Modeling the Evolution of Incised Streams. III: Model Application

Abstract

Incision and the ensuing widening of alluvial stream channels represent important forms of channel adjustment. Two accom- panying papers have presented a robust computational model for simulating the long-term evolution of incised and restored or rehabili- tated stream corridors. This work reports on applications of the model to two incised streams in northern Mississippi, James Creek, and the Yalobusha River, to assess: 1 its capability to simulate the temporal progression of incised streams through the different stages of channel evolution; and 2 model performance when available input data regarding channel geometry and physical properties of channel boundary materials are limited in the case of James Creek. Model results show that temporal changes in channel geometry are satisfactorily simulated. The mean absolute deviation MAD between observed and simulated changes in thalweg elevations is 0.16 m for the Yalobusha River and 0.57 m for James Creek, which is approximately 8.1 and 23% of the average degradation of the respective streams. The MAD between observed and simulated changes in channel top width is 5.7% of the channel top width along the Yalobusha River and 31% of the channel top width along James Creek. The larger discrepancies for James Creek are mainly due to unknown initial channel geometry along its upper part. The model applications also emphasize the importance of accurate characterization of channel boundary materials and geometry.