Surface water and groundwater are intimately connected by a two‐way flux between the stream and underlying aquifers. The National Water Model (NWM) currently only considers a one‐way flux, where groundwater can enter a stream but cannot return to the aquifer. The Northern High Plains Aquifer, USA is used as a case study to investigate the consequences of omitting two‐way stream–aquifer fluxes on streamflow prediction capabilities of the NWM during hydrologic extremes. Instead of traditional field techniques to identify stream–aquifer fluxes, this study presents an integrated approach to classify likely stream regimes using three identification methods: United States Geological Survey (USGS) gage data, simulated stream–aquifer fluxes from an existing USGS Groundwater Availability Model, and the normalized difference vegetation index from remote sensing. For flood events, the modeled flood response for losing streams is characterized by statistically significant earlier peak discharges and an overestimate of the observed flood volume when compared to gaining streams. For drought events, our study found no statistical difference between losing and gaining streams, however, modeled streamflow from the NWM overestimated the observed USGS hydrograph. The systematic overestimate of streamflow by the NWM could be, in part, due to the lack of a losing stream mechanism which was on average 0.1% streamflow loss per streamwise km along the river.

中文翻译：

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美国北部高平原含水层国家水模型中地下水-地表水交换机制的影响

溪流和下层含水层之间的双向通量使地表水和地下水紧密相连。国家水模型（NWM）当前仅考虑单向通量，地下水可以进入水流，但不能返回含水层。以美国北部高平原含水层为例，研究了在极端水文情况下省略双向河水含水量对NWM径流预测能力的影响。代替传统的现场技术来识别河流含水层通量，本研究提出了一种使用三种识别方法对可能的河流流态进行分类的综合方法：美国地质调查局（USGS）量具数据，来自现有USGS地下水可利用性模型的模拟河流含水层通量，以及来自遥感的归一化植被指数。对于洪水事件，对损失的河流建模的洪水响应的特征在于，与增加的河流相比，统计上显着的早期峰值流量和观测洪水量的高估。对于干旱事件，我们的研究发现损失和增加的水流之间没有统计学差异，但是，NWM的模拟水流高估了观测到的USGS水位图。NWM对河流流量的系统性高估可能部分是由于缺乏流失机制，流失机制平均导致沿河每流向km的流失量仅为0.1％。与损失河流相比，模拟的损失河流洪水响应的特征在于统计上显着的早期峰值流量和观测洪水量的高估。对于干旱事件，我们的研究发现损失和增加的水流之间没有统计学差异，但是，NWM的模拟水流高估了观测到的USGS水位图。NWM对河流流量的系统性高估可能部分是由于缺乏流失机制，流失机制平均导致沿河每流向km的流失量仅为0.1％。与损失河流相比，模拟的损失河流洪水响应的特征在于统计上显着的早期峰值流量和观测洪水量的高估。对于干旱事件，我们的研究发现损失和增加的水流之间没有统计学差异，但是，NWM的模拟水流高估了观测到的USGS水位图。NWM对河流流量的系统性高估可能部分是由于缺乏流失机制，流失机制平均导致沿河每流向km的流失量仅为0.1％。