Storms Challenged Our Water Management Skills

Over the past two months, a spectacular sight has drawn people to the banks of the Santa Ana River and Santiago Creek: a torrent of debris-filled muddy water surging down the normally dry stream bed toward the Pacific Ocean. During six years of drought, they had seen nothing to compare with the sight.

Upstream in Riverside County, behind Prado Dam, another rare scene met the eyes of observers: 25 billion gallons of water, inundating 4,000 acres to depths reaching 60 feet. Only three times previously had the dam, built in 1941, held back so much water--in 1969, 1978 and 1980.

This accumulation of water behind the dam was the reason for the heavy stream flow that greeted spectators along the river bank. With the region’s watershed saturated and the threat of widespread flooding imminent, the Army Corps of Engineers began releasing water to relieve the immediate crisis and to ensure adequate management of any later storms.

That volume overwhelmed the Orange County Water District’s recharge facilities. OCWD manages the ground water basin, a natural underground reservoir from which most of the urbanized county area pumps 75% of its domestic water supply. The district is able to capture the normal flow of the river during most of the year, holding it in deep ponds until it seeps into subsurface layers of sand and gravel. But heavy storms like those that have greeted the new year cannot be contained.

Over the past five years, OCWD has spent $40 million to construct new facilities on the Santa Ana River and Santiago Creek to capture storm flows. New recharge basins, pipelines, pumps and an inflatable rubber dam, together with extensive improvements to existing facilities, netted the district about $16.8 million worth of water from the December and January storms. February storms are yet to be fully calculated, but will also be worth millions of dollars. The quantity was estimated at 100,000 acre-feet, which will go a long way toward replenishing the ground water supply. (An acre foot is 326,000 gallons, enough to supply an average Southern California family for a year or more.)

The district normally transfers part of the captured Santa Ana River flow into its newest recharge facility on Santiago Creek, pumping the water through a 4.5-mile pipeline. But the pumps were turned off during the January rains when large volumes of storm runoff were released from Villa Park Dam. For the first time since its completion in the spring of 1990, Santiago Basin was full. About 4.5 billion gallons of high-quality storm water filled this reservoir before it overflowed into the creek channel.

The district’s inflatable rubber dam, constructed just last fall, performed well during the big storms. The 320-foot-long, 7-foot diameter cylinder, which spans the river at Imperial Highway, can be inflated or deflated in about half an hour. The dam is used for diverting water into the district’s recharge system. The dam must be deflated, however, when high-volume flow creates a potentially unsafe condition.

A second rubber dam will be built farther downstream, and OCWD is negotiating with the Corps of Engineers for greater conservation behind Prado Dam. These measures will help the district capture more, although not nearly all, runoff during major storms.

The 100,000 acre-foot bonanza from the December and January storms gave a sorely needed boost to the ground water basin, despite heavy losses to the ocean. Still, we need a series of wet winters in order to reach normal storage levels. OCWD regularly maintains 200,000 acre-feet of vacant storage for holding storm water, but during six dry years, that unfilled capacity grew to about 400,000 acre feet. By way of comparison, after the drought of 1976-77--the driest two-year period on record--basin overdraft reached 450,000 acre-feet.

OCWD’s basin management expertise was soundly tested during this recent extended drought, and our ability to capture storm flows was challenged by the heavy rains that finally arrived.

Nonetheless, we are proud of the ground water basin’s condition after six difficult years. This vast underground reservoir of fresh water is a priceless resource. In fact, for the nearly two million people living in northern and central Orange County, it is virtually the only insurance against drought and shortage.