Thursday, December 13, 2012
North Texas lakes lower than normal after a warm autumn, no rain
Water distributors worry about finding alternative means of supply.
A year after greater-than-normal precipitation pulled North Texas out of a prolonged, heat-induced drought, higher-than-normal temperatures may soon have the region clamoring for water again.
Rainfall deficits have steadily grown since early April, and area lake levels have followed suit. Lavon Lake, a major water source for North Texas Municipal Water District (NTMWD) member cities, is about 9 ½ feet below its ideal level of 492 feet. Lake levels have been dropping from that mark since May 18.
"Anytime reservoir levels fall below the conservation pool, we're considered in drought conditions," said Denise Hickey, NTMWD spokesperson. "While we're much better than a year ago, we're still in a drought situation."
NTMWD is the water supplier for 13 cities in Collin, Dallas, Denton, Rockwall, Kaufman, Hunt, Hopkins and Rains counties in North Central Texas. It uses water from reservoirs at Lavon Lake and Jim Chapman Lake, among other locations. Its largest source, Lake Texoma, has been offline since 2009 because of invasive zebra mussels. With water from the Sabine River Authority and the East Fork Raw Water Supply Project, the district provides water to more than 1.3 million people.
But it relies on certain lake levels to maintain effective storage, regulation and controlled release of that water. The reservoir's top section is a flood pool, operated by the U.S. Army Corps of Engineers (COE), which stores rain runoff to prevent flooding. When it rains, the COE can release some water to fill the water conservation pool, to which water districts have state-allocated access. A lake is considered full when the conservation pool is at its optimum level - of which all area lakes are short.
"Our water restrictions will remain at Stage 2 for now, because typically fall and spring see heavy rains that replace the reservoir supply," Hickey said. "If we don't get those rains, we'll have to evaluate our water supplies, and may have to strengthen restrictions."
As for that replacement rain: one futile "heavy rain" season down, one to go.
Jamie Gudmestad, a meteorologist with the National Weather Service (NWS) said in August that weather and climate models showed a 30 to 40 percent chance of greater than normal precipitation from November to February.
But North Texas saw no measurable rainfall last month, and, coupled with a very dry October, eight straight months of precipitation deficits have exceeded 10 inches across the region, according to a recent NWS 2012-13 Winter Outlook report.
Statewide reservoir capacity has dropped more than 12 percent, to 64 percent, over the past six months. Though capacity remains about 6 percent higher than it was this time last year, inadequate rainfall has led to a steady decline for North Texas lakes typically healthier than lakes elsewhere around the state, the report says.
The Upper Trinity Regional Water District (UTRWD), which services all of Denton County and portions of Collin and Dallas counties, is facing the same situation. Water sources Lewisville Lake, Ray Roberts Lake and Jim Chapman Lake are below their optimum levels: Lewisville Lake is about 6 ½ feet below, Ray Roberts Lake is about 7 feet below and Jim Chapman Lake is nearly 5 feet short.
"The dryness and above-normal temperatures are not typical for this time of year," said Jason Pierce, UTRWD watershed and contract services manager. "We have not seen the rains that bring lakes back up to a reasonable level. It emphasizes the need and importance of water conservation."
UTRWD customers are under Stage 1 restrictions, but Pierce said the district is "carefully watching and monitoring lake levels." If necessary rain doesn't fall on the area but does fall farther east, that water drains into Jim Chapman Lake and keeps the UTRWD with a source to tap into, he said.
Levels are also low at Dallas Water Utilities (DWU) lakes, which provide water for most of Dallas County and small portions of Collin, Denton, Kaufman, Ellis and Tarrant counties. Grapevine Lake, Lake Ray Hubbard, Lake Tawakoni and Lake Fork are all at least 4 feet lower than ideal height - accounting for about 17 percent depletion in available water - according to DWU figures.
The UTRWD is in the permitting process for adding Lake Ralph Hall to its sources, and will come to a critical point in that 10-year process in January, Pierce said. According to the water district's projections, it could need Lake Ralph Hall by around 2025 to avoid a serious water shortage - a situation that extended drought could hasten it toward.
Natural relief is not in the winter forecast. Normal precipitation levels expected through February wouldn't alleviate drought conditions given the lack of rain in recent months. Prevailing El Nino Southern Oscillation (ENSO) -neutral conditions - which historically mean less precipitation - and a trend toward warmer winters will likely lead to an even drier region, the NWS says.
Such a climate isn't conducive for an area already plagued by drought. Dry fall months have forced warm-season vegetation into early dormancy, thus keeping away cold-season grasses. "Without adequate precipitation this winter, the threat of wildfires will persist, particularly on days with strong winds and low humidity," the NWS says.
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