Recommended Wilmington Drain Plan

Habitat and Park Design
An invasive species removal program will be developed for Wilmington Drain to remove invasive plant species from the channel banks and in-channel island. A natural park featuring walking trails and educational opportunities will be constructed on the west bank of the channel and south of Lomita Boulevard in an area that is currently undeveloped. Interpretive signage will be installed at the major park access nodes located in the new parking lot south of Lomita Boulevard, and at the trail heads on Lomita Boulevard and Pacific Coast Highway.

Channel Improvements and Bank Stabilization
Wilmington Drain will be excavated and re-graded to provide increased hydraulic capacity. A total of approximately 15,500 cubic yards of sediment will be removed. The box culverts under Lomita Boulevard and Pacific Coast Highway will be cleaned and the transition zone in channel above and below box culverts will be graded. The sediment plug on the northeast side of the island will be removed to open up the low flow channel on the east side of the island. Streambank stabilization measures will be incorporated into the channel design to diminish adverse effects of high flow velocities. Existing gabions on the west channel bank, near Pacific Coast Highway, will be stabilized, as needed.

Two trash netting systems will be installed, one north of Lomita Boulevard at the outlet of the concrete lined portion of the Wilmington Drain and the other in the Project 510 storm drain entering Wilmington Drain from the east. Porous paving will be utilized in the new parking lot immediately south of Lomita Boulevard. Pedestrian trails will be developed in the new passive recreation park, and along the west side of the channel. Litter receptacles will be provided at the major park access nodes located in the new parking lot south of Lomita Boulevard, and at the trail heads on Lomita Boulevard and Pacific Coast Highway. Smart Irrigation Controllers will be utilized for the irrigation system installed in the newly created nature park.

The combination of in channel/end of pipe BMPs, source control/site design BMPs and the excavation associated with the recommended alternative will have a positive effect on water quality in Wilmington Drain and Machado Lake. The combination of these BMPs will reduce trash, sediment and metals loading from wet weather flows to Machado Lake. They may also provide slight reductions in bacteria concentrations in Wilmington Drain. However, the ability to achieve additional improvement in the water quality of Wilmington Drain is directly dependent on the implementation of stormwater BMPs, to the extent practicable, throughout the contributing watershed of Wilmington Drain.

Wilmington Drain
Recommended alternative
Recommended Park Plan

Wilmington Drain Recommended Plan Performance Measure Results
Project Goal Performance Measure Result
Satisfy water quality objectives -Reduce sediment load to Machado Lake and downstream receiving waters
-Reduce wet weather metals load to Machado Lake (Cu + Pb)
1 million pounds per year

217 pounds per year
Enhance recreational opportunities -Provide walking trails and educational opportunities -Yes
Provide flood protection -Provide capacity equal to or better than 1977 condition -Yes
Provide a sustainable project -Years before major excavation required
-Routine clearing of vegetation required
8-15 years
1 time per year
Enhance habitat -Net loss of protected habitat -0 acres
Achieve cost efficiency -Estimated capital cost
-Estimated operational cost
-$442,000 per year
Minimize short-term construction impacts -Dredged material removal requirement -15,500 cubic yards

Project Schedule

Construction will begin Summer of 2012.

If you have questions or comments, please call the outreach coordinator at (213) 978-0317. The project description, concepts and design are preliminary and subject to change.