Mahon Slough

Several months into the Suisun Marsh project, another one kicked off; this time, in San Rafael.

The first look at the site was a little surprising. What I’d seen of San Rafael up to this point had been typical upscale Marin County. Yet this site, although it was only blocks from downtown, was in a light industrial neighborhood. Auto repair shops backed up onto Mahon Creek, with old cars and trailers parked within feet of the water. A brownfield site, a former coal gasification plant, was across the street; a large vacant lot in appearance, contaminants were held in by a retaining wall and a clay cap.

The creek floodplain had been filled long ago, and pre-project it was a steep-sided tidal ditch with impervious clays on either side. Once, trying to take a soil sample, I had to run to the hardware store to buy a hammer and chisel to break through the surface. Not surprisingly, the creek periodically flooded the surrounding neighborhood. Sometimes the floods were severe.

The overall project was an extension of what is now Andersen Drive; then it was an abandoned railroad right-of-way. There were enough scattered puddles that qualified as wetland to require a few acres of mitigation. Overall it was a small project, yet it had drawn considerable local collaboration. The mitigation site had been chosen with the help of two influential conservation organizations, and as a result the project had their support.

The first day into the mitigation site I had to crawl through a hole in a chainlink fence overgrown with weeds. Two small homeless camps were nestled back in the weeds, but I saw very little human presence.

The mitigation design evolved into a block-long excavation of fill material on either side of the creek, re-establishing the historic floodplain. A planting plan was developed with the help of a local firm, with typical salt marsh species on the lower elevations and a narrow fringe of high marsh at the transition to upland. The permitting process, while a bit more involved than the previous project because of different agency representatives, went smoothly. My colleague and mentor Janet O’Neill flew out from Virginia on one occasion to assist with agency meetings, to excellent effect. I learned quite a bit about how to move permits through the process efficiently.

Then I moved on to projects in other parts of the country, and didn’t have time to track construction. For some reason I thought it hadn’t been built. It later turned out that it had only been delayed for a few years; actual construction took place in 1997.

On a whim, I drove by the site in 2007. I’d been on nearby Rt 101, and was curious what had ever become of the area. I drove over the small bridge, and saw a tidy and aesthetically pleasing salt marsh in the midst of a thriving new urbanism neighborhood.

It was perhaps the surroundings that surprised me more than anything. There was a shiny new office building next door, and a park across the street. There were people everywhere, many of them walking. There was a trail on one side of the mitigation site, as we has envisioned; now it had side paths to the office building, with landscaped gardens among the paths. There was no trash, which is unusual in tidal areas. Clearly, someone was maintaining the site, picking up every little scrap of debris.

The goals of the project had been modest, with the primary focus on increasing floodplain capacity. Habitat goals were limited to species typical of urban areas, because of the small size of the site and the surroundings, there had never been any illusions about use by rare species. Especially given the simple goals, the project had been remarkably successful.