Saccarappa Falls Nature-Like Fishway Modeling and Design

As part of project/dam surrender and removal efforts at the Saccarappa Hydroelectric Project (Saccarappa), Alden provided S. D. Warren Company d/b/a Sappi North America (Sappi) with the final design and fish passage analysis for nature-like fishways in the upper channels at Saccarappa Falls. The final design involves reshaping the existing bedrock channel into a form that is more conducive to fish passage while mimicking the morphology of a natural bedrock channel. Alden provided agency consultation while developing the design and will ultimately provide construction support. The proposed design complements a proposed double Denil fishway over the lower portion Saccarappa Falls designed in partnership with Acheron Engineering.

Alden conducted a site visit and reviewed existing geotechnical, hydrologic, site constraints, and other site data prior to developing the final design for the nature-like fishways. The final design was achieved by way of iteration between a 3D CAD representation of the proposed bathymetric surface and a 3D computational fluid dynamics (CFD) model. Expected small-scale roughness of the channel bed was incorporated into the CAD surface through a novel texturizing technique based on a high resolution laser scan of the existing bedrock surface. The CFD model was used to simulate proposed conditions at four discrete design flow rates. Hydraulic data output by the CFD model (e.g., depth and velocity) informed subsequent improvements of the proposed surface in CAD. Sappi and agency review and feedback was provided at 30%, 60%, 90%, and final drafts of the design. Fish passage effectiveness of the final design was analyzed by Alden biologists and engineers using USFWS’s SMath models developed for assessing velocity impediments by estimating fatigue, survivorship, and work. Alden also provided engineering consultation and inspections to support project construction.