Discussion of “Turbulent Open-Channel Flow in Circular Corrugated Culverts” by S. A. Ead, N. Rajaratnam, C. Katopodis, and F. Ade

Abstract

The authors should be complimented for tackling one of the most challenging problems in hydraulic and fisheries disciplines, the determination of the flow conditions that allow unimpeded fish passage through culverts. Recently, this problem has received a lot of attention throughout the U.S. and Canada with the design and implementation of the stream simulation approach ~Maxwell and Papanicolaou 2001!. This approach requires the use of culverts with gravel bottoms, known as countersunk culverts that ‘‘mimic’’ the natural streambed conditions upstream or downstream of a road crossing. The objectives of the present discussion are: ~i! to elaborate on some of the results presented by the authors with respect to the habitat suitability index ~i.e., the index that relates fish behavior to flow characteristics ! and ~ii! to generate a discussion on the importance of turbulence and secondary flows in the design of culverts facilitating fish passage during periods of fish migration. The authors, based on their experimental findings, provide empirical equations @Eqs. ~5! and ~6!# that relate the local streamwise velocity, u, with the prolonged fish speed, u p . These equations can be used to draw the isovels ~i.e., the velocity contours! per cross section and delineate the regions through which fish may ascend. Eqs. ~5! and ~6! were developed by accounting for the ‘‘dip’’ observed in the streamwise velocity profile that was attributed to the presence of secondary currents.