JAWRA Blog

April 2010 Article: “Ecologically Functional Floodplains: Connectivity, Flow Regime, and Scale,” by Jeffrey J. Opperman, Ryan Luster, Bruce A. McKenney, Michael Roberts, and Amanda Wrona Meadows.

Recent stream restoration efforts seem to place a lot of emphasis on designing to a single characteristic such as bankfull flow. The ideas in this article offer a more complex, nuanced view which looks at the flood regime in its totality.

The authors propose a conceptual model encompassing three basic elements: (1) hydrologic connectivity between the river and the floodplain, (2) a variable hydrograph that reflects seasonal precipitation patterns and retains a range of both high and low flow events, and (3) sufficient spatial scale to encompass dynamic processes and for floodplain benefits to accrue to a meaningful level.

For streamflow, the authors consider three kinds of representative floods. The “floodplain activation flood” is a small-magnitude flood that occurs relatively frequently and supports many of the processes ascribed to overbank flow pulses. The “floodplain maintenance flood” is a higher magnitude flood capable of performing geomorphic work including bank erosion and deposition on the floodplain that creates and maintains floodplain surfaces and contributes to heterogeneous floodplain topography. The third kind, “floodplain activation floods,” are rare, high-magnitude events that result in extensive geomorphic changes.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

In their April 2010 JAWRA article, “Protecting River Corridors in Vermont,” Michael Kline and Barry Cahoon describe river corridor planning in Vermont, whereby corridors are sized based on the meander belt width and assigned a sensitivity rating based on the likelihood of channel adjustment due to stressors. The approach is fundamentally based on restoring fluvial processes associated with dynamic equilibrium, and associated habitat features.

The authors freely concede Vermont has large geomorphic datasets based on rigorous assessment protocols — Vermont is, after all, a small state — but the techniques seem to have great value nationwide.  The article gives examples of how “active” restoration projects to confine a river to a fixed channel have consumed program budgets and required continued investments to correct failures. So Vermont switched to a restoration program that embraces the concepts and practices associated with dynamic and deformable rivers. Thus river corridors are delineated based upon existing and estimated meander belt width. The purpose of a river corridor easement is to give the river the space to re-establish a natural slope, meander pattern, and floodplain connection.

The authors note a passive approach may often be a desirable alternative due to its lower upfront costs and maintenance, but like active restoration, it is highly dependent upon reducing watershed stressors, and landowner willingness to accept changes in land use.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]