Modular and Scalable Downstream Passage for Silver American Eel

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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.

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A major component of an Atlantic salmon population model developed by NMFS is the survival of smolts and kelts passing downstream at hydropower projects.  To obtain this information, NMFS contracted Alden to estimate downstream passage survival of Atlantic salmon smolts and kelts at 15 hydroelectric projects on Maine’s Penobscot River and its tributaries.  These desktop survival estimates focus on direct mortality attributable to passage at dams and to multiple dam passage.  An established turbine blade strike probability and mortality model was used to estimate direct survival of fish passing through turbines at each project.  Survival rates for fish that pass downstream over spillways or through fish bypass facilities were estimated based on existing site-specific data or from studies conducted at other hydro projects with the same or similar species.  Most of the projects included in the study have upstream passage facilities for anadromous species (river herring, American shad, and/or Atlantic salmon), as well as operating downstream bypasses for juvenile and adult outmigrants.  Some of the projects have installed narrow-spaced bar racks or overlays to reduce fish entrainment through turbines.

The results of Alden’s survival analysis provided data in a level of detail that would have been extremely expensive and difficult to accomplish with field studies.  Typically, turbine passage survival studies conducted in the field only evaluate one or two turbines operating at one or two gate settings (i.e., flow rates). The methods and model developed for NMFS for Atlantic salmon on the Penobscot River are transferable to other river systems and species.  The theoretical model for predicting strike probability is applicable to most species and the blade strike mortality data for rainbow trout are considered representative of many other species. 

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