CFD as a Tool for “Nature-Like” Fishway Design

The decommissioning of the Saccarappa hydroelectric project required the design and implementation of modernized fish passage. Through the use of CFD modeling, our team helped to guide the engineering of the design. But the project was not as straight-forward as one would think. Making fish passage functional in a river that sees a wide range of flows required as much art as it did engineering.

Curious about how we helped to accomplish this? This talk presents a case study in the use of 3D CFD as a practical tool in the design of a nature-like fishway on the Presumpscot River in Westbrook, Maine.

CFD and Nature-Like Fishways: A Case Study

Three-dimensional (3D) Computational Fluid Dynamics (CFD) modeling is becoming a widely used tool for designing and evaluating fish passage measures. Traditional measures, such as fish ladders, lend themselves well to CFD analysis thanks to regular, relatively simple channel geometries; however, more novel measures, such as the increasingly-popular “Nature-Like Fishways” (NLFs), are characterized by complex geometries and large discrepancies in spatial scales (reach-scale to roughness-element-scale) that are difficult to fully resolve in a CFD model. As such, these novel approaches to fish passage require similarly novel approaches to CFD modeling.

The final design was achieved by way of iteration between a 3D CAD terrain model and a 2D/3D hybrid CFD model. Proposed channel roughness was incorporated into the CAD surface through a novel texturizing technique based on a high resolution laser scan of the pre-existing river bed. Fish passage effectiveness was analyzed using USFWS’s SMath models. The project is currently under construction, therefore, practical lessons-learned in implementing such a complex, non-traditional design will be presented in addition to the CFD methodology.