Saturday, 15 July 2006

Devils Lake Basin Water Utilization Test Project.

David Hopkins, Dean Steele, Mike Sharp, and Ramesh Gautam. North Dakota State Univ, NDSU- 225 Walster Hall, Fargo, ND 58105-5638

Above-average rainfall since 1993 has led to rising water levels in Devils Lake and other surface waters in the surrounding basin of northeastern North Dakota. The lake is presently at the highest level since European settlement. The basin (9,870 km2) is essentially considered a closed system, though records indicate it has naturally overflowed to into the Red River of the North. Flood damage from the 7.8 m increase in the elevation of Devils Lake has been extensive since 1993 and has locally devastated agriculture, homes, businesses, roads, etc. Currently, $550 million have been expended in mitigation efforts. The severe and prolonged impact of the wet climatic cycle on the local economy prompted the State of North Dakota to construct an outlet to the Red River of the North watershed; pumping began in late summer 2005. A parallel solution under consideration is the development of new irrigation areas to utilize some of the excess surface water in the basin. Currently the irrigation project is in a test phase to determine its effectiveness and sustainability. The effectiveness of potential irrigation development will be assessed by the additional EvapoTranspiration (ET) achievable under irrigation compared with nonirrigated agriculture in the basin. Remote sensing methods for ET are expected to be the only viable way to achieve basin-wide estimates of the water utilization—or flood mitigation effectiveness—that may be possible if irrigation development continues as a consequence of the test phase results. The sustainability of potential irrigation development will be assessed by soil and water compatibility investigations, which are critical because many of the soils in the basin are considered only conditionally irrigable because of drainage limitations and soil chemical properties. Because of these reasons soil water budgets and soil/water compatibility studies must utilize the most accurate research tools and techniques. The primary objectives of the research are to: 1) Determine how much additional surface water in the Devils Lake basin can be utilized via sprinkler irrigation of agricultural crops compared with non-irrigated crops. 2) Evaluate effects of irrigation on soil physical and chemical properties at sites selected to represent dominant soil map units within the basin and thereby refine soil-water compatibility guidelines. 3) Extrapolate test project results to estimate the total volume of water that could be prevented from entering Devils Lake through proposed development of irrigation in the basin under the constraints of the project's soil-water compatibility findings. Ten test sites have been selected with eight having full-size center pivot irrigation systems that were installed last summer; two sites have smaller irrigation systems for specialty crop production. Comprehensive soil investigations, baseline soil sampling, and water balance instrumentation installation was completed by autumn of 2005. Irrigation is planned for the 2006 through 2008 field seasons. All test site locations, instrument clusters, and soil profile investigation sites have been georeferenced and will be coupled with GIS analyses of digital soil survey data (SSURGO). A baseline soil salinity survey was conducted at each site with a VERIS system in late spring 2005 to provide a spatial estimate of salinity zones in each field; this process will be repeated yearly at the end of the irrigation season. To assess changes in actual soil salinity several transects (8 points each) have been established along gradients in apparent salinity as measured with the VERIS device and will be used as permanent temporal sampling locations. These transects can be sampled yearly or at the end of the last irrigation season to pinpoint critical zones and changes and trends in the landscape.

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