.8% of the total). Stranding pool area was greatly reduced at steady‐state flows exceeding 4,531 m3/s, but the highest net gain in stranding area was produced by 850 m3/s decreases in flow when river discharges were between 5,381 and 5,664 m3/s. Current measures to protect rearing fall chinook salmon include limiting flow fluctuations at Priest Rapids Dam to 850 m3/s when the dam is spilling water and when the weekly flows average less than 4,814 m3/s. We believe that limiting flow fluctuations at all discharges would further protect subyearling fall chinook salmon.

Water Velocity Tolerance in Tadpoles of the Foothill Yellow-legged Frog (Rana boylii): Swimming Performance, Growth, and Survival

“…In the mid-channel environment at the calibration flow of 1.45 cms, the percent error in predicted depth and velocity averaged 11% and 25%, respectively. This is comparable to error reported in previous 2D modeling studies (21% for depth, 29% for velocity over gravel substrate in Pasternack et al 2006; see also discussion in Tiffan et al 2002) and reflects both error in surveying bed topography and limitations within the model assumptions.…”

“…The hydrodynamic modeling was completed using River 2D, a two-dimensional, depth averaged finite element model that is freely available and used by the California Fish and Game Department, U.S. Fish and Wildlife Service and others in fish habitat evaluation studies (Steffler and Blackburn 2002;Tiffan et al 2002;Hanrahan et al 2004;Gard 2005). The model is designed specifically for use with natural streams and rivers; it incorporates local roughness values, variations in wetted areas as flows fluctuate and supercritical/subcritical flow transitions.…”

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

“…3a) (Tiffan et al, 2002). The Columbia River above Priest Rapids Dam drains primarily mountainous regions in Canada, Idaho, Montana, and Washington, over which spatio-temporal distributions of precipitation and snowmelt modulate the timing and magnitude of river flows (Elsner et al, 2010;Hamlet and Lettenmaier, 1999).…”

Using a continuous riverscape survey to examine the effects of the spatial structure of functional habitats on fish distribution

“…Using a continuous survey of a functional habitat (species grain) at the segment scale (10 4 m) (species extent), areas occupied by shoals were detected, providing useful information for barbel and nase conservation. Such spatially explicit and continuous studies, at a scale large enough to elucidate the effects of habitat structure on fish distribution, are relatively new, but nevertheless provide advances in managing restoration of habitats (Baxter 2002;Labbe & Fausch 2000;Tiffan et al 2002;Torgersen & Close 2004). In these occupied areas, our results highlight the importance of supplementation for feeding habitat patches.…”