Optimal approach for upstream fish passage design: One-size-fits-all or made-to-order?

Abstract

Nearly 60,000 large dams (higher than 15 m) occur worldwide in addition to an estimated16 million smaller impoundments with individual surface areas larger than 100 m2.Theresulting habitat fragmentation threatens global riverine biodiversity and sustainable fishpopulations. Two opposing approaches for selecting fish passage designs to mitigate riverfragmentation are possible: develop a limited number of standardized (reference) designsfrom which a design for a candidate dam is selected (one-size-fits-all approach) versusconduct scientific fish passage studies specific to each dam and targeted fish species(made-to-order approach). The two approaches vary in probability of effectiveness, costof supporting biological studies, and overall project cost and schedule impact. To addressthis conundrum, we analyzed 73 USA dams to identify two groups that differed markedlyin fish passage planning approaches. Snake River dams are similar in design, flow, geologi-cal setting, and target fish species. By contrast, MississippiRiver dams are relatively dis-similar in design, flow, and geological settingbut generally similar in target fish species.We conclude that the more similar a candidate dam for fish passage is to a reference setof similar dams (i.e., the Snake River dams), then the more likely fish passage technologycanbesuccessfullyextrapolatedtoaproposeddaminthesameoranearbywatershed.As a general strategy, we recommend that damsin a region be clustered using key hydro-logic, structural, operational, and biological variables. These variables can be used toassign a new dam or retrofit an existing dam to a cluster to which they are most similar,thereby optimally extending existing knowledge to new applications. In the process, reli-ance on the less efficient and more expensive made-to-order approach can be reduced. dam mitigation, fish passage, Fish Passage Program, fishway design, fishway planning, riverfragmentation