Growth and the Risk of Flooding


TLR Staff Report

Over the past three years, 1,084,822 net square feet of impervious surface has been added in the town of Chapel Hill. Another 2,555,539 net square feet is being added as a result of construction in progress.

What does that mean?

Natural “pervious” surfaces, especially those with trees, absorb water and so reduce the volume of precipitation entering streams as well as the rate at which it enters. Impervious surfaces that water cannot penetrate, such as asphalt or building roofs, do the opposite, increasing the volume of water entering streams as well as the rate at which it enters, which can cause flooding.  The transformation of forested or undeveloped land into neighborhoods, commercial buildings, roads and other structures typically entails the conversion of pervious surface into impervious surface.



Carraway Village


Chandlers Wood


Chapel Hill High School


Azalea Estates


Grove Park






Fordham Apartments


Park Apartments


Sancar Turkish Center






Murray Hill


Glen Lennox phase 1




Currently, there are at least 10 more approved projects in Chapel Hill which, when fully built out, will add another 1,360,942 square feet of impervious surface. Here’s the list:



Tar Heel Lodging


Carolina Flex Park


1165 Weaver Dairy Road


Orange County Human Services




St. Paul’s Village


S.E.C.U. (MLK)


American Legion property


Carolina North (MLK)



                  1,360,942 NET SQ FEET

Currently being built


Completed past 3 years


                                  GRAND TOTAL


In addition to these approved-but-not-yet-built projects, there are over a dozen pending concept plan proposals that developers have or are expected to present to the Chapel Hill Town Council for feedback.

As things currently stand, the council will not know how much additional impervious surface these projects will add because the Chapel Hill planning staff has changed the concept plan application.

The exact number of square feet of existing and proposed impervious surface is no longer required to be submitted by the applicant. Instead, applicants only need to indicate that their proposed project will meet the present Land Use Management Ordinance threshold.

Plans, however, are underway to rewrite the LUMO in order to give “users a better tool for planning, managing, and executing the community’s vision for growth and development.”

Building regulations require developers to ensure that the amount of stormwater runoff from their site post-construction is not greater than the amount pre-construction for 25-year storms — storms that are likely to occur at least once every 25 years. However, due to the increase in the intensity of rain events, controls can become overwhelmed.

Given the council’s and community’s focus on climate change, information on the actual net impervious surface increase would enable the council to be aware of possible future flooding issues and, therefore, be more specific in their feedback to applicants.

TLR reached out to Town officials for comment and we are still awaiting a definitive reply.

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10 Comments on "Growth and the Risk of Flooding"

  1. Who wrote this article? It’s disingenuous, at best.
    Discouraging dense development in Chapel Hill (or any other town) only exacerbates the problems of our existing low-density neighborhood sprawl. It may have been an an acceptable strategy fifty years ago, but it’s suicidal in today’s climate-changing world.

    “The more people that live in a given area, the lower each individual’s carbon footprint.” — Anthony Wells

  2. Local Reporter | October 6, 2019 at 4:56 pm | Reply

    Your statement “discouraging dense development…” is confusing. How does it relate to the article? All the article does is cite the square footage of impervious surface that has been or will be added in the Town. This is publicly available information calculated by analyzing every project on the Town website. Most of the projects were approved up to seven years ago and are only now being built.

  3. So, now I’M confused – does this mean you ARE encouraging dense development? Obviously, you cannot have dense development without larger amount of impervious surface, unless of course, you want to go higher. Are you advocating for taller structures then?

    btw, May I ask who the “local reporter” is that I’m talking to? It seems a bit Orwellian not providing any individual name.

    • Local Reporter | October 6, 2019 at 7:00 pm | Reply

      The article is a news article, which does not encourage, discourage, or advocate for or against any action – it presents the facts. You are welcome to submit a guest column for consideration. As stated in our “About Us” articles with no byline are collaboratively written.

  4. I would like to know what happened to my second comment and your second response. Both have disappeared. Is this how your paper plans to be the “civil forum” you claim to be?

    Dare I say it… fake news?

  5. “Given the council’s and community’s focus on climate change, information on the actual net impervious surface increase would enable the council to be aware of possible future flooding issues.”

    There are two main aspects to climate change, the first is mitigating the Town’s impact on climate change. The second is about adapting to the impacts of climate change.

    If we as a Town want to focus on the first (per the Paris Accord commitments we signed up for) what we really need is data on the impact that increased density can have on reducing GHGs, versus concerns about tall, dense building that will push development into the suburbs and increase sprawl, driving and climate change.

  6. Do as I say–not as I do. What I find most interesting is that the very people advocating for dense development live in homes with large lots–not in the type of apartments they want to cram everyone else into. If they so support dense development they can begin by subdividing their own lots–and complaining to the developers of all of the new McMansions of multi-acre lots–instead of arguing with people who live on a scale much smaller than their own.

  7. I agree with Ms. Hunter and with what I take to be the gist of the article, namely that if we want our land use decisions to align with our espoused environmental goals we need more and better data about the environmental impacts associated with different land uses. Eliminating the requirement for applicants to provide detailed information about how their projects will increase impervious surface will make the permit review process faster and cheaper, which potentially could yield public benefits, but if doing so denies the Town government the information it needs to adapt to the effects of climate change, then expediting permit review may come at too high a cost.

  8. With all the projected housing, either in progress or planned for, will you please tell us where we are going to get our water from? OWASAonly has a very limited catchment area, certainly not enough for the huge projected population increase!

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