Carson City, Nevada
Expanded retention basin protects Carson City from potential disaster
In 2004, the Waterfall Fire destroyed 8,700 acres of forest in the Vicee Canyon watershed near Carson City. Douglas County manager, Larry Werner, warned that the loss of groundcover meant the rate of runoff during a 4-percent-annual-chance flood had the potential to severely affect the northwest side of the city. Carson City implemented extensive mitigation efforts in the watershed including soil remediation, fire control, and runoff retention. These now help reduce flood hazards in the city, which has experienced 31 major flood events since its founding in 1851.
Photo by George Armstrong - FEMA
Located in the foothills of the Sierra Nevada mountains, Carson City is just east of several canyons, including the Vicee Canyon. These canyons act as a key water source for the area, but also put the city at risk for flooding. After the Waterfall Fire, which increased the city’s exposure to a flooding event, the city secured a FEMA Public Assistance Grant for $793,987 to cover 75% of the planned flood mitigation project. The city funded the remaining 25%. The money was used in part to expand an existing retention basin at the bottom of the watershed, which would slow down or partially contain run-off and debris flow in the event of a flood. The projects were completed in August 2005.
Although Vicee Canyon has so far been spared from a flood event that tests the efficacy of the mitigation actions, it is estimated that the losses avoided during a 1-percent-annual-chance flood event could total $12 million.
Benefits of mitigation
Expanding the basin took creative thinking
The FEMA Public Assistance grant covered a significant expansion of the basin in Vicee Canyon, but city officials wanted the basin to be even larger than funds would allow. Rather than asking FEMA for more money, the city partnered with a local contractor who was building a freeway through the city and needed landfill for the project. The contractor agreed to haul additional materials away from the basin site, allowing the city to get to 200 acre-feet within the allotted budget.
“FEMA did a good job keeping the project under a certain (cost), and we were able to expand it with the help of the freeway contractor. It all worked out”
Flood models help Carson City design mitigation efforts to prevent disastrous flooding
Over the next few years, Carson City is planning several flood mitigation projects focused on capacity upgrades. These include installing new piping and inlets on South Carson Street to reduce flood risks in the center of the city, constructing underground water systems in areas of town where they do not exist, and adding sediment and retention basins in northern areas of the city. Funding to support these projects will come from stormwater utility rate increases along with federal grants, if available.
Lemon Grove, California
Regular maintenance ensures effectiveness of drainage infrastructure