Optimal locating satellite observation reaches for manning’s equation: From surface water and ocean topography mission river Database

Abstract

Timely accurate measurement of river discharge is critical for water resource management. Construction and operation of a gauging network is expensive and time-consuming. With the advance of earth observation technologies, estimating discharge through remote sensing using Manning’s Equation has become an increasingly popular approach for filling the gaps in gauging observations. However, there is a lack of proper guidance to find a suitable Satellite Observation Reach (SOR) for this purpose. Here, we provide a practical approach, relying solely on various globally available data, for identifying optimal location of SOR for the rivers listed in the global Surface Water and Ocean Topography Mission River Database. A Manning-based Suitability Indicator (MSI) was developed, which integrates three sub-indicators: Fluctuation of Surface Extent, Stability of Channel Terrain, and Uniformity of River Flow. 21 gauges of 15 rivers around the world were selected as the case study sites. The MSI of about 200 candidate reaches were investigated at each site, and SOR was finally located at the reach with the highest MSI. Time-series Manning-based hydraulic variability (M_hv, an indicative discharge) was computed through the remotely sensed imagery at each SOR. The derived M_hv was finally compared with observed river discharge (Q_ob) for method validation. There is substantial concordance between M_hv and Q_ob at the SOR locations with R² of 5 sites above 0.9, 14 sites above 0.8, and 18 sites above 0.7. This indicates the reliability of the proposed approach. Our method may be easily applied to future data from the Surface Water and Ocean Topography (SWOT) mission, through efficiently converting SWOT signals to discharge at SOR locations using Manning’s Equation, and therefore, to initiate successful and effective discharge monitoring regionally and globally.