Published: March 21, 2008 06:23 pm            

NWS: Trinity River nears flood mark

Hydrologist says homes, roadways shouldn’t be threatened

Runoff from heavy rains in North Texas earlier this week have sent the Trinity River over its banks in Henderson and Navarro counties.

National Weather Service Hydrologist Bob Carle said Friday the forecast is calling for the river crest to measure 42 feet in Trinidad by Sunday evening. Flood stage, the elevation at which the overflow of the natural banks of a body of water begins, is 33 feet. A reading of more than 40 feet is termed moderate flooding for the Trinidad gauge, according to the NWS.

“The river is still going to rise quite a bit at Trinidad,” Carle said. “You’re just going to have a whole lot of lowland flooding around the river. Most likely to be affected are those farming and ranching along the river.”

Carle said he does not expect any residences to be threatened or roadways to be under water as a result of the overflow.

That wasn’t the case in 1990, when record Trinity River flooding forced evacuations in some parts of southwest Henderson County and left parts of State Highway 31 near Trinidad and Malakoff and U.S. Highway 287 between Bethel and Corsicana completely underwater.

Carle said the NWS recorded four to six inches of rainfall in Dallas and Collin counties in a 24-hour period and pockets of heavier rain Monday and Tuesday. The water from those storms has worked its way to Henderson County over the past three days.

According to the Trinity River Authority, elevation at the Trinity River gauge measured 22.5 feet on March 18. By Wednesday, the measurement was 27.22 feet. Friday afternoon it was approaching 38 feet.

The gauge at Trinidad was moved last year and the NWS is watching this flooding closely to see if adjustments need to be made in how the statistics are kept.

“The gauge was moved upstream about a mile. I’ve been in contact with someone on the river who is keeping an eye on how things are working out,” Carle said. “We’ll see if water is in the same locations as when the river crested at 37 feet last year before the gauge was moved. If you remember last year when you had all the rain, that water along the Trinity spread out a long way.”

The U.S. Geological Survey, the owner of the gauging equipment, wanted it moved because the old site was no longer safe, Carle said. The site was moved to a newly constructed bridge with a wider shoulder. The move changed the river’s elevation at the gauge by five feet. To compensate the flood stage was raised from 27 feet to 32 feet at the gauge.

“We want to determine if the water spread out a half mile on each side of the river at 35 feet before the move (if) it would now do that at 40 feet,” Carle said. “We were trying to measure the same amount of water in the stream, but it will happen at a different stage value.”

Record readings at the 27-foot floodstage were 49.80 in 1942, 48.30 in 1908 and 48.11 in 1990.

        

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