Using nature-based solutions to reduce the impacts of local flooding
Increasing climate impacts are threatening the health of the Nisqually River Delta (NRD) and the fisheries it supports. United States Geological Survey (USGS) research concluded that Interstate 5 is exacerbating flood impacts by restricting flow where it crosses the delta.
While the Washington State Department of Transportation (WSDOT) has launched the Nisqually Bridge Replacement Plan to protect the portion of I-5 crossing the NRD, the Nisqually Indian Tribe (NIT) is partnering with Long Live the Kings and others to seek more comprehensive nature-based solutions to reduce local flooding impacts.
While flooding along the Nisqually River and within the Nisqually River Delta (NRD) is a natural phenomenon, USGS research sponsored by the Nisqually Indian Tribe (NIT) and Washington Department of Transportation (WSDOT) forecasts that these flooding events are growing in both intensity and frequency due to climate-driven weather changes and sea level rise. Further, the study concluded that Interstate 5 is exacerbating flood impacts by restricting flow where it crosses the delta via the Nisqually Bridge.
This is a significant threat to the vital salmon habitat prized by the tribe, with flooding events impacting salinity levels and sediment delivery in ways that reduce habitat function and harm salmon. It also threatens Nisqually Wildlife Refuge infrastructure and the tribe’s homes and infrastructure, including the Nisqually Indian Reservation and important NIT landmarks. The USGS study also predicts an extreme flood event overtaking I-5 by 2040, posing enormous risks to a vital piece of regional infrastructure.
WSDOT has launched a Nisqually Bridge Replacement Plan process to protect the portion of I-5 crossing the Nisqually River Delta (NRD) from future flooding and sea level rise. WSDOT has finalized a Planning and Environmental Linkages Study (PEL) and has a NEPA review scheduled to begin in Summer 2023. While the final PEL calls for solutions to “enable environmental restoration and ecosystem resiliency at the I-5 crossing of the Nisqually River Delta area,” the preferred design alternative has yet to identify specific nature-based solutions to reduce flooding, increase climate resilience, and improve habitat.
This project will advance plans for habitat restoration within the NRD, using nature-based solutions to improve floodplain connectivity, sediment distribution, and ecological function. The constrained configuration of the Nisqually River mainstem, with flow likened to a “fire hose,” does not allow for effective sediment delivery to the delta, limiting the development of adequate surge plane habitat.
Potential solutions to be further detailed in the design include the use of woody debris within the river to reduce water speed and improve sediment delivery, the reconnection of historic creeks with the mainstem Nisqually River to improve water and sediment distribution, and the use of native plantings to create habitat for wildlife and reduce erosion. The nature-based solutions sought by the Nisqually Indian Tribe (NIT) present an opportunity to reduce future flooding impacts, increase climate resilience, and expand vital salmon habitat.
By taking action now, the NIT has a once in a generation opportunity to ensure benefits from this planned bridge redesign flow back to the NIT and deliver a breadth of ecosystem and community resilience benefits which will serve the tribe for decades to come.
Year predicted to have an extreme flood
Acres that could benefit
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