How To Limit Monumental Thirst For Water? -- Conservation Approaches Ballard Locks

With regional water demand expected to exceed supplies later this decade, the largest supplier - the Seattle Water Department - regularly raises concerns about how many times its customers are flushing their toilets, or whether they are watering their lawns too much.

But those uses are like a drip from a faucet compared with the biggest flush of all: the Hiram Chittenden Locks in Ballard, where the Army Corps of Engineers uses almost as much water daily as the entire Seattle water system and all its 1.4 million customers throughout the region.

This month, the city and the Corps will try to find ways to reduce the amount of fresh water going through the locks. If any water is saved, officials say, it might be used by Seattle for its water system.

Water to operate the locks comes from the Lake Washington system. Lake Washington and Lake Union are not direct sources of Seattle's water supply, but because Seattle's water comes from the same sources that feed the lakes, and because federal law requires the lakes be maintained at a set level, the locks and the city are drawing on the same water.

On a typical summer day, the locks will suck about 200 million gallons of water from the lakes to allow boats to go through and keep salt water out of the lakes.

On the same day, the Seattle Water Department will supply 240 million gallons to its customers, who get their water from 28 different water districts - including districts serving a majority of east King County's communities.

More than 70 percent of the Lake Washington system's water comes from the Cedar River near North Bend. But the river has other demands on it as well: Before it ever reaches the lake, water is drawn off into reservoirs and pipelines that are part of the Seattle Water Department's Cedar River water system, which supplies most of the Eastside and North King County.

Lake Washington's water level is based on the level of Lake Union in 1916, when the locks were opened. Under federal law, it can't vary more than a foot above or below that level. That means when the locks are drawing heavily on the lakes - most commonly during the summer - an extra flow may be needed from Cedar River reservoirs to maintain the proper level.

And water officials are concerned that as demands grow, the river may not be able to fill the lakes, fill the reservoirs - and still maintain enough flow for its resident fish.

Water-supply experts from the Corps and the city Water Department hope their study will identify a way to operate the locks that doesn't draw so much fresh water.

One suggestion that has come up in the past is to use treated waste water from Metro's sewer plant to fill the locks, but Frank Urabeck of the Corps said the public probably wouldn't stand for it.

Instead, the Corps and Seattle are looking at hooking up a computer system to the locks to monitor the water better, according to Urabeck, a planner for the Corps.

He said the Corps put in a monitoring system in 1975 but the salt water destroyed it.

The locks run on the same system as they did in 1916, when they were opened. There is no pumping involved in moving the water. Gravity moves the fresh water from Salmon Bay, just west of the Ballard Bridge, to fill the locks, and then the water is flushed out to Puget Sound.

Because Lake Washington and Lake Union are higher than Puget Sound (6 to 26 feet, depending on the tide), the water naturally moves from the higher - or the fresh-water - side to the lower side. But salt water is heavier than fresh water and can come into the lake under the fresh water when the locks are open. Preventing that from happening is a key job of the flushing action.

Allowing too much salt water into Salmon Bay, on the fresh-water side of the locks, could turn the lakes into a saltwater marsh. To prevent the salt water from going into Salmon Bay, the large lock has an underwater barrier on the fresh-water side that can be raised and lowered.

If that doesn't stop all the salt water, there's a 1,600-foot-long trench beneath Salmon Bay. The trench is 600 feet wide and 20 feet deep, and the salt water sinks into the trench; an outlet pipe allows it to drain back into Puget Sound.

Watching the outcome of the study of conservation at the locks will be Eastside water districts, which haven't been happy with the way they are treated by Seattle. These districts have a big stake in whatever comes out of these discussions.

"Half of of our communities depend on what Seattle does with its water," said Don Davidson, chairman of the East King County Regional Water Association. "We would like to have more input in what happens to the water.

"Managing the system is the key to the future. You can't just put another hole in the ground and expect to get water."

But Davidson said the big problem is that most people, including him, don't understand the function of the locks and its connection to the water supply.

That's what the study will try to find out, says Walt Anton, chief planner for the Seattle Water Department.

"Obviously it's worth doing," Anton said.

Officials conducting the study plan to send their recommendation to Corps headquarters in Washington, D.C., in March.

MOVING BOATS UP AND DOWN

The Hiram Chittenden Locks connecting Pget Sound to Lake Union and Lake Washington operate around the clock, using up to 7 million gallons of fresh water each time they open to raise boats to the lake level. There are two locks - one 825 feet long, one 150 feet. Both opened July 4, 1917.

HOW THE LOCKS WORK 1. A boat enters the lock from Puget Sound, which is 6 to 26 feet lower than the lakes, depending on the tide level. 2. After the lock's gates are closed (with some salt water inside), fresh water from Salmon Bay is released into the lock lifting the boat up to the lakes' level. 3. After the lock fills with fresh water, the gates are opened to Salmon Bay. The procedure is reversed for boats going into Puget Sound.

BLOCKING SALT WATER FROM THE LAKES The locks use a submerged, 20-foot-tall barrier to block salt water from entering the lake when the gates open. (Because salt water is heavier that fresh, it sinks to the bottom.) Salt water that gets past the barrier sinks into a trench under Salmon Bay, and is drained back into Puget Sound.

SOURCE: U.S. ARMY CORPS OF ENGINEERS.