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Los Angeles, California is still one of the fastest growing cities in the world, and space has become even more sensitive and limited than ever. “The county is facing a severe housing shortage, and a need for more housing and price attainable housing”1, according to Diana Victoria Coronado of the Building Industry Association. High-density cities have simultaneous challenges. Land development is lucrative and designers are continuously challenged by space, site constraints, and regulations; so every square foot is maximized and justifiably scrutinized.
Since every new Los Angeles development in design must meet stormwater pollution requirements, engineers and designers are finding relief with stormwater solutions from credible companies with products that are flexible enough to fit their conservative intentions for the land; and goals for maximum value.


Photo Credit: – trekandshoot

The Porter Ranch community of Los Angeles is in its initial phases, but this high-profile master planned living experience has already received attention and been awarded Builder of the Year by the Building Industry Association of Los Angeles & Ventura. Porter Ranch offers more than just an array of model home options. When this site reaches completion, it will feature “unrivaled amenities such as the new K-8 Porter Ranch Community School, the Porter Ranch Town Center, nature areas, hiking trails, the 14-acre Holleigh Bernson Memorial Park, a planned 50-acre park, and a planned high-end retail center”2, according to Toll Brothers Incorporated.
The Porter Ranch geography and grading plan involves leading a significant amount of rainwater runoff/flow through a stormwater treatment system, approved under the Stormwater Quality Management Plan (SWQMP), before discharging to the City of Los Angeles storm drain lines. According to Michael Frasco of Bio Clean Environmental, “The site’s geography due to the hillside, made getting stormwater to the onsite retention basins a challenge. In areas where retention was not possible, the Modular Wetlands System Linear (MWS Linear) were implemented to achieve biofiltration treatment before discharging to the L.A. City storm drain.”


Figure A: Modular Wetlands System Linear Side-by-Side Orientation


Design engineers are faced with a set of challenges. The overall development may be spread out, but Porter Ranch’s steep hillsides, whose housing tracts consist of a network of drainage flumes, and catch basins, make bioretention infeasible. Porter Ranch is also a master planned development with an array of storm drain entry points like curb inlets, grate inlets, drainage channels to catch basins (submerged pipe), etc. All of these entry points are facilitating acres of newly terraced housing platforms, roof runoff, and impervious areas that create very high volumes of stormwater requiring treatment. To add to this already challenging set of obstacles, are space restraints. Los Angeles developments can be a lucrative endeavor, but buildable space is at a premium, and solutions that allow civil engineers and developers to meet all of these challenges within a small footprint as well as meet city regulations are rare.
According to the Los Angeles Water Quality Control Board, “Pollution conveyed by stormwater degrades the quality of drinking water, damages fisheries and habitat of plants and animals that depend on clean water for survival. Pollutants carried by stormwater can also affect recreational uses of water bodies by making them unsafe”.3
The City of Los Angeles has championed initiatives and policies for protecting California’s water quality. The city holds stormwater solutions to a high standard and there is a selective process before systems are trusted to deploy on the front lines of mitigating pollution risks associated with construction.


Every L.A. real estate development comes with stormwater approval challenges, but now solutions are much easier to assign. The widely adopted and proven Modular Wetlands System Linear (MWS Linear) stormwater Best Management Practice (BMP) has been approved by the Los Angeles Water Quality Control Board for use as an “alternative compliance solution” for on-site biofiltration. Demonstrated to the board through third party verified testing, the MWS Linear uses its high performance media and patented horizontal flow for equivalent or better pollutant removal to standard biofiltration. In addition to this new L.A. approval, the system has also been issued Full Trash Capture Certification from the California State Water Resources Control Board and it is approved by the Washington State Department of Ecology’s Technology Assessment Protocol – Ecology (TAPE) program for General Use Level Designation (GULD).
The MWS Linear gives engineers tasked with designing the most efficient outcome, a space savings solution to comply with low impact development (LID) requirements. The MWS Linear is an easily applicable, dependable, and versatile option given space conscious project and development criteria.

Curb Type
Downspout Type
Vault Type
Grate Type









The key is in the MWS Linear’s patented horizontal flow design. The MWS Linear is the only proprietary solution on the market that can take advantage of multiple inlet configurations in a single system. In the case of this project, multiple area catch basins were routed to a single MWS Linear and took advantage of a curb inlet. This adaptability minimizes the need for other catch basins on site.
The MWS Linear is customizable, allowing for height adjustments. The units on this project were all shallow installations, allowing for utilities to traverse under the systems for access to building pads and street lights. The first phase of the Porter Ranch project implemented a Modular Wetlands System Linear 8-16 model at a depth of merely 4’-5” and some units were as shallow as 3’-6”. This is a huge advantage and benefit for engineers designing sophisticated runoff systems along the steep Santa Susana hillsides. The system also has the capability for built-in high flow bypass [As Seen in Figure A]. This allows the pretreatment chamber to be used as the primary catch basin and eliminate the need for another bypass structure.

Modular Wetlands System Linear Installation Porter Ranch, Los Angeles
Modular Wetlands System Linear Installation Porter Ranch, Los Angeles

The second phase of the Porter Ranch project implemented three MWS Linear systems to address drainage areas that could not be directed to bioretention basins on site. Phases three through five are in process and will use MWS Linear systems to round out this luxury class leading development in the highly desirable Porter Ranch district of Los Angeles.



    1. Diana Victoria Coronado via Building Industry Association-Los Angeles-Ventura Chapter Facebook Page:
    2. Toll Brothers Inc. Website :
    3. Los Angeles Water Quality Control Board Website:


The Modular Wetlands System Linear Advantages

The Modular Wetlands System Linear (MWS Linear) is the most efficient and versatile biofiltration system on the market, and the only stormwater biofilter using horizontal flow which improves performance, reduces footprint, and minimizes maintenance.


Modular Wetlands System Linear Advantages

  • Washington State’s Department of Ecology (DOE) Technology Assessment Protocol – Ecology (TAPE) with General Use Level Designation (GULD) Approval Without Plants: With or without plants (open planter or sealed), the system maintains superior performance in any design configuration.
  • Can Accept Existing Pipe Below Surface: Piping into the system opens up numerous configuration and design options, like downstream use or diverting for retrofits.
  • Works Months Without Requiring Maintenance: The easily accessible pretreatment chamber traps and isolates trash, sediments, and hydrocarbons. A unique feature, proven to keep maintenance frequencies & costs at industry-leading lows.
  • Can Accommodate High Flow Internal Bypass: The Side-By-Side Orientation option allows abnormal high flows to bypass from pretreatment directly to the discharge chamber.
  • Design Flexibility & Safety: Space-saving design provides low excavation and installation costs, plus there is no dangerous depressed planter bed.