Flooding threatens wetlands, water pipe

Friday, June 5, 1998 | 10:15 a.m.

So much silt is flowing into the Las Vegas Wash after last year's floods that the water will violate proposed water quality standards.

Runoff rushing through the wash is destroying marshes that slow and filter the water, threatening drinking water, a delivery pipe and the future of a wetlands park.

A 10-mile stretch from Southern Nevada's wastewater treatment plants to Lake Las Vegas will violate the proposed state standard for sediment, 80 milligrams per liter of water. The Nevada Environmental Commission will consider the standards on June 17. There are no sediment standards for the wash.

Erosion in the past year has cut four feet of soils into the channel and destroyed more of its sparse plants. Similar floods this summer could cripple a drinking water delivery pipe for North Las Vegas, because the water flows so fast.

Kurt Segler of Henderson chaired a technical subcommittee studying the problem of high particle counts and erosion in the Las Vegas Wash. "Within a year the loss of temporary erosion controls from the floods has been drastic," he said Thursday, showing a bare brown channel stripped of green marsh plants.

At Lake Las Vegas in 1991 the wash deposited about 51 tons of silt a day. That load has jumped to 1,600 tons a day in the past year, Segler told the Lake Mead Water Quality Forum, a group of federal, state and local drinking water and wastewater experts.

Forum director Allen Biaggi said the first step will be putting an agency in charge of the wash. Recent recommendations will put the responsibility in the hands of the Southern Nevada Water Authority.

Biologist Larry Paulson urged immediate action to protect the valley's drinking water pipe from future flooding. "Erosion is a long-standing problem in the wash," he aid. "People have stood by and watched the wash erode away."

Paulson said floodwaters should be collected in the valley to stop erosion in the wash channel.

If the water quality standards to control silt proposed by the state had been in place and enforced the Las Vegas Valley would not have lost the wetlands, Paulson said.

"That should be a red flag to us that there are more and more threats upstream," he said, noting more treated sewage and runoff from the growing valley as immediate problems.