WSP01315 - Laserfiche WebLink

Home Browse Search

ODjJ52 for the development and calibration of these models are described. It is hoped that the tools described in this paper for incorporating consideration of ground water into the planning process will enable the planner to develop the water resource wisely. MODELS FOR WATER-RESOURCE PLANNING Electric-analog and digital models have been used for water-resource planning throughout the United States and foreign countries. Models have been developed that accurately portray the ground-water system and predict the changes imposed by man. Analog and digital models simulate the hydrologic properties and boundaries of the hydrologic system, The theoretical foundation for both models is the finite-difference approxi- mations of the flow equations. The major difference between the two models is that in the digital model flow equations are evaluated mathe- matically and in electric-analog models they are simulated with a resistor and capacitor network. Each type of model has certain advantages, depending on the system to be modeled (Prickett and Lonnquist, 1968). The analog model can handle very large and complex hydrologic problems such as one that involves two or more aquifers with varying degrees of hydraulic connection. It also provides a visual display of the aquifer characteristics (transmissivity and storage) and boundaries (the bed- rock-alluvium contact and the stream). This display is very useful in explaining to the layman the operation of the hydrologic system. The digital model can handle nonlinear problems (such as changes of trans- missivity with time) with greater facility, The digital model commonly requires less time than a comparable analog model for construction, programing data input, and readout of results. Until very recently computer capacity was a serious limitation to the use of a digital model. The development of high-speed and large-capacity computers now has made it possible to solve quite complex hydrologic problems using a program such as that described by Pinder (1970). Models can simulate changes in quantity and quality of water and the effects of economic and legal constraints on water utilization, Some of the major water-management problems that have been evaluated with models include: effects of irrigation wells on stream flow, dewatering of waterlogged land, ground-water mining, salt-water intrusion, and effect of lock- and dam-construction on the water table. Electric-analog models have been used to simulate ground-water hydrology in a variety of geologic environments, Two hydrologically complex areas where analog models have been used for water-resource planning are Houston, Texas and the San Luis Valley, Colorado. In the Houston area three-dimensional flow was simulated in an area of 5,000 square miles (Wood and Gabrysch, 1965). By inter- connecting three layers of resistor-capacitor networks, the model simulates a thickness of aquifer of about 1,500 feet. This model was used to evaluate problems created by development of ground water in the 3