Development of a Probabilistic Framework to Predict Erosion using Soil Parameters
Emily D. Brown
Zack Nixon
Freese and Nichols, Inc.
Winston-Salem, NC
Celso Castro Bolinaga, PhD
NC State University
Raleigh, NC
Streambank retreat has become a growing concern among society over the past decade. Development in previously rural environments has led to increases in impervious cover and changes in hydrologic conditions. Precipitation runoff is getting to streams quicker, with less time for runoff to infiltrate into the soil. Streambank stability becomes threatened with the increased flows and over time, erosion occurs, creating potential safety and water quality concerns. Depending on native soil properties, watershed characteristics, and anthropogenic influence, the severity of erosion can vary. Thus, the ability to determine and predict rates of streambank erosion and associated sediment loading in streams is important. The objective of this work was to develop a probabilistic framework to estimate the likelihood of erosion using streambank geometry and site-specific soil properties. Data from eight (8) streambanks in the City of Durham within the North Carolina Piedmont were included in this analysis, with each site having unique streambank geometry, local gage data, and soil properties. Streambank characteristics used in this analysis included streambank geometry, slope, and the scaled flow data from the nearest USGS gage. Soil properties used in this analysis, as determined using the Jet erosion test (JET), included critical shear stress, erodibility coefficient, alpha, soil moisture content, soil temperature, percent of material passing the #200 sieve, D84, and D16. In addition to field measured soil moisture content, a range of moisture contents from 10% up to 40% were analyzed to determine the associated erosion rates. A PSHA framework, a framework traditionally associated with earthquake predictions was used to determine the probability of occurrence of erosion rates coupled with the rate of exceedance for a given moisture content for each of the eight streambanks.
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