Reports identified flood concerns as far back as 1991
County: Development did not make current flooding worse
Government officials are making the rounds to assist with those affected by the flooding in Lemmon Valley. This comes after residents have repeatedly complained about flooding in the area, from flash floods in 2015 through today.
About 20 homes remain flooded.
Governor Brian Sandoval toured the area Friday.
“My heart is broken for the residents in Lemmon Valley who are still dealing with significant flooding in their neighborhoods including some homes which remain uninhabitable,” he said. “We have been working with Washoe County, the lead for this event due to the location, and will continue to support the County’s efforts and the residents who are still suffering.
“I have signed a letter to the President requesting an extension of the current disaster declaration to ensure that Washoe County will be included in the final financial request. We have also taken several steps and will remain in contact with the residents until they recover from this catastrophe and their community is made whole.”
Sandoval outlined a number of aid efforts:
- A state damage assessment team visited the affected area on the morning of Sunday, February 25, 2017.
- Based on feedback from members of the affected community, (the Nevada Division of Emergency Management (DEM)) activated the State Emergency Operations Center to coordinate resources requested by Washoe County on the morning of February 25, 2017.
- A FEMA Incident Management Assistance team was also deployed to the state to support the planning and coordination effort.
- Beginning on the morning of February 26, 2017, DEM has coordinated daily briefings on the event to identify resource requests and bring together state and local partners.
- DEM has also conducted two additional damage assessments with FEMA and the Small Business Administration to determine damages for federal support in the event of a Presidential Major Disaster Declaration.
- DEM has coordinated fulfillment of resource requests to assist in Washoe County’s response efforts within Lemmon Valley, to include but not limited to:
- Nevada Division of Forestry hand crews to assist with sandbagging efforts
- Portable toilets
- Potable water tanks
- Support from the Nevada Division of Housing, the Department of Health and Human Services, the Nevada Division of Insurance and other state agencies to support immediate needs of affected local residents
- Also, at DEM’s request, a team of engineers from the U.S. Army Corps of Engineers arrived in Lemmon Valley on March 3, 2017, to provide technical assistance regarding flood mitigation efforts.
At a community meeting focused on traffic and growth impacts in the North Valleys, held Tuesday at City Hall, a number of residents expressed frustration with the flooding.
One person blamed development in the North Valleys for making the flooding worse, but officials said that is not the case with the current flooding.
Although a number of reports, dating as far back as the early ’90s, warned of increased flood damage if mitigation measures were not adopted, Washoe County Engineering and Capital Projects Director Dwayne Smith stressed that the amount of moisture in the region is unprecedented, and there’s no place for the water to go.
“Anything that goes into the basin that would stop water from going into the ground — a building, a roadway, any type of physical structure that would reduce the impervious surface — the issue is that it doesn’t allow the water to get into the ground in the same way that it did historically,” he said.
Smith said in 2015, after flash flooding in the summer, that North Valleys drainage ditches were not meant to withstand the force of these storms.
“They meet minimum design standards,” he said. “Anything over that, it’s going to overwhelm these systems. Washoe County’s job is to maintain the ditches. Are they perfect? Absolutely not, but (county staff) busted their tails out there during the floods and the following week.”
The county’s 1991 flood control master plan identified closed-lake basins as one of several sources “that warrant additional consideration in the selection of flood control options… Base flood elevations have been recently adopted by FEMA for Silver Lake and Lemmon Valley playas. Increasing development will result in increased runoff volumes to the playa and increased peak discharges through the existing developments. This area should be included in the Flood Control Master Plan.”
Hydrologic analyses of Lemmon Valley, prepared in 1996 for the City of Reno, warned that, in regard to future development, “since Lemmon Valley is a closed basin with no outlet for flood runoff other than evaporation, increased impervious areas anywhere in the valley can cause the amount of water entering the playa, and thus the level of the playa to increase.”
A report by Manhard Consulting, conducted for the county in 2010, outlined flood mitigation options, but when it came to Lemmon Valley, the cost of large-scale projects was determined to exceed potential benefits.
“Like the Marlin Channel, the segment of Lemmon Channel … is also susceptible to flooding — but less frequently. The existing safe conveyance capacity of the system is roughly equivalent to that of a 20-year storm event. A single improvement alternative or Complete Solution was examined for this channel. With an estimated cost of roughly $10 million, it is difficult to state that this is a recommended action. With a 20-year system capacity, there is only a 40% chance this system will be over-inundated at least once in the the next 10 years. In addition, there appears to be no minor or partial improvements that would increase system function and minimize localized flooding risks. Because large flows from extreme storm events exceed the system capacity, incremental system improvements will only move the limiting feature to another portion of the system. In the worst scenario, if partial improvements are made without carefully consideration to upstream and downstream impacts, it is possible areas along or adjacent to this channel could experience flooding where there had previously been none.”
Smith said that there are mitigation measures required for new developments in the area.
“When a new development comes in, certainly within a closed hydrobasin, they have to provide engineering solutions to offset those impacts. That’s done through routing, that’s done through detention basins, and in the event when you’re bringing in fill into the flood plain, you have to move the same equivalent volume. You can’t bring something in without taking something out.
“Is it a perfect solution? Of course it isn’t. The struggle that we see is we’ve got a 42-square mile (area that drains into that basin). When you start looking at a single building, or you start looking at a parking lot, as you can imagine, the basin doesn’t event know it. You get get more and more buildings, more and more pavement, more and more sidewalks, now there might be a little bit more of an effect … but it’s being dealt with through our development codes.”
Smith said, however, that the amount of water from storms last fall through today made the current flooding worse, and the impact from development is minimal.
“When we’re dealing with the persistent moisture condition that we’re in, and the saturated ground condition … none of the ground anywhere is absorbing the water in the same way it would be doing under normal circumstances because it’s saturated,” he explained. Persistent moisture is “the reason for the flooding we’re having within Swan Lake this year.”
This past week, Smith visited the flood-impacted areas with the U.S. Army Corps of Engineers.
“Given the situation of the residents in the flood plain and the closed hydrographic basin, and after meeting with experts locally and from the Corps of Engineers, the reality is that there is no immediate, short-term solution to keep water from impacting the residents located within the flood plain,” he explained. “However, there are possible solutions we have been exploring and are continuing to evaluate as we help the community recover.”
The county said that six of its departments is assisting residents.
“Washoe County has reached out to more than 300 residents in Lemmon Valley in the neighborhoods near Swan Lake,” the county indicated in a press statement. “Residents affected by flooding who haven’t been in contact with Washoe County are asked to call 775-785-8600. Washoe County Social Services has provided food, water, shelter and clothing based on the expressed needs of Lemmon Valley residents.”