Our scientists and engineers have broad experience designing, modeling, and testing fish passageways, including ladders, lifts, and natural channels. We work with clients to determine the best approach for providing fish passage or improving an existing fishway. Our team routinely performs biological field and laboratory studies to determine the efficacy of fish passage devices. It’s also common for our clients to benefit on physical and computational fluid dynamic (CFD) modeling, the results of which we use to help map flow and optimize fish passage designs.

Our long-standing working relationship with FERC, USFWS, NOAA and many regional, state, and local agencies benefits our clients looking for licensing support or agency consultation.

"I know the Staff at Alden is ready to help me solve whatever challenge I have. We’ve developed a great partnership as a result of our project work."

Compliance Lead

Hydropower Dam

Featured Projects

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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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Natural Resources & Environmental Planning
Using Turbine Survival Models and Existing Data to Understand the Impacts of Hydropower Projects on an Endangered Species

Using Turbine Survival Models and Existing Data to Understand the Impacts of Hydropower Projects on an Endangered Species

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The Electric Power Research Institute (EPRI) has funded laboratory studies at Alden on the biological efficacy of fine-mesh screens for safely collecting larval and juvenile fish. However, little information existed on the effects of fish return systems on larval or early juvenile survival. Alden performed two years of laboratory evaluations on factors affecting larval fish survival in fish return systems at cooling water intake structures (CWISs). The project provided the additional data necessary to determine the overall biological efficacy of larval fish collection and return systems. The study was designed to evaluate the effects of velocity, drop height, length, drops and bends on larval fish survival through a fish return system.

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Environmental Management & Compliance | Natural Resources & Environmental Planning
Fish Survival in Fish Return Systems at Cooling Water Intakes

Alden performed two years of laboratory evaluations on factors affecting larval fish survival in fish return systems at cooling water intake structures

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Alden’s engineers and biologists conducted extensive CFD modeling and biological evaluations to help the Holyoke Gas & Electric Department (HG&E) develop an effective downstream passage solution for endangered shortnose sturgeon at the Hadley Falls Station on the Connecticut River. The results of these studies produced engineering and hydraulic design criteria for an exclusion rack and downstream bypass.  The CFD modeling examined flow conditions for several alternative rack designs, as well as the bypass discharge to ensure safe downstream passage of fish and minimal interference of upstream migrants trying to locate the entrance to a fish lift.  Alden also developed conceptual designs and preliminary cost estimates for the preferred alternatives and conducted biological testing in a large laboratory flume with various configurations of bar racks and bypass entrance designs with juvenile shortnose sturgeon.  Agency acceptance of the final design was obtained by HG&E after Alden completed a desktop analysis of total downstream passage survival using the laboratory bypass efficiency data and theoretical estimates of turbine survival.

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Natural Resources & Environmental Planning
Holyoke Hydroelectric, Hadley Falls Station

CFD modeling and biological evaluations were used to develop effective downstream passage for endangered shortnose sturgeon