STREAM BANK EROSION ASSESSMENT USING CUMULATIVE TRACTIVE FORCE AND A SUBMERGED JET TEST DEVICE IN URBANIZING CLAY STREAMS, TEXAS

Urbanization increases storm frequencies, volume, and peak discharge which increase channel down cutting, widening and sediment loads. Stream erosion is a billion dollar problem in Texas. Stream bank erosion is shown to be a product of both submerged and subaerial processes which are a product of bank height and flood frequency. The goal of this research was to assess cumulative subaerial and submerged stream erosion rates and their relationship to tractive force and seasonality. Cohesive stream banks in the rapidly urbanizing Blackland Prairie of North Central Texas, an area with over 40% of the states population, were chosen for study. In situ erosion monitoring at seven field sites with contributing drainage areas from 3.7 – 650 square kilometers were conducted by utilizing erosion pins and pressure transducers with dataloggers for determination of erosion rates. Erosion pins were placed at two locations on the cutbank wall; one-third bankfull height and two-thirds bankfull height and monitored over one year.

The range of erosion rates from the one-third bankfull and the two-thirds bankfull heights during the monitoring period were a function of subaerial bank processes and flow duration, and ranged from 12.300 mm – 192.532 mm and 11.940 mm – 283.527 mm, respectively. Mean subaerial values are five times greater than the submerged values. Submerged jet test values (ASTM-D5852) acquired from samples taken at the same locations as the erosion pins allowed determination of potential critical tractive force and potential time rate of erosion (cm/hr./Pa). This test information was compared to monitored field erosion, flow duration, cumulative tractive force, and subaerial processes. Erosion predicted with submerged jet test values and cumulative tractive force are similar to monitored submerged flow erosion but underestimate subaerial rates. New techniques were developed for monitoring cumulative tractive force for quantification of erosion in stream channels.