Nevada Flood Awareness Week is scheduled for Nov. 1-7 to help Nevadans prepare their home, family, businesses and pets for flood disasters.
There will be a flood awareness information booth and an interactive flood model at the Walmart Supercenter in north Carson City, 3200 Market St., from 1 p.m. to 3 p.m. Sunday. Another event is scheduled from 10 a.m. to 3 p.m. Nov. 4 at Fire Station No. 118 on S. Main Street in Yerington. There will also be a Flood Awareness Open House at the Douglas County Community Center, 1329 Waterloo Lane in Gardnerville, from 11 a.m. to 6:30 p.m. Nov. 5. Events in other communities are listed at www.NevadaFloods.org.
According to John Cobourn, water resource specialist at University of Nevada Cooperative Extension, Flood Awareness Week is held in early November because the area gets its biggest river floods in the winter. When a weather pattern known as a Pineapple Express or atmospheric river occurs during the winter months, a series of strong storms move across the Pacific Ocean from the region of Hawaii to California and Nevada. When these storms reach the snowy Sierra mountains, they can bring heavy rainstorms as high as 10,000 feet. When this happens, the rain melts much of the snow, and the rivers draining the mountains can rise to flood stage. The National Weather Service in Reno says a large Pineapple Express storm can occur during any winter, regardless of the presence of a drought or an El Nino, Cobourn said.
The Truckee, Carson and Walker rivers have had 15 winter floods in the past 150 years, or about one every 10 years. The largest river floods since 1950 occurred in 1950, 1955, 1963, 1986 and 1997. In 1997, some Reno casinos near the river had five feet of water on the first floor. The total estimated cost of flood damages in Washoe County was in excess of $686 million. Carson City, Lyon and Douglas counties sustained damages estimated at close to $30 million.
Nevada has a different kind of flood hazard from late spring through early fall. While summers are generally dry, monsoon patterns to our south can bring warm, moist air up from the Gulf of California. This summer’s and last summer’s monsoon seasons (July –September) produced flash floods in Clark, Washoe, Douglas, Carson City and Lyon counties. Since summer floods are caused by cloudbursts, Cobourn said, they affect smaller areas than winter storms. Most often, a thunderstorm unleashes an inch or more of rain high in one or more local mountain canyons. Within a half hour or so, a wall of water can emerge from the canyon onto an alluvial fan at its foot. Each time such a large flood occurs, possibly 30 to 60 years apart, the fast-moving water, carrying sand and rocks, can cut a new path down the convex surface of the fan. Almost all neighborhoods on alluvial fans are at risk from flash flooding, so property owners should be wary of building structures in vulnerable areas on fans.
If you can’t make it to a local flood awareness event, go to www.NevadaFloods.org, where information about floods and how to prepare for them is available.