The day after Memorial Day much of the Greater Houston area was underwater as a result of flooding caused by a major storm that in some areas brought up to 11 inches of rainfall in just six hours.

The flooding and damage brought on by the May 25 storm was far less, however, in the more developed areas of Fort Bend County and areas of the county protected by levees, such as in Sugar Land and Missouri City. Local officials said this could be attributed to the effectiveness of the county’s flood and drainage infrastructure.

Despite experiencing less flooding and damage than other areas after the most recent storm event, Sugar Land and Missouri City both have areas within the city limits where drainage can be improved, officials for both cities said. These drainage improvement projects have been outlined in the master drainage plans for each city.

“We have laid out a pretty aggressive plan that has been backed by City Council,” Sugar Land City Engineer Chris Steubing said. “We feel confident moving forward that we have identified most of the areas in the city where we think there are issues or concerns.”

Local effects

Fort Bend County’s flood control and drainage infrastructure for any development in the county must meet criteria to withstand a 100-year storm event, or anywhere from 12.5 to 13 inches in 24 hours, said Mark Vogler, district drainage manager and chief engineer for Fort Bend County. The rainfall that occurred on May 25 in the county was classified as a 120-year event that produced anywhere from eight to 11 inches of rainfall in six hours.

“The county experienced an extremely high amount of rainfall that fell between four and six hours in duration,” said Gregory Frank, a drainage engineer for some of Fort Bend County’s levee improvement districts. “Our design locally here on this part of the Gulf Coast is about 12.5 inches in 24 hours. We had 10 inches of that in four to six hours, so for that duration of [the] storm, we easily exceeded a short duration 100-year event.”

Although the rainfall exceeded what the infrastructure is designed to handle, Vogler said the flood control system in the county still functioned well and provided some extra storage beyond what was required because of other safety factors built into the design.

The storm did cause flooding of homes and land as well as some street ponding and the overflow of detention ponds particularly in the more rural areas of the county where the systems were unable to handle a rain event of that magnitude, Vogler said.

“The Memorial Day rain was very significant, and I got numerous calls and messages from property owners throughout the more rural parts of the county about their land being flooded or having water in their house,” Vogler said. “I cannot say absolutely that no houses within levee [improvement] districts got water in them, but I will say that I have not heard of any. That’s not to say that it did not occur, but if there were any homes [in the LIDs] that flooded, there were very few of them.”

The city of Sugar Land experienced about 11 inches of rainfall in eight hours during the May 25 storm, Steubing said. The storm caused some street flooding and ponding, but no significant structural damage, property loss or loss of life was reported.

“When the rain event occurred on Memorial Day, we had some calls come in about high water on the streets, and that was about it,” Steubing said.

The city streets pond to a certain level above the top of the curb with that kind of rain event, but will then recede within a timely manner, he said. The morning after the storm hit, about 95 percent of the city’s streets were passable, and there were only a handful of areas that still had standing water.

“This was a good test of our systems and strategies, and we have identified areas where we can still improve, as you should always be looking for, but all in all the city fared very well for such a pretty intense rainfall,” Steubing said.

In Missouri City the volume and intensity of the storm caused street ponding, high water in the city’s streams and channels, and flooded some vehicles, Assistant City Manager Scott Elmer said.

“While there was significant street ponding, high water in streams and channels and some measure of overland flooding, overall, Missouri City faired pretty well,” Elmer said. “Most of the damage identified to date has been from flooded vehicles. Structure flooding that has been reported has been relatively minor.”

Elmer said the streets in Missouri City are part of the stormwater system and are designed to flood to carry water away from structures. Because of the flat topography of the area, the roadways had to be designed to play a role in area drainage, he said.

Ongoing improvement efforts

Flood control and mitigation in Fort Bend County are a joint and collaborative effort between the county, the cities and the various LIDs and municipal utility districts, all of which have their own roles to play, said Andre McDonald, president of Fort Bend LID No. 2 and the Fort Bend Flood Management Association.

Both Sugar Land and Missouri City have a number of areas that are protected by levees, which are managed by either LIDs or MUDs.

Sugar Land has several LIDs that protect a majority of the city, with the exception of the north side of town, where there is no need for levee protection, Steubing said.

There are approximately 40 agencies that have flood control roles in Missouri City. The list includes LIDs, MUDs, drainage districts, municipal management districts and flood control districts in both Fort Bend and Harris counties, Elmer said.

The LIDs and MUDs that offer levee protection provide flood and stormwater management resources to those who reside or conduct business in the geographic area protected by the LID or MUD, McDonald said. The LIDs and MUDs are responsible for the upkeep and maintenance of the levees, pump stations, drainage ditches, detention and retention ponds.

The cities in the county have different responsibilities when it comes to flood control.

“The city’s flood control role is to coordinate, design, require, implement and establish drainage infrastructure and standards to achieve the goals of no structure flooding and passable major thoroughfares during a 100-year storm event,” Elmer said.

In both Sugar Land and Missouri City, improving drainage within the cities is a major priority and is something that is constantly being monitored and addressed by city officials.

As part of Sugar Land’s efforts to continually improve drainage within the city limits, Steubing said the city has a significant amount of drainage work that is underway or that is planned in the city’s five-year capital improvement plan. The city will be spending upward of $40 million over the next five years on drainage improvement projects throughout the city in areas where issues have been identified, he said. Most of the projects are designed to mitigate extensive street flooding and reduce the risk of structural flooding.

Missouri City has developed a master drainage plan for each of the eight watersheds within the city. Improvements identified include drainage channel widening, regional detention basin construction and drainage structure improvements.

Elmer said these master drainage plans are updated as necessary and new development is constructed in accordance with these plans. The plans also lay out a roadmap for needed drainage improvements to prevent structure flooding and to maintain major thoroughfares in a passable condition in the event of a 100-year storm.

“Missouri City has completed the implementation of the improvements in about half of the drainage plans and is working toward completion in the others,” Elmer said. “Recent rains did not reveal any drainage issues that were previously unknown to the city.”