Quantitative Testing of Model of Bedrock Channel Incision by Plucking and Macroabrasion

Abstract

River incision can play a role in societally relevant or human timescale, which requires careful engineering planning and design. Physically based incision models can help us perform the engineering computations to prevent erosion damage to engineering structures such as bridges and channel-bank protection works. This paper presents a field application of our previously published work, in which we developed a mechanistically based model of bedrock incision by plucking and macroabrasion (a process of fracturing of the bedrock into pluckable sizes mediated by particle impacts from bedload). The plucking–macroabrasion incision model is tested quantitatively with Unnamed Drainage #1 in Southern Indiana, which showed obvious channel incision over the past 19 years, destroying a highway bridge foundation. The field data of incision rate, hydraulic conditions, rainfall, grain size characteristics, and morphological conditions were collected in the field or obtained from previous studies and the National Oceanic and Atmospheric Administration (NOAA). The plucking–macroabrasion incision model successfully creates a concave-upward profile with knickpoints (sudden change in slope) similar to the field condition and quantitatively simulates and explains the recorded distance of knickpoint-migration and incision rates in the past 19 years. The model is input with sensible parameters estimated with some degree of certainty from the field data. Sensitivity analyses were also implemented for some parameters. Appropriate amended versions of the model are anticipated to be able to simulate quantitatively the evolution of other bedrock streams under various input or boundary conditions over human timescale.

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