Groundwater reserves are maintained by a recharge system, which replaces water that is pumped from wells. OCWD’s facilities have a recharge capacity of approximately 300,000 acre-feet per year. About two million people depend on this source for more than three-quarters of their water. Groundwater producers (city water departments and other local agencies) pump water from the groundwater basin and deliver it by pipeline to consumers.

Along a six-mile section of the Santa Ana River that belongs to OCWD, a system of diversion structures and recharge basins captures most of the water that would otherwise flow into the Pacific Ocean. The district has 1500 acres of land for use in its recharge program.

The current average annual base flow of the Santa Ana River is approximately 140,000 acre-feet. Storm flows add an average of 60,000 acre-feet per year, ranging from 10,000 to 500,000 acre-feet. The base flow may increase by 100,000 acre-feet over the next 20 years due to urban development in upstream areas. More buildings and paved areas mean greater quantities of storm runoff, and growth in population and industry causes a proportional increase in wastewater discharges into the river channel.

Water that flows down the Santa Ana River, together with supplies imported from the Colorado River and from the State Water Project, is channeled into nine recharge basins. These lakes and ponds, with depths ranging from 50 to 150 feet, were formed in years past by sand and gravel mining operations.

The soil along this stretch of the Santa Ana River is coarse-grained and sandy. Therefore, water readily seeps into natural storage spaces below ground surface, a process called percolation. A pattern of interlaced levees built of sand helps to slow the river’s flow so that more of the water can percolate through the bottom of the river channel.

Groundwater is stored in porous underground layers of sand and gravel called aquifers. Certain aquifers reach the surface in this area of Orange County (the forebay) and can be easily recharged, while in other areas a layer of dense clay overlies the aquifer and prevents efficient percolation.

The district’s deep recharge basins, such as Anaheim Lake, Warner Basin and Kraemer Basin, gradually accumulate a thin layer of fine sediments and biological material that slows and can even stop percolation. Although the percolation rate in a newly cleaned deep basin can reach 10 feet per day, the rate can drop to nearly zero after six to eight months.

Each of these deep basins is periodically emptied by means of submersible pumps, and the clogging layer is removed by scrapers or by a sand-washing device. Clogging affects only the upper two to three inches of soil. When one basin is being cleaned, the supply to other basins is maintained by means of bypass pipelines. A twice-yearly cleaning cycle, which has replaced a single annual cleaning, increases percolation by as much as 40 percent.

Water diverted to Burris Pit during heavy rains is pumped through 4.5 miles of pipeline to the district’s Santiago Creek recharge facility for storage and percolation. Up to 90,000 gallons per minute can be transferred via this pumping system. The Santiago Creek recharge basin, the district’s newest, has a capacity of 13,000 acre-feet.

Prevention plays an important role in solving the problem of clogging. A flocculation system at the Imperial headgates is being considered which could coagulate suspended solid particles so that they will settle out of the water as it passes through a series of desilting ponds. Three of these ponds between Imperial Highway and Lakeview Avenue help reduce the sediment load in water that is diverted to the recharge basins. This slows the formation of a clogging layer and thereby helps to maintain efficient percolation.

OCWD’s hydrogeologists are carrying out extensive explorations in order to determine the structures and mechanisms that affect the district’s natural subterranean reservoir. Special wells drilled to depths as great as 2,000 feet are equipped with monitoring devices that reveal the pathways of groundwater migration, the dynamics of the recharge process, and potential new sources of water. By analyzing the data obtained from these wells, the district is able to modify its recharge operations and to expand the usage of the groundwater basin to meet anticipated demand.

More than 100 species of wildlife are found on district lands, and OCWD cooperates with environmental organizations to preserve the natural habitat of these animals.

Recreational opportunities include river trails for horseback riding, bicycling and jogging; and several of the recharge basins are stocked for sport fishing.

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