First season of dam sediment removal concludes

PALMDALE — The Palmdale Water District’s multi-year effort to remove sediment from behind Littlerock Dam and increase the reservoir’s storage capacity completed its first season of removal, in November, due to rainfall, General Manager Dennis LaMoreaux reported, on Monday.

The project removed some 58,000 cubic yards of sediment, between Sept. 12 and November, he reported, adding 36 acre-feet of capacity. An acre-foot is equal to 326,000 gallons.

The reservoir collects rain and snow melt from the watershed in the San Gabriel Mountains and is one of three sources of water for the District. The others are groundwater pumped from wells and State Water Project water carried through the California Aqueduct.

Sediment has built up behind the dam since 1992, reducing its water storage capacity.

The project is intended to remove 1.7 million cubic yards of sediment from the reservoir over 12 years. This will increase the reservoir’s water storage capacity by about 700 acre-feet.

The District contracted with Innovative Construction Solutions of Costa Mesa to remove 64,000 cubic yards of sediment, in 2022, and truck it to a local gravel pit.

This portion of the project cost is $2.8 million, of which $1.1 million is

from grants, officials said.

The plan originally called for removing 120,000 cubic yards annually, for 12 years. However, bids for the project, as designed, were more expensive than anticipated.

Instead, District staff negotiated a smaller project for the first year with Innovative Construction Solutions of Costa Mesa. The company is familiar with the Littlerock Dam, having removed debris following the Bobcat Fire, in early 2021.

The sediment removal project was postponed in the 1990s, after discovery of the endangered arroyo toad in the area. After years of environmental studies and steps to protect habitat, the District began the project with construction of a subterranean grade control structure, which began, in October 2018, and was completed, in early 2020.

The grade control structure was required before sediment removal could begin, to shore up the ground and prevent erosion once sediment is taken out of the stream and protect the arroyo toad habitat.