浙江西苕溪水环境容量模型与参数灵敏度分析

Water environmental capacity model and its parameters sensitivity analysis for Xitiaoxi River in Zhejiang Province, China

针对浙江西苕溪河月流量丰枯悬殊较大、流速小、存在倒流的特点,建立了零维反复流水环境容量模型.以水功能区为基础划分计算单元,选取频率P=50%、75%、90%和近10年最枯月流量为设计水文条件,分别计算了西苕溪CODCr、氨氮、总氮、总磷的水环境容量值;对模型参数进行了蒙特卡罗模拟分析,95%置信水平下,CODcr环境容量置信区间为[17982t/a,45489t/a],氨氮为[493t/a,1624t/a],总氮为[435t/a,1332t/a],总磷为[20t/a,147t/a];模拟结果给了流量、降解系数不确定条件下水环境容量的所有可能值,为决策者提供了更全面的信息.参数灵敏度分析结果表明,各站流量对各污染物环境容量均最敏感,方差贡献占73.3%～99.1%,而降解系数中除k2对CODCr具有一定影响外,其余影响最小,说明计算水环境容量时,选择合适的设计流量极为重要.

Aimed at the characteristics of uneven distribution of flow within a year, low velocity of flow and backward flow for Xitiaoxi river, the zero dimension water quality model, which considers the impact of bidirectional flow, has been set up to calculate water environmental capacity. The water functional areas are plotted as calculated unit, and the flows of the most dry month under different hydrological year of P=50%、75%、90% and the lately 10 years are used as design flows, the water environmental capacity results of CODCr, N-NH3,TN and TP are calculated. The confidence intervals for them under confidence level 95% are [17982t/a,45489t/a], [493 t/a, 1624 t/a], [435t/a, 1332 t/a ]and [20 t/a, 147 t/a] by Monte Carlo simulation. The result shows the possible value of water environmental capacity under the uncertainty of the flows and degradative coefficients. It provides comprehensive information for dicision maker. The sensitive analyse of parameters show that the flow of all hydrological station is the mostly sensitive parameters for water environmental capacity, which contribute 73.3%～99.1% of variance. While, the degradative coefficients are the least sensitive parameters except for k2 has definite impact for CODcr. It explains that selecting design flows is important for water environmental capacity calculation.