Quantitative relations between chemical oxygen demand concentration and its influence factors in the sluice-controlled river reaches of Shaying River, China.

Recent research on the effects of dam and sluice construction on the water environment has attracted extensive attention from academia and governments alike. Because the operation of sluices greatly alters environmental factors such as water flow and sediment load, the water quality in sluice-controlled river reaches (SCRRs) undergoes complex changes compared with those in normal reaches. This work used river reaches near the Huaidian Sluice in Shaying River of China as a case study to analyse the effects of sluice operation on water quality evolution in SCRRs. The most influential factors affecting the rate of change in chemical oxygen demand (COD) concentration in SCRRs were identified through water quality monitoring experiments performed under various modes of sluice operation and by applying a statistical method 'partial correlation analysis'. Then, a hydrodynamic model incorporating sluice operation and a water quality transport and transform model incorporating the release of endogenous loads were developed. Using these two models, the processes of temporal and spatial change of COD concentrations in the SCRRs were simulated under various scenarios designed to represent the dominant factors of influence. Finally, the simulation results were used to develop empirical relationships between the rate of change in COD concentrations and the dominant factors of influence. The results reveal that three factors, i.e., water inflow concentration, gate opening size, and gate opening number, are the dominant factors of influence, and there are logarithmic relationships between the rate of change in COD concentration in the SCRRs and these factors.