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5.2. EXPERT GIS FOR WATER RESOURCE PLANNINGMcKinney et al. The Texas Water Development Board (TWDB) is a state agency responsible for long-term water supply planning. One of its major tasks is to assure water resources for a wide region through good planning and sound water management. TWDB has long practiced a standard for planning that, according to McKinney et al. (McKinney 94), includes the following steps:
Once a plan is developed, comments are requested from both regional and statewide interests. The manual planning process is very tedious and difficult. Originally it was heavily dependent upon the expertise and judgment of a few professional staff members. Moreover, results developed in the manual way cannot be rigorously documented or replicated. Because of this, it was decided at the beginning of the 1990s to have this planning process automated. An expert geographic information system (expert GIS) for long-term regional water supply planning was completed in 1994 by a team at the Texas Water Resources Institute. The planning system comprises the following:
The rule-based system contains expertise acquired from water resources planning experts. The GIS systems stores and analyzes spatially distributed water supply and demand data. It also produces geographic displays of alternative water allocation plans. The task of the the network flow solver is to balance the flows in networks developed by the expert GIS with input from a water resource analyst. The objective for this part is to find the least costly resource allocation solution. The model incorporates source units such as reservoirs and aquifers. Demand areas include counties and cities. Planning problems are represented by a series of points, lines, nodes, and arcs. Line coverage or potential arcs (PARCs) describe ways in which water can be transmitted from supplies to users. Abstractions were developed so that problems could be represented geographically, functionally, and in a planning mode. Given annual yields for reservoirs, water demand forecasts, and institutional requirements, the expert GIS is able to calculate potential water supply deficits or excesses. In case of a deficit, it is able to suggest alternative supplies that are both efficient and cost effective. The rule base includes several categories of rules with more or less specific application. State-wide rules correct obvious problems. Regional rules incorporate specific water supply and demand conditions that apply to that particular area. Generic categories of rules for regional water planning appear to be one of the more powerful aspects of the system. The basic system model is object based. The model was initially tested using a hypothetical example developed by the TWDB. The system was later tested using a case study of the Corpus Christi region for a 50-year planning horizon involving 19 counties. Groundwater costs were developed based on information on well depths and drilling costs supplied by TWDB staff. Surface water costs were estimated for each reservoir based on construction and operations and maintenance costs and firm yields. Demands were estimated for Corpus Christi and other municipalities in the region, as well as for agricultural and industrial use. The system has also been successfully applied to the Coastal Bend planning region of the TWDB. The expert GIS system has been developed so that it can be expanded to include additional constraints and handle large water resources planning regions. According to the development team, the system will be capable of analyzing entire river basins, given appropriate information concerning the supply and demand for water.
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