Estimating river discharge from observed surface water extents and elevations is central to the Surface Water and Ocean Topography (SWOT) mission. Although near global in coverage, SWOT will only observe rivers wider than 50 to 100 m, overlooking smaller tributaries draining into observable river reaches. This is problematic for the Metropolis‐Manning (MetroMan) discharge algorithm, which assumes changes in discharge per location must be balanced by a change in cross‐sectional area, not accounting for potential flow contributions SWOT will not observe within the inversion region analyzed. Here, we quantify the effect of these lateral inflows on the performance of estimated discharges along the Muskingum River using MetroMan. Three scenarios are considered: (1) disregarding lateral inflows, (2) providing MetroMan with observed lateral inflows, and (3) providing MetroMan with uncertain model‐derived lateral inflows to assess the discharge algorithm's effectiveness. Scenarios are expanded to consider multiple lateral inflow magnitudes and distributions. Results indicate discharge retrievals were degraded once unaccounted lateral inflows exceeded 5% of average river discharge. When MetroMan is informed by observed lateral inflows, the derived discharges have a relative root‐mean‐square error (rRMSE) of 23% as compared to 360% when lateral inflows are neglected. More importantly, when MetroMan uses simulated lateral inflows, with peak flow condition percent errors as high as 93%, discharge retrieval performance is similar (rRMSE = 17%). These findings highlight the importance of accounting for lateral flows, even in the absence of perfect measurements.

中文翻译：

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将侧向流量集成到SWOT Mission River流量算法中

从观测到的地表水域范围和海拔高度估算河流流量是地表水和海洋地形（SWOT）任务的核心。尽管覆盖范围接近全球，但SWOT仅能观测50至100 m以上的河流，而忽略了流入可观测河段的较小支流。对于Metropolis-Manning（MetroMan）排放算法，这是一个问题，该算法假定每个位置的排放变化必须通过横截面积的变化来平衡，而不考虑SWOT在分析的反演区域内不会观察到的潜在流量贡献。在这里，我们使用MetroMan量化了这些横向流入量对沿马斯金格姆河估计流量的影响。考虑了以下三种情况：（1）忽略横向流入，（2）向MetroMan提供观察到的横向流入，（3）为MetroMan提供不确定的模型派生侧向流入量，以评估排放算法的有效性。扩展了方案以考虑多个横向流入量和分布。结果表明，一旦无法确定的侧向流量超过平均河流流量的5％，流量恢复将降低。当观察到的横向流量通知MetroMan时，得出的流量的相对均方根误差（rRMSE）为23％，而忽略横向流量的相对均方根误差为360％。更重要的是，当MetroMan使用模拟的侧向流量时，峰值流量工况百分比误差高达93％，排放物的回收性能相似（rRMSE = 17％）。这些发现强调了即使没有完善的测量方法，也必须考虑横向流量的重要性。