Nisqually River Delta Habitat Restoration Design

Using nature-based solutions to reduce the impacts of local flooding

Project Overview

Increasing climate impacts are threatening the health of the Nisqually River Delta (NRD) and the fisheries it supports and USGS research concluded that Interstate 5 is exacerbating flood and habitat impacts by restricting flow where it crosses the delta.

While the Washington State Department of Transportation (WSDOT) has launched the I-5 Marvin Rd to Mounts Rd project to protect the portion of I-5 crossing the NRD, the Nisqually Indian Tribe (NIT) is partnering with LLTK and others to seek more comprehensive nature-based solutions to reduce local flooding impacts and improve key salmon habitat.

The Problem

While flooding along the Nisqually River and within the NRD is a natural phenomenon, USGS research sponsored by the NIT and WSDOT forecasts that these flooding events are growing in both intensity and frequency due to climate-driven weather changes and sea level rise (SLR). Further, the study concluded that Interstate 5 is exacerbating flood impacts by restricting flow where it crosses the delta via the Nisqually Bridge. 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.

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.

Our Solution

As WSDOT’s I-5 Marvin Rd to Mounts Rd project advances through NEPA, LLTK and NIT are advancing toward a 30% design set of restoration concepts for portions of the Nisqually River Delta upstream of I-5.  This project is advancing plans for habitat restoration within the NRD, using nature-based solutions to:

    • – Improve floodplain connectivity
    • – Sediment distribution
    • – Ecological function.

 

Potential solutions being fleshed out in the design include:

  • – Development of side channels off of the Mainstem Nisqually River to improve water distribution and create forested riverine habitat
  • – Use of large, woody debris within the river to reduce water speed and improve sediment delivery
  • – Reconnection of historic McAllister Creek to increase emergent marsh habitat and improve resiliency of delta to SLR
  • – Use of native plantings to create habitat for wildlife and reduce erosion

 

The nature-based solutions sought by the NIT present an opportunity to reduce future flooding impacts, increase climate resilience, and expand vital salmon habitat. By acting 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.

Project Impact

250

Acres covered

2040

Year predicted to have an extreme flood

7,400+

Acres that could benefit

Project Partners

< Swipe left to see more

Project Contact

Keith Estes

Project Manager (he/him/his)

kestes@lltk.org