Wetlands Habitat Management and Restoration Project
Ducks Unlimited and U.S. Fish and Wildlife Service, 1997 – 1999
The Nisqually River estuary is located in south Puget Sound near Olympia, Washington. Approximately 3000 acres of this delta, between Interstate-5 and Puget Sound, are protected by the U.S. Fish and Wildlife Service (USFWS) as a National Wildlife Refuge. About 1000 acres of the refuge are enclosed within a dike system and are currently managed as a mosaic of freshwater wetlands and grasslands. During the past 20 years, management of this area has become increasingly difficult and habitat quality has declined. Weeds and reed canary grass, which limit access for birds and wildlife, have overrun the habitat inside the dike.
Battelle staff while at another organization conducted hydrodynamic and sediment transport modeling to support USFWS efforts using the model RMA-10 for hydrodynamics and RMA-11 for sediment transport. The models were applied simulating a mean tide, mean river flow condition, and the 1996 Nisqually River flood. Numerical modeling was used to evaluate the hydrodynamic characteristics of several alternative configurations, where breaches in existing dikes and dike removal are proposed to allow tidal flushing.
The study showed that full tidal and marine environment restoration was feasible with breaches and dike removal options. Alternatives with dike removal along the western side of the refuge were successful in moving floodwaters off the refuge, thereby reducing flood effects. The highest levels of sedimentation occurred during the river flood event, primarily within dike enclosures in all alternatives. Average tidal and river flow conditions did not show excessive erosion at dike breach/removal locations. Salinity was shown to encroach into newly breached regions, returning the habitat to marine tidal conditions. A frequency analysis for water depth and salinity along a transect was performed to examine ecological succession when the wetlands are returned to estuarine tidal conditions.
Project Highlights
- Hydrodynamic (RMA-10) and sediment transport (RMA-11) models were used to conduct simulation of flow through a marsh with wetting and drying schemes.
- Models showed clearly that the proposed action would reduce flood impacts and restore marine and tidal environment.
- Model results can be used to evaluate habitat changes when returning the site to estuarine tidal wetlands.
- Models allowed design and selection of restoration actions.
Contacts and Project Team
Tarang Khangaonkar (CO-PI), Salish Sea Modeling Center
Steve Breithaupt (CO-PI), PNNL
Steve Liske, Ducks Unlimited, Inc.
Jean Takekawa, U.S. Fish and Wildlife Service
Publications
Breithaupt S and T Khangaonkar. 1999. Nisqually National Wildlife Refuge – Habitat Management and Restoration Project. Hydrodynamic and Sediment Transport Model Development. ENSR Document Number 2334-001-800, Redmond, WA.
Khangaonkar T, S Breithaupt, and J Takekawa. 2000. Simulation of Dike Removal/Breaching to Restore Estuarine Wetlands Habitat. In Proceedings of AWRA’s Annual Water Resources Conference – Water Quantity and Quality Issues in Coastal Urban Areas, pp. 69-72. American Water Resources Association, Middleburg, VA.