Groundwater Management
A natural reservoir in times of sparse rainfall, this underground resource provides nearly 70 percent of the water consumed by more than 2.3 million residents of Orange County. As the water in this groundwater basin is withdrawn to satisfy Orange County’s water needs, OCWD uses water from the Santa Ana River comprised of storm water runoff, recycled water and other natural sources to replenish this valuable groundwater basin.

A significant portion of the Santa Ana River flow is directed through OCWD’s constructed wetlands above Prado Dam in Riverside County to naturally improve water quality. The various river flows support fish and bird habitats in the Prado basin as they travel to Orange County’s groundwater basin.
 
Endangered Species Conservation
Prado Basin is home to several rare and endangered birds and waterfowl species. As part of a conservation agreement with the Army Corps of Engineers (the Corps) and the U.S. Fish and Wildlife Service (USFWS), OCWD has created more than 800 acres of habitat for the endangered least Bell’s vireo and Southwestern Willow Flycatcher, and funded more than $3 million in mitigation and monitoring measures for the vireo program.

OCWD’s vireo mitigation program has been one of California’s great environmental success stories. The program includes restoration of vireo habitat and the trapping of cowbirds that invade the vireo nests. When the three agencies first began negotiating in 1986, there were only 19 pairs of vireo song birds in the Prado Basin. Today, the number of male territories is approaching 1,000 and continues to grow as more fledglings are produced and reach maturity. 

OCWD contributed $1 million to the USFWS as seed money to create the Santa Ana Watershed Association (SAWA) to lead the removal of a non-native plant called Arundo donax that has overrun the area. Arundo is a major threat to the ecosystem of the entire Santa Ana River watershed. Its removal effectively restores and enhances the environment.  Since its inception, SAWA has raised more than $30 million and removed 3,500 acres of Arundo.

Restoring Water Quality
The Santa Ana River flow (during non-storm seasons) consists primarily of highly treated wastewater from upstream communities, resulting in water with high nitrate levels. Part of the Santa Ana River flow that is captured behind Prado Dam is routed through a specially constructed wetland area. By putting the river water through this network of ponds behind Prado Dam, OCWD has created a natural, cost-effective process for reducing nitrate levels and purifying the water for future percolation into Orange County’s groundwater basin.

Within the 2,150 acres of land OCWD owns above Prado Dam lies 465 acres of constructed wetlands, including a system of 50 shallow ponds. Originally, the wetland area was used for farming barley. In the mid-1970s, the fields were turned into pounds used for duck hunting.

In the early 1990s, research was conducted to determine what water quality benefits, if any, would occur if part of the Santa Ana River flow passed through the wetlands. Research conducted by scientists from Northwestern University and University of California Berkeley investigated the effectiveness of the wetlands naturally removing nitrate, the fate of the nitrogen removed, and the effects of various wetland manipulations upon nitrate removal rates. The results from the studies indicated that the wetlands are a very effective and economical means for nitrate removal currently removing nearly 360 tons per year from the Santa Ana River.

The wetlands are an extremely cost-effective treatment process. Nitrate removal at a conventional treatment plant would cost approximately $15 per pound, compared to about .50¢ per pound using the natural wetlands process. The wetlands project allows OCWD to improve water quality beyond regulatory requirements so that Orange County has the best source of water quality possible.  By taking this innovative approach to water quality issues, OCWD improves groundwater quality, enhances the environment and minimizes treatment costs. A permit from the Corps allows half of the flow of the Santa Ana River, about 80 cubic feet per second (cfs), to be diverted through the wetlands. In the late-1990s, OCWD reconstructed its wetlands to maximize the capability of captured river flows and to improve operational efficiency.

Storm Water Capture
OCWD’s Prado wetlands are the largest constructed wetlands on the west coast of the United States. Prado Dam is the primary flood control facility along the Santa Ana River. When the Dam was built, the Corps, which owns and manages the Dam, considered conservation an incidental function of the dam. Initially, the water conservation level behind the Dam was limited to a storage capacity of 8,000 acre-feet.

Later, an agreement with OCWD, the Corps and USFWS allowed for increased conservation from March 1 to September 30 each year to store up to 26,000 acre-feet. In 2004, a temporary agreement was reached between OCWD and the Corps to store more water from November to March each year. The additional water captured behind the Dam is used to recharge the groundwater basin. The added storage capacity allows OCWD to increase its use of local water resources, saving water users millions of dollars in imported water purchases.

Natural Resources Project Research Posters:
1. Effects of Exotics on Native Fish (3.8MB PDF file)
2. Riparian Restoration in a Suburban Landscape  (4.0MB PDF file)
3. Riparian Restoration and Endangered Birds (5.1MB PDF file)
4. Wintering Bird Population Studies on the Santa Ana River (1.9MB PDF file)
5. Reptiles and Amphibians of the Santa Ana River (2.6MB PDF file)