Experimental Study on the Impact of Pulsed Flow Velocity on the Scouring of Benthic Algae from a Mountainous River

The decrease in periodic scouring of pulsed flows in regulated rivers can result in algal communities dominated by filamentous algae, not available as food sources for fish and macroinvertebrates. To study the pulsed flow velocity required to scour benthic algae from natural river beds, the removal effects on the algal biomass and resistances of different species were tested in a laboratory flume at different velocities of 0.8, 1.1, 1.4, 1.7, and 2.0 m/s. The removal of total algal biomass showed a significant positive relationship with increasing velocities, which reached 22% at 2.0 m/s. The biomass removal of green algae and diatoms was higher than that of blue-green algae. The flow velocity at 1.4 m/s had a clear removal effect on filamentous algae. The velocity higher than 1.7 m/s caused a significant increase in the removal percentage of total biomass dominated by diatoms and blue-green algae. To reduce the filamentous algae and retain the diatoms and blue-green algae, a range of near bed flow velocity was suggested to be 1.4-1.7 m/s. This range could serve as a reference for required pulsed flow velocity to reduce the growth of excessive or nuisance periphyton.