GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 77.07 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 June 23, 1977 GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 77.07 Subject: PUBLICATIONS--Report, "Simulation procedure for modeling transient water-table and artesian stress and response," by J. E. Reed, M. S. Bedinger, and J. E. Terry. The subject report, published as U.S. Geological Survey open-file report 76-792, describes a computer program, SUPERMOCK, that was developed to model a ground-water system affected by surface hydrology; i.e., stream stage, evapotranspiration, etc. The prototype flow system is an alluvial aquifer overlain by a relatively thin confining bed. The model consists of three components--a soil-moisture accounting component, a vertical flow component, and a horizontal ground- water flow component. The soil-moisture accounting component is a parametric rainfall-accretion model that is used to compute changes in soil-moisture storage, and recharge and discharge from the zone of aeration to the water table. Infiltration to soil moisture is computed as a function of precipitation in excess of evapotranspiration, the amount of soil moisture already in storage, and parameters describing the hydraulic properties of the soil. The vertical-flow component is used to compute the altitude of the water table in the fine-grained material above the aquifer. Water-table altitude is computed as a function of transient flow through the fine-grained material above the aquifer and transient altitude of head in the aquifer. The horizontal-flow component computes accretion to the aquifer and the transient altitude of the potentiometric surface in the aquifer. Stresses simulated on the aquifer include changes in stream stage, withdrawal by wells, and accretion (infiltration and evapotranspiration through the fine-grained material above the aquifer). The level of discretization can be different in the three components of SUPERMOCK. Generally, parameters are constant over the modeled area in the soil-moisture accounting component. The exceptions to this are root depth, which varies from node to node, and the hydraulic conductivity from the base of the root zone down to the water table, which is constant over user-defined areas. In the vertical-flow component, parameters are discretized as constant over user-specified areas. In the horizontal-flow component, parameters can be discretized node by node. However, the results of the interaction of model parameters and model stress in the three components--soil moisture storage, water-table head, and potentiometric head--all vary from node to node. The approaches used in SUPERMOCK should be of interest to others concerned with modeling ground-water systems. Please bring this report to the attention of personnel concerned with modeling ground-water systems. Additional copies of the report are available on request. (s) Charles A. Appel Charles A. Appel (for) Chief, Ground Water Branch Water Resources Division WRD Distribution: A (w/o attach.), B (limited), FO-LS, SL (Subdistrict Offices, w/o attach.), S (w/o attach.)