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Water 2019, 11(4), 735; https://doi.org/10.3390/w11040735

A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream

1
Department of Civil Engineering, National Chiao Tung University, 1001 University Road, Hsinchu City 30010, Taiwan
2
Technical Service Center, U.S. Bureau of Reclamation, Bldg. 67, P.O. Box 25007, Denver, CO 80225-007, USA
*
Author to whom correspondence should be addressed.
Received: 26 February 2019 / Revised: 5 April 2019 / Accepted: 7 April 2019 / Published: 9 April 2019
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Abstract

A study approach is developed to assess the longitudinal channel slope under the equilibrium condition as well as the transient evolution of a mixed alluvial-soft-bedrock stream. Both the historical field data and 2D mobile-bed numerical modeling are adopted. The proposed approach is applied to a 14 km reach downstream of the Ji-Ji Weir, Chuo-Shui River, Taiwan, where continuous maintenance works have been carried out to stabilize this reach. In this study, the temporal evolution of the longitudinal channel profile is assessed numerically with three spatial scales: The large (the entire study reach), the medium (four sub-reaches), and the local (cross-sections) scale. The large scale analysis is the approach for purely alluvial streams and is shown to be difficult to use to characterize mixed alluvial-bedrock streams. The local scale analysis shows that the soft-bedrock incision has a widely fluctuating slope, reflecting the compound environmental forcing and complex riverbed setting. With the medium scale analysis, the longitudinal channel profile is found to follow a predictive trend if the reach is partitioned into four distinctive sub-reaches. Characteristics of the dynamic channel slope evolution in different spatial scales are computed and presented. The study results can be used to select the proper locations and types of the engineering stabilizing structures in a mixed alluvial and soft bedrock stream. View Full-Text
Keywords: soft bedrock; SRH-2D; head-cutting; mixed transition; knickpoint; spatial scales; river morphology soft bedrock; SRH-2D; head-cutting; mixed transition; knickpoint; spatial scales; river morphology
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wu, K.; Yeh, K.-C.; Lai, Y.G. A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream. Water 2019, 11, 735.

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