November 30, 2023

Elevating Our Drainage Standards and Flood Damage Prevention Regulations

There are three aspects to our flood mitigation efforts:  local, regulatory and regional.  While, as the name implies, our ongoing Regional Drainage Improvement Program fits squarely within that third category, one of the deliverables in the first phase scope of work is very much regulatory in nature.  Over the past several months the Program engineering team has assisted staff and our citizen Building and Standards Commission in proposing revisions to our drainage design and flood damage prevention regulations, which have now been adopted by Council.

It was, candidly, a tedious and highly technical (some would say boring) deliberation, which made it easy to lose sight of what these amendments are all about.  The major takeaways are that (1) based on best available science (i.e., the most updated floodplain maps), new homes will generally have to be built one foot higher than the minimum required currently; and (2) we’ve now formally incorporated the commercial drainage standards, borrowed from the City of Houston, that we’ve historically utilized but not previously codified, to go along with our existing residential drainage standards.

Prior to this amendment, the minimum standard for new home construction (and substantial improvements) has been for the finished floor elevation (FFE) to be at one foot above the 100-year floodplain, or at the 500-year floodplain, whichever is higher.  Moving forward, it will be one foot above the 500-year floodplain in most cases.  What’s driving this change are the updated floodplain maps being issued by the federal government.  While the completion of Project Brays last year is definitely a factor in lowering water surface elevations, that’s offset by the increased rainfall assumptions on which the new maps are based.  By tying the minimum FFE to best available science, including further map revisions over time, we’re ensuring homes built in the coming years will be better protected against future storms.

Our existing residential drainage standards remain largely the same, with mostly just clean-up type amendments.  The basic principle we’ve had in place for going on 20 years is that residential construction cannot add fill to the floodplain; if anything we’ve made those provisions clearer and easier to enforce.  Also, now that they’re combined in the same part of the City Code, we’ve taken this opportunity to bring the residential drainage standards into better alignment with the flood damage prevention ordinance.

More significant is our formal adoption of commercial drainage standards, not simply for the sake of having them on our own books, but also because of recent and ongoing changes in the approach to storm water management for commercial development throughout the region.  Like residential, commercial development also cannot result in increased fill.  However, and critically, there are heightened on-site detention requirements to mitigate both new and redeveloped existing impervious cover.  Meaning developers must actually reduce the amount of storm water leaving their sites, not merely preserve the status quo.

If you’ve made it this far, you probably have a sense of why I say it was such a tedious deliberation.  But that shouldn’t detract from its importance.  Updating these ordinances is a big deal and goes a long way toward fulfilling the regulatory component of our flood mitigation policy.  Couple that with all the progress we’ve made this year on our Regional Drainage Improvement Program (see the latest update presentation and the website), we’re very well positioned to make a strong case for the outside funding it will take to begin implementing the ambitious regional infrastructure projects we’ve been working on.  And, of course, these regulations will help make us that much more resilient against flooding and save costs associated with mitigation in the long run.

Much appreciation to Development Services staff, the Building and Standards Commission and the engineering team at Ardurra, all of whom did a great job in thinking through and presenting these revisions for adoption.  The new regulations will go into effect early next year, as Council directed they be delayed by 60 days so as not to create unfair surprise for property owners or developers who may be currently designing projects but not yet submitted their plans to the City.