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Forecast: James River flooding threat low; Overland flooding is real possibility
Feb 22, 2013 (The Jamestown Sun - McClatchy-Tribune Information Services via COMTEX) --
Flood outlooks along the James River and Pipestem Creek remain low although snow pack levels are increasing, according to Allen Schlag, hydrologist with the National Weather Service in Bismarck.
"Generally speaking we're in good shape," he said. "There is snow up north but not like 2009 or 2010. The snow out there currently should be fairly easy to control by the dams."
The flooding outlook includes:
--about 10 percent for minor flooding of 12 feet, 6 percent for moderate flooding of 14 feet and 5 percent for minor flooding of 15 feet along the James River at Grace City
--about 11 percent for minor flooding of 9 feet, 6 percent for moderate flooding of 11 feet and less than 5 percent for major flooding of 13 feet along Pipestem Creek at Pingree.
The probability calculations do not include any flooding caused by ice jams and assume normal levels of precipitation through the next three months.
Flooding below the Jamestown and Pipestem dams, measured at LaMoure, is also low with a 9 percent chance of minor flooding of 14 feet, 5 percent chance of moderate flooding of 16 feet and less than 5 percent chance of major flooding of 18 feet.
NWS gauges measured the James River at 2.78 feet in Jamestown and just below 7 feet in LaMoure Thursday afternoon.
"The control of the river at Jamestown with the two dams has kept the probability of flooding at LaMoure pretty modest," Schlag said. "There is enough snow on the ground south of Jamestown that it wouldn't take much to see overland flooding. It just doesn't translate into much of a problem along the James River."
The possibility of overland flooding is tied directly to the amount and timing of spring rains.
"A really big rain event could pose serious problems," Schlag said. "But those kinds of spring rains on top of snow events are pretty rare."
There are also other factors affecting the amount of spring runoff and the possibility of overland flooding. These include the dry condition of the soil, which has resulted in the frost going deeper into the ground. Both could impact how much of the spring snow melt and rain would soak into the ground or run into the streams and prairie potholes.
"It all depends on how the spring melt occurs and the amount of rain that occurs," Schlag said. "They pay me to think in worst case scenarios. The worst case scenario is heavy rains on top of the snow pack before the frost goes out."
Sun reporter Keith Norman can be reached at 701-952-8452 or by email at knorman@jamestownsun.com
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