Company:
Santa Margarita Water District
Status:
Awarded
Awarded:
Water Project of the Year
Additional Files
Additional Information

Gobernadora Multipurpose Basin

Project Location:

Coto de Caza

Project Description:

Orange County is highly dependent on imported water resources. Rancho Mission Viejo (RMV), in partnership with Santa Margarita Water District (SMWD) and Orange County Public Works (OCPW), have taken an innovative approach to securing local water by recycling a wasted water source—urban nuisance runoff. Through the construction of a truly unique multi-functioning 26-acre basin system, urban nuisance runoff is captured while providing additional key benefits including regional flood protection and improvement of water quality.

FACILITY FEATURES
The multipurpose Gobernadora Basin facility is divided into two basins: a 10.9-acre Upper Basin and a 15.3-acre Lower Basin. The combined maximum flood control storage is approximately 120 acre-feet. The lower basin is further divided into two independent sub-basins connected to the upper basin via two 95-foot-long spillways. The upper basin is subdivided further into four interconnected water quality cells that include: 1) a side weir alongside its east embankment for peak flow diversion and bypass of sediment to the natural alluvial channel, and 2) a low-water diversion structure for the collection of nuisance flows generated from the upper watershed during dry weather conditions.

Most of the treated dry-weather flow is captured by SMWD in the Gobernadora Basin and reclaimed back into an offsite non-potable water reservoir via a pump in the upper basin connected to an existing SMWD force main. 0.3 cfs of flows are purposely bypassed downstream to ensure a continued irrigation source for the Gobernadora Ecological Restoration Area. In addition, two groundwater wells are located within the perimeter of the upper basin to capture part of the recharged groundwater that is conveyed to the basin pump station. The flood control function of the Gobernadora Basin is provided during wet weather conditions by storing a portion of the storm hydrograph inside the upper and lower basins. Gravity outlets and emergency spillways are located along the south embankment of each lower cell to attenuate the downstream outflow into the Gobernadora Creek with the ability to facilitate a 1,500 year storm event.

PROJECT BENEFITS
The benefits produced by the basin are made possible due to advanced engineering design including dynamic controls that adjust operation according to flow conditions, inflatable rubber diversion dams, wetland water quality treatment, extensive flood detention, groundwater pumping wells, and a complex pumping facility to transfer treated flows to a non-potable water system and an important regional ecological area for habitat and environmental preservation. As an uncommon joint partnership project between public sector agencies and a private land developer, there are many beneficiaries from this project including over 155,000 residents.

The 26-acre Gobernadora Multipurpose basin provides several beneficial functions including:

• Water Recycling
• Groundwater Recharge
• Groundwater Recovery
• Flood Mitigation
• Urban Stormwater Treatment
• Stream Stabilization and Habitat Restoration
• Wetlands and Open Water Habitat
• Regional Trail Connection

NEW WATER SOURCE DEVELOPED
Perhaps the most important purpose of this project is the introduction of an untapped water resource to the region and reduces dependence on imported water supplies that are becoming increasingly scarce, particularly during the state of California’s worst drought on record. This project represents sustainable water resource management and creative problem solving for significant water supply challenges. Between 350 acre-feet and 800 acre-feet are projected to be captured on an annual basis and reused as non-potable water for Orange County. This added supply of non-potable water reduces the application of potable water supplies for non-drinking water needs such as irrigation and recreational turf. It also protects the integrity of the local groundwater aquifer by allowing a portion of the flows to recharge into the aquifer and prevents a long-term reduction in the aquifer’s storage capacity.

SUSTAINABILITY
Additional sustainability functions of this system include improvement of the Gobernadora Creek watershed’s water quality, important flood protection that protects critical downstream ecological habitat from streambank erosion and excess sediment deposition, and the introduction of wetlands habitat beneficial to a wide variety of native wildlife species.

Project Justification:

DESIGN BASED ON RISK MANAGEMENT, PERFORMANCE BASED DESIGN, AND PROJECT COST ECONOMICS
The project had major geotechnical engineering challenges associated with earthquake loading.  These challenges were addressed by performing failure risk analyses, and evaluating earthquake induced deformations and associated future potential damage repair costs.  Our systematic approach is detailed below:

• “Failure” or “Dam Break” analyses were performed to evaluate the potential for damage to downstream infrastructure and life safety consequences under full reservoir conditions. 

• Upon confirmation of minimal damage potential for downstream infrastructure and life safety, parametric earthquake induced deformation analyses were then performed utilizing “CBC design level” and “Deterministic” seismic input values.  Several empirical and Newmark models were used to determine deformations.

• Based on the deformation magnitudes associated with the critical seismic input level, a corresponding “cost of repair” (COR) was developed.

• Geotechnical analyses and remediation design were also performed for the full liquefaction mitigation case and an associated cost was developed.

• The COR for the deformation-based repair scenario and the full liquefaction mitigation scenario were then analyzed economically and compared with the overall cost of construction. 

• Based on economic cost analyses, it was decided by the stake holders to set aside a reserve equal to the COR based on the deformation-based design.  In addition, site- specific inspection criteria were developed to evaluate the need for repair after major earthquakes.

• The final deformation based “repair” design resulted in excess of 10 million dollars in costs savings relative to a full liquefaction mitigation design.

Special Circumstances:

SPECIAL RELATIONSHIPS GENERATED:

PUBLIC-PRIVATE PARTNERSHIP DEVELOPED: Unique to most utilities and infrastructure projects, this project represents a successful collaboration involving a private developer (Rancho Mission Viejo), a public agency (Orange County Public Works) and a water district (Santa Margarita Water District) that collaborated to address multiple important water resource needs.

GENERATED FUNDING / ECONOMIC BENEFITS: One of the key lessons learned that can be applied to other developments seeking to implement a program similar to this is the benefit generated from creating public-private partnerships to expand funding opportunities through grants. 32% of the capital cost of this project was funded through public grants given its wide-reaching benefits.

COLLABORATION BETWEEN MULTIPLE AGENCIES ALLOWED FOR MULTIPLE BENEFITS FROM A SINGLE INFRASTRUCTURE SYSTEM: Multi-purpose systems provide a unique opportunity to reduce capital costs by sharing infrastructure space and similar function to generate a net benefit, rather than cost.

OBSTACLES OVERCOME:

PHYSICAL SITE CONSTRAINTS:
• The footprint of the site was constrained by coastal scrub sage habitat on one side and Gobernadora Creek on the other three sides
• Geotechnical constraints included high groundwater, liquefaction, and poor soil conditions
• The facility was constructed within a 100-year floodplain
• Gobernadora Creek is an active alluvial stream with variable streambed elevation and sediment delivery
• Potential for lateral streambank erosion along Gobernadora Creek

REGULATORY CONSTRAINTS:
• Streambed wildlife habitat
• California Division of Dam Safety
• US Army Corps of Engineers
• Santa Ana Regional Water Quality Control Board
• California Department of Fish and Wildlife
• Water rights

OTHER ACCOLADES RECEIVED:
• Urban Land Institute (ULI) Orange County Best of the Best 2015 Special Recognition for Sustainability Contributions
• Orange County Business Council (OCBC) 2015 Green and Sustainable Development Award
• California Legislature Assembly Certificate of Recognition

Project Attachments:

Not Applicable

Award Citation::

Rancho Mission Viejo, Santa Margarita Water District, and Orange County Public Works collaborated to develop a new water supply source by recycling urban nuisance runoff. Through the construction of a truly unique multi-functioning 26-acre basin system, urban runoff is captured and recycled while providing regional flood protection and water quality improvement benefiting over 155,000 residents.

Suggested Award Summary:

Orange County is highly dependent on imported water resources, and Rancho Mission Viejo (RMV), in partnership with Santa Margarita Water District (SMWD) and Orange County Public Works (OCPW) have taken an innovative approach to securing local water by recycling a wasted water source – urban nuisance runoff. Through the construction of a truly unique multi-functioning 26-acre basin system, urban runoff is captured while providing additional key benefits including regional flood protection and improvement of water quality.

PROJECT BENEFITS
The benefits produced by the basin are made possible due to advanced engineering design including dynamic controls that adjust operation according to flow conditions, inflatable rubber diversion dams, wetland water quality treatment, extensive flood detention, groundwater pumping wells, and a complex pumping facility to transfer treated flows to a non-potable water system and an important regional ecological area for habitat and environmental preservation. As an uncommon joint partnership project between public sector agencies and a private land developer, there are many beneficiaries from this project including over 155,000 residents.

The 26-acre Gobernadora Multipurpose basin provides several beneficial functions including:

• Water Recycling
• Groundwater Recharge
• Groundwater Recovery
• Flood Mitigation
• Urban Stormwater Treatment
• Stream Stabilization and Habitat Restoration
• Wetlands and Open Water Habitat
• Regional Trail Connection

FACILITY MAIN FEATURES
The multipurpose Gobernadora Basin facility is divided into two basins: a 10.9-acre Upper Basin and a 15.3-acre Lower Basin. The combined maximum flood control storage is approximately 120 acre-feet. The lower basin is further divided into two independent sub-basins connected to the upper basin via two 95-foot-long spillways. The upper basin is subdivided further into four interconnected water quality cells that include: 1) a side weir alongside its east embankment for peak flow diversion and bypass of sediment to the natural alluvial channel, and 2) a low-water diversion structure for the collection of nuisance flows generated from the upper watershed during dry weather conditions.

CEC

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