Optimizing Management of Surface Water and Groundwater in the Platte River Valley, Eastern Nebraska, using the Farm Process for MODFLOW

Cooperating agencies: Papio-Missouri, Lower Platte North, and Lower Platte South Natural Resources Districts, and the Eastern Nebraska Water Resources Assessment

A model of the dynamically integrated hydrologic components of water system in the Platte River Valley near Ashland, Nebraska,(view detailed map) was constructed. The model used the Farm Process, version 2, for MODFLOW 2005 (FMP2) to simulate the period 2000-2009, and assess the effects of changes in on-farm irrigation efficiency, land use, and irrigated acres on groundwater levels and streamflow for improved water management.

Heliborne electromagnetic (HEM) surveys conducted by the USGS provided information about the physical properties of subsurface materials in part of the active model area.

The model consisted of an approximately 15-feet-thick silt and clay confining unit overlying an alluvial aquifer that ranges from 50 to 250 feet thick and overlies bedrock of Cretaceous and Pennsylvanian age. Over approximately 12 percent of the 327-square-mile area, layer elevations and hydraulic conductivity were estimated from a helicopter electromagnetic resistivity survey. Simulated streams included the Platte and Elkhorn Rivers and several tributaries. The model was calibrated to measured water levels and recorded streamflow.

FMP2 allows the simulation and continuous analysis of all available human and natural water-use components, and provides detailed water budgets to track all flows into and out of sub-allocation units defined by vegetation type or discrete areas such as natural vegetation or urbanized land. FMP2 uses reference evapotranspiration (ET), crop coefficients, soil type, root depth, and vegetation-uptake parameters to calculate plant-water demand. Remotely sensed land-use data were used to assign the vegetative cover and irrigated areas. Each sub-allocation unit was assigned on-farm efficiency, and, if irrigated, irrigation wells, which provided water when base irrigation and precipitation were less than the crop demand. Undeveloped sub-allocation areas such as grassland and riparian vegetation also were tracked. Sub-allocation-unit water budgets included irrigation pumpage, ET, recharge, and runoff for each monthly stress period and weekly time step.

Simulation results closely matched published average crop water-consumption values, and provided detailed information about how groundwater and streamflow were affected by on-farm efficiency, changes in irrigated acres, and crop type.

Related Study

Helicopter Electromagnetic and Magnetic Geophysical Survey Data, Oakland, Ashland, and Firth Study Areas, Eastern Nebraska, March 2007

Keywords

Ashland, Nebraska, groundwater model, heliborne electromagnetic, survey, water management, airborne geophysics

Contact

Derek Ryter
Steve Peterson
U.S. Geological Survey
5231 South 19th St .
Lincoln , NE 68512-1271
(402) 328-4100

 Back to the Nebraska projects page