Putting local wiggles back into rivers: a design workflow to reincorporate river width variations into historically straightened reaches

Historical river management practices commonly involved river reach straightening (Wolf et al., 2021) where the planform variations of river location over some length were removed and replaced by a relatively straight downstream trend. Notably, river reach straightening generally also included a simplification of downstream river width variation such that re- constructed reaches were designed to convey specific flood magnitudes. Many decades later river management practices have changed to include river restoration and related efforts aimed at reviving river dynamics, associated functions and more recently resiliency in the face of climate change. Here, we offer a relatively straightforward approach in an attempt to meet these goals in some measure by reincorporating downstream river width variations into reaches that have been historically straightened.

There is growing recognition that downstream river width variations at the local scale of order the channel width are a basic attribute of rivers (e.g. Richards, 1976; DeAlmeida et al., 2012), and therefore likely correlate with a more dynamic riverscape characerized,  for example, by spatial differences of the local flow velocity and depth. Ecological theory suggests that a more dynamic riverscape with environmental gradients can promote biological recovery (Wohl et al., 2015), thus providing a link between potential recovery and resilience, and the reincorporation of downstream width variations along straightened river reaches. We use scaling theory (Chartrand et al., 2018) and an analytical model (Lei et al., 2024) to develop an open-source basic design workflow which produces example river reach geometries with downstream width variations which are evaluated using an open-source morphodynamic model. The design workflow can be incorporated into broader approaches and procedures used to develop testable restoration design alternatives, and, importantly, the proposed workflow can also help the restoration community work towards an improved conceptualization of river restoration (Wohl et al., 2015) for circumstances where river-adjacent land is not available and restoration options are constrained.

References
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2. Richards, K. S., Geological Society of America Bulletin, 87, 883–883, 1976.
3. de Almeida, G. A. M. et al., Geophysical Research Letters, 39, L06407–L06407, https://doi.org/10.1029/2012GL051059, 2012.
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5. Chartrand, S. M. et al., Journal of Geophysical Research: Earth Surface, 123, 2735–2766, https://doi.org/10.1029/2017JF004533, 2018.
6. Lei, Y. et al., Journal of Geophysical Research: Earth Surface, 129, e2024JF007641, https://doi.org/10.1029/2024JF007641, 2024.