Abstract:
Population growth in the intermountain west, coupled with frequent drought and the prospects of climate change, are challenging the security of water supplies and the agricultural economy in Wyoming and the region. Agriculture is the largest user of water in Wyoming and the intermountain west and accounts for approximately ninety percent of the total amount of water withdrawn from streams and aquifers. However, only a portion of applied water is consumptively used. The rest is returned to streams or aquifers. Some of the potential benefits include recharge of alluvial (shallow) aquifers that serve as underground storage reservoirs, increased likelihood of maintaining late season flow and a steadier more reliable source of water downstream resulting from the return flow pattern of an interactive stream-aquifer system. This project will apply new methods and techniques to directly quantify return flow from controlled agricultural systems in the Spence/Moriarty Wildlife Habitat Management Area in the East Fork watershed in the Upper Wind River Sub-Basin in Wyoming. This location is ideal for this study as we can work directly with the managers controlling the application and timing of the irrigation water. We will use a water balance approach at the “reach scale” to quantify the return flow in the system. To directly measure and monitor the pathways and timing, we will employ new methods in hydrogeophysics and tracers at the field scale. Geophysics tools will be used to map subsurface flow paths, monitor and quantify return flow. In addition, we will use tracers such as isotopes and geochemical markers to directly measure and monitor return flow in the system. Results from this study will be compared to an irrigation return flow study conducted in the Upper Green River Basin in the 1980s. An understanding of the quantity and timing of return water flow is critical for effective water management for downstream water users and maintaining agriculture water security in the state.