Prediction of channel degradation rates in urbanizing watersheds

In urbanizing watersheds, as land use changes, and storm sewers and impervious surfaces are increased, both the frequency and magnitude of discharge increase, resulting in stream channel down-cutting and widening and related loss of structures and engineering works. A simple model for assessing the time rate of degradation in watersheds is given. The model relies oil a continuous Simulation of watershed discharge based on local climate (SWAT-DEG) instead of a dominant discharge approach. Unique to this approach is the use of in situ erosion parameters derived from submerged jet tests, which give both the allowable tractive force as well as erodibility coefficients. The model is used in concert with the Watson-Harvey analysis of channel evolution. Four methods were used to verify and validate the model for estimating rates of degradation. A case study of channel stability assessment using this tool was made in north central Texas (USA). Rates of incision were nonlinear and ranged from 0-76 mm/year.