CEE 6400 Final Project, Logan River Irrigation Return Flow

Climate and environmental uncertainties are driving many communities to adopt water conservation strategies related to agricultural water use and irrigation efficiency. While water managers are equipped to understand the technical aspects of improved irrigation efficiencies(e.g. application rate), there are few tools to represent how a water balance responds to changes in management practices. This study seeks to understand the extent to which irrigation excess serves as recharge to streamflow and how this relationship varies with different irrigation practices. We developed a model to predict infiltration and runoff (surrogate for recharge)as a function of applied irrigation,precipitation, evapotranspiration, and soil type. This model was applied to a section of the lower Logan River between Main Street and Mendon Road, which is notably impacted by agricultural operations during the summer growing period. We used this model to evaluate the extent to which irrigation recharge supplements flow at Mendon Road and also evaluated the impact of irrigation timing and irrigation efficiency on recharge. Our model showed that observed flow at Mendon Road had a similar trend and magnitude to modeled recharge during low flow conditions.In addition, we found that irrigation timing had little impact on recharge while reducing the rate of irrigation application by 40% corresponded to a 75% reduction in recharge during summer months. On a broader scale, the results of this case study demonstrate the importance of considering “the paradox of irrigation efficiency” in water resource decision making.