Demonstration of Field Scale Applications to Control Water Logging and Stalinization
* Can the effects of field scale applications to improve efficiency of irrigation and subsurface drainage be extrapolated to the regional and basin scale thru modeling toward optimal water management in the Arkansas River Valley, Colorado?
Water logging and salinization pose a threat to sustainable irrigated agriculture in the Western United States., including Reclamation irrigation projects. The intent of this research is to evaluate effects of field scale improvements in irrigation efficiency and drainage. The results will be used to calibrate, refine and validate Colorado State University's surface and ground water flow and solute transport modeling in the Arkansas River Valley, Colorado. In turn, the modeling tools will be used to rank, evaluate, and implement solution strategies. Results will be provided to local growers, canal companies, conservancy districts, and local resource agencies such as the Natural Resource Conservation Service (NRCS) and Colorado State Extension.
Need and Benefit
Many river systems in the Western United States (which contain Reclamation irrigation projects) are not well represented by geospatially related modeling tools that simulate the effects of conjunctive water management decisions for multiple uses on surface and ground water flow and solute transport and their impacts on irrigated agricultural productivity over regional or basin-wide scales.
Water logging and/or salinization are significant problems associated with irrigated agriculture in the Western United States (including Reclamation's projects), within river basins such as the Colorado River, Arkansas and South Platte Rivers in Colorado, Pecos River in New Mexico and the Central Valley Project in California. These two conditions result in reduced crop yields, increased nonbeneficial water use by phreatopytes and evaporation from soil surfaces, increased dissolution of potentially harmful soluble salts and trace elements, and impairment to downstream water quality and quantity. Water management improvement strategies are needed and must be evaluated and applied to sustain irrigated agriculture in areas where salinization and waterlogging continue to erode productivity and beneficial use. These strategies must be technically feasible, cost effective and consider legal, institutional, social, and environmental constraints.
In addition, improvements in irrigation water management may be one means to help meet increasing water demands in many areas of the Western United States.. Water demand along the Front Range of Colorado from the city of Pueblo to Fort Collins is expected to increase by more than 50 percent by 2030. Current agricultural water allocations may be sought thru leasing or purchase to help slake the demands of urban and industrial needs along the Front Range. In addition to tools for understanding impacts due to surface and ground water interactions, tools are needed to evaluate the long term impacts of water transfers or leasing arrangements on the agricultural economy, downstream water rights holders, and the environment
Colorado State University, with local, State and Federal support, including Reclamation, is developing geospatially related modeling tools to simulate surface and ground water interactions and salt transport in the Arkansas River Valley toward optimal water management. Groundwater Modeling System (GMS) models have been developed that links MODFLOW (ground water flow) and MT3DMS (contaminant transport model for solving finite approximations of the flow and salt transport equations within a spatial-referenced GIS). The initial research developed and used these modeling tools to diagnose the extent and severity of the problem and to predict how possible reductions in ground water recharge through improved irrigation efficiency and reductions in canal seepage would impact soil salinity and water table levels. For example, a 50 percent reduction in recharge from improved irrigation efficiency and a reduction of canal seepage by 90 percent was predicted to reduce the average water table elevation by 1.48 meters and average soil salinity by about 550 milligrams per liter over the period 1999 - 2001.
An objective of the next phase is evaluate field scale applications, including irrigation and drainage efficiency improvement to refine and calibrate the modeling tools in order to extrapolate the results to regional or basin scale.
Ultimately, basin-scale modeling tools will be available to evaluate and rank water management solutions relative to their effectiveness in helping control waterlogging and salinization and impacts on return flow quantity and quality within legal, institutional, environmental and social constraints. The tools will useful for not only the evaluation of impacts from irrigation efficiency improvements, but the impacts of water leasing or water rights purchases on the regional area and downstream water rights holders.
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