by Gerhard Epke
The problem of concrete debris in our creeks, particularly around downtown San Anselmo, has been written about previously in Creek Chronicles—it constricts the channel, inhibits fish movement and is an eyesore. Last September Friends of Corte Madera Creek Watershed and the San Anselmo Public Works Department spent a week removing concrete from the creek and disposing of it properly. By directing $10,000 of mitigation money to help pay for labor, we helped expand the Town’s effort, which ultimately re-moved more than 10 tons of rubble.
This debris, only part of which was removed, includes cinder blocks, fence post foundations, old water heaters, metal pipes, but mostly it is broken pieces of old sidewalks and driveways that were at some point repurposed as creek bank stabilization. The creek also contains large amounts of cobble- and boulder-sized rocks that were imported to stabilize banks. Unfortunately, the concrete pieces and rocks weren’t large enough to withstand fast-moving water and ended up being carried into and down the channel.
After some trial and error, we have learned that surprisingly large pieces of concrete can be removed from the creek quite easily as long as they are not embedded in the bank or cemented to bedrock. A few strong bodies with long pry-bars dis-lodge the concrete from the creek bed and either roll it into an impro-vised sled or wrap it with a chain. Then comes the one crucial piece of equipment, which is a backhoe like the one owned by San Anselmo DPW. Operated from the top of the bank, the backhoe can drag and hoist the debris straight out of the creek and into a dump truck.
This is the second year in a row that San Anselmo has undertaken this effort. Both times the Marin County Flood Control District helped coordinate permits with state and federal regulatory agencies and Conservation Corps North Bay helped with heavy lifting. In 2016 concrete removal took place between Sir Francis Drake Boulevard and the former Sunnyside Nursery. This year it took place between Creek Park and the former Great Acorn building at 800 San Anselmo Avenue.
Some very big pieces of concrete remain in this reach of the creek in San Anselmo—footings of over-hanging buildings, ill-conceived earthquake retrofits, foundations of structures long-gone. An interesting presentation to the San Anselmo Town Council from October 25, 2016 can be viewed online. It goes into some detail on the flood reduction benefits if these larger pieces of concrete could be removed, but these are large projects without any secured funding or approval. In the meantime, we will try to support San Anselmo to keep this program going. If all goes well, maybe this effort can continue upstream next year. The bridges at Nokomis, Sais, Saunders, Taylor all have plenty of accumulated debris to keep us busy.