Objectively identifying spatial variability in bankfull stage

Authors: Evan Lindroth*, Geography, University Of Illinois, Urbana Champain, Bruce Rhoads, Geography, University of Illinois, Urbana-Champaign
Topics: Physical Geography, Water Resources and Hydrology
Keywords: Bankfull flow, fluvial geomorphology,
Session Type: Paper
Day: 4/6/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Hoover, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Since the 1960’s, the bankfull flow concept has played a prominent role in the development of theories and models concerning the hydrology and geomorphology of alluvial river systems. The bankfull concept is based on a river system consisting of two basic components: a floodplain composed of alluvial material deposited by flooding, and the channel carved through the floodplain. The accuracy and applicability of the concept of bankfull flow has been challenged by inconsistencies between methods of measurement across different reaches. The idea is further complicated by the presence of cutoffs, sloughs, and other topographic pathways that may produce floodplain inundation before flow in the main channel reaches capacity. The present study introduces a quantitative model for identifying bankfull stage at closely spaced transect along a river. This MATLAB-based model calculates and visualizes the effects of changing water surface elevations within multiple channel-floodplain transects along a reach. Analysis based on high-resolution Lidar imagery of channel and floodplain topography reveals key stages at which hydraulic geometry changes abruptly with a rising water surface. By objectively identifying bankfull stage at each transect, the model documents spatial variability in bankfull elevation along a river channel. It also reveals activation of topographic pathways that connect the main channel to the floodplain at sub-bankfull stages. The high-resolution view of bankfull variability yields new insight into the complex relation between channels and floodplains by showing that erosional and depositional processes on floodplains can occur before flows overtop the banks of main channels.

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