Dam built to divert future floodwaters

Greg Harman

Monday, April 24, 2000 | 11:35 a.m.

On paper it had existed for years as part of the Clark County Regional Flood Control District's master plan.

But the 80-foot dam in the River Mountains Range east of Henderson was still unrealized when heavy rains backed up in a wide valley against the mountains' walls in August 1997, sending raging floodwaters into the city.

The flood caused millions of dollar in damage and took at least one life. It also caused delays in the Southern Nevada Water Authority's new water treatment facility planned for the base of the River Mountains.

To ensure its $180 million water plant would be safe from future flooding, the water authority took on the dam project, part of a large detention basin.

"It could have prevented the entire flood," said Marcus Jensen, the authority's director of engineering. Although some areas could have experienced minor flooding from the storm that dropped 2.5 inches in a single hour, the majority of damage could have been avoided, he said.

Before the dam was constructed, all rainfall within the 5.3 square miles of the River Mountains Range collected in a bowl-like valley to be funneled out to Lake Mead at one point. That created the potential for heavy floodwaters to back up.

But the dam was not highly ranked on the city of Henderson's priority list of pending flood control projects, so it was not built in time to prevent damage in the 1997 flood, said Betty Hollister, spokeswoman for the flood control district.

It's ready for the next one.

The dam and diversion works were completed Feb. 22 and are expected to be turned over to the city of Henderson at a Southern Nevada Water Authority meeting Wednesday.

Standing at 80 feet high, the $5.9 million project is built, according to the flood control district, to withstand a 1,000-year flood. The dam, which includes a levee and spillway, is the tallest -- excluding Hoover Dam -- of 30 flood-control dams in Southern Nevada, Hollister said.

The River Mountains dam surpasses the standards normally adhered to by the district, said Steve Roberts, engineering manager for the flood control district, who assisted in the design of the dam.

"They have a big investment there," Roberts said.

"It is going to provide some protection to the residents west of our C-1 channel" in far eastern Henderson and protect future development in the area, Hollister said. The channel routes potential floodwaters north into the Las Vegas Wash and into Lake Mead.

The River Mountains Water Treatment Facility should increase the Las Vegas area's potential daily water supply to 750 million gallons per day, an addition of 150 million gallons. It is expected to be completed in the summer of 2002.

Greg Harman covers Henderson and Boulder City for the Sun. He can be reached at (702) 259-8814, or by e-mail at harman@lasvegassun.com.