Rain causes flooding in area 2008.01.16
By DAVID GREEN
Frozen ground. Melting snow. A couple inches of rain.
Bring out the “Water over roadway” signs.
Those signs bloomed last week as creeks overflowed and fields filled with water.
Upstream toward Morenci, the creek level had decreased to 2.2 feet below flood stage, still flowing far above the average for January or any month of the year.
Conditions changed quite rapidly, said Morenci area climate observer George Isobar, when the temperature warmed and the rain began falling.
“By comparing local climate data with figures from the U.S. Geological Survey, the process unfolds hour by hour,” he said.
The U.S.G.S. maintains a river gauge on the Tiffin River southwest of Morenci. The station is located where Fulton County Road 20 crosses the Tiffin.
“There’s a wealth of information on the U.S.G.S. website for those who have any interest in the rather arcane subject,” Isobar said. “Lots of facts and figures.”
The U.S.G.S. lists the measurement location as Bean Creek at Powers, Ohio—3.5 miles downstream from Silver Creek (at the south side of Morenci) and 5.2 miles east of Fayette.
At this point, the river drains 206 square miles of land. By the time it reaches Stryker, drainage has doubled to 410 square miles.
The river gauge provides a running commentary of water flow.
“At noon Jan. 4, water flow was measured at 145 cubic feet a second (cfs) which is actually below the long-term average for January,” Isobar said.
Data collection began in 1940, leading to a mean flow of 196 cfs for January.
“There was a modest increase 24 hours later to 203 cfs and a little more to 235 at noon Sunday, Jan. 6. A day later, flow had increased to 839 as temperatures rose and snow melted. We had four inches of snow on the ground earlier that week, but there was more standing farther upstream along the Bean.”
Water flow tripled by noon Wednesday, Jan. 8, after 1.37 inches of rain fell, reaching 2,340 cfs. The water depth rose two feet in five hours time and already exceeded the 15-foot flood stage.
“Don’t think that means the creek was 15 feet deep,” Isobar said. “That isn’t how the gauge works.”
The gauge height measured by the U.S.G.S. equipment does not actually determine the depth of the river. Instead, it determines how high the water surface stands above a predetermined level in the measuring equipment.
At typical flow, the Tiffin gauge remains at around 9.5 feet. Therefore, a rise of 5.5 feet is needed to reach flood stage.
Another eight-tenths of an inch of rain fell last Wednesday afternoon and evening and the maximum gauge depth of 18.87 feet was reached at 6:30 p.m. that day—9.4 feet deeper than an average day. The maximum flow was also recorded then, with 3,840 cubic feet of water flowing under the bridge every second.
“There was a pretty steady decrease after that,” Isobar said. “Flow was back to 2,000 cfs by Friday afternoon and the river dipped below flood stage by midnight.”
Flow was down to 800 cfs by mid-morning Sunday and the depth stood at only three feet above the typical height.
The U.S. Geological Service website (www.usgs.gov) provides historical data for the Powers station on the Tiffin River, although data is missing from 1983 through 2000.
Gauge equipment has changed over the years, but the highest level shown in the past quarter century was recorded in March 1982 with a gauge height of 22.7 feet—more than 13 feet above the typical level.
Following are the top flow rates shown. The typical flow of the Tiffin River is less than 200 cubic feet a second (cfs). The maximum flow from the past flood conditions reached 3,840 cfs.
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