Using SWOT Data to Assess the Impact of Ocean Tides and Sea Level Change on Upstream Rivers and Estuaries

Principle Investigator: Steve Nerem (University of Colorado)

Co-Investigator(s): J. Toby Minear

Collaborator(s): Neil Ganju, Richard Ray

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The upstream-most backwater effects of ocean tides on inland rivers and estuaries are not well known presently and pose an additional threat from sea level rise. As sea levels are projected to rise by ~1 m by the year 2100, tides will propagate farther upstream, extending into freshwater waterbodies and wetland areas, adding to flooding threats far from the sea. In addition, even small increases in salinity can have serious impacts on groundwater, wetlands, agriculture and human populations living in these areas. With SWOT, we can, for the first time, observe the extent to which tidal-influence backwater effects influence upstream estuaries and rivers. There are many factors that impact this effect including the height of the high tide on a particular day, the slope of the geoid, potential storm surge, the shape of the estuary and its connectivity to nearby wetlands, in addition to other factors. To help resolve SWOT measurements of water surface elevations in these very low-slope areas, a better understanding of the errors in the SWOT data is needed, including errors in modeling the wet troposphere delay near the ocean-land transition, and understanding potential biases across the swath, therefore we are keenly interested in evaluating SWOT data with ground-based measurements and other satellite data in these coastal areas. We propose to use SWOT data to map the present-day spatial extent of tidal-influence on upstream surface waters, as well as the spatially-distributed mean water surface elevation and tidal range (difference between low- and high-tides) from the coast through the estuary and river system. These three key variables can then be used to project the impacts of sea level rise for these inland surface water regions. This study will use SWOT data to develop a better understanding of tides, tidal effects on inland surface waters and the projected effects of sea level rise in the future.