Optimization of Export Coefficient Model Based on Precipitation Impact Factor and Terrain Impact Factor

According to the economic growth in the world and necessity of industrial and agricultural development, conservation of water resources in large scale is a very important task. The Export Coefficient Model (ECM) has been widely used in estimation of non-point pollution for more than 3 decades. In this study, by applying the precipitation coefficient (alpha) and also the terrain coefficient (beta) to ECM, the structure of the model was modified. Finally, the output of the modified model was compared by observed data. This process is very practical when the water resources are under the impact of pollution sources.

In this study, a part of the Tibetan Plateau has been chosen as a case study in which, the measured agricultural pollution elements such as nitrogen and phosphorus were available. In this study, the ECM outputs and the modified ECM outputs including Alpha and Beta correction coefficients, were compared by the observed data.

Analysis of the ECM outputs together with the modified ECM outputs and comparing the results with observed data showed that the application of alpha and beta coefficients was very effective to increase the accuracy of the model. The relative error between amount of nitrogen which was estimated by the modified ECM and the measured values was reduced comparing to the results of ECM model without using the coefficient: for station 1, 12% and 34% in 2007 respectively; and 18% and 20% in 2015 respectively; for station 2, 16% and 30% in 2007 respectively; and 21% and 34% in 2015 respectively.

This study illustrated that the modified ECM model could provide more accurate results in comparison with the ECM model and would be useful in decision making and planning processes in large-scale agricultural watersheds.