Influence of groundwater discharge on decay process of contamination concentration in river flow

The groundwater discharge may significantly affect the water quality in upper reaches of rivers or in dry season.Based on the 1-D stream water quality model with groundwater discharge taken into account and neglecting the dispersion effect,a new analytical solution for determining water quality is deduced.The physical significances of this solution under two special conditions including without water exchange between groundwater and river stream and without incoming water from upper stream of the river are discussed and the validity of this solution is demonstrated.By comparing the solution with the classical solution which neglecting groundwater discharge,the internal relationship and essential difference between point-source and line-source contamination are discussed,and it is demonstrated that this solution can not be obtained from the simple superposition of the classical solution.By using this proposed solution the influence of groundwater recharge intensity on decay process of contamination concentration in river flow can be quantitatively studied.The application to Yinghe River shows that the calculation error reaches 9.3% if groundwater discharge is neglected in dry season.