Nov. 14--Hot weather brings a spike in demand for water and power, so Hoover Dam keeps humming all summer long.

Things tend to quiet down from October to April, so that's when workers try to catch up on equipment upgrades and large-scale maintenance projects.

Lately, a lot of that work has been geared toward improving power plant performance in the face of the lowest water levels Lake Mead has seen since 1965.

The dam's power customers plan to spend millions of dollars in the coming years to squeeze more electricity from the same amount of water and compensate for a loss of power capacity as a result of the shrinking lake.

The surface of the reservoir dropped 120 feet in the last decade, as the Colorado River came under the grip of the worst drought on record. The resulting loss of water pressure -- known as power head -- has reduced the dam's power generating capacity by 20 percent.

The dam and its power customers can't do anything about the lake level so they are trying to squeeze as much power as possible out of the water pressure they do have.

One change involves devices called wicket gates.

"They look like a circular Venetian blind so they can control how much water can flow into the turbine," said Dan Pellouchoud, an engineer who has been overseeing power upgrades at the dam for the past eight years.

The old cast-steel wicket gates are being replaced with new stainless steel ones that are more streamlined and can open wider to let in a greater volume of water with greater force.

"We make more energy with the same water," Pellouchoud said.

From the lower floors of the powerhouse on the Arizona side of the dam, you can actually hear what he is taking about.

It's the first sound a unit makes as it starts up: a roar of water gushing into the turbine at a rate of 3,200 cubic feet per second, enough to fill an Olympic-size pool in less than half a minute.

Soon the louder sound of the turbine spins up to replace the roar. The water just used to push the turbine is then released from the power plant to fill an order downstream.

Six of the dam's 17 turbine-generators have received new wicket gates since the upgrades began in 2005.

The improvements have resulted in a 3 percent to 4 percent increase in efficiency and the recovery of about 84 megawatts of power capacity lost to low water conditions in Lake Mead. That power has an annual market value of $2.7 million.

Two more units will get new gates as part of regularly scheduled overhauls in the next two years.