What Houston and Other Cities Are Doing to Reduce Flooding
And Make Life Better
Feb. 11, 2021
Despite flooding issues that threaten lives as well as the future of the city, Houston has lagged behind other cities in the state and around the world in encouraging, implementing, or requiring basic steps that can reduce flooding. Harris County, along with six other Texas cities, scored higher than Houston on Environment Texas’ 2020 Scorecard.
But recently the Houston City Council passed a property tax incentive to large commercial developers who use green (nature-based) infrastructure to slow stormwater runoff from their new projects.
Developers are already required to prevent an increase in the amount of stormwater running off projects built on previously undeveloped land. Now Houston taxpayers will actually pay for the cost of doing that if developers use rooftop gardens (green roofs), vegetated swales, permeable paving, trees, etc., known as Green Stormwater Infrastructure (GSI). Also known as Low Impact Development (LID) or even Sustainable Urban Drainage Systems (SUDS), though the latter also focuses on reusing stormwater.
Slowing stormwater runoff reduces flooding. And in addition to passing the property tax incentive to large commercial developers, the City of Houston recently increased its stormwater detention requirements for new single-family residential projects. This was forced in response to Harris County requirements. No tax incentive yet.
However, the City does reduce the city drainage fee based on the percentage of pervious surface on a lot. So planting a garden on your roof, for instance, changes the roof from an impervious surface into a pervious surface and reduces your drainage fee. (See below.)
Elsewhere, cities like Toronto and Utrecht require green roofs, which can reduce stormwater runoff by more than 50 percent. (Toronto provides financial assistance.) Simply disconnecting roof downspouts from the public stormwater drainage system can help prevent the system from being overwhelmed, a practice recommended by the Environmental Protection Agency.
From California to Illinois to New England, cities are asking residents to disconnect downspouts and instead allow rainwater to flow and soak into a yard, among many other things. (Directing roof runoff onto a concrete driveway, seemingly common practice in Houston, is not helping, since it runs directly into the paved street and into the stormwater system anyway.)
We’ve been gathering information for a while with the intention of eventually posting about what Houston and other cities are doing about flooding. It’s complicated!
Flooding Begins on the Land
Stormwater is rain that falls and runs across the ground into our built (pipes) and natural (bayous and creeks) drainage system. The harder the surface, the faster the runoff, the higher the flooding in our streets and streams. Also, the more polluted the water. And the uglier and hotter the city.
In recent years, experts have shown that nature-based drainage and detention systems are cheaper to build and maintain as well as more effective in reducing flood risk than pipes and dams, for instance. (See also here.) There are also more benefits, because you end up with trees and native plants, bees, birds, and butterflies, stuff that actually increases the attractiveness and value of property (and our environment).
In addition, there is increasing awareness that it is more practical and effective to manage flooding in place, to stop raindrops where they fall. As a 2018 study of urban flooding reported, “[m]any cities and towns across the United States are giving considerable attention to plans that support the capture of rain in areas where it falls.” (p. 32)
The American Society of Landscape Architects recommends that every city have a green infrastructure plan, defining urban green infrastructure as “everything from parks to street trees and green roofs to bioswales — really anything that helps absorb, delay, and treat stormwater, mitigating flooding and pollution downstream.”
Nature and Nature-Based Infrastructure is Part of the Resiliency Plan
Also part of the Resilient Houston Plan is conserving land within the city limits as part of a goal of “increasing the area of the preserved or conserved land in the eight-county Gulf Houston region to 24% by 2040.” (p. 153)
Discouraging development in “sensitive upstream areas,” protecting and restoring prairies and wetlands are also goals of the plan. (p. 151) City boundaries do not extend into the “sensitive upstream areas” beyond the Addicks and Barker federal flood control reservoirs on Buffalo Bayou, for example, although those areas are part of the City’s Extra Territorial Jurisdiction. The Memorial Villages, which are in the Buffalo Bayou watershed, also are not part of the City. The plan is to work with “regional partners” on resiliency goals.
The initiative to create a tax rebate for green stormwater infrastructure received widespread support. But during review of the legislation over the past year or so, there were also comments, including from a prominent engineering firm, asking why taxpayers should pay for something that essentially costs developers less to install and maintain than conventional grey stormwater infrastructure, works better, and improves the value of their property.
The tax credit is available only to new structures in greenfields (undeveloped land) or redevelopment in brownfields (land polluted by toxic waste) in a tax increment reinvestment zone (TIRZ). The structure must be larger than a building with four residential units, valued at $3 million or more, with at least $200,000 invested in the green stormwater infrastructure.
The credit lasts for ten years and may not exceed the total cost of the green infrastructure. (For details see Ch. 44 here.)
What Some Other Cities and States Are Doing: A Short, Incomplete List
So basically green stormwater infrastructure (GSI) is anything with soil and greenery or a container, or maybe just gravel, even permeable pavement, and, of course, trees, that can divert, absorb, disperse, hold, slow down, and filter rain runoff. “Daylighting” streams (streams, creeks, etc. that have been buried in concrete pipes) would also be considered green, as are open ditches. We have many creeks and ravines that have been filled in (and built on, flooding as a result). Houston was never so completely flat as advertised.
The City of Houston does provide some small financial incentives to the little people for green infrastructure. As noted above, the City’s Drainage Fee is based on the amount of impervious surface on your land. That means rooftops, driveways, patios, etc. So reducing the amount of impervious surface on your property reduces your drainage fee.
Here is what some other cities and states are doing or suggesting to make themselves more like “sponge cities”:
We Can Do This At Home!
Some resources for understanding and using green infrastructure to help Houston reduce flooding:
City of Houston Infrastructure Design Manual, Stormwater Design, Ch. 9, 2020
Environmental Protection Agency video: Reduce Runoff: Slow It Down, Spread It Out, Soak It In
The Top 14 Super Trees for Houston from the Port Houston and Houston Wilderness Tree Planting Program