Big Rock Creek water storage plan considered

One such project being studied would use the normally dry Big Rock Creek, south of Pearblossom, which runs roughly northward from the foothills into the Valley, as a means of transporting water from the California Aqueduct to the underground aquifer.

The Antelope Valley State Water Contractors Association — which includes the Antelope Valley-East Kern water agency, Palmdale Water District and Littlerock Creek Irrigation District — hired consultants Kennedy Jenks to complete a feasibility study for releasing water from an existing turnout in the Aqueduct, into Big Rock Creek, and allowing it to percolate through the stream bed into the aquifer below.

The idea was that the creek would provide a cost-effective means of underground water storage, to “get it in there, get it in cheap,” PWD Resource and Analytics Director Peter Thompson said, in a presentation, on Monday, about the project to the District’s Board of Directors.

“We thought Big Rock Creek would be good for that,” he said.

The presentation was intended to provide directors with an overview of the study, prior to the draft report being presented to the Association, on Feb. 9.

However, the feasibility study, in 2019, found problems with the plan. This included flooding over Avenue T that would cause an unacceptable hazard, as well as providing limited recharge capacity with smaller flows to avoid flooding Avenue T — only about 800 acre-feet of water annually. (An acre-foot is 326,000 gallons of water.) The target for the project was up to 20,000 acre-feet per year.

The latter issue is because the times water is available for recharge from the Aqueduct — during wet years — are the same the normally dry creek bed is running, Thompson said.

“We got poor results and that was due to completing with Mother Nature,” he said.

With the problems identified in the original plan, the Association looked to alternatives. Two proved to have enough merit to warrant further study.

The alternatives needed to prevent flooding on Avenue T, as well as Avenue S. Therefore, one option is to build culverts beneath both streets to direct the flow from the stream bed below the streets, instead of across them.

The culverts are cost-effective, at about $190,000 to $260,000 to construct, with a recharge capacity of about 2,200 acre-feet annually.

In addition, this alternative provides a public benefit by preventing flooding of Avenue T from natural flows in Big Rock Creek, Thompson said.

The second alternative selected for further study is a recharge area near the stream bed, but not within it. This would take advantage of the better ability to percolate through the soil that is in the stream bed, but without the other complications.

Two options are under consideration for this alternative, using different but adjacent properties. Additionally, the two options could be combined into one larger recharge basin.

“This comes closer to that 20,000 acre-feet,” Thompson said, but it is also more costly, between $2.1 million and $3.3 million, depending on which option chosen.

The project alternatives have been vetted by the Watermaster Engineer, which is tasked with ensuring the health of the region’s groundwater basin. The response was “very positive,” Thompson said.

A drawback to either alternative is the limited capacity of the State Water Project at that point of the California Aqueduct.

This means pursuing any of these alternatives will require coordination with other State Water Project contractors to juggle water deliveries, Thompson said.

The culverts alternative also requires coordination with Los Angeles County Public Works, as they are responsible for those streets.

agatlin@avpress.com