After Harvey, Houston wants to change how it develops. What you need to know

Jan. 30, 2018Houston Chronicle

Mayor Sylvester Turner last week rolled out a series of proposed changes to the rules that govern how Houston protects against floods as it develops, and they are a departure from years of incremental tweaks.

More to the point, they also may be hard to follow for those who aren’t accustomed to combing through the city’s 370-page Infrastructure Design Manual.

So what would these changes, if enacted as announced, mean for you? A few points to consider:

  • Elevation

The most visible change would force all new buildings to be elevated two feet above the ground (or two feet above the projected water level in a 500-year storm, for properties within the 500-year floodplain). Current rules mandate that buildings be constructed one foot above the flood level in a less severe 100-year storm, and all other structures can sit at ground level. (Technically, they have to sit a foot above the nearest sewer manhole, which typically means the structure can sit on the ground.)

Builders would not be able to meet these new requirements by adding two feet of dirt on top of their properties and would need to instead lift the structures to the required height, Turner said.

  • Right of way

Another change that would be apparent to many residents is a city plan to be more aggressive in keeping drainage ditches clear of blockages.

A common example of this – obvious in neighborhoods such as the Heights and Old Sixth Ward – can be found when homeowners fill the drainage ditches along their lots with dirt and gravel to gain a parking space.

The idea was one of many recommendations produced by a task force led by city “flood czar” Steve Costello. The group endorsed the aggressive approach even though a homeowner’s ditch may have been plugged 15 years ago by the previous homeowner.

The city will give homeowners a chance to remove obstructions themselves, he said; if the owner refuses, the city will do the work and bill the homeowner.

  • Detention 

An important but admittedly invisible rule change is one to require builders redeveloping large parcels of land to detain more storm water on site than the rules currently require.

In short, detention requirements force builders to hold storm water on their properties and release it slowly into the surrounding drainage system. These rules serve as Houston’s main method of controlling flooding through day to day regulations. (If you see a grate under your spot in a parking lot, for instance, there’s a good chance it flows into an underground detention basin.)

Costello’s task force debated ideas ranging from keeping the status quo to more than doubling the amount of detention required when any pavement is added on any lot in the city.

The key recommendation was to end the city’s current practice of “grandfathering” existing pavement when calculating detention requirements. That policy, much maligned by neighborhood leaders, means that the city does not make developers add detention if the sites they are redeveloping already were paved.

In other words, a builder redeveloping a half-paved, 10-acre tract into a fully paved site today would need to detain only the stormwater the newly paved 5 acres would produce. Under the task force’s recommendations, the same builder would need to provide detention for the full 10 acres of pavement.

Such a project would qualify as “redevelopment,” however, only if the builder ripped up the existing pavement and returned the site to dirt before building on it. A mechanic repaving the parking lot of a shop he bought from a prior owner, for instance, would not need to add detention.

Some key detention rules didn’t change. The group recommended exempting lots smaller than 15,000 square feet, which covers the vast majority of residential lots in the city and some small commercial sites. Those lots still are presumed to be 65 percent covered in pavement even if they aren’t, so even a redevelopment project paving over the entire site would only need to provide detention for 35 percent of the pavement.

The panel also chose not to change the volume of required detention (in other words, the ratio of gallons of detention required per square foot of added pavement).

  • ‘Fill’ dirt

Another change that won’t always be visible but could be important block by block was the task force’s recommendations related to “fill,” which can cause drainage problems when a new home is placed atop a pad of new dirt, thereby shedding rain water onto the lower properties around it.

Costello’s task force decided a clause in the city’s infrastructure design manual should be adjusted to allow water to drain as it historically had on the lot, rather than forcing it to flow to the street, believing the current wording encourages builders to add fill when they might not do so otherwise. The task force also lowered the volume of dirt above which builders must have an engineer certify that the site is being shaped to drain properly.

City officials expect to release proposed legal language in the coming weeks, then submit the new rules for City Council consideration by mid-February. If approved, there likely would be a months-long grace period before the new rules take effect, Turner said.