River authority lowers Lake Conroe water level ahead of expected storms next week

Ahead of a stormy outlook over the next week, the San Jacinto River Authority began releasing water from Lake Conroe Friday, a move that was not made prior to the storms that swept through the area and sparked the flooding of hundreds of homes at the beginning of May.

The release was prompted by a request from the city of Houston.

According to Houston Public Works spokesperson Erin Jones, the decision was made to prepare for what is expected to be a week of heavy rainfall as part of the city’s “active storm management protocol.” The National Weather Service’s seven-day precipitation forecast total has the area seeing up to six inches of rain.

That would be enough to cross the four-inch threshold for what the city considers heavy enough rainfall to trigger a lowering of Lake Houston by 12 inches.

However, that forecast is not the same as the city’s current outlook, which specifically targets the area north of Interstate 10.

“Right now, it’s showing three, six inches widespread south of I-10, with one to three inches possible north of I-10. So that’s, again, still one to three inches,” Jones said. “If that increases, which it could over the next few hours, next few days, then they would make that decision.”

( Update: The city announced it would begin lowering the level of Lake Houston by 12 inches on Sunday.)

Jones said the storms earlier in May had not met that threshold, with forecasts showing just up to four inches. Once the storm started and projections crossed the threshold, the Coastal Water Authority opened its gates.

“There was so much rain, it did not have a significant impact to reduce flooding,” Jones said.

Lowering the lake levels frees up space in the reservoirs to accommodate additional storm runoff, giving managers more flexibility to control water releases that can contribute to flooding downstream.

Jones pointed out that the two lakes also provide drinking water for the region, so the city and other agencies must balance flood preparation with water to service the area.

Friday’s release sent water from Lake Conroe to Lake Houston via the West Fork of the San Jacinto River, the first in what likely will be a series of choices throughout the weekend to move water into Galveston Bay. Once water levels in Lake Conroe reach an acceptable level with short- and long-term forecasting in mind, attention will turn to Lake Houston.

When the forecast for rain exceeds four inches across a widespread area, the city and Coastal Water Authority, which operates Lake Houston, will give 24 hours notice before beginning to drain that reservoir. According to Jones, it takes about 24 hours to lower the lake by 12 inches.

Moves to divert water in advance of excessive rainfall began after the city and the river authority agreed to end seasonal lake lowering to keep water levels safe. The seasonal lowering already had been suspended for two years due to a drought.