Investigations, Circulars, publications of general interest (such as leaflets, pamphlets, booklets), single copies of Earthquakes & Volcanoes, Preliminary Determination of Epicenters, and some miscellaneous reports, including some of the foregoing series FOREWORD THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM The Regional Aquifer-System Analysis (RASA) Program was started in 1978 following a congressional mandate to develop quantitative appraisals of the major groundwater systems of the United States. The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which in aggregate underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and accordingly transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies, both to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities, and to provide a means of predicting the regional effects of future pumping or other stresses. The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number, and where the volume of interpretive material warrants, separate topical chapters that consider the principal elements of the investigation may be published. The series of RASA interpretive reports begins with Professional Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

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A water‐budget model was developed to aid the study of transport of nutrients in surface and subsurface flows across a marsh. The model is based on field studies of Wingra marsh adjacent to Lake Wingra in Madison, Wis., and was used to calculate monthly totals of actual evapotranspiration, surface runoff, and subsurface drainage from April 1970 through August 1976. About 90% of the water entering the marsh comes from urban storm runoff. The remainder is precipitation (8%) and deep ground‐water inflow (2%). Water leaves the marsh through evapotranspiration (7%), shallow ground‐water discharge (8%), and surface outflow (85%). The model was used to estimate the water‐table elevation at an observation well where direct measurements were taken (November 1975 through October 1976). The observed depth to the water table ranged from 0 to 150 cm below the surface and the simulated value usually was within ± 10 cm. This suggests that the model adequately computes the water budget for the marsh and provides a sound basis for calculating dissolved and suspended material loads transported through the marsh into Lake Wingra.

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