SJRA Starts Seasonal Release to Lower Lake Conroe

After the Easter weekend, the San Jacinto River Authority (SJRA) started its seasonal-release plan. The river authority is currently releasing at a rate of 529 cubic feet per second (CFS) from Lake Conroe. At that rate, the lake should reach its target level of 200 feet above sea level by the end of April, according to Jace Houston, general manager of the SJRA.

Seasonal Release from Lake Conroe, 529 cfs from one tainter gate open six inches.
SJRA Seasonal Release on 4/15/2020. One tainter gate open six inches releases a slow, steady stream of 529 cfs. Image courtesy of SJRA.

The slow rate of release avoids flooding downstream property and the lower lake level provides additional capacity in the lake. That additional capacity provides a buffer against flooding for downstream residents.

About Seasonal Lake Lowering Policy

Houston said the River Authority will hold the lake at 200 feet through the end of May, then allow it to reach its normal level for most of the summer.

Lake Conroe actually reached 200.75 feet before SJRA began its seasonal lowering this week. A reduction of .14 feet equates to about one and two-thirds inches of lowering so far.

At 200.75 feet, Lake Conroe was actually above its highest average monthly level for the year, which is 200.44 feet in May. The normal level for April is 200.32 feet.

Lake Conroe seasonal levels by month. From SJRA board presentation by Chuck Gilman in January.

Earlier this year, a bitter fight broke out between upstream and downstream property owners over the seasonal lake lowering policy. The SJRA board decided to extend the lake lowering plan, but modify it. In the fall, they will let the City of Houston, which owns two-thirds of the water in the lake, decide whether to take the lake down below 199.5 feet.

The extra lowering in the fall helps protect against hurricanes and tropical storms, such as Harvey and Imelda. The SJRA begins slowly lowering the lake in August for the peak of hurricane season in September and then letting it resume its normal level again in October. For the exact details of the policy adopted by the board in its February meeting, click here.

Lake Houston Level Declining

Despite the start of the seasonal release and last week’s rains, the level of Lake Houston has declined this week. And rivers are far from flooding.

Normal level for Lake Houston is 42.5 feet, but City is still lowering lake for spillway maintenance.

Uncertain Weather for This Weekend

Jeff Lindner, Harris County meteorologist, predicts that storms this weekend could bring several inches of rain. “With the Gulf of Mexico water temperatures running several degrees above average for this time of year, winds blowing off the Gulf will need little time to supply a rich moisture-laden air mass.” 

The NWS predicts a 30-40% chance of showers and thunderstorms for this weekend as a front passes. However, Lindner notes, models diverge widely in their predictions. The Global Forecast System (GFS model) predicts that most rain will happen over the Gulf with little impact to land.

However, the European Medium Range Forecast Model (ECMWF) predicts a very wet weekend with several rounds of storms and several inches of rainfall for much of southeast Texas.

Which Model is Better?

ECMWF is considered one of the premiere global forecasting models for the mid-latitudes. Statistically, it has been more accurate than the GFS model.

NOAA has tripled spending on supercomputing capacity to make GFS the best model in the world again.

Posted by Bob Rehak on 4/15/2020

960 Days after Hurricane Harvey