Inter-Departmental Correspondence

Department of Public Works



January 7, 2011


January 25, 2011







Honorable Board of Supervisors


James C. Porter, Director of Public Works


Colma Creek Flood Control Channel Wall Repair Project



Acting as the governing board of the San Mateo County Flood Control District, adopt a Resolution:



Certifying the Initial Study / Mitigated Negative Declaration, dated August 26, 2010, for the Colma Creek Flood Control Channel Wall Repair Project; and



Authorizing the Director of Public Works to proceed with preparing plans and specifications for the Colma Creek Flood Control Channel Wall Repair Project; and



Authorizing the Director of Public Works to proceed with advertising for bids on the Colma Creek Flood Control Channel Wall Repair Project, and reporting back to this Board with recommendations on awarding a contract.



In January 2008, there was significant wall movement in a 270-foot section of the Colma Creek Flood Control Channel (Channel) upstream of Spruce Avenue, in the City of South San Francisco (City). The wall movement and subsequent storm events created substantial pavement cracking along North Canal Street, significant soil subsidence adjacent to the wall on the south side of the Channel, and posed a threat to the City’s large diameter sanitary sewer pipe.


On February 12, 2008, your Board adopted Resolution No. 069270, which declared an emergency and approved work to install a temporary bracing system to minimize additional wall movement. On October 7, 2008,your Board adopted Resolution No. 069729 which approved a contract to fill the voids caused by soil subsidence adjacent to the walls.


To complete permanent repairs, the Department authorized two separate task orders in accordance with an existing on-call services agreement with Camp Dresser & McKee, Inc. (CDM), to prepare the Initial Study (IS) and Mitigated Negative Declaration (MND) for the Colma Creek Flood Control Channel Wall Repair Project (Project); and to prepare design alternatives and plans and specifications for the selected alternative.


The proposed Project involves the construction of a U-shaped concrete channel for a length of approximately 380 feet from upstream of the Spruce Avenue Bridge to immediately downstream of the Spruce Avenue Bridge. Several alternative channel designs were considered for the Project, however the U-shaped concrete channel was selected as the preferred alternative. The U-shaped concrete channel will remove the current risk of channel bottom scour, improve the geotechnical reliability of the channel, provide long-term functionality, and protect the channel immediately upstream of the Project and the Spruce Avenue Bridge area. The Project is also consistent with the downstream channel section from Spruce Avenue to Produce Avenue (2,800 feet long). Department staff has presented the preferred and alternative designs to the Colma Creek Citizens Advisory Committee for their consideration and they concur with the selected alternative.



The IS/MND, prepared by CDM, identified potential adverse effects during construction. Those effects will be reduced to less-than-significant levels through the implementation of specific mitigation measures as identified in the Mitigation Monitoring and Reporting Program, pursuant to Section 21081.6 of the California Public Resources Code. A 30-day public review period was completed in compliance with the provisions of the California Environmental Quality Act (CEQA) and no comments were received.


In order to expedite the project schedule, we are requesting that the Board authorize the Director of Public Works to proceed with preparation of the plans and specifications and call for bids for the Project to help ensure construction of the Project during the summer/fall 2011 construction season. In a subsequent Board action, we will present plans and specifications for your Board’s adoption and recommend awarding the project to the lowest responsible bidder. Your Board has previously approved the use of this “streamlined” process to shorten the time required to award a contract in order to ensure compliance with specific funding or construction deadlines.


County Counsel has reviewed and approved the Resolution as to form.


Approval of these actions contribute to the Shared Vision 2025 outcome of a Healthy Community by maintaining the integrity of the flood control facility and adjacent infrastructure for the benefit of the public.



The estimated cost for construction is approximately $2,800,000. The cost associated with Department staff time and consultant fees is approximately $300,000, which will be financed by District Funds. There is no fiscal impact associated with certifying the IS/MND.


There is no impact to the General Fund.