Abstract
AbstractRecent analysis of equilibrium and quasi‐equilibrium channel geometry in engineered (fixed‐width) rivers has successfully shown that two temporal scales can be distinguished, with quasi‐static (long‐term) and dynamic (short‐term) components. This distinction is based on the fact that channel slope cannot keep pace with short‐term fluctuations of the controls. Here we exploit the distinction between the two temporal scales to model the transient (so time‐dependent) phase of channel response, which is the phase wherein the channel approaches its new equilibrium. We show that: (a) besides channel slope, also the bed surface texture cannot keep pace with short‐term fluctuations of the controls, and (b) mean transient channel response is determined by the probability distributions of the controls (e.g., flow duration curve rather than flow rate sequence). These findings allow us to set up a rapid numerical method that determines the mean transient channel response under stochastic controls. The method is based on distinguishing modes (i.e., sets of controls) and takes the probability density of each mode into account. At each time step, we compute the mode‐specific flow, sediment transport rate, and corresponding change in bed level and surface texture. The net change within the time step is computed by weighting the mode‐specific changes in bed level and surface texture with the probability density of each mode. The resulting mean transient channel response is a deterministic one, despite the controls being stochastic variables. We show that the proposed method provides a rapid alternative to Monte Carlo analysis regarding the mean time‐dependent channel response.
Highlights
When addressing channel response to natural or anthropogenic change of the controls, one needs to distinguish between three channel response phases: the initial, transient, and equilibrium phase (Blom, Arkesteijn, et al, 2017)
The transient phase of channel response marks the period in between: it covers the phase of adjustment of channel slope, channel width, and bed surface texture after the initial phase has been completed and before the equilibrium phase has started
Its foundation is the elementary assumption that slope and bed surface texture are not affected by short-term changes of the controls, as their response is associated with a longer time scale
Summary
We propose a method to rapidly model river response under stochastic controls of flow rate, sediment discharge, and downstream water level. The proposed method provides a computationally cheap alternative to the mean outcome of Monte Carlo analysis. Sea level rise initially induces bed erosion where enhanced backwater effects or spatial changes of channel width reduce the sediment flux
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
