Automated analysis of lateral river connectivity and fish stranding risks. Part 2: Juvenile Chinook salmon stranding at a river rehabilitation site

Abstract

The dynamics of fish stranding have not been academically investigated within the context of physical adjustments to rivers for habitat enhancement purposes. River projects may aim to help fish populations but instead may function as attractive nuisances reducing populations because of unaccounted‐for stranding risk. This study applies a novel algorithm to predict spatially explicit, meter‐resolution fish stranding risk at a river rehabilitation site in California to address three scientific questions. Postproject disconnected wetted area predictions were validated against water surface elevation measurements and time lapse photography of flow reductions and stranding events. A comparison of preproject, final design, and postproject topographies revealed that the occurrence and severity of stranding events is highly sensitive to side‐channel topographic structure and postproject morphodynamic change. Even with moderate flows, side‐channel exits tend to close off by bars built across them via bedload transport. Implications for river management practices and river rehabilitation project design are discussed.

Systematic comparison of 1D and 2D hydrodynamic models for the assessment of hydropeaking alterations

“…Approaches for the estimation of fish stranding risk typically rely on predictions of both the wetted area and vertical dewatering velocities (e.g., Larrieu & Pasternack, 2021; Larrieu, Pasternack, & Schwindt, 2021). Therefore, a 1D model might not be adequate for the quantification of fish stranding risk in more complex river morphologies and during low flow conditions, mainly due to the limited accuracy of predicting the wetted area.…”

“…More heterogeneous river morphologies might reduce adverse impacts of hydropeaking due to increased availability of shelter (refugia) during peak flows (Person, 2013; Vanzo, Zolezzi, & Siviglia, 2016). However, also the stranding risk of fish is found to increase in more complex and heterogeneous morphologies, as a result of direct stranding on gravel banks or trapping inside channels or potholes (Larrieu & Pasternack, 2021; Tuhtan et al, 2012).…”

Fish stranding in relation to river bar morphology and baseflow magnitude: Combining field surveys and hydrodynamic–numerical modelling

“…When the turbines are shut down, previously wetted areas fall dry. In general, if the speed of such sudden flow decreases exceeds fish's capability to follow the receding water levels, they can strand on the river bars or become trapped in shallow side channels and potholes (Cushman, 1985; Larrieu & Pasternack, 2021; Nagrodski et al, 2012; Young et al, 2011). Subsequently, the loss of fish per drawdown event is a likely cause of diminished fish populations if occurring multiple times per season (Bauersfeld, 1978; Hayes et al, 2021; Sauterleute et al, 2016; Schmutz et al, 2015).…”

Applying a two‐dimensional hydrodynamic model to estimate fish stranding risk downstream from a hydropeaking hydroelectric station

“…However, small‐scale fish stranding data can be challenging to upscale to the level of the riverscape. Some studies modelled the variation in wetted area and dewatering ramping rate to gauge fish stranding areas (Juárez et al, 2019; Larrieu & Pasternack, 2021; Sauterleute et al, 2016) and estimate the risk of stranded fish with little or no fish stranding data collected from the specific study site (Burman et al, 2021; Casas‐Mulet et al, 2016; Hauer et al, 2014; Sauterleute et al, 2016; Tuhtan et al, 2012).…”

“…The outputs of hydrodynamic models include the wetted area of a river at different discharges, which can subsequently be used to estimate stranding risk (Valentin et al, 1996) by identifying the dewatered areas with fish stranding potential (Juárez et al, 2019; Larrieu & Pasternack, 2021; Mandlburger et al, 2015; Tuhtan et al, 2012; Vanzo et al, 2016). By modelling the wetted area during the high and low discharge peak and over the course of the fish growing season, the change in wetted area available to fish during hydropeaking events can be calculated and matched to their life histories.…”