Andersen Drive
Marin County, California
Where Andersen Drive now runs through San Rafael, bordered by tidy landscaping, there was once an abandoned railway corridor. Small depressions held shallow pools of water in the rainy season, and under the regulations in force at the time of the project these qualified as jurisdictional wetlands.
The mitigation site had been chosen with the assistance of local conservation organizations. Where Mahon Slough crossed what would be the course of Andersen Drive, and where a small bridge needed to be built, flooding was a recurring problem. During prolonged winter storms which coincided with higher tides, water spilled over the banks of the narrow, confined slough.
The chosen site was between Lincoln and Lindaro Streets, where historic fill had created a flat area on either side of the slough, overgrown with weeds and so hard-packed that in places it was completely bare soil. The banks of the slough were nearly vertical, with only sparse vegetation. Small businesses, auto repair shops and such, backed up on the project area. At some time in the past an attempt had been made to build a trail along the slough, but now it was fenced off and overgrown with shrubs, occupied by homeless encampments. Despite being located in the midst of affluent Marin County, it was not a particularly pleasant location.
The concept envisioned excavating back the banks of the slough and planting the restored floodplain with native vegetation. Given the urban neighborhood and the constraints thus imposed, the goals were realistic: Increase floodway capacity in an attempt to reduce or eliminate local flooding, provide a vegetated buffer to filter runoff and provide water quality benefits, and provide a small island of native salt marsh habitat able to support a few of the more tolerant local species of wildlife. Primarily this was assumed to apply to more mobile species, for example offering a resting spot for migrating small birds.
Andersen Drive was only my second restoration project as a consultant, and the concept had been developed by someone else... I'm not sure who. I was with TAMS Consultants at the time, working about half-time from an office in Concord CA and flying back and forth from Chicago. My role was to complete the Mitigation and Monitoring Plan and contribute to some of the permits necessary to build the project. Wetlands Research Associates (WRA), a local San Rafael firm, was my subconsultant for the project and prepared the planting plan (a simple mix of saltgrass, pickleweed, marsh gumplant, and a few other species well suited for the location).
I learned a great deal on the project. We needed to identify all utilities crossing or approaching the site, and avoid or relocate them; ultimately only a few wires stabilizing utility towers needed to be moved. There was a brownfield site adjacent to the project area, a long dismantled coal gasification plant, so we needed to test our soils and be sure that there wasn't any residual contamination within the restoration area (there wasn't, except for a few places where adjacent businesses had parked vehicles and some motor oil had leaked into the surface layers of soil). Then, we drew one of the more infamously difficult project managers at the San Francisco District of the Corps of Engineers, making for an interesting Section 404 permit process and some very entertaining meetings. My then-colleague Janet O'Neill, a former Corps person, proved to be invaluable during this time. I learned a lot working with her.
As with any project in tidal areas, grading elevations were crucial. They needed to correlate with tides so that the site would be occasionally inundated, encouraging salt marsh species and discouraging weeds; but we had targeted a high marsh community, so inundation couldn't be too frequent or too deep. I had to work closely with hydrologists who provided the information necessary to put the proposed contour lines on the drawings.
Although we completed all design and permit-related tasks sometime in 1993, the Andersen Drive project (at least our segment of it) wasn't built until 1997. Because of the delay, I'd lost track of it and didn't visit the site until nearly 10 years later. I was astonished by what I found.
The run down industrial neighborhood I remembered was now a vibrant mixed-use area. Once there had been no almost one on the streets; now a nearby park was crowded, and people walked in and out of a nearly new office building next to the site. A paved trail ran the length of the project area, actually being used by local residents. Most impressively, there was almost no debris. Someone... the office building management? The City?... was actively maintaining the area, and doing so in a meticulous manner. The correlation between ground elevation and tides seemed just right, with the presence of native salt marsh species as evidence of success. There were surprisingly few weeds.
I'd expected the salt marsh design to work, assuming competent implementation. What I hadn't expected was the turnaround of the entire neighborhood, there had been no easy way to predict that. Instead of merely being a tiny salt marsh restoration, the project now contributes green space to a larger area, to a classic example of new urbanism planning. While I don't normally seek out small urban restorations, since these are inherently constrained, and while my decision-making role in this one was limited, I'm proud to have been part of it.
Mahon Slough with restored salt marsh
Restored salt marsh in an urban environment
Copyright and all other rights reserved © 2010
Kenneth S. Mierzwa ken.mierzwa@gmail.com
April 10, 2010
April 10, 2010