Managing flow ramping operations at run-of-river hydroelectric projects

摘要

Run-of-river projects are promoted as a more sustainable alternative to traditional storage projects because they don’t alter the flow regime in downstream reaches. Although true run-of-river operations follow the daily flow regime, they can cause rapid short-term changes to streamflow of sufficient magnitude to dewater habitat and strand fish. In this paper we examine how run-of-river projects affect the short-term temporal and spatial pattern of flow change and identify the factors influencing fish stranding at these projects. Although many new run-of-river projects in British Columbia are located on non-fish bearing streams, they affect flows downstream in waters inhabited by salmon and trout. Guidance on managing ramping and stranding effects on these projects is lacking in the literature, which focusses on storage projects, where flow releases are reliably delivered from reservoir storage. Run-of-river projects lack the storage necessary to offset utility disconnection events, which can suddenly decrease streamflow, stranding substantial numbers of fish. In British Columbia utilities and regulators have identified specific operating and environmental conditions where juvenile fish stranding is likely, supporting a risk-based approach to setting, managing, and implementing ramping rate mitigation. Stranding risks vary between habitats of different gradients and channel morphologies, and habitats immediately downstream of projects are at highest risk, although risk remains high for dozens of kilometres downstream on some projects. This work demonstrates the value of season-specific ramping rates, to mitigate high stranding risk during the spring. Using new information gained from the monitoring of these projects in British Columbia, we describe a management approach to increase operational efficiency while better avoiding fish mortality from stranding.