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Long Term Geomorphic Impact of In-Stream Structures and River Recovery Post-Removal
Long Term Geomorphic Impact of In-Stream Structures and River Recovery Post-Removal
I am interested in how rivers respond to various direct human modifications. Human-induced changes to rivers tend to reduce temporal and spatial heterogeneity—or simplify—a river corridor. In Thompson, Puklin, and Marshall (2016) we explored the status of gabion structures (stone-filled, wire-mesh baskets used to construct revetment walls, grade-control sills, or groin deflectors) installed in the early 1960s along the Zealand River, NH and the impact of those gabions on channel morphology 50 years after installation. Gabion sills installed in the 1960s mostly failed within 25 years of project completion and were completely ineffective by 2014. Gabion walls displayed widespread damage in 2014, but continued to exert a control on channel width, floodplain connectivity and patterns of channel incision and deposition. Although gabions were intended to stabilize the river, they enhanced vertical channel incision, failed to prevent bank instability, and created localized channel widening and avulsions associated with depositional reaches.
I'm also interested in how a river corridor responds following removal of in-stream structures and building longer term restoration monitoring datasets to better understand how systems respond following restoration. I have ongoing research monitoring river restoration sites and am always looking for new sites to add.
Photos of courtesy of Deep Creek stage zero restoration in the Ochoco National Forest, Oregon, United States courtesy of Dr. Sarah Hinshaw.
Photos of collapsed gabions along the Zealand River in NH
Geomorphic context in process-based river restoration
Geomorphic context in process-based river restoration
Process-based restoration, which focuses on restoring conditions under which river processes such as stream flow and sediment movement create and maintain a functioning river corridor has gained attention and emphasis in recent years
In Wohl et al. (2024), we emphasize the need to consider and integrate geomorphic context into the restoration process. This is motivated by personal observations that process-based restoration is sometimes used in a ‘one-size-fits-all’ manner in which a specific form of process-based restoration (e.g., beaver dam analogs in the U.S. Intermountain West or leaky dams in the U.K.) is used throughout a river network without consideration of reach-scale process and form. We have also observed that process-based restoration is some-times assumed to be inherently more natural or sustainable than form-based restoration but can be used inappropriately if the restoration activities cause or enhance unsustainable or undesirable changes. Although we emphasize process-based restoration, incorporation of geomorphic context is relevant to any form of river restoration. We focus on process-based restoration because restoration designs that include ongoing geomorphic processes such as erosion and deposition are especially dependent on an appropriate understanding of geomorphic processes.
Considering the geomorphic context, as shown above, is important when thinking about the type of process-based restoration for a given river system.
Large wood as a tool for process-based river restoration
Large wood as a tool for process-based river restoration
I've worked with practitioner groups and agencies across the U.S. to install and monitor wood structures (beaver-dam analogues, post-assisted log structures, engineered logjams). Most recently, I've been involved in monitoring efforts assessing whether large wood added to a river for flood attenuation and habitat restoration goals is successful in achieving those restoration goals.
Model simulations of flow around large wood installed as a restoration measure. Here we are looking at whether large wood is successfully attenuating peak flows and providing pool habitat.
Full Citations
Wohl, E., Rathburn, S., Dunn, S., Iskin, E., Katz, A., Marshall, A., Means‐Brous, M., Scamardo, J., Triantafillou, S. and Uno, H., (2024). Geomorphic context in process‐based river restoration. River Research and Applications. https://doi.org/10.1002/rra.4236
Thompson, D.M., Puklin, L.S., & Marshall, A. (2016). The long-term impact of channel stabilization with gabion structures on Zealand River, New Hampshire. Ecological Engineering. https://doi.org/10.1016/j.ecoleng.2016.07.016.
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