Simulation and Analysis of Stream-Aquifer Systems

As defined for this study, a stream-aquifer system is a hydrologic system in which there is an intimate hydraulic interrelationship between one or more aquifers and a perennial stream. The objectives of this study are to better understand the response behavior of typical stream-aquifer systems, to look at the response behavior as influenced by water management practices, and to consider the problems and possibilities of integrated management of groundwater and surface water supplies within stream-aquifer systems. A brief history of water development practices and policy, particularly in the Western United States, indicates that the tendency over the years has been to attempt to improve efficiency of use and increase water availability by means of coordinated management of sources and uses of water within hydrologic units. This tendency is manifested by the concepts of basin planning, multiple purpose projects, and comprehensive planning. Also, history shows that surface and groundwater have typically been developed separately with little regard for the interrelationships between the two. Through the cooperation of the U.S. Geological Survey, major stream-aquifer systems in the Western United States have been identified. The Soil Conservation Service provided information on water management problems, causes, and needs found within the major stream-aquifer systems. Components of stream-aquifer systems are classified into (1) input variables, (2) system parameters, (3) output or system responses. Techniques for modeling stream-aquifer systems are discussed, and the mathematical model technique used is presented. Over 160 stream-aquifer systems were simulated, utilizing mathematical models and digital computer solutions. The response behavior was measured in terms of the change of groundwater levels and the pattern of outflow to the stream. The latter system response is emphasized because of the effect upon other water users which is often not considered when changes are made in water management practices. The influence of such variables and parameters as (1) the total water added to the aquifer, (2) the time distribution of the water added, (3) the areal distribution of the water added, (4) the aquifer hydraulic characteristics, (5) the geometric characteristics of the aquifer, and (6) the initial configuration of the water table surtace are discussed with results presented in tabular and graphical form. The effect of common water management practices (drainage, phreatophyte control, improvement of irrigation efficiency, and lining of canals), along with further water management practices desirable in a fully integrated streamaquifer system are discussed