水情变化对平原河网水质输移影响模拟研究:以苏州吴中河网为例

INFLUENCES OF FLOW REGIME CHANGES ON WATER QUALITY OF RIVER NETWORKS IN WUZHONG DISTRICT,SUZHOU

平原地区地势平坦,河网复杂,水情变化对水质输移有重要影响。降雨可以增加河网稀释容量,提高水体复氧能力,加速对污染物的输移降解过程;同时在平原区闸站的联合调度下,降雨也改变了区域水动力特征,使得水流和污染物的流通变得复杂。基于太湖水量水质模型,采用丰、平、枯3个典型年的雨情资料,模拟计算了苏州吴中区水质过程,对比分析不同雨型下河网水质的动态变化过程及空间分布特征。结果表明:1)降雨越多,水环境质量越好,在干旱年份河网水量也能够维持稳定,污染物浓度水平与平水年大致相当;2)不同营养盐对雨情变化的敏感性各有不同,敏感性从高到低依次为总磷(TP)、氨氮(NH_4^+-N)、总氮(TN)和高锰酸盐指数(COD);3)与枯水年相比,丰水年水质改善较为显著的河道主要分布在临湖地区,与太湖无水量交汇的河道水质改善的程度稍弱。闸门的调度对水量和水质的变化也有重要影响,闸门关闭会在一定程度上减弱局部河网流通性,形成污染物聚集,恶化局部水质。

The change of water regime has an important influence on water quality in plain area with complex river network.Rainfall can not only increase river dilution capacity,improve reaeration ability and accelerate transport and degradation process of pollutants,but also change the regional hydrodynamic characteristics under the joint dispatching of sluice gates in plain area,which makes the distribution of flow and pollutant even more complex.Using water flow and quality model,dynamic changes and spatial distribution characteristics of river water quality were analyzed under three hydrological conditions.The results showed that： 1） Water quality could be improved for wet year.For dry year,water qaulity could also be maintained at the level of normal year through the regulation of the sluice egates; 2） The sensitivities of nutrients to rainfall were different,whose levels from high to low were as follows： TP NH_4^-N TN COD; 3） Compared with the dry year,districts where water quality had improved markedly in wet year mainly concentrated in the areas adjacent to lake zone,while rivers with no intersection of water with Taihu just achieved slight improvement in water quality.In addition,the regulation of the gates and pumping stations obviously had an important influence on water flow and quality.While the gates were closed,circulation of the local river network would be weakened to a certain extent,and as a result,the pollutants would be aggregated and local water quality would get worse accordingly.