At its February 2020 board meeting, the San Jacinto River Authority (SJRA) Board of Directors will consider NOT lowering Lake Conroe during the spring and fall rainy seasons. Lake Conroe residents have mobilized to protest the lowering which they see as a costly inconvenience. They have started spreading disinformation about the policy. The SJRA Board has reportedly already received more than a hundred letters protesting the policy.
Reason for Lowering and Current Status
The strategy of lowering Lake Conroe on a seasonal basis reduces the risk of flooding downstream residents by increasing the capacity of Lake Conroe to store water. The SJRA Board of Directors and City of Houston review the strategy annually. Both entities own water rights in Lake Conroe.
This year’s seasonal lowering of Lake Conroe ended October 1st. However, as of this morning, the lake level is down to 198.77′ MSL (mean feet above sea level). That’s 2-3 inches below the target level for the fall lowering. The lower level is due to evaporation and low rainfall; the SJRA stopped releasing water on October 1.
After Hurricane Harvey, the State of Texas called on the SJRA Board of Directors and the City of Houston to participate in regional strategies to reduce flooding. The temporary lowering of Lake Conroe has reduced releases from Lake Conroe during storms. SJRA and downstream communities realize and understand the inconvenience that the strategy can create around Lake Conroe. We ask for understanding for the duration of this temporary mitigation strategy.
Seasonal Lake-Lowering FAQs
The City of Houston and the SJRA collaborate on the decision to temporarily lower Lake Conroe for flood mitigation because it effects the water supply of both entities.
How Long Will It Continue?
Seasonal lake lowering is a temporary flood mitigation initiative to increase the capacity of Lake Conroe to catch rainfall and runoff while long-term and short-term flood mitigation strategies are implemented downstream.
The motion made by the SJRA Board states that the intent of the proposal is to provide “a near-term, temporary flood mitigation benefit while more permanent mitigation strategies, such as dredging of the lower West Fork, are completed.”
When Does It Happen?
Seasonal lake lowering occurs twice annually – first in April/May and second in August/September.
How Much is It Lowered and for How Long?
In the spring, releases begin on April 1st. SJRA gradually reduces the level of Lake Conroe to 200’ mean feet above sea level (msl)—one foot below the normal Lake Conroe pool level of 201’ msl. Starting on June 1st, SJRA recaptures flows to restore normal lake elevation to 201’ msl.
In the fall, releases begin on August 1st. SJRA gradually reduces the level of Lake Conroe with a goal of reaching 200’ msl by August 15th. After August 15th, gradual lowering continues with a goal of reaching (and maintaining) 199’ msl—two feet below normal pool—by August 31st. Starting October 1st, SJRA begins to capture flows to restore normal lake elevation to 201’ msl.
What If The Lake Is Already Down?
If the lake level has already dropped to the target elevation due to evaporation, no releases are made.
What if It Rains While the Lake is Already Lowered?
If a storm enters the forecast while seasonal releases are being made to lower the lake level, releases are stopped and the river is allowed to drain out until rainfall is out of the forecast.
Is There Science Behind This Policy?
Two engineering reports by Frees & Nichols from early 2018 show the benefits in terms of flood mitigation and the potential negative impacts to water supply. These reports as well as additional information about seasonal lowering can be found at: https://www.sjra.net/floodmanagement/.
Has it worked? Is there real value in terms of flood mitigation?
Yes. Looking at recent rainfall events, seasonal lowering resulted in both lower peak lake levels during storms and lower release rates from the dam.
For example, the spring 2019 seasonal lowering created an additional one foot of storage space to capture rainfall in early May 2019 when storms hit the Conroe and Lake Houston areas. Lake Conroe caught significant rainfall and runoff during the storms causing the lake to rise more than a foot. If Lake Conroe had entered this event at or near full, the peak release rate would have been higher thereby increasing the peak flow in the West Fork of the San Jacinto River.
Is There a Benefit to Lake Conroe?
Seasonal lowering also reduces the peak Lake Conroe level during storms, which reduces negative impacts around the lake such as damage to docks and other personal property. During Harvey, several hundred homes around Lake Conroe flooded.
Data for the May event, and for all releases from the dam, including those during seasonal lowering periods, can be monitored by visiting SJRA’s home page at www.sjra.net. Click on the “Lake Operations and Rainfall Dashboard.”
What is the cost of the release?
Lake Conroe was built as a water supply reservoir in the 1970s through a partnership between SJRA and the City of Houston. Two thirds of the water in Lake Conroe belongs to the City of Houston and one third to SJRA. The City of Houston can call for the release of its water at any time, and water supply reservoirs are built to fluctuate as demands or operational needs dictate.
Releases such as those made for dam repairs and seasonal lowering are not charged to any particular customer, therefore it is not possible to assign a value to the water released. In addition, temporary, non-customer releases do not reduce long-term water supplies, therefore they are not considered lost revenue.
To be considered as lost revenue, releases would have to happen at a time when the SJRA could not meet demand with water from Lake Conroe. But that has not happened.
And most important, if the water supply in Lake Conroe were ever threatened, say from drought, the SJRA would not be releasing water anyway. The lake level would already be far below the target level, making a release unnecessary.
Is This a Permanent Program?
No. Seasonal lowering is a temporary flood mitigation strategy that must be reconsidered each year by the City of Houston and the SJRA Board of Directors while more permanent mitigation strategies, such as dredging of the lower West Fork, are completed.
How Do I Make my Opinion Known to the Board?
The SJRA Board of Directors welcomes input regarding the seasonal lake lowering strategy. If you would like to contact the Board please visit: https://www.sjra.net/about/board/ or email firstname.lastname@example.org.
Posted by Bob Rehak on 11/23/2019
816 Days since Hurricane Harvey