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RO�'k-�.s WmtI111 11J (t <br /> Since its original development in the early 1980s, the USGS has made four major releases, and <br /> MODFLOW is now considered to be the de facto standard code for aquifer simulation. There are <br /> several actively developed commercial and non-commercial graphical user interfaces for <br /> MODFLOW. Visual MODFLOW is a software program developed by Waterloo Hydrogeologic <br /> that was used as the front-end software for the MODFLOW code in developing the Little Turkey <br /> Creek model. <br /> Model Domain and Boundary Conditions <br /> The area covered by the Little Turkey Creek watershed flow model is shown in Figure E-1 and <br /> encompasses an area of about 8.74 square miles. The western, northern and southern boundaries <br /> of the model coincide with the watershed boundaries. These boundaries are simulated by <br /> "inactive flow" boundary conditions, consistent with the CGFM that assumes no inter-watershed <br /> flow. <br /> The eastern boundary is the Hwy 115 location. This is a geographical, rather than a hydrological <br /> boundary and groundwater outflow to the east is simulated by a "drain" boundary condition <br /> which allows any flow towards the eastern boundary to be taken up by the drain. <br /> Recharge <br /> Recharge input into the model is assumed to be"net recharge"which is that portion of infiltrating <br /> precipitation and surface water that actually contributes to increasing groundwater storage. Net <br /> recharge is equal to the total recharge from direct infiltration of precipitation minus the <br /> evaporation and evapotranspiration losses. <br /> Based on the CGFM,total recharge cannot exceed the total precipitation in the watershed. Since <br /> it is known that a large proportion of the total precipitation exits the watershed as surface water <br /> runoff and evapotranspiration, the "net" recharge is a small fraction of the total precipitation, <br /> typically 5 to 10% of the total recharge in western high elevation basins in the western US. Most <br /> recharge to groundwater occurs during the spring snowmelt period when evaporation and <br /> evapotranspiration is low, so net recharge is assumed to be some fraction of the winter <br /> precipitation, typically 25 to 30% of the winter precipitation in western high elevation basins in <br /> the western US. <br /> In the Turkey Creek watershed, average annual precipitation is about 19 inches, and winter snow <br /> precipitation is about 4.5 inches. These average annual precipitation values would limit the <br /> potential net annual recharge to groundwater in the Turkey Creek watershed to between 1 and <br /> 1.5 inches. <br /> TRANSIT MIX-HITCH RACK RANCH <br /> HYDROGEOLOGY AND IMPACT ANALYSIS <br /> E-4 <br />