Quantifying Geomorphic Change to a Point Bar in Response to High Flow Events Using Terrestrial LiDAR, White Clay Creek, Delaware

Abstract:

Light Detection And Ranging (LiDAR) can accurately measure three dimensional surfaces for quantifying fluvial erosion and deposition. Point bars are topographic features that form on the convex bank of a meander. While point bars are considered to be formed by depositional processes, they display features such as chute channels and scour holes that suggest that erosion (due to high flow events) may significantly influence point bar evolution. Through the use of Terrestrial Laser Scanning (TLS), we observed how a point bar on the White Clay Creek near Newark, Delaware responded to a flood event with a return period of 5-50 years. Pre-flood and post-flood LiDAR scans were completed in April and May of 2014. Scans were referenced to a common coordinate system, vegetation points were removed, and two 0.10 m resolution gridded Digital Elevation Models (DEMs) were created. A DEM of Difference (DoD) was created by subtracting the pre-flood DEM from the post-flood DEM. Total deposition was 43.58 m³ and total erosion was 79.15 m³, with a net volumetric change of -35.57 m³ over an area of 630.32 m². Erosion was dominant on the surface of the scroll bar and on the upstream end of the point bar. The pre-flood surface had a large chute channel adjacent to the scroll bar that was filled in during the storm, particularly on the downstream end. Deposits from the storm also extended the point bar into the river channel on the downstream end of the study site. Our results suggest that 1) sediment deposited on point bars is eroded frequently by flood events; and 2) TLS can provide useful estimates of erosion and deposition. If TLS surveys are repeated through time, sediment residence times in point bars can be quantified. This information is useful for creating accurate sediment budgets and for remediating contamination issues.