Some Progress on the Ross Valley Watershed Program

by Sandy Guldman

 Detention Basins

Although detention basins are essential to providing protection from large floods, they remain controversial and are bogged down by protests. A lawsuit challenging the County’s purchase of the former Sunnyside Nursery growing ground in Fairfax was settled and feasibility studies are in progress to evaluate its use as a detention basin. Preliminary feasibility studies have also been completed for Lefty Gomez Field.

No reports on the results of feasibility studies of the Phoenix Lake Dual Use Facility have been released, although based on the feasibility study being prepared by AECOM, a full dam replacement alternative for the Phoenix Lake dam appears to be the preferred alternative compared with two dam retrofit alternatives. From environmental and constructability standpoints, Marin Municipal Water District and the Marin County Flood Control District agree that full dam replacement will be a significant challenge. The District is working with MMWD for an interim Phase 1 construction project and operations procedure and delaying the full dam replacement.

Temporarily holding back overflow from Phoenix Lake would reduce flooding in Ross. Photo by Charles Kennard

Temporarily holding back overflow from Phoenix Lake would reduce flooding in Ross. Photo by Charles Kennard

Three alternative groups of projects that could be used as a substitute for the Memorial Park Dual-Use Facility have been identified. This project, called the San Anselmo Flood Protection Project, includes no work at Memorial Park or anywhere else in the Sorich Creek sub-watershed. To be acceptable to the Department of Water Resources (the funder) the San Anselmo Flood Protection Project must provide the same benefits that the Memorial Park facility would have provided, cost about the same, and be completed by the end of 2020.

That will be challenging, but is considered feasible. The alternatives are:

Alternative 1: Detention basin at the nursery site and creek capacity improvements in the Morningside neighborhood.

These measures are removal of the Mountain View Avenue Bridge, and 3,500 feet of flood barriers, such as low walls or berms, reaching from Sir Francis Drake to Brookmead Court. Although many residents of the Morningside neighborhood have been supportive of this project, it would require the approval of the owners of 59 parcels to construct the barriers. This will be challenging to accomplish in the limited time available.

Alternative 2: Detention basin at the nursery site, removal of Building Bridge 2 in downtown San Anselmo, and installation of 375 linear feet of flood barriers.

This project would require the approval of the owners of 13 parcels, which might make it easier to finish on time. All of the in-stream capacity measures would occur in downtown San Anselmo. It would be necessary to protect two structures down-stream of the work from higher water surface elevations resulting from the increased flow in the channel.

Alternative 3: Removal of Building Bridge 2, modification of two buildings that overhang the creek and obstruct flow, and the installation of 375 linear feet of flood barriers.

This project would require the approval of the owners of 31 parcels. It would be necessary to protect four structures downstream of the work from higher water sur-face elevations resulting from the increased flow in the channel.

Current plans are to begin preparation of the Environmental Impact Report (EIR), required by the California Environmental Protection Act, for the San Anselmo Flood Protection Project early in 2017. The

Project-level EIR provides a greater level of site-specific detail than the Programmatic EIR (PEIR). The Project EIR can be visualized as a small circle inside the larger PEIR; however, it can also be taken out of the PEIR and function on its own in the event the PEIR is not completed in time for construction to be finished by December 31, 2020.

In-stream Measures

This broad category includes replacing bridges or modifying buildings that limit creek capacity, changing the channel by widening or deepening it, and reclaiming parts of the floodplain. Replacements for several bridges are in a design phase, but the process has slowed because if there are no upstream detention basins, the bridges must be made wider and higher to accommodate the higher flows expected without basins. Plans to increase the channel capacity in downtown San Anselmo are being developed; these plans include modifying structures that intrude on the channel and removing rubble and bedrock that reduce capacity (see Alternatives 2 and 3 above).

US Army Corps of Engineers Project, Corte Madera Creek

Design work is underway. To its credit, the USACE is meeting regularly with regulatory agencies, like the Regional Water Quality Control Board and NOAA Fisheries, to obtain input on proposed designs to facilitate permitting. Fish passage and riparian habitat are major issues.

Alternatives include top-of-bank flood barriers, set back flood barriers, and deepening or widening sections of the earthen and concrete channels. Removal of the existing fish ladder behind the Ross post office is also included. A full alternatives analysis will be released when the draft Environmental Impact Statement/EIR is issued, scheduled for fall 2017.

Creek Cleanup

With financial support from the Ross Valley Stormwater Fee, crews from Conservation Corps North Bay worked with public works staff to identify problems and clean creeks in Larkspur, Ross, San Anselmo, and Fairfax as well as in unincorporated Marin County. The work was done in September and October 2016. Concrete rubble was removed from a section of the creek in San Anselmo near Sir Francis Drake Boulevard in September 2016

Public Meetings

A community workshop was held on November 30, 2016 to receive public input on the San Anselmo Flood Protection Projects, three of which are described above. A Flood Zone 9 Advisory Board meeting was held December 20, 2016 as this was being prepared.

A presentation to the San Anselmo Town council is scheduled for January 10 on the San Anselmo Flood Protection project. A scoping meeting for the PEIR for the Ross Valley Watershed Program will be held January 18, 2017 from to 9:30 p.m. at the Ross School Library.