Dry Weather Diversions in California - Diverted by Diversions?

From Beachapedia

NOTE: This article was originally written in 2003 when California's Clean Beaches Initiative was initially being implemented under Proposition 13. It was updated in 2010 to include projects funded under Propositions 40 and 50.

Introduction – What Are Diversions?

In order to understand diversions, it is first necessary to understand that in most areas of the country there are two sewer systems – a “sanitary sewer system” that takes wastewater from toilets, sinks and other drains inside buildings to a sewage treatment plant and a “storm drain system” that collects rainwater and excess water (“runoff”) from irrigation, car washing and other activities and routes that water, without treatment, to storm drain channels, rivers, creeks, and ultimately to a lake or the ocean.

Since storm drain systems do not include any treatment, various contaminants such as fertilizers, pesticides, herbicides, gasoline, oil, radiator fluid, and animal waste get washed into the storm drains and ultimately reach the ocean or other receiving waters. Water runs down hill until it reached sea level or a confined water body. This means that “urban runoff” from areas many miles away from the ocean can cause water quality and health problems at the beach. In Southern California, portions of Riverside County 50 miles or more from the ocean can drain to the Santa Ana River, which flows to the ocean at the border between Huntington Beach and Newport Beach.

In some areas of the country there is just one “combined sewer system.” In these areas, dry weather urban runoff is sent to a sewage treatment plant and does not directly flow to the beach. This helps prevent beach closures and health advisories during dry weather, but creates big problems during rain events. During major rainstorms, the amount of rainfall runoff can easily overwhelm the capacity of sewer lines, causing a mixture of raw sewage and rainwater to spill out of sewer manholes and go directly to the beach. This is called a “Combined Sewer Overflow.” Many east coast cities are working to separate their sewer systems to avoid this problem. San Francisco County is the only coastal area in California that has combined sewers.

So, what’s the answer to the problems caused by urban runoff? The best long-term solution is to control pollution at its source so that it never gets to the storm drain system. This involves minimizing the use of toxic chemical products and eliminating them, where possible. It also involves implementing Low Impact Development practices, water conservation and recycling efforts, avoiding over-watering, fixing car leaks, picking up after your pet, and other common-sense practices recommended in Surfrider Foundation’s brochure 20 Ways to Cleaner Oceans and Beaches.

Until source control measures can be effectively implemented, many cities are installing “dry weather diversions” to divert urban runoff to the sanitary sewer system and sewage treatment plants. These systems are designed to operate only during periods of dry weather. During any significant wet weather, the systems are typically shut off or bypassed to avoid the “combined sewer overflow” problem described above. Diversion structures vary in complexity from temporary inflatable dams and portable pumps to complex engineered systems with automatic controls, flow meters, and alarm systems. The systems may be gravity flow or rely on pumps. In many cases there is some type of screening, filtering, or centrifugal separation device installed as part of the diversion that keeps trash and large solid particles out of the sewer lines.

Advantages/Benefits of Diversions

Diversions can completely stop the flow of polluted urban runoff from a particular storm drain from reaching the ocean or other receiving water body during dry weather. To the extent that beach closures and health advisories are caused by flows from a given storm drain, directing the dry weather flow from that drain to the sewer system should eliminate or greatly lessen that problem. Another advantage of diversions is that they can potentially catch a sewer spill that has flowed into an upstream portion of the storm drain and divert it back into the sewer system before it reaches the beach.


As mentioned above, the main disadvantage of diversions is that they must be bypassed and are therefore not effective in wet weather. The most serious beach closure episodes typically occur during periods of rain, and the lingering effects of polluted rainwater runoff may last 72 hours or more after the end of the rain event. In any given jurisdiction, other limitations may be the capacity of the sewer lines, the capacity of the sewage treatment plant, or the unwillingness of the sewer agency to accept the diverted dry weather urban runoff. Sewer collection and treatment agencies are formed to handle sewage, not urban runoff, and they are not required to accept such flows. Some agencies may have prohibitions against accepting urban runoff, or may limit the flow to avoid capacity problems in their lines or at the treatment plant. Another concern is that since diversions are fairly new and the constituents in runoff can vary widely, the degree to which these constituents may pass through the treatment plant and cause problems in the receiving water or with uses of recycled water are unknown.

Disadvantages of Diversions

The main potential disadvantage of diversions is that they may discourage efforts at source control of pollutants and may also discourage water conservation. During dry weather, a beach city may think that their beach closure problems are “solved” by the diversion, only to find out that they have significant problems during rainy periods or when the diversion is otherwise not in operation. It is important that source identification and control efforts continue to minimize both the pollutant load and the dry weather water flow. Ideally, there should be no dry weather urban runoff flow to the beaches.

Dry weather diversions are but one tool to address the problem of beach closures. Some wastewater agencies (see below) require a demonstration that all feasible source control reduction measures have been implemented before they will allow a diversion to be connected to their system.

Another disadvantage of diversions is that they only protect the final receiving waters, not the creek, stream, or wetlands areas upstream of the diversion. If discharge of excessive flows or pollutants is impacting human health or the environment in these upstream areas, the diversion will do nothing to address these problems.

A final disadvantage of diversions may be cost. The capital cost to install diversions varies widely, depending on such factors as the flow, the nearness and relative elevation of sewer lines and the degree of automatic control desired. The cost may range from a few thousand dollars to hundreds of thousands of dollars. Depending on the sewer agency, there may also be a continuing cost based on the flow rate and/or the concentration of contaminants.

Wastewater Agency Diversion Acceptance Policies

As mentioned above, dry weather diversions are not possible unless the local sewer agency agrees to accept the diverted flow from the storm drain system. A few agencies have prepared detailed acceptance policies. Two such agencies in southern California are the Orange County Sanitation District (OCSD) and the South Orange County Wastewater Authority (SOCWA).

Orange County Sanitation District

OCSD is a large wastewater collection and treatment agency that handles approximately 240 million gallons per day of wastewater generated by residents and businesses in north and central Orange County. OCSD was drawn into the urban runoff/dry weather diversion business by the well-publicized beach closings in Huntington Beach during the summer of 1999. In April 2000, OCSD adopted a resolution for accepting runoff on a long-term basis on non-rain days. On September 27, 2001, OCSD adopted a second resolution that limited the total amount of urban runoff flow to 10 million gallons per day (MGD) and waived any fees for the first 4 MGD. Flows in excess of 4 MGD are charged at a rate of $321 per million gallons.

Other requirements include:

  • The diversion shall be designed to exclude wet weather flow and must have a lockable shut-off device accessible to OCSD.
  • The applicant must apply for and obtain a permit from OCSD prior to discharging.
  • The permit applicant must demonstrate that other disposal alternatives have been considered, evaluated and deemed not feasible.
  • Debris and pollutants of concern must be prevented from entering the sewer system.
  • The daily total flow must be measured.
  • The applicant must employ Best Management Practices (BMPs) designed to minimize or eliminate dry weather urban runoff.
  • The quality of the discharge must meet OCSD’s wastewater discharge standards, the discharger must conduct quarterly self-monitoring and must submit reports to OCSD.
  • Discharges must be shut off no later than the commencement of any measurable rainfall and cannot be resumed without written approval from OCSD.

South Orange County Wastewater Authority

SOCWA serves 17 cities and communities in south Orange County and has a total sewage treatment capacity of approximately 38 MGD at four treatment plants. The total available capacity for dry weather diversion flows at SOCWA’s treatment plants in Aliso Canyon and Dana Point is about 1 MGD. SOCWA adopted Resolution No. 2001-23 on December 6, 2001 as a “Nuisance Flow Diversion Policy.” Similar to OCSD, SOCWA’s policy requires that a permit application be completed and a permit granted prior to beginning a diversion. The discharger must demonstrate that all other disposal alternatives have been considered and found not to be feasible. The discharger’s total flow (wastewater plus diverted flow from the storm drain system) must stay within their “capacity ownership” limits. Dischargers must measure flows, analyze the discharges, and submit periodic reports to SOCWA. 24-hour composite samples are required to be collected and analyzed twice per week. Dischargers must also submit plans and specifications for the diversion project to the Member Agency or SOCWA. The resolution requires the installation of a lockable shut-off device and gives SOCWA the authority to require the installation of appropriate pretreatment devices “to remove grease and oil, trash, debris, and other objectionable substances prior to connection to the sewage collection system.” The resolution states “pumped diversions are the preferred method of discharge in order to prevent debris from entering the sewage collection system and to control the maximum rate of flow.”

SOCWA’s resolution further states:

“Diversion of nuisance flows to the SOCWA and Member Agency wastewater systems should not be considered as a permanent or long-term solution to the problem of dry weather nuisance flows; provided, a Member Agency may consider certain diversions as permanent components of an overall program to reduce nuisance flows to creeks, streams or the ocean.”

The affected Member Agency or SOCWA may require the project applicant to implement BMPs and pollution prevention strategies to minimize or eliminate nuisance flow from the area or site served by the proposed diversion project.

SOCWA’s resolution states that diversions may be permitted only from April 15 to October 15th and “shall be designed to shut down prior to the “first flush” during a storm event. A diversion of nuisance flows may be permitted beyond the dry weather period so long as the system is properly designed and approved by the receiving Member Agency and SOCWA to shut down prior to the “first flush” of any significant precipitation event. Permits may be issued for up to 5 years and may be renewed for additional periods. Notices of each diversion project must be sent by SOCWA to the appropriate Regional Water Quality Control Board upon permit issuance for such project.

Survey of Southern California Diversion Projects

In 2003, Surfrider Foundation contacted representatives of the State Water Resources Control Board (SWRCB), several Regional Water Quality Control Boards, and several coastal cities to gather data on diversion projects throughout southern and central California. A starting point was the Clean Beaches Initiative (CBI) project lists on the SWRCB's Clean Beaches Initiative website. These lists showed SWRCB and RWQCB contacts for the approved projects. These indicated contacts provided additional contacts at various cities who provided information on past, present and future diversion projects. For the initial list (Proposition 13) of approved CBI projects, a total of $30.35 million in projects was approved. Projects that were entirely or primarily diversion projects totaled $11.76 million, or 38.7% of the total authorized amount.

The State Water Resources Control Board CBI website now has listings for additional projects authorized and funded under Proposition 40 and Proposition 50. Under Prop 40, $42.9 million in total finding included approximately $19 million (44.4% of the total authorized amount) for diversion projects. Under Prop 50, $18.8 million in total funding included approximately $6.3 million (33.5% of the total authorized amount) for diversion projects.

The lists of CBI projects shown below are only the projects where storm drain flow is being diverted into the sewer system. There are many other projects (including storm drain filtration and treatment systems, sewer line upgrades, conversion of septic systems to sewers, wetlands and bio-swale construction, and source identification and reduction) on the complete lists, which can be viewed on the State Water Resources Control Board website.

A lack of diversion projects for a certain county (e.g., Santa Barbara) should not be interpreted as lack of effort in addressing beach water quality problems. The city of Santa Barbara has instituted several innovative programs funded by Measure B, which was approved by the voters on November 2000. The city and county are actively exploring opportunities for creek restoration, as well as evaluating the use of storm drain filters, bio-swales and ozone treatment systems. Several such projects have been initiated or have been proposed for funding under CBI, including some constructed wetlands and a septic-to-sewer conversion at Rincon. The city of Buenaventura (Ventura County) has requested CBI funding to treat urban runoff at Surfer’s Point. Other treatment alternatives that have been implemented or have been proposed at popular surfing areas include a filtration/disinfection system and septic system repair at Malibu (Los Angeles County), a high volume urban runoff treatment system at Salt Creek (Orange County), an ozone treatment system at Moonlight Beach in Encinitas, and constructed wetlands, a vegetated channel, and storm drain filters at Cardiff Reef (San Diego County).

Surfrider Foundation’s research into diversion projects was not meant to be exhaustive or all-inclusive, but rather to provide a representative indication of the approximate number, status and cost of diversion projects in several California coastal communities.


Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Pacifica State Beach - Divert Urban Runoff, Sewer Line Replacement, Construct Wetlands $1,100,000 Prop 40


Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and location Authorized Amount Funding Source
Santa Cruz - Main, Cowell & Seabright Beaches – Divert Urban Runoff $1,475,000 Prop 13
Santa Cruz - Main, Cowell & Seabright Beaches - Divert Urban Runoff/Retrofit Pump Station $1,000,000 Prop 40
Capitola Beach - Wetland Treatment System/Divert Urban Runoff $600,000 Prop 40


Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Pacific Grove, Lovers' Point – Divert Urban Runoff $500,000 Prop 13
Seaside – Monterey State Beach – Divert/Retain Urban Runoff $565,000 Prop 40

Comments on Monterey County Programs: The source abatement and diversion program at Lovers' Point in Pacific Grove was initiated after a 70,000-gallon sewage spill into Monterey Bay National Marine Sanctuary on January 12, 2000.


Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Monterey Bay National Marine Sanctuary - Divert Urban Runoff $1,500,000 Prop 40


Pre-CBI or Non-CBI Diversion Projects
Name and Location Authorized Amount
The city of Santa Barbara is evaluating several possible diversion projects. -


Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Kiddie and Hobie Beaches, Channel Islands Harbor – Study/Divert Urban Runoff $705,000 Prop 13


Pre-CBI or Non-CBI Diversion Projects
Name and Location Comments
Santa Monica, Pico/Kenter Storm Drain One of the first diversion projects in California
Santa Monica, Ashland Ave. Storm Drain -
Venice City Beach at Brooks Avenue -
Redondo Beach - Herondo Street Storm Drain Still a problem even with the diversion?
Venice City Beach at Windward Ave. -
Bel Air Bay Club -
Manhattan Beach Pier -
Alamitos Bay Completed in 2000

Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Mothers' Beach - Marina Del Rey - Study/Circulation Improvements/Divert Urban Runoff $2,000,000 Prop 13
Will Rogers State Beach (Temescal Canyon) – Divert Urban Runoff $800,000 Prop 13
27th/28th St., Manhattan Beach – Divert Urban Runoff $200,000 Prop 13
Will Rogers State Beach (Santa Monica Canyon) – Divert Urban Runoff $1,020,000 Prop 13
Wilshire Storm Drain Outlet (north of Santa Monica Pier) - Divert Urban Runoff $980,000 Prop 40
Redondo and Torrance Beach - Divert Urban Runoff $650,000 Prop 40
Topanga Beach - Divert Urban Runoff $608,000 Prop 40
Dockweiler State Beach/Westchester Parkway - Divert Urban Runoff $550,000 Prop 40
Venice Beach/Rose Avenue - Divert Urban Runoff $550,000 Prop 40
Santa Monica Beach/Ashland Avenue - Divert Urban Runoff $550,000 Prop 40
Will Rogers State Beach/Pulga Canyon - Divert Urban Runoff $550,000 Prop 40
Will Rogers State Beach/Sunset Blvd - Divert Urban Runoff $550,000 Prop 40
Will Rogers State Beach (PCH & Marquez) - Divert Urban Runoff $870,000 Prop 40
Santa Monica Beach at Montana St. -Divert Urban Runoff $600,000 Prop 40
Long Beach - Colorado Lagoon Beaches - Low Flow Diversions, Bioswales, and Culvert Modification $3,823,868 Prop 40
Multiple Los Angeles County Beaches - Expand Diversions $5,000,000 Prop 50

Comments on Los Angeles County and City Programs: There are approximately 342 storm drains that reach the ocean from Point Dune to the Palos Verdes Peninsula. Palos Verdes Estates has an additional 24 storm drains. Diversions are typically routed to the LA City Bureau of Sanitation’s Hyperion Treatment Plant in El Segundo or Los Angeles County’s treatment plant in Carson.


Pre-CBI or Non-CBI Diversion Projects
Name and Location Comments
San Clemente – Riviera District Low cost gravity flow system
San Clemente – Linda Lane -
Aliso Creek Diversion At Coast Highway
J03P02 storm drain (Aliso Creek) In conjunction with operation of treatment system (temporary) and constructed wetlands
Huntington Beach – 9 pump stations Approx. 0.9 MGD total flow
Newport Dunes Gravity flow, 0.026 MGD. Cost was $60,000 to design and construct.
Los Trancos & Muddy Canyon pump stations, PCH/Crystal Cove 0.6 MGD
Huntington Beach Pump Station; Greenville Banning Channel; Santa Ana River Channel; Talbert Channel (4 separate projects) 0.972 MGD
Laguna Beach – 10 dry weather diversions Diversions installed beginning in 1997 through 2002. Four additional diversions and one upgrade were completed in May 2003.
Dana Point/Capistrano Beach Diversion at Camino de Estrella/Camino Capistrano plus approx. 8 diversions along Beach Road in Capistrano Beach (30,000- 40,000 GPD total flow).

Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Dana Point Harbor, Baby Beach – Divert Urban Runoff/Source Abatement Study $750,000 + $130,000 Prop 13
Doheny State Beach - Divert Urban Runoff $750,000 Prop 13
Newport Bay - Divert/Treat Urban Runoff/Source Abatement Study $500,000 Prop 13
Huntington State Beach - Divert Urban Runoff $1,000,000 Prop 13
Doheny State Beach, Dana Point/Del Obispo - Divert Urban Runoff $500,000 Prop 40
Capistrano County Beach - Divert Urban Runoff $500,000 Prop 40
City of Laguna Beach, Pacific Ocean Coastline - Divert Urban Runoff $1,200,000 Prop 40
North Beach, San Clemente - Divert/Treat Urban Runoff $1,800,000 Prop 40

Comments on Orange County and City Programs: The Orange County Board of Supervisors allocated $250,000 in FY2000 matching funds for coastal cities (Huntington Beach, Newport Beach, Laguna Beach, Dana Point and San Clemente) urban runoff treatment and diversion programs. In FY 2001 the Board of Supervisors allocated $1,000,000 in matching funds for all cities for urban runoff treatment and diversion projects.

The Los Angeles Times reported in January 2000 that Laguna Beach was diverting 38% of it runoff during the dry season and hoped to have all city drains diverted by 2007. The same article indicated that Dana Point planned to eventually divert 1 million gallons per day flowing through 26 storm drains in the area from Doheny Beach through Capistrano Beach. San Clemente had proposed two storm drain diversion projects as of the date of this article.

In 2003 Newport Beach had one existing diversion at Newport Dunes and was planning on installing five more (four along Coast Highway and one at Santa Ana Delhi Channel where it discharges into Newport Bay).

Although not directly related to diversions, Huntington Beach is planning to install eight filters to catch debris from 12 storm drains that discharge onto the beach. The filters were planned to be installed in September 2003. The $646,000 installation is being funded through a $4-million water quality grant that the city received through Proposition 13 water bond funds.

In March 2012 the Orange County Register reported that San Clemente was embarking on a $225,000 runoff-diversion project at Linda Lane Beach. It will be paid for by the city's Clean Ocean Fund, which uses a voter-approved fee that costs San Clemente households $4 to $5 per month to carry out projects and programs designed to reduce beach pollution from dirty storm runoff.

Orange County has some information on dry weather diversions operated by the county on their website. Additional information on diversions operated by Orange County Sanitation District is available in this presentation.


Pre-CBI or Non-CBI Diversion Projects
Name and Location Comments
Mission Bay Sewer Interceptor System Diverts storm drain flows away from Mission Bay
Additional City of San Diego Diversions City Council approved a plan in August 1997 to spend $3.3 million to divert dry weather flows from additional storm drains around San Diego to the Point Loma Wastewater Treatment Plant.

Clean Beaches Initiative Projects - Propositions 13, 40 and 50
Name and Location Authorized Amount Funding Source
Imperial Beach - Divert Urban Runoff $250,000 Prop 13
Coronado Beach – Divert Urban Runoff $1,000,000 Prop 13
Imperial Beach at Palm Avenue - Divert Urban Runoff $1,292,000 Prop 50

Comments on San Diego County and City Programs: The San Diego Regional Water Quality Control Board estimates that over 100 storm drain diversion projects have been installed along the coast between Laguna Beach (Orange County) and the U.S.-Mexico Border. The city of San Diego obtained a $6.1 million federal grant in July 2003 to construct a network of diversion projects. The grant is the largest ever to a West Coast City from the U.S. EPA intended to combat the effects of urban runoff. The planned diversion projects will handle flows up to 400 gallons per minute. The city will contribute $2.65 million to install diversions at 28 coastal locations and rehabilitate 47 diversions along the shoreline of Mission Bay that were installed in 1985. The first 18 diversion projects were scheduled to be completed by summer 2004, with the remainder to be completed in 2005.

Total Southern California Diversions

The report Forty Years after the Clean Water Act, A Retrospective Look at the Southern California Coastal Ocean (2012) includes a discussion of diversions which states:

"In response to this growing awareness, the state, cities, and counties began taking measures to address runoff sources of bacteria. Since 2001, California’s Clean Beaches Initiative Grant Program has provided nearly $100 million from voter-approved bonds for beach water quality improvement projects, to be used in combination with funding from local municipalities. One of the more effective and widely used best management practices for runoff has been diverting storm drain flows to the sanitary sewer system during dry weather so that runoff is ultimately treated before it reaches the ocean (Figure 15).

This increased investment in managing runoff has resulted in further improvements in beach water quality throughout the region. Heal the Bay, a local environmental advocacy organization, provides annual letter grades of southern California beaches based on water quality monitoring data. Since the Clean Beaches Initiative started in 2001, the number of beaches with poor grades (D or F) during the summer (AB 411) period has dropped from 12% to 5%, and now nearly 95% of all beaches in southern California receive annual grades of A or B."

The referenced Figure 15 shows the cumulative number of completed diversion projects in Ventura, Los Angeles, Orange and San Diego Counties from 1997 through 2010. Approximately 125 projects had been completed through 2010.


It is clear that diversion of storm drain flows into the sewer system during dry weather is a tactic that many coastal communities in southern California are using to address the serious problem of beach closures and beach health advisories caused by high concentrations of indicator bacteria. The good news is that diversions seem to be effective during dry weather, which can be well over 300 days per year in southern California. The bad news is that they cannot be used during wet weather and that serious pollution problems and human health threats caused by polluted runoff still occur on a regular basis during rainy periods. The further bad news is that diversions do nothing to address the sources of pollution, encourage water conservation, or protect water quality or habitat upstream of the diversion.

Diversions can be an effective band-aid, but unless we modify our societal bad habits, water (mis)use practices, and infrastructure flaws that cause and exacerbate the problem, we will continue to have unhealthy beaches and unhealthy watersheds that feed the beaches.

This article is part of a series on Clean Water which looks at various threats to the water quality of our oceans, and the negative impacts polluted waters can have on the environment and human health.

For information about laws, policies, programs and conditions impacting water quality in a specific state, please visit Surfrider's State of the Beach report to find the State Report for that state, and click on the "Water Quality" indicator link.