In mountain, snow driven catchments, snowmelt is supposed to be the primary contribution to river streamflows during spring. In these catchments the contribution of groundwater is not well documented because of the difficulty to monitor groundwater in such complex environment with deep aquifers. In this study we use an integrated hydrologic model to conduct numerical experiments that help quantify the effect of lateral groundwater flow on total annual and peak streamflow in predevelopment conditions. Our simulations focus on the Upper Colorado River Basin (UCRB; 2.8 × 10⁵ km²) a well‐documented mountain catchment for which both streamflow and water table measurements are available for several important sub‐basins. For the simulated water year, our results suggest an increase in peak flow of up to 57% when lateral groundwater flow processes are included—an unexpected result for flood conditions generally assumed independent of groundwater. Additionally, inclusion of lateral groundwater flow moderately improved the model match to observations. The correlation coefficient for mean annual flows improved from 0.84 for the no lateral groundwater flow simulation to 0.98 for the lateral groundwater flow one. Spatially we see more pronounced differences between lateral and no lateral groundwater flow cases in areas of the domain with steeper topography. We also found distinct differences in the magnitude and spatial distribution of streamflow changes with and without lateral groundwater flow between Upper Colorado River Sub‐basins. A sensitivity test that scaled hydraulic conductivity over two orders of magnitude was conducted for the lateral groundwater flow simulations. These results show that the impact of lateral groundwater flow is as large or larger than an order of magnitude change in hydraulic conductivity. While our results focus on the UCRB, we feel that these simulations have relevance to other headwaters systems worldwide.

中文翻译：

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模拟科罗拉多河上游流域的地下水流连接。

在山区，积雪驱动的集水区，融雪被认为是春季春季河流流量的主要贡献。在这些流域中，由于难以在具有深层含水层的复杂环境中监测地下水，因此没有对地下水的贡献进行充分记录。在这项研究中，我们使用综合水文模型进行数值实验，以帮助量化侧向地下水流量对预开发条件下年总流量和峰值流量的影响。我们的模拟集中在上科罗拉多河流域（UCRB; 2.8×10 ⁵  km ²）一个有据可查的山区流域，其流量和地下水位测量均可用于几个重要的子流域。对于模拟水年，我们的结果表明，包括横向地下水流量过程，峰值流量最多增加57％-对于通常被认为独立于地下水的洪水状况，这是一个出乎意料的结果。此外，包含侧向地下水流量适度改善了模型与观测值的匹配。年平均流量的相关系数从无侧向地下水流量模拟的0.84提高到无侧向地下水流量模拟的0.98。在空间上，在地形较陡的区域中，横向和非横向地下水流情况之间的差异更加明显。我们还发现上科罗拉多河子流域之间有或没有侧向地下水流的流量变化幅度和空间分布存在明显差异。进行了一个敏感性试验，将水力传导率的比例缩放了两个数量级，用于模拟地下水的横向流量。这些结果表明，地下水侧向流动的影响与水力传导率的变化幅度一样大或更大。虽然我们的研究结果集中在UCRB上，但我们认为这些模拟与全球其他上游水源系统相关。这些结果表明，地下水侧向流动的影响与水力传导率的变化幅度一样大或更大。虽然我们的研究结果集中在UCRB上，但我们认为这些模拟与全球其他上游水源系统相关。这些结果表明，地下水侧向流动的影响与水力传导率的变化幅度一样大或更大。虽然我们的研究结果集中在UCRB上，但我们认为这些模拟与全球其他上游水源系统相关。