Parameter determination to calculate water environmental capacity in Zhangweinan canal sub-basin in China.

Zhangweinan canal sub-basin (ZWN) has the most serious water resource shortage and water pollution problems in north of China. To calculate the water environmental capacity in ZWN, determination methods for design flow rates and degradation coefficients were discussed in this study. Results showed that 90% and 50% hydrological guarantee flow rates were suitable to be the design flow rates for rainy and dry seasons, respectively. Degradation coefficients of COD(Mn) and NH3-N were 0.25 day(-1) and 0.15 day(-1) for branch streams and 0.5 day(-1) and 0.25 day(-1) for mainstreams, respectively in ZWN. With one-dimensional water quality simulation model, water environmental capacities were calculated to be 82,139 tons/yr for COD(Mn) and 2394 tons/yr for NH3-N in ZWN.