A Modeling Approach for The Quantification Of Fish Stranding Risk: The Case of Lundesokna River (Norway) — ASN Events

A Modeling Approach for The Quantification Of Fish Stranding Risk: The Case of Lundesokna River (Norway) (#122)

Davide Vanzo , Annunziato Siviglia 1 , Guido Zolezzi 2 , Knut Alfredsen 3 , Matteo Tancon 2
  1. ETH, Zurich, Switzerland
  2. University of Trento, Trento, Italy
  3. NTNU, Trondheim, Norway

 River reaches downstream hydropower plants regularly experience severe discharge reductions (dewatering) due to production shutdowns. Such rapid dewatering processes result in harmful, even lethal, conditions for the biological communities. Focusing on fish community, several eco-hydraulic features, e.g. wetted area variation, dewatering rate (water depth rate of change), grain size heterogeneity, habitat availability, are recognized to determine the stranding risk2 . The goal of the present work is to understand and quantify the hydromorphological controls on fish stranding risk via an unsteady two-dimensional numerical modeling describing flow depth and velocity for each computational cell. The stranding risk is evaluated concurrently considering the dewatering rate and the wetted area variation, which represent two crucial Ecologically-Relevant Hydraulic Parameters (ERHPs), generally considered separately by existing legal requirements1 . The proposed modeling approach is applied to the case of Lundesokna, a Norwegian river regularly subjected to rapid hydropower plant shutdowns. In particular we quantify the tradeoffs between the selected ERHPs and a suite of hydropower shutdown alternatives. Results show that the river morphology has a relevant role in finding effective dewatering scenarios that offer the best ecological-economical tradeoffs. Among the tested scenarios we identify which ones provide the greatest benefits in terms of eco-hydraulic response. Moreover the outcomes underline the need of fully unsteady modeling when aiming at accurately estimate hydraulic features under hydropeaking conditions. Eventually the present study provides a useful background for analysis of critical impacts of hydropeaking in Lundesokna River, but also it might contribute in debating and benchmarking eco-hydraulic modeling strategies.

  1. Baumann P., Kirchhofer A. and Schalchli U. (2012). Risanamento deflussi discontinui - Piani cazione strategica. Un modulo dell'aiuto all'esecuzione Rinaturazione delle acque. Technical report, Ufficio federale dell'ambiente, Bern, CH.
  2. Hauer C., Unfer G., Holzapfel P., Haimann M. and Habersack H. (2014). Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking. Earth Surface Processes and Landforms
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