Though Not Imminent, Potential For Highway 395 Flooding Remains

Posted By on May 9, 2017

by Joey Crandall,  · 4 min read

There is a possibility that the record-level snowpack still stored up in the Sierras, given a continued gradual snowmelt from moderate temperatures, could easily pass underneath Highway 395 in the Cradlebaugh Bridge area — as well as other bridges and culverts along the Carson River — without incident in the coming months.

“While there is a high volume of water still stored in the watershed snowpack, it is important to know that it is not the volume of water throughout the season that matters as much as the speed that the snowpack melts that creates peak water flows that have the potential to impact bridges and/or roads,” said Nevada Department of Transportation spokesperson Meg Ragonese on Monday.

A rapid onset of warmer temperatures, though, or a new series of strong rainstorms, could quickly change things.

“If we have overly-warm temperatures or further strong rainstorms, though, the amount of runoff could lead to temporary or sustained flooding, including the potential of overtopping U.S. 395,” Ragonese said.

The temperatures in the 80s to close out last week brought both the West Fork of the Carson River in Woodfords and the the East Fork of the Carson River in Gardnerville briefly to flood stage Friday night. Roughly 18 hours later, the main stem of the Carson — which crosses under 395 at Cradlebaugh Bridge — reached monitor stage and remained there through Sunday morning.

Cradlebaugh Bridge Saturday evening.

This week, renewed sunny skies and warmer temperatures have the National Weather Service projecting the West Fork to again approach flood stage Wednesday and Thursday night. NWS projections have the main stem of the river potentially reaching near monitor stage again early Friday morning before easing back off.

The Valley is under a flood advisory through mid-Friday morning.

NDOT is paying particularly close attention to the river levels.

“We will continue to very closely monitor snow melt-off, river flows and other factors associated with potential flooding of state roadways, including US 395 near the Carson River and Cradlebaugh Slough,” Ragonese said. “We do not anticipate any imminent flooding of U.S. 395 in the Cradlebaugh Slough area, but there remains the potential that a quick winter snow melt-off or heavy future precipitation may bring regional flooding.”

Ragonese stated that when flows on the Carson River exceed roughly 5,000 cubic feet per second (they hit 5,000 cfs on Saturday, according to United States Geological Survey readings), the potential of the river escaping its banks and flooding waterways and low-lying areas directly north of the river channel (and over 395) is heightened.

The flows exceeded 8,000 cfs when the Highway 395 flooded in January and 10,000 cfs when it flooded again in February.

Ragonese noted, though, that flows as low as 5,500 cfs can overtop some or all of Highway 395.

“We do have established action plans to help protect public and infrastructure safety and define detour routes if any specific bridges or roads are impacted by flooding,” Ragonese said. “Our NDOT road maintenance staff is ready to quickly deploy, if needed, to help protect the safety of drivers and establish safe road closures and alternate detour routes.

“We also have an established list of NDOT staff volunteers who are trained to help protect public safety by manning road closure areas. This month, we are also training additional NDOT administrative staff volunteers to help guide the public and provide additional information if there are any future flood-related road closures.”

Because 395 is a divided road at Cradlebaugh, the option exists of running both directions of traffic on the northbound lanes, if they remain clear.

“There have been times in the past when we have been able to establish traffic control allowing both directions of freeway travel on the northbound lanes,” Ragonese said. “If a quick snow melt does bring flooding, there is the potential that we would be able to continue to allow both directions of U.S. 395 travel for a limited amount of time on northbound lanes if waters did overtop southbound lanes.”

That would, of course, depend on the specific circumstances and extent of any potential flooding, she added.

Ragonese also stated that NDOT is currently evaluating potential projects to increase flow capacity in various areas receiving flood flows, as well as monitoring and mitigating, if necessary, any riverbed erosion underneath Carson Valley-area state bridges created by winter flooding.

“We are also looking at potential other projects that can be done post-flooding to fix or prepare for future concerns,” she said.”