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Washoe County: FEMA flood plain lines drawn with out-dated surveys

By Carla O'Day
Published: Last Updated on

Washoe County might initiate a revision of the current FEMA-designated flood plain boundary and pool elevation of the Lemmon Valley hydro-basins because the existing line was identified using antiquated surveys.

County staff recently discovered the current FEMA flood plain is based on outdated surveys and topographical analysis. Use of better tools — such as laser imaging, detecting, and ranging — have helped identify areas along the perimeter of the flood pool that do not reflect actual pool boundaries, a report to county commissioners says.

In such areas, buildings exist within the flood pool elevation at 4,924 feet above mean sea level. But like many areas that were mapped using older techniques, county officials say the property owners are likely not aware of the situation.

“In addition, preliminary analysis focused on updated regional storm patterns, new precipitation measurements, and subsequent lake level responses has revealed that under several scenarios the true impacts from the 100-year storm event may result in water elevations higher than currently identified,” Dwayne Smith, Washoe County director of engineering and capital projects, wrote in a report to commissioners.

“While precipitation events cannot be predicted or stopped, to help reduce the potential for possible future damaging events, staff recommends that more accurate analysis and understanding of the potential impacts is necessary to develop meaningful strategies to protect the area residents and businesses.”

The Washoe County Community Services Department has been responding to and monitoring flooding issues in the Lemmon Valley area. This includes field activities, such as barrier operation and pump maintenance, development and implementation of flood mitigation strategies, and collaborating with regional partners to align stormwater and flood policy.

Protections were put into place during the 2016-17 water year when precipitation fell at record levels, resulting in saturated soil and extensive runoff of stormwater.

Commissioners on Tuesday held off approving a $149,796 contract with Brown and Caldwell for the Swan Lake Surface Water Exportation Feasibility Study, which will evaluate the potential for export water outside of the East Lemmon Valley closed hydrographic basin.

Additionally, a $107,460 agreement with Carano, an engineering services company, was also put on hold for the Swan Lake Flood Mitigation Strategy Analysis feasibility study. It’ll evaluate potential long-term options for the basin for the possible diversion of upstream flows and to contain floodwater within the Swan Lake boundary.

Commission Chairman Bob Lucey said votes on the contracts with Brown and Caldwell and Carano were put on hold, along with a vote on whether to revise the current FEMA-designated flood plain boundary, until the commission chambers are back open for the public.

The chambers have been closed to the public since March due to the COVID-19 pandemic. However, the public can watch meetings virtually and make comments in writing, by voicemail, by email or via Zoom.

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