On the estimation of nose velocities and their influence on the physical habitat simulation for Barbus bocagei

Abstract

[EN] Although more explicit habitat simulation models for calculating instream habitat are being developed, current applications of PHABSIM for instream flow assessments are based on average velocities. This article focuses on the behavior of Barbus bocagei (a species native to the Iberian Peninsula) in terms of focal (nose) height and velocities. In a four-year research project, we first surveyed habitat use in four rivers (by underwater observation) and developed site-specific and generalized habitat suitability criteria (category II) for focal velocity and focal height (distance from bed). Second, we calculated focal velocities from the average in four different ways and computed the consequent errors to compare the models' precision in the 4 study sites. Third, as a practical approach, habitat criteria for focal velocities were introduced in a selected example, to measure the changes affecting W.U.A./flow functions. We discuss the problems in implementation and the general consequences for instream flow studies.