Predicting Rates of Channel Development
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Tidal marsh restoration to recover threatened estuarine species, protect shorelines from storms and tsunamis, and provide other ecosystem services is incomplete without restoration of the tidal channels that link them to adjacent rivers, bays, and ocean, and provide habitat for estuarine fish and wildlife. A significant uncertainty associated with tidal marsh restoration is whether tidal channels should be actively excavated or passively allowed to erode through tidal flushing. Financial costs of active channel excavation need to be weighed against the opportunity cost to estuarine fish of slow, passive, tidal channel erosion. If channel network erosion is quick, then the passive approach is feasible. If channel network erosion is slow, then active excavation may be required to maximize ecological benefit to estuarine fish. GIS analysis of aerial photos of historical dike failure and marsh restoration sites was used to track channel network development through passive erosion over time. Channel network development rates were highly variable between sites, but scaled with site size. This positive scaling is likely the consequence of large marshes having disproportionately more channelized tidal prism and less over-marsh sheet flow, while small marshes have disproportionately more sheet flow. Depending on site size and the equilibrium geometry of reference marshes, the time required for restoration site channel networks to passively erode to full expression was estimated to require 6 to 60 years.
Documents and Presentations
Link to ESRP Learning Project Synopsis
Link to Final ESRP Webinar pdf
Notes
The final report for this project is currently being submitted for publication. For a copy of the draft manuscript, please contact esrp@dfw.wa.gov
Link to PRISM snapshot
