SD Model For The Predicting Of Non-point Source Pollution

Nowadays in China, the non-point source pollution remains a great threat to the land's surface water although we have almost finished point-source pollution controlling jobs. The non-point source pollution is affected by many ways, some are natural factors such as rainfall, underlying surface etc; some are social factors such as the social and economic activities of our human beings. The influence is hard to foresee and control for its randomness, universality and hysteresis quality.The normal ways for studying the non-point source pollution is to simulate the runoff processes by setting up a mathematical model, such as BASINS,SWAT,STORM etc. But they can not be applied to most of Chinese medium and small cities, because a large numbers of observed data needed is lacked.A new concept"the relative non-point source pollution degree"is introduced in this thesis. To calculate it, a base value is set at the initial time of the simulation, the pollution degree at the other time are expressed as multiples of the base value, so there comes the trend of the non-point source pollution degrees of the total period. The System Dynamics (SD) method which is a scientific method used to analysis the problems in a motive way was used in the simulation, With the specialized SD software Veinsim, a big non-point source pollution system which has a large amount of varieties with very complicate relations among them can be well simulated, though the observed data is relatively less than the normal models.A new city construction in Wulijie, Wuhan is studied in this thesis. A SD model for non-point source pollution predicting which has 3 subsystems is built. 65 relationships among 3 level varieties, 6 rate varieties, 26 assistant varieties and 11 constants are simulated by the model. 4 scenarios are set up for simulation. The main results are as follows: In the simulation time period(2010-2050), if the level of non-source pollution controlling remains as low as present (10%), the degree for pollution will rise quickly to 10.6 times in 40 years; but if the level is greatly improved (reach to 70%), the trend of pollution degrees rise first, then fall, and the peak value in 2036 is relatively low (which is 3 times to present), the output degree is even better than present (which is only 0.9 times to present). After compared all the results among the 4 scenarios, it lead to the following conclusion: in order to keep a good quality of land surface water, the level for non-point source pollution controlling must be at least 50%.The model in this thesis contains not only"runoff process"as normal models always do, but also the social and economic activities of our human beings which are a direct pollution source, which is unusual in the non-point pollution studies at present. The results of the pollution trend can be used as a reference for city directors. This model is a new and useful attempt for the study of non-point source pollution predicting,...