Possibility of San Joaquin River flooding seen
Sacramento BeePotential flooding this spring is possible on the San Joaquin River system but less likely on the Sacramento River, according to a hydrologic outlook by the National Weather Service.
Well above average snowpack in the Sierra Nevada will keep rivers swollen this spring throughout the north state. Last week's snow survey report showed that the average statewide snowpack measured 165 percent of normal.
The weather service's Sacramento office noted that the highest risk for potential flooding is on the San Joaquin River and its tributaries due to the heavy snowpack and limited space in reservoirs.
Alarmed at a weakened levee on the San Joaquin River, Stanislaus County supervisors on Tuesday declared a state of flood emergency.
Damages "could run into millions of dollars," Stanislaus County Chief Executive Officer Rick Robinson said, and the declaration could clear the way for state and federal financial relief if Gov. Jerry Brown agrees.
The levee was not identified, but Supervisor Jim DeMartini said it's near Gomes Lake.
The area north of Crows Landing Road and west of Carpenter Road normally is dry-to-marshy, but swells into a larger body of water during wet seasons.
Rising water has eroded 8 feet into the levee; with 30 feet of earth remaining, it's probably not an "imminent threat" but must be closely watched, Robinson said. A breach would threaten 7,000 acres of farmland and 10,000 head of dairy cattle.
Flooding has forced evacuation of trailer parks and could damage parks, roads and bridges in Stanislaus County, and the water may not recede before July, officials say.
Reservoir levels as of late last week were already above what they usually are this time of year: New Melones at 132 percent, Don Pedro at 117 percent, Lake McClure at 132 percent, Friant Dam at 114 percent and Pine Flat at 140 percent.
In anticipation of snowmelt, water watchers are dumping large amounts of water from the reservoirs.
Peak times to see rivers swell from snowmelt usually occur around mid- to late May. That means flooding is possible downstream on the San Joaquin system for the next eight to 10 weeks, according to the weather service.
Risk due to snowmelt on the Sacramento River and its tributaries is lower due to channels being able to contain high flows and reservoirs having greater capacity.
Still, the snowpack for the northern Sierra stands at 174 percent of normal. And reservoirs have a good amount of captured runoff: Lake Shasta and Oroville have 104 percent of their average for this time of year, and Folsom Lake has 105 percent.
Source: http://www.sacbee.com/2011/04/06/3531041/possibility-of-san-joaquin-river.html#ixzz1IxTBwOSz
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