Earthen berm ready to handle floods at Mount Charleston
The earthen berm designed to shift floodwaters away from the Rainbow subdivision on Mount Charleston is essentially done.
Later this year, the 2,350-foot-long project will be turned over to the state, which will maintain the berm intended to shield homes from flooding like the ones that hit mountain homes two years in a row.
Crews are now doing tasks such as grading work on the access road leading to the berm, said Michael Balen, a lead engineer for the U.S. Forest Service.
The Army Corps of Engineers is the construction manager, and Forest Service staffers have built the berm. The Corps did an inspection and gave the Forest Service a punch-list of minor tasks to finish, such as touching up cracks in grout — or concrete — poured between the rocks.
After another inspection the berm will be turned over to the state of Nevada, which will assume liability for the structure, including keeping it clear of debris.
“It’s functional right now,” Balen said. “It would handle a flood.”
He expects the final work to take about two or three weeks.
Work has gone smoothly, Balen said. But he added that the weather slowed the schedule a bit. One of the latter phases was pouring wet cement between rocks, a task that can’t be done in cold weather.
“The snow and the cold really put a crimp on the progress,” he said.
The $3 million project is intended to divert water from the housing in the Rainbow subdivision and safely down the mountain.
Work had started Oct. 10 with tree removal, and earth-moving equipment reshaped the mountainside to carry water downward away from homes. Boulders line the berm to prevent erosion.
The Army Corps of Engineers developed a plan that was ready to go in June, but the deal between Clark County and the federal government fell through when county attorneys didn’t want to assume the legal liability for the berm, which is being built on Forest Service land.
The state reached an agreement with the Corps after Gov. Brian Sandoval toured the area in August, after a July 28 flash flood hit the subdivision.
Flooding became an issue at the subdivision only after the Carpenter 1 Fire in 2013, which destroyed almost 28,000 acres, including vegetation on higher ground above the homes that had acted as a barrier to flooding. The first flood to hit the area after the Carpenter 1 Fire came in September 2013.
Then the July flood washed out county roads and damaged water lines with about $1.4 million in damage.
It also hit 10 homes with damage estimated at $849,000, according to the county. Some of the homes were filled with mud and debris.
As for the monsoon season of 2015, it’s too early to know how severe the rainfall will be, said Andrew Gorelow, a meteorologist with the National Weather Service office in Las Vegas.
The monsoon season lasts from July through September.
“Monsoons are always unpredictable around here, especially ahead of time,” he said.
But the lack of vegetation played more in the flooding of the past two years than the amount of rainfall.
In 2012, Mount Charleston had 13.8 inches of rainfall during its monsoon season. But in 2013 and 2014, it was only 5.47 inches and 6.9 inches, respectively, according to weather service data.
The average rainfall of each monsoon season since 1980 is 6.72 inches, according to the weather service.
The berm project has changed in scope. The preliminary design length was 1,200 feet. The length was increased to 2,350 feet to protect more homes after the Corps heard feedback from residents and extended it to add a greater degree of protection to 15 of the homes.
The berm is designed for a 25-year flood event, which has just a 4 percent chance of being equaled or exceeded in any year.
Officials plan to remove the berm after vegetation grows back.
Contact Ben Botkin at bbotkin@reviewjournal.com or 702-405-9781. Find him on Twitter: @BenBotkin1.
