Long Term Simulation of Water Quality Applying System Dynamics for the Variation of Population and Land Uses

Abstract

In water pollution of closed watershed, especially in urbanized area, there is a tendency for a nitrogen or a phosphate pollutant load to increase. In this paper, annual variations of water quality T-N and T-P, were examined for long term (1975-95) by model simulation in Imbanuma basin. The model has two sab-models, the one represents a variation of runoff load and the other represents a variation of population and land uses. In the runoff load sub-model, total load quantity is determined by multiplying population or land uses area by the unit quantity. In the population and land uses sub-model, System Dynamics was applied, and outputs are calculated to yield annual variation of population and various land uses area by feed-back loops. These feed-back loops are mainly determined by interviewing responsible persons in rural offices. This sub-model's output fits the real data of population and land uses area. The total model's output fits the real data of water quality.