Fish Passage
Fish Passage
Fishery populations are one of the better indicators of a watershed’s health. Anadromous fish populations—those that migrate to the ocean and then return to spawn—are especially important indicators. Barriers to fish passage are one of the biggest impediments to the restoration of Corte Madera Creek as long-term fisheries habitat.
Assessment of Barriers to Fish Passage
National Fish and Wildlife Foundation funded an assessment of barriers in the main creeks of the watershed done by Ross Taylor and Associates. The inventory and fish passage evaluation of stream crossings within the Corte Madera Creek watershed were conducted between June and October of 2005. The primary objective was to assess passage of juvenile and adult coastal rainbow trout/steelhead (Oncorhynchus mykiss) and coho salmon (O. kisutch) and develop a project-scheduling document to prioritize corrective treatments to provide unimpeded fish passage at road/stream intersections and at other manmade impediments such as low-elevation dams. The report of their work includes a detailed explanation of their methodology and rationale for the assessment, along with appendices describing each identified barrier in these creeks: Fairfax, Ross, San Anselmo, and Sleepy Hollow creeks. The team did not assess Corte Madera Creek because the barrier posed by the concrete channel was well known. These documents are found under Education and Outreach/Reports:
- BarriersReportandAppendices.pdf
- StreamXingCatalogFAIRFAXCK.pdf
- StreamXingCatalogROSSCK.pdf
- StreamXingCatalogSANANSELMOCK.pdf
- StreamXingCatalogSLEEPYHOLLOWCK.pdf
Treatment of Barriers
The National Fish and Wildlife Foundation also funded preparation of preliminary designs for treatment of three barriers on San Anselmo Creek. Those designs can be viewed under Education and Outreach/Reports. Obtaining permission to treat the barriers at Saunders and Pastori creeks required the permission of private property owners and that permission was unfortunately denied.
With the support of the Town of San Anselmo, which owned the Lansdale project area, we were able to obtain funding to fully implement treatment of the Lansdale barrier. This involved installing baffles in a 350-ft long culvert to eliminate the velocity barrier and constructing a pool-and-drop structure at the downstream end of the culvert to eliminate a 4-ft drop. The work was completed in 2012 and the Lansdale culvert now allows passage of 95% of all age classes of salmonids at fish passage flows. The plan set for the design is shown in:
Barriers in Corte Madera Creek
There are two barriers to fish passage in Corte Madera Creek. The more challenging one is the upstream half of the concrete channel built by the US Army Corps of Engineers in the 1960s to mitigate flood risk in the lower part of the watershed. Unfortunately, not only did it not succeed at mitigating flood risk, the concrete channel created a velocity barrier to spawning salmonids and temperature barrier to smolts attempting to emigrate. The entire mile-long channel provides no shelter from predators for all age classes. The second barrier is a non-functional fish ladder at the upstream end of the concrete channel.
Fish Resting Pools
Friends funded early designs and acquired grant funds from the California Coastal Conservancy for 65% designs to retrofit the inadequate fish resting pools in the channel in the upstream half of the concrete channel. Resting pools are not necessary in the downstream half where high tides allow spawners to move upstream. The final designs for the resting pools are described in reports prepared by the team of Michael Love & Associates and GHD, available under Education and Outreach/Reports.
Ross Fish Ladder
In October 1971 the US Army Corps of Engineers had completed the first mile of the concrete channel and stopped work for the winter. They installed a temporary wooden fish ladder in Ross at the upstream end of the concrete channel where the invert of the concrete channel was a few feet lower than the natural channel upstream. However, the Town of Ross successfully sued to halt construction from continuing upstream and the temporary fish ladder is still in place, 54 years later. It is ineffective and a barrier to fish passage. There are plans to replace it with a structure providing a smooth transition to the naturel channel upstream when the Marin County Water Conservation and Flood Control District can obtain funding.