Driveway Surfaces That Would Not Be Considered "Impervious"
 

As you know, the impervious surface rules of the Comprehensive Shoreland Protection Act limit the percentage of a lot that can consist of "impervious surfaces" to 20-30% of the size of the lot (assuming the lot is in the protected shoreland). The "impervious surface" definition from the act is below.

VII-b. "Impervious surface'' means any modified surface that cannot effectively absorb or infiltrate water. Examples of impervious surfaces include, but are not limited to, roofs, decks, patios, and paved, gravel, or crushed stone driveways, parking areas, and walkways unless designed to effectively absorb or infiltrate water.

Depending on the shape of the lot, a driveway can take up a lot of impervious square footage. My question is whether permeable pavers (examples can be found in a google search) would fall into the definition of being "designed to effectively absorb or infiltrate water" and therefore would not count toward the impervious surface rules. Are there examples of other driveway surfaces that would also not count as impervious?

I believe that the new Meredith Village Savings Bank branch in Wolfeboro used some sort of "pervious" pavement. It appears to be asphault with a larger aggregate in it. If it truly is accepted as "pervious" it would be the easiest solution.

UNH was has been experimenting on a pervious asphalt which is probably the same as you are talking about at the MVSBank PW. I may be wrong, but I think it is down in the 125 area. I forgot exactly where it is. Anyway, the state is accepting this but I heard it is expensive.

Why would crushed stone be considered impervious?It is used for exactly the opposite purpose in drainage situations.

I agree, the pendulum on drainage has swung to far.
But this is their logic, that the stone will eventually fill up with fines and become impervious. The problem is they don't think it through and apply this same logic to these "new" materials AKA the pervious asphalt.

Most of the companys that make pavers are jump on the bandwagon and making pavers for the application. Although most are kind of bulky and ugly.
One thing to remember with these surfaces is they will in time need maintence. Which is something to consider when figuring out what type of surface to consider.
For instance ,the concrete and pavement even needs to be "cleaned" And the process for this is by blasting water into the surface and vacuuming it out. Not very enviormently friendly if you need to use cleaning agents and then what do you do with the water after you have sucked it back out of the pavement?
I just went to a seminar for the Techo-bloc pavers they just came out with.
Pretty good stuff for the person that falls under the CSPA to meet some of the restrictions.

Passing by Disney World on I-4, I noticed a new series of concrete dams placed along the wide Interstate ditches there. They are about 300 yards apart, but differ in that the "dams" are engineered with a 10" empty space in the middle—top to bottom.

The effect on floodwaters is to make a series of temporary huge holding ponds, but allow floodwaters to pass through and gradually permit the holding ponds to drain out.

Around Lake Winnipesaukee's many hills, it seems that the same principle can be applied to the many culverts associated with hillside lots. That is, rather than place the usual single culvert, stack two or more smaller culverts to create the same temporary roadside holding ponds: Silt-laden floods would be delayed from rushing to the lake.

As krm advised, the stones fill up with "fines".

The top photo is of a developer's deep ditch filled with "rip-rap". As can be seen, grass has started growing in from the right side. Since this 2007 photo, after only three years in existence, this ditch is now 60% full of sand!

The bottom photo shows (I think) the futility of using rock to stop erosion on a collapsed lakeside shoreline.

Note the stumps to the right, and one eroded stump to the left. The loss of cover precipitated another mature tree's fall into the lake. Due to loss of tree cover (leaf "canopy") there are about a dozen collapsed shorelines within an afternoon's paddle from my place. Some are many times higher and wider than this one. :(

Interesting post APS but as usual it looks like your twisting things to make your point.First of all,I have no dog in this fight and don't have an opinion either way.

APS states "The bottom photo shows (I think) the futility of using rock to stop erosion on a collapsed lakeside shoreline".That rock surely lokks like it was put in AFTER the collapse or it would have the dirt sitting on top of the rock.

APS also states "The top photo is of a developer's deep ditch filled with "rip-rap". As can be seen, grass has started growing in from the right side. Since this 2007 photo, after only three years in existence, this ditch is now 60% full of sand!
Well wouldn't the grass or anything else grow there anyway if the riprap was not present?I'm not sure what your point is with respect to crushed stone being permeable.If crushed stone gets filled in with dirt and grass then it will end up pretty much the same as if the stone wasn't there right?

Slower is better for runoff...
 

Well, you're right. Expect that new rock to be soon covered over with rain-washed mud.

That was my point. Crushed stone is a look-good/feel-good, but temporary impermeability fix; alternatively, I like "catch basins" or "holding ponds" as solutions.

I defend tree canopies because my one-acre lot is heavily forested and has done very well to withstand the periodic flooding that starts uphill from a developer's totally-treeless 110 acres.

The best thing I did to stop flooding was a large berm at the top of my driveway, creating a small holding pond. The intact canopy—which includes a dozen white pine trees I planted as a kid—readily slows, then absorbs, any excess runoff to either side.

The three newest buildings in my immediate vicinity have a history of all kinds of soil, silt, and runoff issues—not to mention poorly conceived septic "arrangements".

The biggest house—still unfinished after three years—has a semi-circular driveway of about 500 feet in length (pictured). Rain has eroded the clay embankment (center) and clogged the drains several times since they were installed in 2007. The most important drain, installed uphill late this summer, was itself washed out two weeks later! The builder's answer? Truck in more fill to refill the gullies!

The gray clay from that embankment roils the lake after each rain. The bottom photo is of 10' of normally clear lakewater after a rain. It takes a day or two to see the bottom again. :(

Crushed rock and drains are far less effective remedies than slowing the velocity of runoff to start with. IMHO.

Uh oh,I seem to agree with APS's last post.

How About This?
 

http://www.grassypavers.com/?OVRAW=d...ID=27619896522

I was actually looking for "open weave" (for lack of a better description) concrete pavers when I ran across this one -- similar to what I had in mind with the concrete pavers, but I couldn't find those.