Development of Monthly Unit Effluent Load Method and its Investigation

Abstract

Preserving the water quality of lakes and ponds is very important as they are one of the main water sources. Therefore, comprehensive watershed management is indispensable in order to achieve the above objective which requires the precise estimation of runoff pollutant loads. The unit load method is widely used to calculate estimated runoff loads. However, this technique does not take seasonal fluctuations or the effects of irrigation into account because yearly average values are used in this method. The monthly unit load method, developed by the Ministry of Agriculture, Forests, and Fisheries, shows the monthly fluctuations and the effects of irrigation since fertilizer time or the irrigation period is taken into account. We calculated the estimated runoff load using this method and compared it with the measured runoff load. The calculated values of the fertilized month were much larger than measured values. Then, we divided the monthly amount of fertilizer by 5: 3: 2. After the above changes calculated runoff pollutant loads were very accurate. In conclusion, more accurate estimation of the amount of fertilizer used and the amount of time involved, will lead to a more accurate estimation of pollutant loads.