COMMENTARY\River management important for water quality.

Byline: Lynne Plambeck Special to the Daily News

Dry rivers in the west all have their own rugged and individual beauty, just made for horses and cowboy hats.

Our Santa Clara River is no exception, although it is not as dry as many others. Its banks are often lined with shimmering cottonwoods and dense riparian vegetation filled with the chatter of birds.

Many areas have enough year-round surface water to support the last populations of an endangered fish, the unarmored three-spined stickleback that appears as tiny flashes of silver light in the shallow water. In other areas, the water sinks beneath the sandy, windswept surface only to reappear as an unexpected raging torrent during infrequent winter storms.

But beneath their desolate countenance, dry rivers usually store large quantities of ground water in their alluvial soils. These soils often stretch as wide as 100 feet on either side of the surface banks, and form a bowl or reservoir for the underground water. This water is pumped by local water companies, providing a reliable source of clean water to the community.

Just how reliable is this limited resource? Like all renewable resources, the water we pump from the Santa Clara River is limited by the degree of replenishment, or recharge it receives from annual rainfall. Just as you cannot cut more trees than you can grow in a certain number of years or the forest will disappear, you cannot pump more water than the basin absorbs, or you will not have a sustainable water source.

Like all our natural resources, our ground water is a gift that we must treat with care so as not to lose it. That is why watershed conservation and ground-water management have become the issues of the '90s.

Watershed conservation is a simple concept. It means protecting recharge areas so that rainfall can continue to replenish the aquifer (the scientific name for the underground soils that hold the water). It also means reducing or eliminating sources of pollution in the recharge areas so the ground water in the aquifer stays clean.

The Santa Clara River has two sources of recharge, both originating from rainfall. One is surface flow on the river itself that sinks into the aquifer. This is the largest source of recharge. The other is the hillsides and flood plain around the river and its tributaries.

As we build and pave our valley, we are reducing the recharge to our ground water. When we box-channel an area of the river or a tributary, we eliminate recharge in that area. That is why it is imperative for the continued reliability of our water supply that we do not surround the river with concrete.

Narrowing the stream bed, erecting berms, and constructing buildings in the flood plain also severely reduce recharge because the surface flood flows pass through these areas at a much faster rate, allowing less time for the water to sink into the ground. It just makes good sense not to build in the flood plains, both from a water-supply perspective and for public safety.

Of course we must not only be concerned with how much water is returned to the aquifer, we also must think about how much we are taking out. When a community pumps more water out of the ground than can be recharged, it is called over-drafting. There are several very bad consequences from over-drafting an aquifer. First and foremost, the aquifer begins to collapse and often becomes incapable of being recharged. Thus, the ground-water supply is further reduced.

This collapse, called subsidence, can also have other harmful effects such as causing structural damage to buildings. In areas of severe overdraft, such as Phoenix, Ariz., the ground has dropped as much as nine feet. Some areas of the Antelope Valley have also suffered subsidence of several feet. Because of the damage to buildings, litigation has been launched that held water companies responsible for the damage they caused to structures from over-pumping.

A third undesirable effect of over-drafting is the loss of water quality. As the ground water is pumped lower and lower, the natural salts and minerals in the water become more concentrated. The flushing action normally performed by surface water becomes less efficient because it does not reach the lower levels. Ultimately, the water becomes undrinkable.

According to hydrologists, the Santa Clara River has an average annual yield of 25,000 to 32,000 acre-feet, depending on which study you read. An average family uses about half an acre-foot per year, so this is enough water for 50,000 to 64,000 homes. It will easily supply our current population, except in times of drought. But Los Angeles County has already approved over 52,000 additional homes. Where will this water come from?

Some of it will come from the Castaic Lake Water Agency. Its job is to bring State Water Project supplies down the California Aqueduct from the Sacramento River Delta and sell it to the four water retailers who then supply individual homes. But this is also a limited supply, subject to the amount of snowfall in the Sierra Nevada. Also, enough fresh water must continue into the Delta to ensure the health of fish and farms.

This is where ground-water management becomes important. If we use state water in the winter and spring, when there are excess flood flows and melting snow, we will allow our ground water to naturally recharge. Then in the summer months, when the Delta needs all the surface flow it can get, we use our replenished and delicious ground water. Sounds easy and logical, right? Then why don't we have ground-water management in this valley?

The main reason is development. Everyone wants water for his or her project, so they don't like to discuss the realities of supply. We cannot build very much more without severely affecting supply. Like farmers in the Central Valley who cannot grow without sufficient water, we cannot continue to build huge housing developments without water to supply them. Soon, current residents will begin to suffer cutbacks tdro supply this new development. There is a fairness issue here that needs to be aired openly in the community.

I urge all the companies and agencies that supply water to the Santa Clarita Valley to begin public discussions on water supply and ground water management.