US Army Corps of Engineers
Environmental Engineering Project of the Year
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Lower Santa Ana River Reach 9 Phase 2B Project

Project Location:

Orange County and Riverside County Boundary Along 91 Freeway near Green River Golf Course

Project Description:

Project History and Timeline:
The Lower Santa Ana River Reach 9 Phase 2B Project (“Project”) consists of flood protection and environmental restoration along 5,700 feet of the Santa Ana River surrounding the Green Giver Golf Course in Orange County near the Riverside County line. The Lower Santa Ana River flood protection is a feature of the Santa Ana River Mainstem (SARM) flood risk management project authorized for construction by the Water Resources Development Act of 1986, Public Law 99-662. Reach 9 downstream of the Prado Dam is designated to provide environmental open space and wildlife access, along with improvements for flood risk management.

Prior to the Perennial Stream Restoration project, the south bank grouted riprap protection (close to Highway 91) was designed by the in-house staff of the Los Angeles District and construction was awarded to Harper Contracting, Inc., in 2009. This provided an opportunity for environmental restoration due to the temporary diversion of the river. An AE Services contract was awarded to WRC Consulting Services, Inc., in early 2010 for the design of environmental habitat restoration within the project boundaries bound by bank protection/Highway 91 and the golf course. This restoration project serves as environmental mitigation for the temporary and permanent loss of riparian and upland habitat due to construction within Reach 9 and other areas of SARM features. It provides stream environments and habitat appropriate to support the threatened Santa Ana sucker fish as well as riparian woodland habitat intended to support the endangered Least Bell’s vireo and other special-status birds. The Santa Ana sucker is a fish that was common in Santa Ana River streams prior to the 1970s but is now rarely found.

Project Strategies and Details:

Flood Risk Management. The flood protection measures include the south bank grouted stone bank protection to protect the highway and roadway infrastructures and plain riprap protection measures along the created meandering banks where soils are vulnerable to erosion by the river flood flow or lateral storm drain outflow (more than 15 laterals).  The flood flow is a potential 30,000-cfs release from Prado Dam. The bank-full discharge is approximately 6,000 cfs, using the golf course as overflow when the flood exceeds this level. 

Environmental Restoration. Flows along the Perennial Stream Project average a daily flow of 125 cfs during the non-flood season. To create a perennial stream habitat suitable for the Santa Ana Sucker fish, the following features were included:
• A stream bed consisting of various mixtures of sands, gravels, cobbles and boulders for substrate.
• The channel was designed for a non-flood low-flow inundation depth varying from 12 to 18 inches to support juvenile and young fish and from 18 to 24 inches for adult fish.
• The stream width varies with pools containing slower flows and riffles with higher velocities.
• Riparian trees and large boulders create shading and refuge areas along the stream edge and shallow inundation areas. To enhance the perennial stream habitat, restoration of riparian woodland habitat native to the Santa Ana River corridor was accomplished by the following project features:
• Detailed topographic grading of the banks with varying slopes and terraces for riparian and upland plantings. Soil was backfilled on top of the grouted stone bank protection to create opportunities for habitat establishment.
• Emergent plants were planted along the water edges along with Black Willow cuttings to help naturally stabilize the river banks.
• Arroyo Willow cuttings were planted on the banks and overbank areas where surface runoff and groundwater moisture can benefit riparian plants.

• Understory native plants were planted within the Black Willow and Arroyo Willow communities to help stabilize the ground. Other features of the project included:
• Riprap side drain channels that protect existing drainage systems for conveying stormwater runoff from the hills south of the project site under the 91 freeway and into the Santa Ana River.
• Replacement of the access driveway and vehicle bridge leading to the Green River Golf Club.
• New entry sign and landscaping for the Green River Golf Club.
• Restoration of golf course turf in an area that was needed for construction of the project diversion channel.
• A California native wildflower buffer zone between the golf course and the project restoration area.
• A bank protection maintenance road running along the top of the grouted stone bank protection.
• Relocation and improvements to the Santa Ana River Trail bikeway that runs through the project area.


Plant monitoring started in 2012 one year after the first phase of construction and monitoring of the stream began in 2013 after major construction completion. The monitoring results are encouraging. Along with the installed vegetation, an impressive number of other native riparian plant species have naturally colonized into the project area. The density and diversity of the establishing vegetation suggests a high potential for this project to meet the following ultimate restoration goals:
• 9.74 acres of Perennial Stream Habitats Including stream bed, Black Willow and emergent plants
• 5.8 acres of Arroyo Willow Dominant Riparian Woodland
• 2.7 acres of Mule Fat Scrub
• 7.36 acres of transitional scrub and perennial herbaceous plants

The channel banks have experienced minimal storm flows since they were constructed and show signs of successfully withstanding erosion from flows up to a 450-cfs release from Prado Dam. Areas with dense vegetation showed signs of very minor erosion, while the recently planted areas sustained the expected minimal damage. The banks edges show signs of naturally stabilizing themselves as the vegetation continues to mature.
While the grouted stone bank protection provides flood protection for flows up to a 30,000-cfs release from Prado Dam, the Perennial Stream restoration portion is expected to change over time. Erosion and deposition are expected to occur and will likely sustain a natural stream habitat favorable to the Santa Ana Sucker fish. Vegetated sand and gravel bars have already started to establish in the wider areas of the low flow channel. The combination of armored flood control structures and a flexible restoration area will allow the Lower Santa Ana River Reach 9 Phase 2B Project area to adapt to changing conditions while meeting both flood protection and restoration goals.
Monitoring of the restoration area will continue for a 5-year period following construction completion. Surveys for wildlife habitat and water quality has been conducted on a quarterly basis since 2014 and will continue through 2019. Fish, amphibians, reptiles, birds and mammal species are already utilizing the developing stream and riparian woodland habitats in the project area. Over 60 bird species have been spotted, including special-status species like the California gnatcatcher and Cooper’s hawk. The diversity and abundance of wildlife species is only expected to increase as the project matures.


The Lower Santa Ana River Reach 9 Phase 2B Project has a high potential for replication among other natural stream restoration projects. The naturalistic grading of the channel side slopes provides greater habitat diversity by creating planting terraces at varying elevations. For example, plant species like Black Willow can be placed on terraces close to the low flow invert of the river, allowing for periodic inundation with water. Other riparian plant species like Arroyo Willow and Western Sycamore trees can be placed on terraces set at slightly higher elevations where less-frequent inundation areas are beneficial for their establishment.

Creation of the perennial stream habitat itself serves as an example of how habitat restoration can be accomplished in channels that have been highly modified from their natural condition. Modifications to traditional pool and riffle design were necessitated by constraints from protecting structures and land uses. The shallow-flow areas were created to widen the river bottom and simulate “pool” conditions without deepening the riverbed. The narrow section reaches were designed to produce “riffle” conditions without steepening the river bottom. Combining the low-flow meander pattern and varying channel geometry allows the river to restore its ecological diversity. The channel geometry ensures that diversified flow velocities are present in support of Santa Ana sucker fish habitats.

Project Justification:

Many stream restoration projects have been planned, designed, constructed and monitored in Southern California since 2000. The Santa Ana River stream restoration projects constructed along the Green River Golf Course in Orange County, however, is unique in terms of its features, technical challenges, and project coordination and permitting efficiency. The project has been nominated for an engineering award, as it involves comprehensive engineering planning, analysis, design and construction to provide backbone support beneficial for successful habitat establishment as well as needed protection for critical infrastructures.
This project features the creation of Santa Ana Sucker habitat and support for the riparian community within the main channel of the Santa Ana River.  The project’s features and difficulties include:
1.  The creation of a meandering stream within a limited area bound by Highway 91 and the golf course.  The original ditch is small, straight and concrete-lined; a geomorphologic investigation was performed and a meandering low flow channel with sinuosity similar to the historical channel (which extends to Highway 91) was created within the corridor where the old concrete ditch was present.  It is noteworthy that the narrow, confined urban ditch was replaced by an open-space environmental corridor.
2.  The most significant challenge lies in creating a sand and gravel bed with pool and riffle zones within the Santa Ana River downstream of Prado Dam, where the river is flat and sandy.  The perennial stream was built with varying widths and channel gradients to accommodate pool and riffle creation. “Double Deflectors” were built to accelerate the flow velocities while providing shelters for adult fish swimming through the turbulent flows.  A sophisticated “Rock Placement Plan” was provided during the design phase to guide construction.
3.  Equally important is providing the proper velocity and depth parameters for habitat establishment. The stream was built with dynamic changes in the cross sections to provide deeper and shallower inverts for adult and juvenile fish as well as to provide various slopes and depths for riparian plant diversity.  The design parameters were confirmed with a two-dimensional combined river and floodplain model.
4.  A typical issue of in-stream restoration is the conflicting criteria needed to maintain channel stability and flood control reliability while allowing for the natural development of wild habitats. The stream has been subject to a certain degree of erosion typical of a natural stream, but integrity and overall stability (including the areas near the bank protection and storm drain outlets) are intact.
5.  Attention to detail can be found in many areas of the project, including the design of shading stones, riffles and pools, management of flow diversion, construction and planting phasing,  engineering structural protection (south bank and lateral drains) through the meandering stream banks.. 
6.  Although the project was confined to the area between the golf course and the highway bank protection, design creativity was applied to minimize the impacts of hard lined banks and urban landscaping, in addition to considering flood protection and stream habitat needs.
7.  Project execution was extremely efficient, considering that the perennial stream project was initiated in April 2010, the construction plan was approved in August 2010, and construction of the first phase was started in late 2010. Project monitoring construction of various phases was completed in 2013. Quarterly monitoring was undertaken, and habitat development has exceeded expectations. 
8.  The project’s success was due to both the technical and management excellence of the participating parties: U.S. Army Corps of Engineers Los Angeles District, WRC Consulting Services, Inc. (Design Prime Consultant), San Marino Environmental Associates (Santa Ana sucker biologist) and Harper Contracting, Inc.  (Construction Contractor).  The contributions of the Orange County Public Works Flood Division, Green River Golf Club, the US Fish and Wildlife Service, and other regulatory agencies in timely participation in meetings and reviews were a key factor in the project’s success.

Special Circumstances:

This project has bonded the team members including USACE staff, construction group, engineers, and biologists.  We continued to observe and monitor restoration progress. A true partnership has been developed based on our common passions for restoration in the Santa Ana River. It has been a joy for us to see the plant growth and water splashing over the boulders. We shared notes and discussed areas of improvements. The relationship and passion will definitely benefit the project as habitats are establishing along the way.

Project Attachments:


Award Citation::

A natural stream was successfully re-created along the Santa Ana River near the Green River Golf Course.  Featuring the Santa Ana sucker fish and a riparian community, the project involved major design and construction challenges in order to overcome unfavorable pre-project conditions. To date, pools, riffles, river bends, gravel bars and riparian plants have been established; one may no longer recognize that this habitat sanctuary was once a typical urban concrete drain.

Suggested Award Summary:

The Santa Ana River Perennial Stream Restoration Project is located within a one mile long flood control channel surrounding the Green River Golf Course. Unlike many other restoration projects, this project highlights an endangered species—the Santa Ana sucker fish—in addition to facilitating riparian planting. It is highly dependent on its civil engineering design to create a natural meandering stream with special fishery features within a confined space between the golf course and Highway 91.

The natural stream features include pools, riffles, river bends, gravel beds, sandbars, terraced inverts and banks, and shading trees and stones.  Through a rigorous planning process for goal -setting, scoping, and approach definition, a concept plan was derived by the USACE consultant team (WRC Consulting Services, Inc., and San Marino Environmental Associates, Inc.) and approved by stakeholders ( U.S. Army Corps of Engineers, Orange County Public Works, the Orange County Green River Golf Course, California State Parks, the California Department of Fish and Game, and other regulatory agencies).

Many talents have been drawn upon to overcome unfavorable pre-project conditions and the conflicting objectives such as structural stability for flood and erosion control versus preservation of the natural setting for the Santa Ana sucker fish and the riparian wetlands. 

A comprehensive design process was undertaken to detail survey control, grading, utility relocation, rock placement, erosion control, landscaping, irrigation, flow-diversion, construction phasing, and the other special features stated above. Detailed two-dimensional hydraulic modeling of the created channel under various flow conditions was performed to provide erosion-control guidelines and to confirm the flood control function and verify overall creek stability. 

This project component was added during the construction of the south bank protection. To reduce the reconstruction costs, design analysis, final design, and preparation of construction plans and specifications were expedited under close coordination with Harper Contracting, Inc. , Inc. USACE Construction Contractor.  Regulatory agencies participated in every phase of project, and comment resolution was timely incorporated for project approval.

The project has been successfully constructed following strategized phases for earthwork, rock placement, lateral drain placement, flow diversion, seeding and planting. A program for monitoring the performance of special design features and plant growth was developed and has been implemented following each phase of construction.


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