In Southern California, millions of pounds of trash and debris accumulate annually in roads, parking lots, and urban areas during the long dry season and are then flushed into storm drains by the first major rainfall. In the City of Manhattan Beach (City), most of these storm drains empty directly into the Santa Monica Bay (SMB) in the Pacific Ocean, or they convey flows to the City boundary where they are intercepted by other storm drains in other cities. Trash and debris poses a health hazard to people, wildlife, fish, and other aquatic life. A Total Maximum Daily Load (TMDL) was established for trash in the Santa Monica Bay, which limits discharges of the specified pollutant (in this case, trash). To reduce trash within the Santa Monica Bay and on the beach and to address the TMDL, the City is implementing the Santa Monica Bay (SMB) TMDL High Flow Capacity Trash Treatment Control Device (HFCTTCD) Project (Project) by installing trash capture devices within the storm drain systems tributary to the Santa Monica Bay for which trash has not previously been addressed.
The Project will provide multiple benefits while assisting the City in addressing regulatory requirements. Project goals are summarized as follows:
- Enhance water quality within the Santa Monica Bay
- Enhance the quality of the beach and shoreline
- Meet trash limits define by the Los Angeles Regional Water Quality Control Board (LARWQCB)
- Educate the community about the benefits of stormwater management
The following figure illustrates the improvements proposed as part of the Project. The Project will include 3 HFCTTCDs on 3 different storm drains (located on 14th Street, 24th Street, and 39th Street) along with implementation at various different catch basins and inlets.
Trash capture devices will be installed in catch basins/inlets and along the storm drain pipe. The City evaluated the drainage systems requiring trash capture to determine the preferred implementation approach. For storm drain systems with a small number of catch basins, it was found to be more effective to implement trash capture devices at each of the catch basins. Where the drainage systems have many catch basins, implementing a HFCTTCD on the storm drain before the outlet was found to be more effective. A HFCTTCD is a regional structure that removes trash from the drainage system (rather than holding it at the catch basin); therefore, it addresses several catch basins at a single location.
Connector Pipe Screens (CPS) and Filter Inserts will be installed inside several catch basins near and along Ocean Drive to prevent trash from leaving the catch basin and going into the storm drain and ocean. The screens will allow trash to accumulate within the catch basins. Accumulated trash will be removed by maintenance crews regularly. HFCTTCDs will also be installed along several pipes to remove trash, debris, and sediment directly from the storm drain itself. These devices will be located underground on the existing storm drain and will remove trash/debris conveyed in the storm drain before it reaches the outfall at the Santa Monica Bay. Maintenance crews will remove accumulated trash from the HFCTTCDs regularly by lifting the manhole access lids that will be located in the street or sidewalk. A few example photos are included below.
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