Surprising salmonid response to water diversion at four run-of-river hydroelectric projects in British Columbia

M.D Hocking,F.J.A Lewis,K Akaoka,A Harwood,T Hatfield,S.G Faulkner

doi:10.1139/cjfas-2020-0246

M.D Hocking, F.J.A Lewis + Show 4 more

Open Access

https://doi.org/10.1139/cjfas-2020-0246

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Abstract

Run-of-river (RoR) hydroelectric power provides renewable energy with potentially less impact on fish habitat productivity than large, reservoir-storage hydroelectric projects. This is the first empirical study of resident fish response to water diversion at RoR projects in BC, where the abundance of rainbow trout (Oncorhynchus mykiss) was monitored in four small streams using a before–after control–impact design. Although flows in the diversion reaches of these projects were reduced by 63% to 70%, the total biomass of rainbow trout increased from 35% to 157% across the streams compared with the “before period” and “control reaches”. The response to water diversion differed among age classes: adult biomass increased with reduced flows in the growing season; juvenile biomass increased with reduced flows in the winter, higher stream conductivity, and increased flows in late summer; and fry biomass increased with higher stream conductivity and temperatures. One novel way to contextualize these shifts in resident salmonid productivity and differential growth and (or) survival by age class is via a size–density approach, which we use here to demonstrate how the carrying capacity of a stream for rainbow trout is affected by water diversion.

Highlights

As demand for water and hydroelectric power increases, resource managers need to understand how alteration of the natural flow regime affects the sustainability and productivity of river ecosystems (Power 1995; Poff et al 1997; Poff and Zimmerman 2010) to balance hydroelectric power generation and maintenance of aquatic ecosystem services
Natural flows and flows diverted from the diversion reach were similar among the four project streams, with mean annual discharge (MAD) ranging from 5.00 to 6.89 m3/s and average instream flow in the diversion ranging from 1.49 to 2.55 m3/s, resulting in mean annual decreases in flow of 63% to 70% (Supplementary data, Table S31)
The positive salmonid response to flow diversion was aided by consistent release of the instream flow requirement, and by a restricted maximum diversion rate, which allowed frequent spills throughout the year, increasing the instream flow release and maintaining the features of the natural flow regime

Summary

Introduction

As demand for water and hydroelectric power increases, resource managers need to understand how alteration of the natural flow regime affects the sustainability and productivity of river ecosystems (Power 1995; Poff et al 1997; Poff and Zimmerman 2010) to balance hydroelectric power generation and maintenance of aquatic ecosystem services. Despite the potential advantages in limiting greenhouse gas emissions, hydroelectric projects can have harmful environmental effects, where they include high-head dams that impound large reservoirs that alter physical and chemical habitats both upstream and downstream of the dam, leading to substantial impacts on stream ecology (Ligon et al 1995; Rosenberg et al 1997; Nilsson et al 2005), especially fish such as salmonids (Baxter 1977; Murchie et al 2008; Korman et al 2011) These drawbacks and the emergence of lower cost renewable technologies with even lower emissions (Sims et al 2003; Greenblatt et al 2017), have led to criticism of hydroelectric energy as a sustainable form of renewable energy (Ansar et al 2014), shifting development towards smaller-scale hydropower production options such as “run-of-river” (RoR) that may have less of an ecological impact on salmonid fishes and key ecosystem services (Anderson et al 2015; Gibeau et al 2017).

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