Silt fills reservoir’s inlets after flooding in southern Utah

Posted at 6:29 PM, Oct 01, 2014
and last updated 2014-10-01 20:29:13-04

GUNLOCK, Utah - Cities in southern Utah are still cleaning up the mess from a flash flood that fell in the area on Saturday. The storm brought down a lot of water, but it also brought down a lot of dirt

The dirt covered some streets and filled drains. But it also filled the inlets at Gunlock Reservoir. Officials with the Washington County Water Conservancy District said it happens after just about every major storm.

“The drainage of the Santa Clara River tends to bring a lot of debris and sand when it floods,” said WCWCD Associate General Manager Barbara Hjelle.

The siltation  has been such a concern, Hjelle said they estimate it’s lowered the reservoir's capacity to hold water by about a third since it was built in the 1970s.

Siltation is an issue they deal with at all water collection sites, but particularly at Gunlock because it’s a direct stream collection.

“Sand Hollow and Quail Creek, as off-stream reservoirs, don’t have that collection,” Hjelle said. “But they do have the mirror problem of having to manage the pipeline and the debris and so forth at the diversion structure.”

That’s why the water district will periodically bring in heavy equipment to remove the sand and debris that collects at the inlets. Hjelle said burn scars upstream complicate the problem, as it means more material is washed down.

“Not only the amount of silt, but they’re bigger floods because there’s nothing to hold the water on the landscape,” Hjelle said.

There’s not really a long-term solution to the ongoing problem. Hjelle said they just have to watch the sandbar levels in the water and clean it out when it gets too full.