Littlerock Dam

WATER MANAGEMENT — Construction continues at Littlerock Dam on a grade control structure, the first phase of a project that will remove years of sediment to increase the water reservoir’s capacity.

PALMDALE — As construction at Littlerock Dam continues, the Palmdale Water District advised residents Tuesday that Mount Emma Road will be temporarily closed at times while water is released from the dam to lower the water level in the reservoir during work on the first phase of a sediment removal project intended to increase the water storage capacity of the reservoir.

The closures will be sporadic, as rainfall fills the reservoir to a point to impact the construction project, General Manager Dennis LaMoreaux said.

Water was released for a few hours on Tuesday, after the recent rains had caused the reservoir’s water to seep toward the hole where crews are building an underground grade control structure. The water was not at a level to inundate the hole, but was seeping in like groundwater, LaMoreaux said.

The culverts beneath Mount Emma Road used to direct the water away from the reservoir do not have the capacity for a release such as this and can overflow the road. Los Angeles County closes the road in such situations for safety reasons, he said.

The process may be repeated at times in the coming weeks, given weather conditions and progress on the construction project.

The Littlerock Reservoir Sediment Removal Project has been in the works for some 25 years. The project calls for removing more than 1.16 million cubic yards of sediment that has built up behind the dam since 1992, reducing the water storage capacity by 500 acre-feet, according to district officials.

An acre-foot is 325,851 gallons, or approximately the amount of water a typical Antelope Valley household used in one year, before the most recent drought reduced usage.

The first phase is construction of a subterranean grade control structure, which began in October.

The grade control structure is required before sediment removal may begin, in order to shore up the ground to prevent erosion once sediment is taken out of the stream.

The structure is a staircase dam that will be underground, under the water level of the reservoir. It will be built at a place called Rocky Point, where the stream that feeds the reservoir, Littlerock Creek, meets the high water mark, about one mile upstream from the dam.

To construct the underground dam, wells were first built to divert water from the creek around the construction site to the reservoir to dry out the soil. The reservoir was lowered to its minimum level in preparation for the project.

Construction is continuing as planned, with installation of the concrete set to begin in the next week or two.

“That’s the vital part. That will bring it up to the stream elevation,” LaMoreaux said. “Right now, we’re starting 44 feet below the surface in a reservoir in winter.”

The water released from behind the dam is not lost, but is absorbed into the underground aquifer, resupplying the area’s groundwater.

“We’re definitely not wasting the water. It’s going into the aquifer. It’s not going into Lake Palmdale,” he said.

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