SUMMARY OF INFIL3.0 NOTE: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ABSTRACT INFIL3.0 is a grid-based, distributed-parameter, deterministic water-balance model that calculates the temporal and spatial distribution of daily net infiltration of water across the lower boundary of the root zone. The bottom of the root zone is the estimated maximum depth below ground surface affected by evapo- transpiration. In many field applications, net infiltration below the bottom of the root zone can be assumed to equal net recharge to an underlying water-table aquifer. The daily water balance simulated by INFIL3.0 includes precipitation as either rain or snow; snowfall accumulation, sublimation, and snowmelt; infiltration into the root zone; evapotranspiration from the root zone; drainage and water-content redistribution within the root-zone profile; surface-water runoff from, and run-on to, adjacent grid cells; and net infiltration across the bottom of the root zone. The water-balance model uses daily climate records of precipitation and air temperature and a spatially distributed representation of drainage-basin characteristics defined by topography, geology, soils, and vegetation to simulate daily net infiltration at all locations, including stream channels with intermittent streamflow in response to runoff from rain and snowmelt. The model does not simulate streamflow originating as ground-water discharge. Drainage- basin characteristics are represented in the model by a set of spatially distributed input variables uniquely assigned to each grid cell of a model grid. HISTORY INFIL3.0 Version 1 06/19/2008 - Initial release. SYSTEM REQUIREMENTS INFIL3.0 is written in Fortran. A Fortran-90 compiler is required to recompile the program. The code has been used on personal computers running various forms of the Microsoft Windows operating system. DOCUMENTATION U.S. Geological Survey, 2008, Documentation of computer program INFIL3.0--A distributed-parameter watershed model to estimate net infiltration below the root zone: U.S. Geological Survey Scientific Investigations Report 2008-5006, 98 p. ONLINE ONLY CONTACTS U.S. Geological Survey Office of Ground Water 411 National Center Reston, VA 20192 (703) 648-5001 ogw_webmaster@usgs.gov