HR: 1340h
AN: H33D-0494    [Abstracts]
TI: Simulation of Conjunctive Agricultural Water Use with the new FARM package for MODFLOW-2000
AU: * Schmidt, W
EM: w_schmid@hwr.arizona.edu
AF: University Of Arizona, Dept. of Hydrology & Water Resources 226 Harshbarger Building, Tucson, AZ 85721-0011 United States
AU: Hanson, R T
EM: rthanson@usgs.gov
AF: U.S. Geological Survey, 5735 Kearny Villa Rd., Ste. O, San Diego, CA 92123 United States
AU: Maddock, T
EM: maddock@hwr.arizona.edu
AF: University Of Arizona, Dept. of Hydrology & Water Resources 226 Harshbarger Building, Tucson, AZ 85721-0011 United States
AB: A new Farm Package (FMP) was developed for the U.S. Geological Survey's groundwater modeling program, MODFLOW-2000 (MF2K), to estimate irrigation water allocations from conjunctively used surface and ground water. The FMP package dynamically integrates irrigation water demand, surface and ground-water supply, and return flow from excess irrigation. Routed surface-water delivery is optional, but can be simulated by coupling the FMP package with the Streamflow Routing Package (SFR1). Applying MF2K with the FMP and SFR1 packages facilitates estimating the allocation of surface and ground-water to farms for simulations of historical calibration or future projections directly within MF2K. These simulations also can be useful for assessing water rights issues and operational decisions as well as for non-drought versus drought supply and demand strategies. Estimates of historic pumpage may be particularly useful where well pumpage has not been recorded, such as agivulture in the southwestern United States. Estimates of future pumpage may be facilitated through the use of climate-model predictions to generate forecasts of potential water supply and demand for irrigation. Legal questions such as adjudications and appropriative water rights also could be assessed with simulations that use the FMP package in areas where there is a history of land use but no direct or complete record of water use. Operational decision in irrigation management depends on the ability to estimate conjunctively used surface-water and groundwater allocations just prior to or during the growing season. Conjunctive management of surface and ground-water is especially needed for periods when the proposed water supply is thought to be insufficient to meet the water demand. Simulations with the FMP package offer several choices of drought policy scenarios, such as acreage optimization that facilitates assessing an economically optimal conjunctive management. The FMP package maintains a dual mass balance of a farm budget and a groundwater budget. Flows between these two budgets are accommodated by head-dependent inflows and outflows, such as the actual evapotranspiration or transpiration from groundwater. All flows of interest, such as irrigation demand, surface-water and groundwater supply, and excess irrigation return flow may depend on these head-dependent inflows and outflows. Consumption of water by individual crops from each farm is simulated with steady-state transpiration, varying with changing water level that is approximated in FMP by an analytical solution. These solutions were validated by soil column simulations with the variably saturated flow model HYDRUS2D. When irrigation demand in the farm budget cannot be sufficiently supplied by surface or ground water, a distortion of mass balance occurs. The FMP package provides the user with several drought policy response options including deficit irrigation, water stacking, and acreage optimization. A hypothetical example with 55 scenarios that represent 5 drought policy scenarios each with 11 parameter-group scenarios demonstrates the consistency and utility of the FMP package under different irrigation conditions. The first real-world application of `MF2K with FMP and SFR1 packages' was a model for the southern Rincon Valley, along the Lower Rio Grande of New Mexico, within the Elephant Butte Irrigation District. Another larger scale application of MF2K with FMP is being implemented by updating the USGS model of the Central-Valley Regional Aquifer System Analysis in California.
DE: 1818 Evapotranspiration
DE: 1829 Groundwater hydrology
DE: 1836 Hydrologic budget (1655)
DE: 1842 Irrigation
DE: 0644 Numerical methods
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting