The flooding is not necessarily because of exceptionally high rainfall, according to Jennifer Dunn, a warning coordination meteorologist with the National Weather Service.
“Probably in the last five years, the annual average has been a little bit higher than maybe the last 20 years, but we’re not necessarily well above what’s considered normal,” Dunn said.
Rather, the source of the flooding can be attributed in part to the growth of Colleyville’s population and the subsequent laying of concrete for new housing developments, Mayor Richard Newton said.
“[As] new development goes in, ... we require a grading plan and a drainage plan, and [we] spend a lot of time on those things,” Newton said. “Typically, the developments are designed well, but by the time lots get sold and builders build houses and they change the grading plans when they build a house, ... there becomes a problem of flow between lot to lot.”
This can lead to issues of flooding when there are fewer avenues for stormwater to soak into, Dunn said.
“As you put more concrete down, that’s less area for the water to soak into and more for it to run off too, and that is where you might see an increase in flooding in certain areas,” Dunn said.
Lourdes McWithey has lived near Little Bear Creek in Colleyville for 17 years. She said she has learned to get used to the flooding that occurs near the crossing of the creek and Bedford Road.
“On Bedford Road across from Sparger Park—it floods,” McWithey said. “[City staff will] watch it and they close the road.”
A 2019 city-commissioned study evaluated 125 road crossings in Colleyville. The study, conducted by design and engineering firm Kimley-Horn, also identified instances of flooding, retaining wall erosion and debris deposits throughout the city.
But big projects mean big money. The list includes roughly $40 million worth of projects at 45 road crossings in Colleyville.
That high price tag is causing city officials to evaluate the way they collect fees for the city’s stormwater fund, Public Works Director Ray Silva-Reyes said.
“We charge $7 per water meter account for stormwater, ... and that doesn’t generate enough to tackle all the operation and maintenance that you have to normally do, plus any capital projects,” Silva-Reyes said.
Those fees are just enough to maintain existing stormwater systems, Kimley-Horn engineer Misty Christian said.
“It’s going to take you ... about $300,000 at least a year just to keep up the maintenance and cleaning out ditches and culverts and silt. It’s definitely a full-time job,” Christian said at a May 19 City Council meeting.
As alternative scales for assessing stormwater fees are still being considered by council, Newton has voiced his support for one that is more equitable.
“The reality of it is ... the runoff is a function of how much impervious area you have,” Newton said. “Some of the houses are so big, they have a high percentage of impervious area if you count all the driveways and patios. ... The [fee structure] I’m a proponent of is that we come up with a charge based on how much impervious area you have.”
That means larger lots with more laid concrete would pay a higher fee, while smaller lots with more permeable ground would pay less.
The Kimley-Horn study commissioned by the city has organized the 45 stormwater projects into a list by low, medium and high priority.
Some of the construction work throughout the city would include adding storm drains, reconstructing retaining walls and elevating low-water crossings.
Six of the 45 identified projects are low-water crossings. Though few in number, they would run up a hefty tab.
“I believe the low-water crossings add an additional $20 million,” Silva-Reyes said. “They’re pretty significant improvements because ... most of these [crossings] are over flood plain areas. ... You would have to raise them all above the 100-year water elevation.”
City Manager Jerry Ducay said there may be early alternatives to remedying flooding events other than immediately raising the roads out of the flood plain.
“The low-water crossings primarily are going to be funded in conjunction with other agencies, like [the Texas Department of Transportation], and they are going to be grant funded,” Ducay told City Council at the May 19 meeting. “At some future meeting, you are going to be asked to share your tolerance as to what kind of increases in [stormwater] fees would be reasonable. ...
“This is definitely a process, ... and it is much more complex and expensive than I think most people realize.”
Colleyville City Council is scheduled to discuss its preferences for the stormwater fee this year.