The Nisqually Delta Restoration Project is the largest project of its kind in south Puget Sound. The restoration construction and subsequent monitoring provides new information to land managers, salmon recovery biologists and others who work to protect natural resources in the Puget Sound region.
Although the project was planned for years, there are still surprises and lessons to be learned. Here are some of the key take-aways for restoration projects of this size:
- Restoration projects influence, and are influenced by, the entire landscape. In this case, project managers were surprised to learn the large influence that Mount Rainier plays on the Nisqually delta. Because the delta had been removed from the tides for so long, the land had subsided, making it lower than the surrounding areas. Normally, sediment from the Nisqually glaciers would travel the length of the river and be deposited at the delta. The lack of sediment deposition has caused the delta to be lower than surrounding areas, and is limiting the revegetation of tidal mudflats.
- The Nisqually delta is starved of sediment. Glacial rivers carry a lot of sediment, like rocks and silt. However, Alder Dam traps most of the Nisqually River’s silt. The scale to which the sediment is trapped became obvious after the restoration project. This sediment is needed downstream–especially at the delta. Without the added sand, rock and silt, the tides gradually erode the delta away. The impacts are compounded in the face of rising sea levels: without increasing the amount of sediment deposited on the delta, several areas are at risk of being inundated.
- Elevation influences recovery. The elevation of each monitoring location influences overall recovery of the landscape. High elevation sites re-grow plants more quickly; sites with vegetation provide better refuge to invertebrates; invertebrates form the basis of the food chain for juvenile salmon.