Automated analysis of lateral river connectivity and fish stranding risks—Part 1: Review, theory and algorithm

Abstract

Riverine fish stranding is of significant concern due to its potentially devastating impacts on fish populations already at risk. Because stranding is dependent on a wide range of biotic and abiotic factors, it is difficult to accurately identify and parameterize fish stranding risks for various river topographies, fish species/lifestages and flow ramping scenarios. This article presents a literature review, new concepts and a novel Python3 algorithm for post‐processing two‐dimensional hydrodynamic numerical model results to identify spatially explicit locations where fish stranding is likely, such as but not limited to downstream of hydropeaking facilities. Compared to previous stranding algorithms, this one is novel in its use of graph theory to find optimal fish escape routes and for its embedding in the free, open‐source river analysis software River Architect. Guided by biological parameter selection and supplied with two‐dimensional hydrodynamic model rasters, River Architect's Stranding Risk module is suitable for characterization of existing pool stranding risks, alternative flow regime and topographic design evaluation and post‐project assessment of rivers during flow recessions.

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

“…In the companion article (Larrieu et al, 2020), a thorough literature was presented about the scope of fish stranding as an ecological process and river management problem. The topic of fish stranding has not been academically investigated within the context of the burgeoning literature about active and passive physical and vegetative adjustments to rivers for environmental stewardship, whether termed restoration, rewilding, rehabilitation, mitigation, or enhancement.…”

“…The companion article (Larrieu et al, 2020) presented a novel fish stranding algorithm that could be suitable for use in real river assessment and virtual design testing. In contrast to existing methods, this algorithm employs a graph-theoretic approach to 2D hydrodynamic model outputs to quantify lateral habitat connectivity for any fish species/life stage of interest.…”

“…Computed combined habitat suitability index rasters are used to weight disconnected area to produce a "disconnected habitat" raster. In addition to a spatially explicit map of disconnected habitat for the applied downramping scenario, a summary metric herein referred to as disconnected habitat area (DHA) is computed to indicate the total amount of high-quality fish habitat disconnected by flow reduction (see Larrieu et al, 2020).…”

“…The companion article (Larrieu et al, 2020) presented a new methodology that characterizes fish stranding risks for a given topography, target species/life stage, and flow ramping scenario.…”

“…The companion article (Larrieu et al, 2020) presented a new methodology that characterizes fish stranding risks for a given topography, target species/life stage, and flow ramping scenario. The concepts detailed in the companion article are briefly summarized here and illustrated with a flowchart (Figure 1).…”