STREAMBANK EROSION ASSESSMENT OF COHESIVE AND NON-COHESIVE BANK MATERIALS USING EROSION PINS AND SUBMERGED JET TESTING, NORTH CENTRAL TEXAS

This research details for the first time, an extensive comparison of the submerged jet erodibilty test and field monitored erosion. Two separate studies were completed over a two year period to determine if a submerged jet test could be used to predict erosion in cohesive and non-cohesive streambank materials. The study areas were in, and adjacent to, the Dallas/Fort Worth Metroplex within the Blackland Prairie and Cross Timbers physiographic provinces. Streambank erosion rates were monitored for a total of 19 months in 12 watersheds ranging in size from three to 239 square kilometers.

Erosion monitoring was completed using erosion pins and water level logging pressure transducers. Erosion pins were placed at two levels on cutbank walls and erosion was recorded in conjunction with measured discharge. Field monitoring of erosion pins produced 27-150 mm of loss over eight months in non-cohesive materials and 30-527 mm of erosion over 11 months in cohesive streambank materials.

A total of 14 submerged jet test samples were collected at the 12 sample sites. Erodibility coefficients produced by a submerged jet test ranged from 0.0019-0.0345 cm/hr/Pa in non-cohesive materials and 0.0012-0.0023 cm/hr/Pa in cohesive streambank materials. The submerged jet test results, combined with flow duration and tractive force, were within 37-41% of measured erosion rates in non-cohesive materials and within 31% for cohesive materials. This corresponds to an overall error of plus or minus one centimeter in cohesive and non-cohesive materials over the study periods. Results from this study are applicable to stream restoration and natural channel design.