Orange County Branch Newsletter

August 2011



By Matt Thomas, P.E.

Conceptual oblique view of Upper Chiquita Reservoir from 3-dimensional model (AECOM)

Nestled on the western slope of Chiquita Canyon, near the southern end of SR-241 Toll Road at Oso Parkway, is the 165 feet tall earthen embankment of the Upper Chiquita Reservoir.   July 18, 2011 marked a significant milestone for this $53 million dollar water reliability project as initial filling and testing operations got underway.

The Upper Chiquita Reservoir will hold over 244 million gallons of treated water, enough water to serve 168,000 local families with approximately 200 gallons of fresh water a day for one week.   

“This project has been a long time coming”, said Dan Ferons, Chief Engineer for the SMWD, who has been a driving force in leading the planning, environmental permitting, land acquisition, ultimate design, and construction of the project, dating back to 1989.  “Because South Orange County is almost entirely dependent on imported drinking water to meet daily needs, new domestic water reserves like the Upper Chiquita Reservoir are needed to ensure sufficient storage in the event of a supply disruption.”

The Santa Margarita Water District has partnered with four south Orange County water agencies and cities to fund the design, construction and maintenance of the project which includes Moulton Niguel Water District, South Coast Water District, City of San Clemente, and City of San Juan Capistrano.  Customers within these service areas will benefit from the added supply reliability the reservoir provides.  They will tap into the reservoir when the imported water supply is interrupted, like the 1999 breakage in the Allen-McCulloch Pipeline or an unplanned shut down of the Diemer Filtration plant in Yorba Linda.  


SMWD’s design and environmental consultants developed detailed plans to provide an adequate construction work area while maximizing avoidance of impacts to the most environmentally sensitive areas of the site. (AECOM)

One of the hallmarks of the Upper Chiquita project has been the robust commitment made to the environment by SMWD and its partners.   Dating back to the 1980s, complicated negotiations and planning were required with Rancho Mission Viejo (owner of the site), the Transportation Corridor Agency (owner of an environmental conservation easement over the property), the California Department of Fish & Game, and the U.S. Fish & Wildlife Service.  These efforts resulted in inclusion of the project in the South Orange County Natural Community Conservation Plan which identified conservation practices during the construction and operation of the reservoir in order to mitigate environmental impacts.   Additional mitigation activities were developed concurrently with the final design, including details for re-vegetation of coastal sage scrub and native grasslands within the project area, and funding for development and maintenance of an additional offsite nature reserve as additional mitigation.



Upper Chiquita Reservoir is a Zoned Earth Fill Dam constructed nearly entirely from materials located on site. (GeoPentech)

To develop the project site, extensive geotechnical and geologic studies were conducted over the course of 5 years leading up to construction.  The resulting Upper Chiquita Reservoir is a Zoned, Earth-Fill Dam, constructed almost entirely of materials found on site.  Because of the comparatively small site size for a project of this magnitude, and the desire to minimize environmental constraints, the design included development of an extensive construction staging plan which helped establish how, when and in what order particular soil materials found on site would need to be excavated, stockpiled, and placed in the dam to make the construction as efficient as possible.    Collaboration with the State of California Department of Water Resources, Division of Safety of Dams (DSOD) was essential during planning and design to help work through these complicated geotechnical and constructability issues, which then positioned the contractor to smoothly meet DSOD’s foundation preparation, soil placement, testing and inspection requirements during construction.   DSOD approved the dam for filling in July 2011.


3-dimensional time-based modeling was used to support water quality analyses. A chloramination boost facility and UV disinfection was developed to address disinfectant degradation within the reservoir. The disinfection facility is part of the 52cfs capacity booster pump station. (AECOM)

The reservoir employs a reinforced polypropylene liner and Hypalon floating cover to protect contents from contamination. This view shows the liner and cover under construction (Layfield/Sukut)


Storage of nearly 250 million gallons of treated water warranted a careful consideration of hydraulics and water quality maintenance strategies.   A series of potential operational strategies were developed for consideration.  Time-based 3-dimensional modeling was used to support water quality analyses, both to establish water age within the reservoir (a predictor of disinfectant degradation) and to help positioning of the inlet and outlet piping to maximize circulation and avoid areas of stagnation.  Resulting from the effort, a chloramination boost facility and UV disinfection system was developed to address disinfectant degradation within the reservoir, with an eye toward minimizing disinfection by-product formation.

The disinfection systems are included within a 52 cubic feet per second (cfs) capacity booster pump station that is included in the project.  The pump station includes four 350 horsepower vertical turbine pump, and a 1500 kW emergency generator.  The pump station allows water at lower elevations within the reservoir to be pumped back into the South County Pipeline (SCPL) for delivery to SMWD and partner agencies.  Water within the uppermost 20 feet of the reservoir flows back to South County Pipeline as gravity flow, as the site was selected to coincide with the SCPL’s typical hydraulic grade line of 860 feet at this location.

“After five years of planning, design and construction, the District is excited to see that the reservoir is nearly complete, " said Dan Ferons, Chief Engineer for Santa Margarita Water District.  "When operational, this new facility will provide a huge benefit to the community by improving local water supply reliability.”   

For more information about the Upper Chiquita Reservoir Project, visit the Santa Margarita Water District website.

Upper Chiquita Reservoir Facts and Figures:
  • Design: Lined and covered reservoir
  • Storage Capacity: 244 million gallons (750 acre feet)
  • Reservoir Height: 165 feet
  • Permanent Footprint: 26 acres
  • Construction cost: $36.1 million
  • Completion: November 2011
Project Lead:
  • Santa Margarita Water District
Partner Agencies:
  • Moulton Niguel Water District
  • City of San Clemente
  • City of San Juan Capistrano
  • South Coast Water District
  • AECOM Technical Services, Inc., Design and Construction Management
  • GeoPentech, Geotechnical Engineering
  • Dudek, Environmental Permitting
  • Moraes/Pham and Associates, Electrical & Instrumentation Engineering
  • Huitt Zollars, Surveying and Preliminary Site Planning
  • Genterra, Preliminary Geotechnical Engineering
  • Flow Science, Hydraulic Modeling
  • Trussell Technologies, Water Quality
  • Miedema & Associates, Project Management
  • Sukut Construction, Inc.