A Practitioner’s Perspective on the Continuing Technical Merits of PHABSIM

Since its initial development and application in the mid‐1970s, the Physical Habitat Simulation System (PHABSIM) and models, which are part of the instream flow incremental methodology (IFIM) developed by the U.S. Fish and Wildlife Service (Bovee and Milhous 1978; Bovee 1982), has been extensively used (Reiser et al. 1989; Hatfield and Bruce 2000; Locke et al. 2008), reviewed (e.g., Wesche and Rechard 1980; Morhardt 1986; Annear et al. 2004), and occasionally criticized (Mathur et al. 1985; Scott and Shirvell 1987; Hudson et al. 2003). Its most recent critic, Railsback (2016), went so far as to title his paper “Why It Is Time to Put PHABSIM Out to Pasture.” This prompted comments from Beecher (2017) and Stalnaker et al. (2017) and a corresponding response from Railsback (2017). Kemp and Katopodis (2017) also provided comments noting the timeliness of the Railsback (2017) paper and promoting further dialogue on the subject. We read all three comments and the author’s response to the first two, and as active instream flow practitioners and independent reviewers of the original Railsback (2016) article, we felt there was more to be said. We note that we have the highest respect for Railsback and his colleagues; we also admit that at the outset of our review of the 2016 article, we were somewhat expecting to be convinced and echo the strident cry for PHABSIM retirement. Instead, we found that many of the core criticisms (of PHABSIM) were weak, wrong (at least by our interpretation), or outdated and misaligned with contemporary PHABSIM practices.

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