SFO/San Bruno Creek/Colma Creek Resiliency Study Working Group
January 30, 2015
South San Francisco Municipal Building,
South San Francisco, CA
DRAFT MINUTES
Attendance: 25 people (see sign in sheet).
9:00 – 9:15 – San Mateo County Supervisor Dave Pine
9:15 – 10:30 – Dilip Trivedi & Chris Potter – Moffat & Nichol
· Scope of Project
· Discussion of Data Collection Effort (list of agencies providing data were noted in the slide presentation)
· Presentation of Hydrologic & Hydraulic Model Setup
· Review the results of the hydraulic analysis;
· Discussion of Sea-Level Rise effects on Lower Watersheds
· See slide deck for maps and data analysis
10:30 – 11:00 – Working Group input and feedback.
After a review of the data by Chris Potter and Dilip Trivedi (Moffat & Nichol), the working group discussed and identified potential issues, as well as adaptation and mitigation concepts. The group tried to avoid making judgments on their viability. The object of this phase of the study was to brainstorm adaptation and mitigation ideas. Selection of actual adaptation and mitigation plans are outside the scope of this study. Adaptation and mitigation measures will be conducted in future studies and meetings.
General Notes:
· Colma Creek’s water flow is approximately 4x larger than San Bruno Creek.
· CalTrain, BART, Highway 101, and PG&E sub-stations and high voltage –power –lines converge within the study area.
· Colma Creek does NOT have a flood/tide gate, while San Bruno Creek does have one.
· San Bruno Creek is mostly within the jurisdiction of the City of San Bruno.
Colma Creek
Jim Porter, Director of Public Works:
How will we address the upstream improvements without impacting the lower end of the creek? And how will upstream improvements impact changes caused by Sea Level Rise (SLR)?
The study was conducted primarily around the confluence of Colma AND San Bruno Creeks. Improvements upstream of Hwy-101, on Colma Creek, WILL impact downstream due to the potential for high volume of fluvial water flows. In the current state, the projected overflow upstream of Hwy-101 will provide flooding relief downstream, which will make any improvement upstream, or downstream, very complex.
Jim Porter also brought up the idea of dredging the Colma Creek culverts, recognizing that the permit process would difficult. San Mateo County has had difficulty in the past in obtaining maintenance permits for performing de-silting of Colma Creek. This option would provide more room for higher than normal creek flows.
General Comments:
Due to the built up nature of the communities along Colma Creek, from the head waters of Colma Creek to the Bay, mitigation options are limited. The primary option for the County is to raise the levee and floodwall elevations. There is the potential for surface detention storage in Orange Memorial Park or the California Golf Club, however, the Park is relatively small and the Golf Club is privately owned.
San Mateo County is limited in their ability to widen the Colma Creek flood control channel based on the limits of their jurisdiction. However, there might be land-acquisition options for County Flood Control, to facilitate channel widening or to develop detention storage areas.
Joe LaClair, BCDC:
Reducing impervious land in the Colma Creek watershed could be an effective component of an overall strategy for addressing fluvial flooding risk.. Some thoughts on trapping more water during high water flow events or reducing watershed flashiness:
· Rain Barrels
· Pervious streets and landscapes
· Groundwater recharging
Dilip, Moffat & Nichol:
A larger regional tidal-barrier structure could be built spanning from the SamTrans Peninsula (the leaf) north to the Bay Trail and Littlefield/Utah Ave, creating a wetlands basin behind the gates. The gates could be left predominately open and then closed ahead of large approaching storm events. This would need to be a structure comparable in size to the Palo Alto Flood Basin gates. Could be designed as an operable sluice gate structure. This would provide protection for both Colma Creek and San Bruno Creek.
Final suggestions/questions:
· Is the Colma Navigable Slough within the jurisdiction of South San Francisco?
· Raise the height of the existing levees and floodwalls
· Build set back levees, which may not be feasible due to urban development.
· Purchase properties adjacent to Colma Creek for mitigation plans.
· Note that permitting agencies seek to avoid hardscape flood channels and prefer more natural based solutions.
· Expand the size of the lower channels?
· Build a flood/tide gate between the Littlefield Avenue side of South San Francisco and “Sam Trans” Island, which could create a flood basin for Colma AND San Bruno Creeks. This would be similar to a solution adapted by the City of Palo Alto. The tidal gates would be open most of the time and could help create a new wetland area. During heavy rains and high tides the gates could be closed to provide a catch basin for high fluvial water flows.
San Bruno Creek
San Bruno Creek is currently affecting SFO, because creek water has been known to back up and flow into SFO’s long term parking lot.
Dilip, Moffat & Nichol:
· Upgrade the current San Bruno Creek tide gate on the North Access Road by the multi-story parking garage to increase the flow capacity. The current tide gate is not considered adequate for any significant increases in fluvial water flows or increased SLR. The existing tide-gate structure has four 5’-dia culverts. For reference, the existing San Bruno Creek structure underneath Hwy-101 has four 8’x10’ boxes.
· The CalTrans Highway 101 culverts on San Bruno Creek have the capacity to convey the 100-yr creek flow rate; therefore this structure is not considered a constriction on the Creek. The existing San Bruno Creek structure underneath Hwy-101 has four 8’x10’ boxes.
· Use the SFO open space on the west side of Hwy-101 for flood retention storage, by building set-back levees at the edge of the Bel Air neighborhood, between 7th Ave, San Bruno Ave and Highway 101, which is the “Cupid Row Canal” portion of the Creek.
· Potential for additional detention storage area immediately upstream of the Hwy-101 boxes, in County Flood Control’s jurisdiction.
· We must be mindful of current high ground areas like the PG&E sub-station and Highway 101, in order to avoid solving one problem while creating another problem.
General Comments:
Are there constraints to building an updated San Bruno Creek tide gate?
Does the Millbrae area between the BART tracks and Highway 101 have the capacity to retain more water from the San Bruno Creek watershed? There is the potential for passing flood flows from Cupid Row Canal south into the Lomita Channel in Millbrae. The structures that pass the Lomita Channel underneath Hwy-101 have additional capacity.
Caltrain is not located properly on some of the maps.
Surface detention/wetland alternatives might have funding constraints for SFO due to bird-strike hazards.
The larger regional tidal-barrier structure alternative, spanning from the SamTrans Peninsula (the leaf) north to the Bay Trail and Littlefield/Utah Ave, would also provide protection for the San Bruno Creek watershed.
Joe LaClair, BCDC:
Would it be possible to use current at-grade airport parking areas near San Bruno Creek and the 101/380 interchange (surface and structural) to create more water retention areas, or at least increase the impervious land area? One way to accomplish this without impacting parking capacity would be additional structured parking. It would be interesting to know the cost benefit analysis, and whether this analysis could build a case for cost-sharing the parking construction. Any detention system in this watershed needs to be designed with endangered species in mind.
How will we address the multiple power lines, sewer lines, water lines and other above and below ground infrastructure in the SFO area between SSF, San Bruno and Millbrae?
Next steps and Wrap-up
The Moffat & Nichol contract with SFO, that was due to expire in March, 2015, has been extended to September, 2015.
Moffat & Nichol will provide a draft study report by late March or early April (6-weeks).
We will reconvene the working group, as needed, after the draft report is complete. The report will be provided to the working group prior to the next meeting/workshop.