How Interventions to Vermont's Floodplains Can Reduce Flooding and Improve Water Quality

Jun. 18th 2018

Vermont’s stream-floodplains offer many natural ecosystem services. These vital ecosystems support biodiversity and habitats, and reduce flood impacts on communities.

Over time, development in communities has threatened stream-floodplain ecosystems. Municipalities have begun to recognize the benefits floodplains offer to reduce flood impacts. Practices like floodplain connectivity and revegetation of floodplains have been implemented by communities to take advantage of the natural services offered by stream-floodplain ecosystems.

However, the full benefits and disadvantages of these stream management techniques are rarely examined at a large spatial scale. A recent study by the University of Vermont’s Gund Institute for Environment and The Nature Conservancy of Vermont looked at three different stream interventions to examine their impact on floodplain ecosystem services. This study assessed the benefits and drawbacks of floodplain reconnection and revegetation on water levels and stream power.

Led by UVM’s Nitin Singh and Beverley Wemple, the researchers used steady-state hydraulic models in two watersheds (Lewis Creek and Mad River) in Vermont’s Lake Champlain basin to examine flood potential and water quality benefits of revegetation and reconnection.

The watersheds represented a range of land use and topographical types. Three model scenarios were developed: floodplain revegetation, connectivity with baseline vegetation where the floodplain was lowered, but not revegetated, and connectivity with revegetation in which the floodplain was lowered and revegetated.

Findings showed that most scenarios resulted in a decrease in stream power and increase in water depth, both of which can reduce erosion and improve water quality. However, impacts from these stream interventions can lead to local and upstream flooding.

Based on the results of this study, researchers suggest managers exercise caution and carefully prioritize any interventions in stream-floodplain ecosystems. One suggestion from this study is to target interventions to upstream reaches that are not heavily eroded or channelized to minimize local and upstream flooding. This study also showed that effectiveness of stream interventions can vary based on stream responses. Pre- and post-monitoring of stream reaches can help with this issue.

Overall, each stream intervention had both positive and negative effects on stream-floodplain ecosystems. Municipalities should evaluate the tradeoffs of implementing interventions and choose the technique(s) that will have the most benefit on ecological restoration and management needs. By better understanding how these natural solutions and interventions affect stream-floodplain ecosystems, it allows decision makers to prioritize areas where implementation of natural solutions and interventions would have the most positive impact.