Modeling Water Surface Elevations to Estimate Discharge in a Braided River Network
Wade Monsen
Mentor: Brett Sanders
NASA’s Surface Water and Ocean Topography (SWOT) mission, launching in 2020, aims to characterize
variations in ocean circulation patterns and terrestrial water storage over spatial and temporal scales not
observable before. From a hydrologic standpoint, the SWOT satellite will measure water surface elevations
along major rivers and reservoirs which will then be used to estimate fluctuations in storage and discharge.
With regard to the SWOT mission, the purpose of this project is to investigate if satellite observations of river
width and water surface slope may be used to identify control points along a river which will facilitate the
estimation of discharge. Since the SWOT satellite is not yet operational, the water surface elevations are
simulated using a two-dimensional (2D) hydraulic model. The site selected for this modeling project is a 10
km reach of the Platte River in Nebraska, US, where a 1 m digital terrain model (DTM) was created from
light detection and ranging (LiDAR) data. The 2D hydraulic model BreZo was used to model the reach and
was parameterized with a 3 m unstructured mesh, based on the 1 m DTM, and a hydrograph from USGS
gauge 06768000. Model elevations, water surface elevations, and depth averaged velocities were extracted
from a low-flow time event and used to assess how flow variables vary over the entire reach. Constrictions in
the channel cross sectional area were found to explain riffles in water surface elevations and classical hydraulic
profiles could be fit to some of these locations to estimate discharge.