Greenitecture: The San Dieguito Wetland Remediation Project

Brief introduction:

The San Dieguito Wetland remediation project is a massive joint effort to restore over 400 acres of tidal wetlands and habitat. After 15 years of planning, the project is under construction, and several areas are mostly completed. The City of Del Mar, PG & E, Southern California Edison, SANDAG and government agencies such as California Fish and game, The Costal Commission, Caltrans, and North County Transit District, to mitigate the effect of the San Onofre Nuclear Power Plant 30 miles to the north. Southern California Edison is footing 70% of the 68 million dollar bill.

These wetlands have been monitored by Coastal Environments, an Oceanographic and Coastal Engineering Service Firm for over 20 years. This firm also designed and and provided topographical surveys for these wetlands. They will continue to monitor the wetlands as they are completed and well established.

Project Objectives:

• Restore the project area to a total, well-functioning ecological unit that includes open waters, wetlands, uplands and bluffs.
• Expand tidal influence within the historic boundaries of the San Dieguito Lagoon to the maximum extent feasible by enlarging the tidal prism, maintaining the tidal inlet in an open condition at the river mouth, creating new tidal basins, and creating finger channels to support subtidal, intertidal and coastal salt marsh habitat.
• Restore native habitat to its historical natural patterns, to the extent feasible, by restoring riparian corridors and natural drainages, removing invasive species, and restoring and enhancing connections to adjacent coastal wetland, riparian and coastal sage scrub habitat.
• Create and enhance habitat for rare, threatened and endangered wildlife species indigenous (now or in the past) to the lagoon area, including nesting habitat for least terns and snowy plovers.
• Provide habitat for Canada geese and other migratory birds on the Pacific Flyway.
• Restore rare coastal wetlands as important habitat for oceanic fish.
• Provide an alignment for the Coast to Crest Trail that provides access for multiple user groups, including hikers, bicyclists, equestrians and users of all abilities, and that does not impact sensitive habitats or species.
• Interpret natural and cultural resources for the public by providing wildlife viewing opportunities, interpretive trails, educational signage, and a Nature Center.

Image 1: site plan. create different wetlands on each side of the freeway. dispose the soil onsite in the pink areas.

Image 2: new berm with culvert and new wetland pool beyond existing vegetation

Image 3: existing lagoon mouth to be dredged. sand will be put on beach.

More description: There are several components to the design of this project. First and foremost, the reason for the project is to expand the wetland habitat. Also, there are specific built up nesting sites local/endangered birds, berms to prevent the river from dumping sediment into the new wetlands, an interpretative/interactive walk and cultural element, and a permanent opening to the ocean.

This project re-creates several wetland basins that have been successionally filled in over the years on both sides of the freeway. Heavy grading and soil engineering is required to create the wetlands. The excavated soil from the wetlands is moved to selected areas on site.

These wetlands have several different designated levels:
Subtidal - water inundation 0 to 6 feet deep
Frequently flooded mudflat – below the average tide height +0’
Frequently exposed mudflat – above the average tide height +1’
Low Marsh – +3’
Mid marsh – +4’
High marsh – +4.5’

Nesting sites:
There are a total of 5 nesting sites in the project with a total area of 12.3 acres. These sites are specifically built for the Western Snowy Plover, California Least Tern, and other shore birds. They range in height from +10’ to +19’ and located near bodies of water throughout the site. A combination of 80% sand and 20% shell fragments will be used as the surface of the flat plateau, which will discourage vegetation and allow for maximum nesting area.

Image 4: future site of nesting habitat, this one will be 19' above sea level

Interpretative element:
While a human/cultural element in any ecological lagoon project may disrupt the wildlife and natural setting, it allows for an understanding of the ecological processes happening in the lagoon, an opportunity to watch the wildlife and birds, and to also enjoy nature. However, they must be designed so that people can have a close interaction with nature, but are not so intrusive that they interfere with the wildlife.

The trail at the San Dieguito Wetlands is so far removed from the estuaries and wetlands that you cant even see wildlife activity. It leaves the walker in a sate of confusion because things are too far away too see. Before renovation, there was a trail that went through the middle of the wetlands. The trail was a former berm of the existing airstrip. Now, the only trail is a new path on the perimeter of north side the site.

Image 5: a stop on the trail, one of the only good places to view the new wetlands

Summary:
As I finish off my thoughts I’d like to list sum up the sustainable efforts of the project:
- establishes large wetland areas for more habitat and greater ecological diversity - creates nesting sites for local endangered shore birds
- opens lagoon mouth for total tidal flush so lagoon can function effectively
- mitigates Southern California Edison’s negative impacts from electricity generation.
- Creates stopping point for migratory birds on the pacific flyway.
- Attempts to teach public about importance of these wetlands