A coupled hydraulic-ecological model for simulating periphytic algal detachment in water delivery canals

In water delivery canals, aging periphytic algae can detach extensively, causing severe clogging and water quality deterioration. However, current research lacks a clear understanding of the hydraulic threshold for periphytic algal detachment. To fulfill this gap, two hydraulic scouring experiments of varying durations were conducted to investigate the effects of water velocity on periphytic algae growing on concrete substrates, and a new algal dynamic model considering detachment threshold and diminishing returns (DDR model) was proposed. Results revealed that water velocity significantly influenced periphytic algal biomass and community composition, identifying a critical value for algal detachment and diminishing returns in scouring effects. The DDR model used water velocity as the independent variable and demonstrated high simulation accuracy for both short-term and long-term algal biomass (the coefficient of determination (R²) > 0.72, Relative Root Mean Square Error (RRMSE) < 0.199). Compared to existing models, the DDR increased R² by up to 67.42 % and reduced RRMSE to 57.92 %. The calibration results indicated that the water velocity threshold depended on the periphytic community. The threshold for Bacillariophyta-rich communities was higher (0.60 m s^-1), while for Cyanobacteria-rich communities, it was lower (0.12 m s^-1). It was concluded that including both the scouring threshold and the diminishing returns in the periphytic algal dynamic model was essential for accurately simulating detached algal biomass. These findings provide valuable insights into the regulation and management of periphytic detachment.