Storm events in the Lake Houston area are more intense than they were decades ago, according to the National Oceanic and Atmospheric Administration’s Atlas 14—a report released in September 2018 that updated Texas’ precipitation frequency estimates.
Lake Houston-area residents are experiencing this intensity firsthand, with numerous neighborhoods flooding twice in less than six months in the May 9 heavy rain event and during Tropical Storm Imelda on Sept. 19.
Houston City Council Member Dave Martin said at an Oct. 30 City Council meeting that he was worried if something was not done about Kingwood’s drainage soon, another flooding event will damage more structures.
“We had less than 2 inches of rain [in mid-October], and we had street flooding,” Martin said. “Something’s happening there. I don’t know what it is, but something has changed, and something has changed dramatically.”
To combat flooding in the region, officials are studying drainage systems in the Kingwood area using the new Atlas 14 data as a reference.
Rainfall intensity
A 100-year storm, or a storm with a 1% chance of occurring each year, in the Lake Houston area now brings about17 inches of rain in a 24-hour period versus 13.2 inches in 2007, according to data from Atlas 14 and the Harris County Flood Control District.
Houston Public Works Director Carol Haddock said the intensity of recent rainfall events is something that worries local officials.
“I am worried about the intensity of rainfall we are seeing in the Houston area,” she said. “It is more intense; it is more rain in an area than we have seen in the last 30 years.”
Both Harris and Montgomery counties as well as the city of Houston adopted Atlas 14 standards into their rainfall data. The counties also adopted new drainage and development standards to help prevent future developments from worsening flooding in the surrounding areas.
In July, Harris County increased its minimum stormwater detention rates by 20%, required projects of 20 acres or more to submit detailed engineering and adopted the 500-year flood plain as the interim 100-year flood plain for development standards.
In October 2018, Montgomery County commissioners adopted guidelines that changed the design of detention ponds, according to an Oct. 7 news release from Montgomery County Precinct 3 Commissioner James Noack’s office.
However, Elm Grove resident Beth Guide said at an Oct. 17 town hall meeting she feels like the counties should work together to ensure development in one county does not negatively affect the other.
“Somebody in Harris County ... needs to sit down and look at those plans as if it were one geographical area and not a county line and another county that they don’t have to deal with,” she said.
The new development standards are not retroactive, so officials have to take different approaches to improve existing drainage in Kingwood.
Studying drainage ditches
A Nov. 11 report from district meteorologist Jeff Lindner determined Imelda’s flooding was caused by street and channel flooding, rather than Hurricane Harvey’s effects on the San Jacinto River.
“Much of the structure flooding that occurred in the Kingwood area was not a result of flooding from the river, but instead flooding of local drainage systems that were overwhelmed from the intense short duration rainfall rates,” the report read.
Carl Woodward, special projects manager for the district, said the district has spent roughly $3 million on maintenance and debris removal in Kingwood’s drainage channels since Harvey as of late September, including the Bens Branch Conveyance Restoration Project that began in August.
Funds for these projects comes from federal storm recovery moneys, the flood control district’s operation and maintenance funds, and Harris Country’s $2.5 billion flood infrastructure bond approved by voters in August 2018, Woodward said.
The district also began a study in September to analyze the level of service on all Kingwood channels, which move water out of Kingwood into the river. The $700,000 study received funding from the district and Tax Increment Reinvestment Zone 10.
Matt Zeve, the deputy executive director of the district, said the study will determine which channels could be enhanced. Engineers will determine drainage concerns and present conclusions in April.
“We know that the drainage in Kingwood, especially on our channels, is at a very high level of service,” Zeve said. “But the people in this area, they want a 100-year level of service.”
While the study needs to be completed to know what projects could improve channel capacity, Zeve said he assumes channels would have to be widened, which could involve buying out homes along the channels.
Street flooding
Meanwhile, Houston Public Works, the entity that manages and maintains much of Kingwood’s storm sewers, is addressing internal drainage. Haddock said flooding in parts of Kingwood is partially due to design standards from when it was built in the 1970s.
Streets built before 1984 were not required to operate as storm-conveyance areas when pipes filled. Areas built after 1984 require pipes to fill in a two-year storm and streets to carry excess rainfall in 100-year events to channels, she said.
“In those older areas, when it gets out of the pipes, it may get out of the streets quicker than an area that we’ve recently designed and built,” she said. “It is a perception the public has that when the streets fill up that they are flooding, and the reality is that we purposefully fill the streets up so the homes aren’t flooding.”
Haddock said the city is also revisiting its design standards to decide what it would cost developers to install larger pipes that could handle rainfall shown in Atlas 14. The last time the city updated its requirements was in the late ’90s and early 2000s, but cost concerns from developers caused the updates to not move forward, she said.
If design standards are updated, however, updating existing storm system pipes to new Atlas 14 data is not realistic or cost-efficient, Haddock said. She said that updating the existing pipes to new Atlas 14 criteria would not result in systems performing any differently.
Instead, the city’s Storm Water Action Team—which launched in January 2017—is committed to ditch-rehabilitation projects and stormwater pipe replacements in the Kingwood area to improve existing drainage.
Following Imelda, public works began inspections of storm sewers in 23 Kingwood neighborhoods. The department was set to complete inspections on Elm Grove and Hunters Ridge in late November after press time.
Editor's note: This article has been updated to clarify that updating the existing drainage pipes in Kingwood to new Atlas 14 criteria would not result in systems performing any differently.
Correction: The original version of this article incorrectly gave Matt Zeve the title of executive director with the Harris County Flood Control District. The article has been updated to reflect the correct title.
