When It Rains, the Water Has to Go Somewhere

Did the rain and the subsequent flooding this week get your attention?

Good. I’m now going to give you a lesson about impervious coverage. No, no – don’t you turn away! Pay attention!

Hillsborough residents – especially those of us who remember Hurricane Floyd – should worry about the increase in impervious coverage in our town.

Attend a Board of Adjustment meeting and listen to an application for an impervious coverage variance. It always seems like such a little thing and the individual applicants often seem annoyed that they even have to be there for such a minor item.

Just to clarify “impervious coverage” to the uninitiated (after all, I’ve noticed how empty those BOA meetings usually are), it’s when you put something over the dirt that will prevent or substantially reduce the natural percolation of water. Breaking it down further, people put down/construct something that stops rain from draining into the earth where it falls.

Okay, that still doesn’t do it for me. Let’s say a homeowner puts in a cement sidewalk 5-feet wide and 20-feet long. They have just installed 100-square-feet of impervious surface. The rain that would have soaked into that 100-square-feet has to go somewhere. The more impervious surface installed, the more water runoff has to be accounted for.

[I’ve done my best. Try Google or go to Wikipedia under Impervious Surface or talk to an engineer who does this type of work. On second thought, forget the engineer; you’ll only get more confused]

To continue, each building lot has a percentage of its surface that may by ordinance be covered by impervious surfaces – usually, for single-family home residential areas, around 15% to 20%, depending on the zoning laws, use laws, lawsuits, and laws I don’t even know about.

With the number of square feet covered by their home, driveway, sidewalk, and, maybe, a small patio, most homeowners max out on their allowable impervious coverage. That’s when they appear before the BOA for a variance to build that sunroom or the tiny little walkway around the pool.

The majority get their variance, although sometimes they have to scale back their projects. They are often irritated: It’s only a small amount and a man’s home is his castle and why did they bother to ask permission they should have just gone ahead with their project and not even asked and it’s a stupid law anyhow.

Okay, now that you have gotten that out of your system, think about the anxiety you may have felt this week watching the rain fall.

Think again.

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Attend a Planning Board meeting sometime when a developer is arguing for an upward change in the amount of allowed coverage in their large subdivisions (just a little bit – maybe 5%) or smaller lots with closer, larger houses. Remember this week’s flooding.

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Update: This was first published by the HNJJ on April 18, 2007, but applies(unfortunately) this week. It came to mind as two of the HNJJ crew were spending their third day carrying wet boxes out of their cellar.

Plus ça change, plus c'est la même chose