State Water Resources Research Institute Program


Project ID: 2007CO152B
Title: Characterizing Non-Beneficial Evaporative Upflux from Shallow Groundwater Under Uncultivated Land in an Irrigated River Valley
Project Type: Research
Start Date: 3/01/2007
End Date: 2/29/2008
Congressional District: 4th
Focus Categories: Water Supply, Agriculture, Groundwater
Keywords: Evaporation, Evapotranspiration, Salinity
Principal Investigators: Waskom, Reagan M. (Colorado State University); Niemann, Jeffrey D
Federal Funds: $ 15,000
Non-Federal Matching Funds: $ 7,778
Abstract: The Lower Arkansas River is an important water resource for Southeastern Colorado, supplying water to more than 100,000 ha (250,000 acres) of irrigated agriculture. Over the last century, intensive irrigation has produced shallow water tables with high concentrations of salt and other minerals in the river valley. These conditions have led to waterlogging and high soil salinity that have decreased crop productivity by 11-19% according to recent research, and they have caused large loading of salts and selenium to the river. These problems can be addressed by reducing excess recharge and lowering the elevation of the shallow water table, but any alteration to water management practices in the valley must also consider Colorado?s legal obligation to maintain historical flows in the Arkansas River at the Kansas border. If the water table is reduced, crop productivity is expected to improve, which would increase the consumptive use of water from the irrigated lands, potentially reducing return flows to the river. However, the lower water table might also reduce the non-beneficial consumptive use of water from adjacent fallow fields and other uncultivated lands in the valley. The savings of water from these areas may be significant, more than offsetting the increase in consumptive use from cropped fields. Non-irrigated lands represent roughly 50% of the alluvial valley, and preliminary estimates suggest that the loss of water from these lands may currently amount to tens of thousands of acre-feet per year. Moreover, similar savings might be possible by lowering saline water tables in other intensively irrigated river valleys in Colorado and throughout the western United States. However, much more work needs to be done to understand how non-beneficial consumptive use depends on the water table depth and other factors such as the vegetation cover and soil salinity. The objective of this proposal is to observe and quantify the relationship between evapotranspiration (ET) losses water table depth for uncultivated areas in the Lower Arkansas River Valley. Two ~10 ha (25 acres) fields - one fallow field and one naturally-vegetated field - will be monitored. ET will be estimated using remote sensing, and water table depth will be measured using ~20 new observation wells in each field. Other variables such as soil moisture, biomass, rooting depth, and soil salinity also will be measured. Together, these observations will allow us to directly identify the role that the water table plays in determining ET losses from uncultivated lands under known soil and vegetation conditions. Ultimately, this research is expected to improve our understanding of the water balance in the Lower Arkansas River Valley and to improve the numerical models that are being used to evaluate potential solutions to waterlogging and salinization problems.

Progress/Completion Report, PDF

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