Walteria Retention Basin Improvements Phase I


The purpose of the Walteria Retention Basin is to retain residual flows received from adjacent catch basins and storm drains, to provide flood protection to nearby residents. The captured stormwater water will then infiltrate naturally into the ground to provide underground recharge. The water may also be pumped to the downstream Wilmington Drain, eventually reaching Ken Malloy Harbor Regional Park: Machado Lake.

The Los Angeles County Flood Control District will begin construction on the $5.8 million Walteria Retention Basin Improvements Phase I project in the City of Torrance. Los Angeles County Public Works is proceeding with three project phases to improve flood protection and maintenance accessibility to conduct future inspections, repairs, and maintenance activity safely. Primary project objectives include:

Phase I will provide safe access for maintenance and inspection purposes of the surrounding perimeter and lower levels of the pump station and will provide improved aesthetics to the facility.

Phase II (future) will follow sub-sequentially to upgrade the existing pump station to increase operational efficiency (with a floating pump station).

Phase III (future) will implement water quality improvements, to remediate foul and nuisance odor.

The project is funded by Los Angeles County Flood Control District.


The 25-acre Walteria Retention Basin and its appurtenant pumping plant is located near the intersection of Hawthorne Boulevard and Skypark Drive in the City of Torrance.

Picture of Lopez Spreading Grounds


  • Remove approximately 38 trees (Trees to be removed have been flagged) which conflict with construction, approximately 150 trees will remain untouched
  • Remove shrubs on fencing and replace deteriorating perimeter barbed wire chain link fence with a galvanized steel picket fence
  • Remove and replace segments of damaged retaining wall
  • Reconstruct basin's perimeter access road due to severe wear and cracking
  • Reconstruct an access ramp to perform maintenance in the basin
  • Repair and recompact eroded basin side slopes
  • Replace existing down-drains with concrete swales to reduce slope erosion
  • Plant 148 drought-tolerant and native trees and additional shrubs and low growing plants surrounding the basin


Construction began March 14, 2022 and completion has been delayed to Spring 2023. Work will continue to occur Monday through Friday between 7:00 a.m. to 3:30 p.m.


The project is in the Construction Phase.

Area residents and businesses, within one mile of the retention basin, have been sent informational flyers to provide awareness of the project and provide an opportunity for questions or feedback.

Trees to be removed have been flagged and conflict with construction, approximately 150 trees will remain untouched.


March 2022 Project Construction Start
March 2022 Tree Removal and Clearing
March/April 2022 Dewatering of the Basin
June 2022 Earthwork and Slope Repair
October/November 2022 Concrete Work and Access Roads/Ramp
March/April 2023 Estimated Project Construction Completion


  • Improve maintenance crew and vehicle accessibility to all areas of the basin for operational needs
  • Improving the ability to address odor-causing floating vegetation; and allowing Vector Control accessibility to address mosquito larvae
  • Enhance facility's aesthetics by replacing chain link fence with galvanized steel picket fence
  • Vegetation enhancements include removing dead and stressed Oleander shrubs which surround the site. Existing oleanders provide inconsistent coverage due to the species susceptibility to pathogens and replenishment of removed trees and Oleander with a diverse group of plant species will improve aesthetics. A rich variety of native and drought-tolerant and native trees and understory shrubs will surround the basin to provide more resiliency in response to fluctuations in climate, while also creating an aesthetic enhancement to the site and surrounding community


The awarded construction cost is $5,715,700.


  • Equipment noise for tree and shrub removal
  • Construction machinery noise
  • Temporary sidewalk closures to replace damaged retaining wall portions
  • Light noise when pumping water out of basin to prepare for construction
  • Increased vehicular traffic entering and exiting basin at entrance located near Hawthorne Boulevard and Skypark Drive


If you have any questions regarding this project, please contact Construction Inspector Wiggen Babakhanians at (626) 607-7426 between 7 a.m. and 3:30 p.m., Monday through Friday. Refer to the Walteria Retention Basin Improvements Phase I project. Individuals with hearing or speech impairment may use California Relay Service 711.


Design Concept


238th Street

238th Street

Southeast side, near Walteria Pump Station

Southeast side, near Walteria Pump Station