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.气候与环境不确定性正推动诸多社区采用与农业用水及灌溉效率相关的节水策略。尽管水资源管理者能够掌握提升灌溉效率的技术层面内容（例如灌水率），但目前鲜有工具能够模拟水平衡（water balance）随管理措施变化的响应规律。本研究旨在明确过剩灌溉水对径流的补给程度，以及该关系随不同灌溉措施的变化情况。本研究构建了一个模型，可基于灌溉施用量、降水量、蒸散发（evapotranspiration）与土壤类型，预测土壤下渗与地表径流（径流补给的替代指标）。将该模型应用于主街与门登路之间的洛根河下游河段，该河段在夏季作物生长期受农业活动的显著影响。本研究利用该模型评估了灌溉补给对门登路河段流量的补给程度，同时分析了灌溉时机与灌溉效率对补给量的影响。模型结果显示，在枯水工况下，门登路河段的实测流量与模拟补给量的变化趋势与量级均较为接近。此外，研究发现灌溉时机对补给量的影响极小，而夏季将灌溉施用量速率降低40%时，补给量可减少75%。从更宏观的视角来看，本案例研究的结果证实了在水资源决策中考虑‘灌溉效率悖论（paradox of irrigation efficiency）’的重要性。