Volume of runoff water

by MIck
(allentown pa. USA)

When land is developed, what is the maximum area of inpermeable surface allowed for a given area of land?

A developer bought an old farmhouse and property, bulldozed the house, haphazardly graded the land, plopped three large homes (in surface area) uphill of an existing home. The result was serious flooding problems for the home owner and the township isn't interested.

Thank you for your time.

Editors' Reply:

Answering your first question, there is no uniform percentage of impermeable surface that is permitted in the U.S. Any such law would be state or local.

Probably the applicable law would be a local zoning ordinance. Be aware though that most zoning ordinances only specify a maximum "lot coverage," or percentage of the area of a parcel of land that may be covered by buildings, or sometimes only the principal building on a lot, such as a home.

On the other hand, zoning laws typically also require a minimum amount of parking, such as two parking spaces per home or one parking space for every 1,000 square feet of a certain type of commercial use. We think the ordinances should include a maximum amount of parking allowed too, but that's a whole different story.

Often parking is required to be paved, which leads to more runoff water.

To comment on the situation you pose, we can't say too much without more details such as the size of the total property.

You say the township isn't interested, so apparently if a zoning law is in effect in your township, what was built was in accordance with permitted uses and any zoning regulations that apply. Another thing to investigate is whether there are subdivision regulations in place in your township, and if so whether the approved subdivision plat was followed and if it was adequate to confine runoff water to the boundaries of the development.

Since you call the grading "haphazard," it could be that the developer didn't exactly do what what was shown on the grading plan, if you're living where one must be shown. Then it becomes an enforcement problem, and you will have to go political and join forces with some other friends and neighbors to get the township to pay attention to your problem.

In many states draining water directly onto a neighbor's property is illegal in one way or another. The problem is that often you must go to court, or at least threaten to do so, to obtain any relief under these laws.

This brings us to the next point. If you haven't talked directly to the developer or to the new property owners, please do so. It's amazing how often neighbors fume about something next door without risking a direct conversation with the culprit.

Do your research first about what your state law says about containing stormwater runoff on your own property, and then have the possibly confrontational conversation.

Larger towns and cities now are required to be enforcing what is called Phase II stormwater regulations under the Clean Water Act. In essence, these require what is called mitigation of any stormwater not handled directly on a single property or development. Check to see if this applies to the place where you live. If you don't know who to ask or if asking the question locally is awkward, you can ask your state's environmental department to give you advice about this.

One slightly encouraging note for you is that as vegetation grows back, even if it's only turf grass, the drainage problem will subside slightly. With any luck the owners of these new large homes will want some lush landscaping that absorbs some or all of the stormwater runoff as it becomes larger and more thirsty.

As a last resort you may have to be the one to plant more water-loving plants on the edge of your property. Search for landscape materials or even trees that are appropriate for wetlands.

Oh, and be sure you've checked out our stormwater runoff page, if you haven't.

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