Using SWOT Satellite Data to Estimate Hydraulic Resistance and Sediment Transport Capacity

Sediment transported by large rivers is a critical component of the global sediment cycle and is central to a broad range of fundamental processes of the Earth system, including river flooding and floodplain sediment dynamics, nutrient and adsorbed contaminant transport, and coastal sediment supply and coastal land loss. Yet, monitoring of bed sediment and sediment transport in large rivers occurs only rarely, if ever. The Surface Water and Ocean Topography (SWOT) satellite mission offers a novel ability to coincidentally measure river water surface elevation, extent, and slope and therefore can provide many, but not all, of the variables used to estimate sediment transport capacity in large rivers. In addition, the SWOT mission provides estimates of remotely-sensed river discharge using algorithms but these algorithms do not account for sediment transport related effects on hydraulic resistance.

For this initial effort, we build on previous work by making use of field measurement data collected routinely by water agencies at in situ gaging stations, including bed sediment data. Using discharge field measurements and SWOT data, we empirically solve for three critical variables that SWOT does not measure directly: depth to the bed, hydraulic resistance, and grain size. We use gaging station data where discharge is already known, combined with SWOT data, to solve hydraulic resistance equations for both Manning's n and the coefficient of friction, Cf. We also solve for the total depth to the bed and channel cross-sectional area. From these inversions, we derive an expression for hydraulic resistance, area and depth, directly from SWOT data for unmeasured sites. These relationships are used to estimate bed shear stress and bedload sediment transport capacity when combined with SWOT water surface elevations, extent and slope data. Through these initial models for hydraulic resistance and sediment transport, formulated from SWOT data, we improve SWOT river discharge products and can estimate bed sediment transport in large rivers.