Hydrologist: Possibility for flooding is there, but may not materialize

Tom Gardner

Tuesday, March 16, 1999 | 10:36 a.m.

RENO, Nev. - A Sierra snowpack that's far above average means the chance of flooding in western Nevada is also higher than normal, according to the National Weather Service's top water watcher.

"It all depends on what happens during the rest of the storm season," Hydrologist Gary Barbato said on Monday.

"Even in areas with high snowmelt flood potential, flooding will only occur if snowmelt is very rapid due to much above average temperatures or if heavy rain occurs at high elevations and quickly melts mountain snowpacks," he said.

Despite a snowpack that's as much as 160 percent of average in places, the overall water content is well below the 180 percent of 1995, the last year that produced runoff flooding.

"We're not anywhere near that high this year," he said.

This winter's storms have dropped the most moisture at the north end of the Lake Tahoe Basin, where the pack is 160 percent of average in the Tahoe runoff and 140 percent in the Truckee watershed. That compares to 109 percent of normal at the south end of the lake in the Carson and Walker runoffs.

The Truckee and Tahoe basins also have far more reservoir space for storing a sudden runoff, with Tahoe more than a foot below its rim and additional capacity in Prosser, Stampede and Boca reservoirs and Donner Lake.

That's not the case along the Carson and Walker rivers, Barbato said.

"Topaz and Bridgeport are filled," he said, and water masters are on the fence.

"If they get another pineapple connection, they'll be sweating it," he said.

The pineapple connection - a series of warm, wet storms that can stretch from the Hawaiian Islands across the Pacific into Nevada - would almost guarantee flooding.

Barbato said the only real reservoir on the Carson - Lahontan - is in good shape because of several weeks of releases that have left it about 5 percent below capacity while runoff has been slow.

While it has been fairly cool so far this year, it also has been reasonably dry.

"Still, we're only in mid-March. As '95 showed, we could have snow piling up until the middle of May," he said. "We reached our peak snow depth some time in the middle of May. The melt didn't really take over until the latter part of May, even on the Truckee."

"Farther south it went into late June and even July on the Walker," he said.