Midcoast Watershed & Drainage
What is a Watershed?
A watershed is the land that stormwater flows over, or through culverts, on its way to a creek, delta, bay, or ocean. Stormwater isn’t treated, so any pollutants left on the ground like trash, oil and dog waste are picked up and carried to the ocean. These pollutants can degrade water quality and harm aquatic and human life. The volume of stormwater runoff from a watershed depends on total acreage and is increased by impermeable surfaces added with development.
Montara & Moss Beach
In the 1970s, a 5.5-mile band of Midcoast shoreline, including Fitzgerald Marine Reserve (FMR), was designated by the State as an Area of Special Biological Significance (ASBS), due to the diversity of habitat and species found on the broad reef. Since 1983, the California Ocean Plan has prohibited discharge of pollutants to the ASBS.
The Critical Coastal Areas (CCA) program, led by the Coastal Commission, lost funding after 2008, but produced these interesting documents about the FMR watershed:
Introduction to FMR Historical Ecology, 2008
FMR Watershed Assessment 2008
FMR Critical Coastal Area Fact Sheet 2010
The Fitzgerald ASBS Pollution Reduction Program was initiated in 2011 by San Mateo County in collaboration with the Resource Conservation District (RCD) and San Francisco Estuary Institute, with the goal to improve water quality and protect beneficial uses of the Fitzgerald ASBS and assist in County compliance with ASBS stormwater regulations.
El Granada
El Granada watershed is not covered in the FMR ASBS report, but the 2013 El Granada storm drain inventory map includes contour lines, creek names, drainage names with acreage, culvert routes with directional arrows and catch basins, and outfall locations with total watershed acreage. Subsequent to that inventory was the Cabrillo Ave drainage improvement project (staff report) financed with Midcoast development mitigation fees.
The 2018 Quarry Park Watershed Assessment and Erosion Prevention Plan (released in 2022 - photos & map at the end) includes an inventory of erosion and sedimentation issues and prioritizes recommendations to address them. Area of Concern #2 is the intersection of Santa Maria Ave and Columbus St, where the Class II stream exits the Park and flows uncontrolled onto urban residential streets. This location drains 299 acres, a majority of Quarry Park’s watershed. The report notes on p.21, “There is no obvious effort to manage this runoff in any form of designed drainage structure ever. During field investigations, stream flow was observed traveling across and down the paved road, choosing its’ own flowpath. Anecdotal accounts from residents report flow exiting the Property has resulted in flooding a large portion of the neighborhood during peak storm events.”
More Resources
SMC Office of Sustainability Stormwater page
San Mateo Countywide Water Pollution Prevention Program: Stormwater treatment requirements for new development to address stormwater runoff pollutant discharges and prevent increases in runoff flows
Drainage Manual for review of new development projects in unincorporated SMC (implemented in draft form since 2019)
SMC Stormwater Resource Plan (C/CAG 2017) seeks to better manage stormwater to reduce flooding and pollution associated with runoff, improve biological functioning of plants, soils, and other natural infrastructure, and provide many community benefits, including cleaner air and water and enhanced aesthetic value of local streets and neighborhoods — main report.
Midcoast Stormwater Drainage Committee 2007-2011
Midcoast Stormwater Drainage Committee (MSDC) convened from 2007 to 2009 to study the extent of drainage problems on the Midcoast, the regulations and policies in place that impact drainage, and various approaches to improving drainage facilities. MSDC June 2009 Final Report recommendations approved by Board of Supervisors:
1. Drainage improvements on 2nd, Kanoff, & East Ave in Montara: Develop a conceptual design report including environmental review, and a capital improvement project, subject to available funding.
2. Conduct public meetings by June 2010 to gauge the Midcoast community’s interest in developing a Midcoast Stormwater Master Plan and implementing stormwater capital projects and enhanced maintenance levels of service subject to approval of local funding sources.
3. Seek Legislative Committee support for legislation that provides funding for stormwater system improvements and provides an exemption from Prop 218 requirements for generating local revenue for stormwater system improvements.
2011 Montara Drainage Improvement Study for 2nd, Kanoff, & East Ave areas. The proposed improvements in the Study were not constructed due to funding constraints.