Computer program for simulation of variable recharge with the U. S. Geological Survey modular finite-difference ground-water flow model (MODFLOW)

[摘要] The Variable-Recharge Package is acomputerized method designed for use with theU.S. Geological Survey three-dimensional finitedifferenceground-water flow model(MODFLOW-88) to simulate areal recharge to anaquifer. It is suitable for simulations of aquifers inwhich the relation between ground-water levelsand land surface can affect the amount anddistribution of recharge. The method is based onthe premise that recharge to an aquifer cannotoccur where the water level is at or above landsurface. Consequently, recharge will varyspatially in simulations in which the Variable-Recharge Package is applied, if the water levelsare sufficiently high. The input data required bythe program for each model cell that canpotentially receive recharge includes the averageland-surface elevation and a quantity termed?water available for recharge,? which is equal toprecipitation minus evapotranspiration.The Variable-Recharge Package also canbe used to simulate recharge to a valley-fillaquifer in which the valley fill and the adjoininguplands are explicitly simulated. Valley-fillaquifers, which are the most common type ofaquifer in the glaciated northeastern UnitedStates, receive much of their recharge fromupland sources as channeled and(or) unchanneledsurface runoff and as lateral ground-water flow.Surface runoff in the uplands is generated in themodel when the applied water available forrecharge is rejected because simulated waterlevels are at or above land surface. The surfacerunoff can be distributed to other parts of themodel by (1) applying the amount of the surfacerunoff that flows to upland streams (channeledrunoff) to explicitly simulated streams that flowonto the valley floor, and(or) (2) applying theamount that flows downslope toward the valley-fill aquifer (unchanneled runoff) to specifiedmodel cells, typically those near the valley wall.An example model of an idealized valley-fill aquifer is presented to demonstrate applicationof the method and the type of information that canbe derived from its use. Documentation of theVariable-Recharge Package is provided in theappendixes and includes listings of model codeand of program variables. Comment statements inthe program listings provide a narrative of thecode. Input-data instructions and printed modeloutput for the package are included.

[发布机构] U.S. Geological Survey

[学科分类] 地球科学(综合)