Arkansas - CSU Geospatial DSS for Integrated Water Mgmt_ Application

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Water Supply Reserve Account -Grant Application Form Form Revised May 2007 benefits and reduction in solute concentrations to expected implementation costs; and (6) cooperate with the MUSIC-USBR project for developing a coupled social-economic-physical model for the Lower Arkansas River Basin in Colorado. A wide range of structural and management strategies will be considered for the Arkansas River Basin, including: adoption of new irrigation technologies for reducing application rates over selected subregions of the Basin; seepage reduction over selected irrigation canal reaches via lining or application of canal sealants; installation of horizontal subsurface drainage in identified subregions; alteration of pumping patterns in existing wells (both rates and timing); alteration of cropping patterns to more salt tolerant crops; removal of invasive phreatophyte plants over selected reaches of the Arkansas River and its tributaries; adjustment of conservation storage accounts and releases from Pueblo and John Martin reservoirs; and storage and release of subsurface drainage effluents in off-stream reservoirs. These strategies will be evaluated as to their impacts on river flow quantity and quality, instream flow requirements for fish and wildlife habitat and recreation; protection of existing water rights, and the Colorado-Kansas interstate water compact. Problems and Opportunities A variety of water-related problems, both old and new, have colluded over the last few years, pointing to the time being ripe for the planning and implementation of several changes on the Arkansas River that could result in improvements to beneficial use of water (including agricultural productivity), environmental health, and water conservation. These changes include both structural and management interventions to the irrigated-stream-aquifer system, including river flow allocations and operations. Evidence to date suggests that although the challenges are formidable, the prospects for enhancement to the system are high. Over the years, while the benefits of an impressive irrigation infrastructure have been enjoyed in the Arkansas River Valley of Colorado, an insidious side effect has taken form primarily in the Lower Valley. The groundwater table has risen and grown saline due to excessive irrigation, seepage from earthen canals, and inadequate drainage facilities. Upward flow from high water tables has salinized and waterlogged many of the rich soils of the Valley, causing crop yields to diminish. Not only have soils been degraded, but river water quality also has suffered. In addition to the evaporative concentration of solutes in applied waters, intensive irrigation of alluvial soils, which are derived from underlying marine sedimentary rocks, may also have accelerated the dissolution of inherent salts and other natural mineral pollutants (i.e., selenium (Se), iron (Fe), and uranium (U)) into the underlying alluvial aquifer as subsurface discharge to the river. Consequently, solute concentrations in the river can rise to levels that threaten not only the productivity of the land but also the ecological health of the river. In addition, over-irrigation has created shallow water tables under irrigated lands, as well as adjacent naturally-vegetated and fallow lands. Evaporative upflux from the water table under this ground, along with evapotranspiration from invasive phreatophytes along the river corridor, can amount to significant volumes of non-beneficial consumptive use. Increases in irrigation efficiency and sealing of earthen canals in the Lower Arkansas Valley (below Pueblo Reservoir} would reduce excess recharge to underlying alluvial aquifers, thereby lessening soil water salinity and waterlogging, along with a consequent increase in crop yields. Return flows to the river would be substantially altered, along with salt and Se loads in these return flows markedly reduced, thereby enhancing river water quality. However, the associated changes in the rate and timing of irrigation diversions and return flows might materially alter the pattern of river 9