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End-of-Pipe TrashTrap – Flood Maintenance Division Hamilton Bowl – LA County DPW

Project Specifications:

Location: City of Signal Hill, CA

Application: End-of-pipe Netting TrashTrap  

Project Profile: Stormwater events were increasing the deposit of trash and debris at the Hamilton Bowl Retention Basin, located in the City of Long Beach, CA. A significant portion of the trash was being subsequently pumped to the LA River via two pumping stations. As a solution for this problem a Netting TrashTrap model NTT-2 was installed on the site, capturing debris from a 70 cfs outfall.

Challenges: The main challenge of this project was to meet or exceed California Trash Total Maximum Daily Load (TMDL) for LA River, meeting the requirements of 97% capture of trash & floatables in 5mm net.

Solutions: A netting system was designed and tested, meeting the TMDL regional regulations. Two nets were retrofitted to an existing 69’’ stormwater outfall structure and took one day to install. The energy of the flow of the stormwater flow drives the trash and debris into the nets and no power is required for the system to operate. The system drains dry after the rain events, so there is no standing water to act as a breeding place for mosquitoes and other vectors. The total area serviced is 270 acres. The device was designed to handle 1hour storm at 0.6 inches per hour. The system met LA Regional Water Quality Board’s “Full Capture Device Certification” for Trash & Debris.  In three years of operation the netting system collected 38,700 pounds of trash and the nets were changed 21 times.

Diego Cadena, Manager of the Flood Maintenance Division was at the installation when it went on line and commented, “We are pleased to have this innovative technology as part of our overall program to address the Trash TMDL requirements. The County is moving ahead aggressively to comply with these requirements and protect our watersheds and the receiving waters.”  Signal Hill Council member Larry Forester observed the facility during the rain event that occurred just after the installation was completed and stated, “This solution to the Trash TMDL regulations works well and is an excellent example of the type of solution that the Coalition for Practical Regulation is seeking. The Coalition certainly wants to clean up the water but to do it under regulations that are practical and cost effective.” Four years after the installation of this system, four more end-of-pipe systems on 4 of these outfalls, one with one net and the 3 others with two nets each, were installed.