Impact of the second branch Yinma River on water quality of Songhua River based on mathematical model

With the assistance of the monitored data of 2007,the impact of the second tributary Yinma River water quality(worse than level Ⅴ water standard) on Songhua River was analyzed.A coupled hydrodynamics and water quality model of Songhua river net was developed.Based on this model,the impact of Yinma River on water quality of main stream of Songhua River was predicted.The results indicated that if the water quality of tributary met level Ⅲ water standard,the water quality of main stream of Songhua River was improved largely from June through August.Ammonia Nitrogen Index was improved more significantly than that of CODCr.The impact was small in low flow months.