More Effective, Cheaper, Easier to Maintain, Better for the Environment than Buried Stormwater Pipes
May 22, 2023
For several years a controversy over open drainage ditches has been swirling around the city of Houston. We’ve been scraping behind the scenes, trying to clear up some of the misunderstanding. But the flow of misinformation hardly slows.
The basic misunderstanding is that roadside drainage ditches — grass-lined, maybe filled with lilies, cattails, frogs, fishes, crawdads — don’t work as well as concrete curbs on the street funneling stormwater through metal drains and into buried concrete pipes.
Nope. Wrong. Except in dense urban areas completely covered in impermeable surface, earthen stormwater ditches work much better than concrete street curbs and buried pipes, according to our expert sources.
An Age-Old Prejudice
It’s an age-old prejudice. People look at earthen ditches and think they are backwards. Too rural, rudimentary, unfinished. Concrete is surely more modern, more advanced! (Other people look at flowering roadside ditches and think: how lovely. They look at a brutal concrete curb and sense that the earth is being smothered.)
Developers discovered this long ago. Private developers are responsible for installing drainage systems in new residential areas, systems which are then turned over to the city for maintenance. Over time developers found that while some people appreciated the natural aesthetic and function of vegetated open ditches, home buyers often viewed ditches with distaste, as noted in a comparative study of The Woodlands. (p. 2) So, despite being more expensive and less effective, developers switched to concrete curbs and buried pipes solely in order to sell more homes. It had nothing to do with function. It was purely aesthetic.
How Much More Effective, More Beneficial? Ten Times More
Open ditches can hold more than ten times as much stormwater as buried pipes, among other important benefits. A typical 3.5-foot-deep roadside ditch 1,000 feet long holds 325,900 gallons of stormwater, according to the City of Houston Department of Public Works. By comparison 1,000 linear feet of 24-inch diameter pipe holds only 23,488 gallons.
Note, however, that the City is not fond of all that pretty greenery inside the ditch, even if it helps filter trash and nasty stuff from the water.
People assume that open ditches foster mosquitoes. But in fact mosquitos are more likely to breed in pipes and in catch basins under storm drains. According to the Environmental Protection Agency, mosquitoes breed in shallow water – less than 3 feet – that has been standing for at least 7 days. The agency actually recommends replacing curbs and gutters with open ditches.
Concrete Increases Flooding
The reason is that open ditches have more co-benefits than storm sewers and culverts, as noted in a recent watershed study by the US Army Corps of Engineers. (p. 14) Ditches help cleanse polluted stormwater runoff, allow the earth to soak up rain, and are cheaper and easier to install and maintain. (p. 22) Curbs and gutters, on the other hand, actually increase flooding by collecting more water faster, eventually overwhelming our built and natural drainage systems (creeks and bayous), according to the National Research Council. (p. 183) And pipes settle and crack and need to be replaced. Ditches don’t.
Note that Houston property owners actually get a modest drainage fee reduction for having an open ditch, which is considered pervious surface, which helps reduce runoff and flooding.
Maintenance. Another Misunderstanding
No, property owners do not have to maintain the ditches in front of their property. Yes, they are responsible for picking trash or other debris out of the ditch that might block the flow of water in front of their house. This is equally true in lower-income neighborhoods and well-to-do neighborhoods, like Hunters Creek Village in west Houston (actually a separate municipality). (p. 263)
But the Ditch Maintenance Section of Houston Public Works is responsible for de-silting and re-grading ditches, as well as flushing culverts under driveways and streets within the city.
And yes, there are wealthy, older neighborhoods all over the city with open ditches: Memorial, Briar Oaks, historic Avondale and Courtland Place in the Montrose area, just to name a few, not to mention in the Heights, Rice Military, as well as in dense, shadeless Gulfton and other parts of southwest Houston; Sunnyside to the southeast, Scenic Woods to the northeast, and much more. Friendswood and the Woodlands, too. Usually it’s a mix of open ditches and buried pipes, perhaps a compromise, perhaps the result of ditches getting (illegally) covered over.
Problems: Dumping, Size, Complaints
The most frequently cited problem with open ditches, particularly in front of empty or sparsely inhabited areas, is illegal dumping of heavy trash and construction debris that blocks the flow during storms. The City of Houston provides facilities for residents to dispose of tires, appliances, heavy trash, tree waste, and more for free, but contractors and commercial businesses are prohibited. Privately operated landfills charge a fee. (See info here.) So likely its cheaper, quicker, and easier for some to just dump stuff where nobody’s looking.
Getting It Fixed
To try to get a blocked ditch cleared or regraded (water needs to flow in the right direction), a resident would either call 311 or contact their city council representative. The city’s Stormwater Action Team (SWAT), created after Hurricane Harvey, works primarily through councilmembers. Last summer, Mayor Sylvester Turner announced an additional $20 million in funding for SWAT projects.
The 311 complaints go to local drainage teams that coordinate with maintenance crews. The 311 call data, along with information from the Harris County Flood Control District and the Federal Emergency Management Agency, also goes to planning teams who determine where the greatest needs are.
But the 311 system can be frustrating, acknowledges someone in the know. The City has some 3,300 miles of storm sewers and 2,800 miles of roadside ditches to maintain, as well as a large bureaucracy.
But everyone should call 311! urged this knowledgeable person. And community members should work with their community groups to get the attention of their council member. Being more politically active and connected obviously helps.
Note that street gutters and drains can also be blocked by trash and debris. The City of Houston has an Adopt-a-Drain program for residents to volunteer to help keep drains clear.
Pipe or Ditch?
The City of Houston requires that both stormwater ditches and pipes be sized to handle at a minimum a rainfall event likely to happen every two years. The National Oceanographic and Atmospheric Administration (NOAA) currently defines a two-year event in the Houston region as 4.43 to 5.17 inches falling in 12-24 hours.
However, with climate change and increasing rainfall, these definitions have to be continually updated, meaning that static storm drainage infrastructure rapidly becomes outdated, if it wasn’t already. NOAA is currently working on rainfall updates, known as Atlas 15.
But the City is never going to be able to keep enlarging our drainage system to keep up with increasing rainfall. Which is why federal agencies (p. 78), Save Buffalo Bayou, Harris County, and even the City itself (p. 21) recommend stopping rain where it falls; slowing down, spreading out, and soaking up rain runoff.
Here are some additional tips on ways individuals can manage rainwater runoff.
What’s the Difference? Where are the Problems?
Normally roads or streets are built higher than ditches so that rain hitting the street runs off into the ditch. Streets with curbs and gutters are constructed below the level of the surrounding ground so that stormwater is collected in the gutters and flows into the underground storm drains.
For that reason it’s not simple to turn a high street with ditches into a low street with curbs and underground pipes. It’s also why streets with curbs and gutters often flood. They are designed to do that – to hold temporarily the backup or overflow from overburdened storm sewers. Residents should also expect occasional ponding in and around ditches. (p. 183)
But there are problem ditches and problem pipes, especially with so much old drainage built on outdated standards. The City’s Public Works Department is currently developing a Stormwater Master Plan based on a two-dimensional model of the City’s drainage system. It will illustrate where existing infrastructure has deficiencies and provide tools to plan improvements more objectively, according to Public Works.
Fishes of the Ditches
In the meantime, here are some of the creatures one might find in ditches.
Toads and Tadpoles