Continued Flooding Expected This Spring As Heavy Snowmelt Begins To Make Its Way To Carson Valley
by Joey Crandall, firstname.lastname@example.org · 6 min read
MINDEN, Nev. — Signs of spring — from the sudden patches of green beginning to pop up to the extra hours of daylight afforded by Sunday’s time change — are beginning to show around Carson Valley.
Following the wettest winter on record (and, in fairness, it’s not officially done yet — the first day of spring is March 20), a literal undercurrent has local and regional emergency planners gearing up.
The question isn’t so much if the region will see more flooding this spring.
Rather, it’s when.
The National Weather Service, in a briefing released last week to regional emergency planners, stated that flooding is a virtual certainty this spring, continuing into the summer, along rivers and streams fed by snow melt as an estimated 500,000 to 700,000 acre-feet of water is released from the Carson River Basin snowpack in the coming months.
“The ground is very wet and there is a lot of snow,” the NWS report stated. “Flood severity depends on spring storms, temperatures.”
At the close of February, soil saturation in the Carson River basin registered at 72 percent — approximately 15 points higher than the previous recorded high for the date and level with the average peak rate over the past 11 years. Peaks are generally reached in May or June.
East Fork Fire Protection Deputy Chief Dave Fogerson stated that public safety partners in Douglas County have been meeting with meteorologists from the National Weather Service to discuss flooding potential in the coming months.
“They (the NWS) are most concerned about flooding potential on the Walker River but the Carson River is a close second,” Fogerson said.
He added that another atmospheric river or a heat wave causing fast snow runoff would be the most likely causes of a flooding event.
The recent spell of warmer temperatures (highs in the mid-70s were reached during each of the past several days in Carson Valley Tuesday) has brought on a series of incremental rises and smaller falls along the East Fork of the Carson River in Gardnerville. Afternoon high temperatures have led to peaks on the river later the same evening or early the next morning.
The East Fork in Gardnerville peaked at 10.90 feet (still about 2.5 feet below the flood stage there) late Tuesday evening — up about 11 inches from a week prior.
Similarly, the main stem of the Carson River, which crosses under Highway 395 between Minden and Carson City, has gained approximately 10 inches over the past week, reading at 4.51 feet (well below the flood stage there of 10 feet) as of Wednesday afternoon.
Current National Weather Service projections show continued gradual rises at all gauges along the East Fork, West Fork and main stem in and around Carson Valley through the end of the next. Daytime highs are expected to tail back into the high 50s and low 60s early next week.
“This mild weather has been great for the reduction of the snow pack at a gradual rate, but we know it won’t hold out,” Fogerson said. “The weather service advised us that we can use the 1982-83 spring runofff as a model for the potential we will see beginning late April through June, with the best chances of an event around Memorial Day.”
An average daily flow of nearly 7,000 cubic feet per second was recorded heading into June of 1983 at the gauge on the main stem of the Carson River heading into Carson City. For comparison, the same gauge registered at more than 10,000 cfs when the flooding over 395 last closed the roadway in February of this year.
The region saw prolonged river and stream flooding on nearly all basins (lasting weeks to months) during the 1983 runoff.
“We are meeting as local government to start making decisions on how to prepare for the potential for another flood,” Fogerson said. “Obviously no one can foresee the future, but we are acting as if it will occur for a planning model. We are unfortunate that we have had two previous flooding events this year, but are fortunate that these events have shown us what may occur again.
“While we are still working the recovery from the two previous floods, we are trying to identify projects to reduce future impacts but these projects will probably not occur prior to the spring run off as the ground is too saturated to move heavy equipment into areas along the river.”
Nevada Department of Transportation hydraulic engineers have been closely monitoring areas of potential roadway flooding throughout the region, according to NDOT spokesperson Meg Ragonese.
“We are expecting a high volume of water out of the watershed (in Carson Valley), but it is not the volume of water that matters as much as how fast it is melting and running off,” Ragonese said. “It is not extended flows during flood events, but peak water flows that have the potential to most impact bridges. What we are all hoping for is a gradual snowmelt from moderate temperatures that can easily pass underneath U.S. 395 and other bridges and culverts.
“If we have a short or overly warm spring and high temperatures early in the season, then the amount of runoff could lead to flooding.”
Ragonese said, like many other emergency planning outfits, NDOT will be carefully monitoring USGS flow meters for the Carson and other rivers throughout any potential high-water events and through the spring and summer runoff.
“We have an established ‘plan of action’ specific to critical bridges across the state to alert NDOT maintenance staff when a bridge should be visually monitored, and if necessary, closed to traffic during very high flows,” Ragonese said. “The main goals are to have a predetermined action plan to protect public and infrastructure safety and define detour routes for each specific bridge. If the spring and summer runoff happens too quickly, NDOT will be ready to quickly deploy road maintenance and safety staff to help protect the safety of drivers and establish safe alternate routes.
“We are also right now evaluating potential projects to review and, if needed, reestablish any riverbed erosion underneath Carson Valley-area state bridges created by winter flooding.”
Further down stream, flowing out of the Lahontan Reservoir, the Carson River is on the cusp of reaching flood stage (9.1 feet) with the most recent measurement showing 9.02 feet as of 11 a.m. Wednesday. Major flood stage there is 9.6 feet.
The Reno Gazette-Journal reported Tuesday that preparations are ongoing regionally to mitigate the expected effects of the substantial runoff, particularly near the later stages of the Carson River south of Fallon.
Three projects intended to help offload the expected runoff near Fallon are in the works.
The main stem of the Carson River near the Lahontan Reservoir is being cleared of brush and debris, boosting the capacity of the channel from 325 cubic feet per second to 1,000 cfs, according to the RGJ.
The RGJ also notes that a $600,000 (Federal Emergency Management Agency-reimbursed) concrete and steel spillway is being constructed to divert water off the V-Line irrigation canal near Fallon at a rate of 1,000 cfs to the Sheckler Reservoir and toward the bombing range at the Fallon Naval Air Station into the Carson Lake sink.
And NDOT is installing a series of 12 six-foot by four-foot box drainage culverts crossing under Highway 95 to help facilitate the travel of water from the V-line to the Carson Lake sink.
“The controlled release of floodwaters into Carson Lake is an important strategy to limit flooding for residents and businesses in Fallon,” Nevada Governor Brian Sandoval said in a release last week. “There are as many as 3,000 vehicles traveling this section of U.S. 95 every day so it is important to do as much preventative work as possible to try and avoid significant flooding when the water is released from Lahontan Reservoir. State, local stakeholders and emergency management officials will continue to work closely together to do all possible to keep this important transportation link open and safe for drivers.”
Highway 95 has been closed this week south of Fallon and Schurz as the culverts were installed. The improvements will also help reinforce the highway against potential flooding in future years, according to Governor Sandoval’s office.
The amount of precipitation in the coming weeks and months will, not surprisingly, directly affect both the timing and severity of the spring flooding.
“Exact flood hazard will depend heavily on spring temperatures and precipitation,” the NWS briefing stated. “But plan for flooding.”
Runoff could be upwards of 253 percent of normal along the East Fork through Gardnerville, 230 percent of normal along the West Fork coming out of Woodfords and 302 percent along the main stem of the Carson.
The National Weather Service states that minor to moderate flooding impacts are likely in Carson Valley.
“We know our issues: flooding of low lying areas including the streets in sections of Aspen Mobile Home Park and Kings Lane subdivision, water over the roadway on the roads between 88/395 and Foothill, and when we hit major flood stage, water across 395 at the Five Clover Ranch (near Cradlebaugh bridge),” Fogerson said. “This provides us our basis for working on a plan. We are looking at community messaging for our low lying areas to ask them to continue their flood preparation efforts, remembering the effects of the January and February floods.
“We are discussing declaring another state of emergency in advance of the event. We will begin discussing public safety preparations, such as additional staffing levels for fire/EMS, law and roads shortly. The County Road Department has hired many contractors and are working aggressively to clean up the damage from the last events so they do not add to the potential event.
“So, we are asking the public to help us. Keep any flood preparation measures in place until June. Have a plan on what you will do: we have seen it twice already, so use past experience to gauge what actions you should anticipate taking. Make a kit of supplies to keep you self-sufficient for 72-hours. Stay informed as we move forward. The National Weather Service is providing us regular briefings on the situation. We will take our cues from them and push out public messaging in concert with them. They are typically able to provide five days prediction for a flood event, so we will have a few days for the public to become prepared when we all stay connected.
“It is the relationships of our community that help all of us the most. On the public safety and local government side, we all stay very well connected and share intelligence with one another for potentials. These relations are built upon trust and stewardship of our community to provide for all of us.”
The NWS stated that the Walker River Basin, specifically the lower elevation locations along that river, is the mostly likely major basin to experience significant and prolonged snowmelt flooding. Flooding impacts there could last well into July.
“The county will adopt the same communication methods we used before by keeping our website and social media current (during any flooding events),” Douglas County public information officer Melissa Blosser said. “Regional PIOs met recently to discuss how we can communicate to the public better as a region. We will continue to improve and build on those efforts. All this information given to us as a warning helps us prepare and keep residents safe. Although we have seen a wet winter, having these types of warnings really helps us get prepared.”