River Bathymetry Analysis in the Presence of Submerged Large Woody Debris

by Laurent White

Citation: White, L. (2003), River Bathymetry Analysis in the Presence of Submerged Large Woody Debris, MS Thesis, Dept. of Civil Engineering, University of Texas at Austin, Dec. 2003

Abstract

The frequent use of two-dimensional hydrodynamic river models requires more detailed bathymetry surveys. For smooth bathymetries, there is little difficulty in developing accurate translations from survey data to model; however, in rivers with significant bottom structure (e.g., large woody debris -- LWD), simple data averaging and interpolation methods may lead to misrepresentation of the bottom bathymetry. It is necessary to distinguish in the data set what is true bathymetry from what is caused by large woody debris. Two groups of methods are investigated to serve this objective: statistical techniques and filtering techniques. In the first group, two approaches are considered: 1) a sigma- discriminator method is developed and shown to effectively separate LWD from the background bathymetry, and 2) a scale-space analysis technique is applied to the same problem, but is shown to be ineffective for clearly discriminating LWD from the background bathymetry. In the second group, linear and nonlinear filters are tested. A synthesized bathymetry is used to compare relative errors associated with each method. Median filtering proves to be the best technique for removing LWD impulse spikes while leaving the background bathymetry relatively unchanged. A method of selecting the minimum filter order based upon the physical scales of the LWD and the statistics of the data separation in the survey is proposed.

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Note - the above thesis is related to two journal papers <more info> <more info> and an earlier technical report <more info>

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