A STUDY OF GIS-SD BASED TEMPORAL-SPATIAL MODELING OF WATER QUALITY IN WATER POLLUTION ACCIDENTS
A STUDY OF GIS-SD BASED TEMPORAL-SPATIAL MODELING OF WATER QUALITY IN WATER POLLUTION ACCIDENTS
Bo Zhang a, 861084640954, zhangbo@zhb.gov.cn.
a Information Centre of State Environmental Protection Administration, 100029, Beijing, China - zhangbo@zhb.gov.cn
Commission WG II/1
KEY WORDS: Temporal, Spatial, Simulation, Pollution, Decision Support, Hydrology
ABSTRACT:
In this paper, the one-dimension river quality system dynamics model was applied to the water quality simulation, and the conceptual GIS-SD frame was constructed. Based on the component GIS and system dynamics model, the experimental system of water quality simulation in water pollution accident was developed. The Songhua River water pollution accident which happened on November, 2005 was used as an example to show how the temporal-spatial change of nitrobenzene concentration can be dynamically simulated. The results showed that the simulation of temporal-spatial distribution of the pollutant in water pollution accident, the model regulation, and the scenario analysis can provide the decision-makers with scientific evidence to optimize the related emergency response measures.
1.INTRODUCTION
Water pollution accident is a major type of China’s environmental accident. It not only causes water quality deterioration and ineffective use of water resource, but also affects the normal activities of economy and society and does serious harm to the water ecological environment. After a water pollution accident occurs, the pollutant enters the river and migrates with water current. During the transportation process, pollutant is influenced by hydraulics, hydrology, physics, chemistry, biology and other factors (Song, X. Sh., Deng, W., 2004), there is nonlinear relationship among these factors which is difficult to be expressed by conventional dynamics method. The migration and conversion of pollutants in the water pollution accident is typically a dynamic, complex, nonlinear system. Dynamic systems are often hard to understand and difficult to model because of the interactions among the spatial elements, and the changes in the structure and function of the system over time. Traditional modelling approaches focus on either temporal or spatial variation, but not both (Ahmad, S., Simonovic, S. P., 2004). In order to better simulate dynamic, complex systems, we should be aware that the system performance in time is affected by the change of conditions in space. So we need to focus on both temporal and spatial variation. During the emergency response of water pollution accidents, the management department needs to understand the migration situation of pollution slick and the changes of pollutant concentration in both time and space as soon as possible to take effective emergency measures. Therefore, it is very important to construct a water quality model with the capability of simulating the pollutant concentration changes in both time and space simultaneously, and help decision-makers to grasp the change trends of accidents in two dimensional spaces (Zhang, B., 2007).
2.METHODOLOGY
System dynamics (SD) is a theory of system structure and a set of tools for representing complex systems and analyzing their dynamic behaviour (Forrester, J. W, 1961). The most important feature of system dynamics is to elucidate the endogenous structure of the system under study, to see how the different elements of the system actually relate to one another, and to experiment with changing relations within the system when different decisions are included. In system dynamics, the relation between structure and behaviour is based on the concept of information feedback and control (Simonovic, S. P., 2002). SD has advantage in water quality simulation due to the dynamic, complex and nonlinear characteristics of water pollution accident. It can be used to simulate and predict the water quality and model regulation in water pollution accidents (Zhang, B., 2007). Although SD models can represent temporal processes of system dynamic behaviour, it can not adequately represent and simulate the spatial elements and the state of the system. Moreover, the simulation results can only be expressed through charts, tables and other simple styles with low level of visualization (Pei, X. B., Zhao, D. Zh., 2000). Therefore, a simple SD model is clearly far from enough for a comprehensive temporal and spatial simulation of complex systems. Geographic information system (GIS) is a computer system for collection, storage, analysis and display of spatial information, and a common technology for processing and analyzing geographic data (Chen, Sh. P., Lu, X. J., Zhou, Ch. H. 2000.). During the integration process of water quality model and GIS, GIS is a powerful tool for spatial discretization, parameterization and visualization of water quality model (Liao, H., Tim., 1997; Ma, W. Ch., Chen, L. M., et al., 2003). Although GIS can effectively manage, query, express, analyze and process static information related to geospatial
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