GroMoPo Metadata for Elkhorn/Loup USGS model

The U.S. Geological Survey, in cooperation with the Lewis and Clark, Lower Elkhorn, Lower Loup, Lower Platte North, Lower Niobrara, Middle Niobrara, Upper Elkhorn, and the Upper Loup Natural Resources Districts, designed a study to refine the spatial and temporal discretization of a previously modeled area. This updated study focused on a 30,000-square-mile area of the High Plains aquifer and constructed regional groundwater-flow models to evaluate the effects of groundwater withdrawal on stream base flow in the Elkhorn and Loup River Basins, Nebraska. The model was calibrated to match groundwater-level and base-flow data from the stream-aquifer system from pre-1940 through 2010 (including predevelopment [pre-1895], early development [1895-1940], and historical development [1940 through 2010] conditions) using an automated parameter-estimation method. The calibrated model then was used to simulate hypothetical development conditions (2011 through 2060). Predicted changes to stream base flow based on simulated changes to groundwater withdrawal will aid in developing strategies for management of hydrologically connected water supplies. Additional wells were simulated throughout the model domain and pumped for 50 years to assess the effect of wells on aquifer depletions, including stream base flow. The percentage of withdrawal for each well after 50 years, which was compensated by aquifer reductions to stream base flow, storage, or evapotranspiration, was computed and mapped. These depletions are influenced by aquifer properties, time, and distance from the well. Stream base-flow depletion results showed that the closer the added well was to a stream, the greatest the effect on the stream base flow. Areas of stream base-flow depletion percentages greater than 80 percent were generally within 1 mile (mi) from the stream. The distance increased to 6 mi near the confluence of the Dismal and Middle Loup Rivers, and the North Loup and Calamus Rivers. The percentage of stream base-flow depletion decreased as the distance from the stream increased. Areas more than 10 mi from the stream generally had a stream base-flow depletion of 10 percent or less. Evapotranspiration depletion was largest in areas closest to streams, specifically in the Elkhorn River watershed. It was also larger in areas of interdunal wetlands within the Sand Hills. Evapotranspiration depletion was negligible in areas greater than 5 mi from a stream, with the exception of interdunal areas in Cherry, Grant, and Arthur Counties. The storage depletion percentage increased as the distance from a stream increased. Storage depletion was largest in areas between streams. Areas experiencing the smallest amount of storage depletion were adjacent to streams. Calibrated model outputs and streamflow depletion analysis are publicly available online. Accuracy of the simulations is affected by input data limitations, system simplifications, assumptions, and resources available at the time of the simulation construction and calibration. Most of the important limitations relate either to data used as simulation inputs or to data used to estimate simulation inputs. Development of the regional simulations focused on generalized hydrogeologic characteristics within the study area and did not attempt to describe variations important to local-scale conditions. These simulations are most appropriate for analyzing groundwater-management scenarios for large areas and during long periods and are not suitable for analysis of small areas or short periods.美国地质调查局与路易斯和克拉克、下艾尔克霍恩、下路易普、下普拉特北、下尼奥布拉拉、中尼奥布拉拉、上艾尔克霍恩和上路易普自然资源区合作，设计了一项研究以优化先前建模区域的时空离散化。此次更新研究聚焦于大平原含水层30,000平方英里的区域，并构建了区域地下水流动模型以评估地下水抽取对内布拉斯加州艾尔克霍恩和路易普河流域基流的影响。该模型经过校准，以匹配从1940年以前至2010年的河流-含水层系统中的地下水位和基流数据（包括开发前[1895年以前]、早期开发[1895-1940年]和历史性开发[1940年至2010年]条件），并采用自动化参数估计方法。校准后的模型随后被用于模拟假设的发展条件（2011年至2060年）。基于模拟的地下水抽取变化预测河流基流的改变，有助于制定管理水文学上相互关联的水资源的策略。在整个模型区域内模拟了额外的井，并抽取了50年以评估井对含水层耗竭的影响，包括基流。计算并绘制了每个井在50年后的抽取百分比，这些百分比通过含水层减少对基流、储存或蒸散的影响而得到补偿。这些耗竭受含水层特性、时间和井的距离影响。基流耗竭结果显示，新增井越接近河流，对基流的影响越大。基流耗竭百分比超过80%的区域通常位于河流1英里（mi）范围内。在迪斯马尔和中间路易普河、北路易普河和卡拉马斯河的交汇处，距离增加到6英里。随着距离河流的增加，基流耗竭百分比逐渐降低。距离河流超过10英里的区域，基流耗竭通常为10%或更少。蒸散耗竭在河流最近的区域最大，特别是在艾尔克霍恩河流域。在桑希尔地区间的湿地中，蒸散耗竭也较大。在距离河流超过5英里的区域内，蒸散耗竭可以忽略不计，除了樱桃、格兰特和亚瑟县之间的间沙丘区域。随着距离河流的增加，储存耗竭百分比逐渐增加。储存耗竭最大的区域位于河流之间。储存耗竭最少的区域通常位于河流附近。校准模型的输出和基流耗竭分析已在网络上公开。模拟的准确性受输入数据限制、系统简化、假设以及模拟构建和校准时可用资源的影响。大部分重要限制与用作模拟输入的数据或用于估计模拟输入的数据相关。区域模拟的发展集中于研究区域内的泛化水文地质特征，并未尝试描述对局部尺度条件重要性的变化。这些模拟最适用于分析大区域和长期内的地下水管理情景，不适用于小区域或短期的分析。