The influence of freshwater biofilms on drag in hydroelectric power schemes

Freshwater biofilms are currently being studied to determine their effect on the capacity of hydroelectric power scheme canals and the structure of their turbulent wall layers. Mean velocity boundary layer profiles and total drag measurements have been conducted in a purpose built recirculating water tunnel on freshwater biofilms grown in a hydroelectric canal. Two different fouled surfaces were compared with a smooth painted surface to determine the effects of the physical characteristics of a biofilm on skin friction drag. A 310% increase in local skin friction coefficient was measured for a biofilm dominated by long filamentous algae streamers, and a 50% increase was measured for a biofilm dominated by a low-form gelatinous diatom.