Meeting today to discuss mudslide danger

A press conference and public meeting will be held at 3:30 p.m. today at the Carson City office of University of Nevada Cooperative Extension, 2621 Northgate Lane, to warn the public that the debris and mudslide hazard is high on Carson City's west side.

With rain a possibility this weekend, city and state officials thought it important to get this message out.

Call John Cobourn, water resources specialist, University of Nevada Cooperative Extension, (775) 832-4144 or JoAnne Skelly, Carson City / Storey County extension educator, University of Nevada Cooperative Extension, (775) 887-2252.

The press release and a map of the area most at risk and an evacuation check list will be posted following the meeting at: www.unce.unr.edu/western. From there click on Carson City debris and mudslide hazard.

USDA Forest Service experts on debris flows studied the damage to vegetation after Carson City's Waterfall Fire last summer. They wrote the Burned Area Emergency Response (BAER) Report, which shows neighborhoods at the foot of burned canyons as being at risk of debris flow damage. Ash, Vicee and North Kings canyons are believed to be at greatest risk.

When a debris flow occurs, large boulders often roll or even float near the front of a wave of material that looks like wet concrete. On steep terrain, debris flows have reached velocities of over 50 miles per hour. At the bottom of a steep canyon, a debris flow can emerge onto an alluvial fan with the momentum of a high-speed freight train.

Much of west Carson City is located on gradually sloping alluvial fans at the foot of the steep mountain front. Because channels on alluvial fans are usually shallow, the actual path of the moving slurry of debris is often unpredictable once it emerges from the confined canyon. It can eventually spread out into what geologists call a "tongue," depositing a layer of mud and rocks on the fan surface.

Carson City has been working hard to stabilize slopes in the burned areas, but the regrowth of vegetation often requires five years before erosion and hazards from debris flows are substantially reduced. The city has also been enlarging its debris basin at the foot of Vicee Canyon. The city government's plan for potential flooding from the burned canyons is to route the floodwaters down city streets to the storm drainage system, and eventually to the Carson River.

Weather events that could trigger a debris flow include a rain-on-snow event this winter, rapid and sustained melting of the snowpack, or a summer thundershower. Last August, after one-quarter inch of rain fell, a small debris flow occurred at the foot of Vicee Canyon. The flow did no major damage, but it did fill up three small basins upstream of the large basin just above North Winnie Lane.

All residents, and especially those in west Carson City, should purchase NOAA Weather radios with alarms that will alert them if a flood watch or warning is issued. This is the best way of learning of hazards in their area. Weather radios are available in most stores that carry radios or clock radios. When a flood watch is issued, conditions are right for a flood to occur. If a flood warning is issued, a flood is imminent, and residents close to the foot of burned canyons should evacuate.

While Carson City has a flood response and evacuation plan, there is generally very little time to respond once a flash flood warning is issued. Residents should have their own flood evacuation plan. When flash flooding, mudslides and debris flows occur, the direction of danger may be uncertain. Residents should have alternate evacuation routes in case their main route has been blocked.

It is particularly helpful to discuss hazards with neighbors before an emergency occurs, to work out the best plan for the neighborhood. In an emergency, neighbors should look after each other and help each other in reach safety. Homeowners in flood-prone areas should also obtain a flood insurance policy through the National Flood Insurance Program.