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RGDSS Ground Water Model Application Release Notes June 24, 2005 Description: The RGDSS ground water modeling activities performed by the State of Colorado were performed using the 1998 version of MODFLOW (McDonald and Harbaugh, 1988) and the graphical interface GMS. The Principia Mathemetica ground water modeling activities were performed using the 2000 version of MODFLOW (Harbaugh, Banta, Hill and McDonald, 2000) and the graphical interface PM-DIAMOND. To accommodate the unique ground water requirements that exist in the San Luis Valley, each version of the ground water model has been enhanced as described in Table 1.1.1. Note that the ET, Drain and Stream enhancements have subsequently been published by the USGS and are now available as standard modules (Banta, 2000 for the ET and Drain Enhancements and Prudic, Konidow and Banta, 2004 for the Stream Enhancements). Also Colorado uses a standard, albeit less elegant, method to process detailed budget reports and resolve convergence issues. The RGDSS results do not depend on a particular version of the MODFLOW program or the graphical interface used. In fact, both versions of MODFLOW used for the RGDSS (Colorado's 1998 and Principia's 2000) produce the same results. Therefore the two independent approaches verify that the RGDSS model results are independent of a particular implementation. This download provides the Principia version of Modflow 2000 as enhanced for the RGDSS project because it produces key output files directly and is independent of the graphical interface. Following is a summary of the enhancements by both. Table 1.2.1 Modflow Model Enhancements Enhancement Description Colorado'sModflow Modflow 1998 2000 A stepwise linear function was ET Package added to better simulate Included Included evapotranspiration (ET) from groundwater The ability to route a portion of Drain drain flows as recharge to the Included Included Package upper layer was added The ability to divert less than 100% Stream of a structures demand and to Package simulate river stage as a function Included Included of discharge using a power relationship were added Relax The ability to control the Package occurrence of cells between Included Included iterations was added Detailed The ability to provide data and Budget report recharge and ET as Not Included Included Reports individual components was added The ability to compare the mass balance to a user specified amount Mass Balance if convergence does not occur. If Not Included Included Override less than the user specified amount continue to simulate (e.g do not abort).