Stairs pipe culverts: flow simulations and implications for the passage of European and Neotropical fishes

Abstract Culvert fishways can improve upstream fish passage in brooks and have been studied in relation to North American and Australian species. Research focusing on fish species from other world regions and, in parallel, effect of baffles on flow turbulence is rare. In this paper we present computational fluid dynamics of a sloped baffle culvert, called “stairs pipe”. We aimed at evaluating if: (1) the flow met the requirements of Neotropical and European species; (2) the flow turbulence was acceptable for fish passage; (3) the flow limited fish movements. The average flow velocities for 5% slope and discharge rates of 5–13 L/s were lower than the prolonged speeds of three Neotropical species, namely, piau (Leporinus reinhardti), mandi (Pimelodus maculatus), and lambari (Piabarchus stramineus) and higher than the sustainable speeds of three European species, namely, dace (Leuciscus leuciscus), barbel (Barbus barbus), and brown trout (Salmo trutta). The turbulence flow characteristics i.e. levels of turbulence kinetic energy were similar to those produced by comparable culverts but higher than those in a fish ladder. The water jet created by baffles at an angle of 30° can limit fish movements, restraining them from jumping. The stairs pipe might improve upstream fish movement in different regions of world; nevertheless, further experimental research should concern the use of different swimming modes in the culvert flow.