Should Decatur Encourage More Pervious Parking Lots?
Decatur Metro | October 19, 2011 | 1:33 pm
I was up in the North Carolina mountains a couple of weekends ago and came across this lovely pervious parking lot at Sunny Point Cafe in West Asheville. Being a good, progressive little establishment, they even had a little sign highlighting the benefits of pervious parking surfaces. I didn’t take a picture of it but as you can imagine it had a lot to do with run-off, etc.
So this got me thinking about Decatur. Why doesn’t Decatur have more pervious parking lots? What are the downsides other than – I assume – additional cost?
Great idea and the City has looked into this sort of thing – BUT – we have a problem. Our soil is mostly clay and doesn’t drain worth a darn. To make this work around here, you’d need to condition the soil (like the home gardner has to do) to make it work. That makes it even more expensive.
Fred, do you know of any known issues with it other than the additional expense upfront? Maintenance, perhaps?
We investigated replacing our condo complex driveways with pervious pavement, and that’s what we were told: The soil underneath is nothing but hardpan clay and rock. The water would just run off, anyway.
So, then wouldn’t that true of all the earth around the city?
Apparently so, which — as the history museum at the courthouse informs us — is why DeKalb County grew cows instead of cotton, back when it grew things. Blame the monadnocks.
So then shouldn’t grass and anything else on your property also be considered impermeable?
And don’t you worry. The monadnocks will be hearing from me!
Basically yes. Our ordinance was most likely cut and pasted from some other municipality without consideration of soil conditions. But KC’s comment indicated that it’s finally being acknowledged and addressed by the Env Sustainability Board, so that’s good.
It’ll just be nice to have some reality-based regs that actually contribute environmentally in a meaningful way while scaling back on the lawn-glorification we have now. Not that I’m anti-lawn. Just that there’s other ways to shape and use your property that have comparable impacts, so they shouldn’t be outlawed or disincentivized arbitrarily.
Hmm. Still seems like a pervious surface would help with some run off issues. We have a river pebble driveway and I know we have less runoff than our neighbors. After a point, it does get saturated and runoff is the same, but it acts like a sponge that absorbs until the porosity is overwhelmed. I would hazard a bet that pervious parking lots would do the same, and then release the amount of pore water they do hold over a period of time. Some porosity is better than no porosity when it comes to flash floods.
Stone Mountain Park has acres of pervious parking.
Our neighbor, the late Ken Gehle, paved his driveway with cobbles. Drains well and is attractive, but the subsurface is not perfect and some pavers wobble. Recommended over gravel or pebbles which can chew up asphalt and may promote a slip hazard if washed out of place.
I have seen it done with pavers similar to what is used in the picture, but with grass planted in the voids. The grass was a drought tolerant zoysia. One advantage of the grass is that it holds the soil, where the pictured lot most likely loses some sediment on a heavy rain. A disadvantage would be having to mow you driveway. The grass might not survive under my ’64 Triumph TR-4, too much oil leaking, but modern cars seem to hold their oil much better.
Soon we’ll be able to park on the lawn at Westchester and College Heights with impunity! Yahoo!
I really like the idea of pervious pavement.. whether it be parking lots, driveways, walkways.. or even streets. The whole concept seems to have been really slow to catch on… perhaps it is extraordinarily expensive?
I saw one of the pervious lots at Stone Mountain. I would like to observe the effect on runoff in a heavy downpour.
Wow, I learned a new word today!
me, too! also one of the newer houses on mcdonough (across from the agnes scott tennis courts) has a pervious driveway…looks cool.
Classy Beetle, BTW. Yours?
No, but dang would that be sweet!
Ironically, I was talking about this very issue today. There’s a great example of making parking lots both pervious and attractive in Senoia, GA (Coweta County). The project was done as part of Senoia’s historic downtown development plan. You can see a some pictures at this site (http://www.historicsenoia.com/parking.html).
The City of Decatur doesn’t give any “credit” for having permeable surfaces like gravel and permeable pavers when it comes to calculating lot coverage. It’s treated just like concrete or asphalt, so there is no incentive to go a permeable rout when trying to manage around lot coverage issues, which is why you probably don’t see as much of it as you probably would otherwise.
Bingo. Hopefully, the current zoning overhaul will look closely at this issue. I may be mistaken but I believe, as it’s written now, a gravel patio would count as impervious while the grass right next to it would not, even though each have very similar absorption and filtration.
The city’s point about car tires compacting the earth is a valid one, but should really only be applied to, for example, gravel driveway area directly impacted by treads. The rest of the driveway should be considered pervious, or at least some percentage of pervious.
Anyone have first-hand experience on how our currently nebulous rules play out?
Here are some definitions from the city code that may just reiterate what’s already been said:
“Impervious cover: A surface composed of any material that significantly impedes or prevents the natural infiltration of water into soil. Impervious surfaces include, but are not limited to, rooftops, buildings, drives, parking spaces, walkways, decks, tennis courts, swimming pools and similar structures, compacted gravel, and any concrete or asphalt surface.”
“Lot coverage: A percentage factor which, when multiplied by the total area of any lot, establishes the total area of impervious cover which may be built on said lot. Where used in the zoning ordinance, the term coverage shall mean lot coverage. “
So then I guess the city just assumes that all gravel is compacted if its used to accommodate cars in some way?
Yep – the City is looking at that based on a recommendation from the Environmental Sustainability Board. It makes no sense to treat surfaces in a binary fashion (permeable/impermeable) when there are really many shades of permeability…
Thanks, KC. That’s the kind of nuanced approach I’d expect from a place like Decatur. Appreciate the confirmation.
Bioretention via trees and landscaping within the parking lot helps reduce storm water through respiration, infiltration, and interception of rainfall. Their are many best management practices that integrate bioretention into the design. It also offsets clay soils.
There a bit** in heels 😉
*they’re
well, NIMBY!
when I was a kid we used to have one next to the elementary school, and let me tell you that wasn’t cool.
#pervyhumor
Sounds like there are examples close by (Stone Mountain, Senioa) and I certainly have long been interested in it. Maybe they have a new way of doing that works with clay soils. Certainly worth another look.
Pervious paving has come a long way, it is more expensive than standard pavement, but when you weight the cost of stormwater structures, land for detention, and the higher land cost of Decatur, pervious sounds like it would be cost effective. There are also new systems that are “heel safe.” Pervious pavers are more expensive than pervious concrete but they are easier to maintain and look better. Pervious concrete was used at the Library in East Atlanta. You can also see pervious pavers at the Alpha Delta Pi house on Ponce at Oakdale. If you design the gravel sub base to hold the right amount of water per code, you dont have to worry about the clay soil issue as much. But, in the end, pervious paving is a bit more expensive here than coastal plain.
http://www.belgard.biz/environmental-pavers-permeable.htm
PS: Gravel parking and driveways aren’t pervious—it’s just an inch or two of gravel over compacted ground. When you compact our soil around here, it may as well be concrete.
The question I have is where in Decatur (city limits) is there likely to be any new paving? Because I can’t imagine any existing lots being retrofitted, at least not the commercial ones.
This is a big deal when you consider the push to encourage diverse housing options, specifically through the use of secondary structures on existing lots. Decatur’s current treatment of this stuff as impervious means that lot coverage ordinances constrain the options of property owners.
Why not? To me, there would seem to be opportunities on underdeveloped properties at least on the outskirts of downtown when redevelopment eventually comes or in our other commercial zones throughout town – particularly if it didn’t count as much towards lot coverage and/or there were incentives to increase density, etc.
Not to mention lot coverage issues on residential properties.
This is just another area where Decatur’s zoning code is behind the times and I hope the Zoning Commission takes a look at it.
In case you missed it, there is a city commission appointed citizen-based task force looking at the totality of Decatur’s zoning regs with the idea of major revisions.
That’s what I meant, Steve.
There aren’t a ton of undeveloped properties but there are quite a few. Between all the un-built mixed use downtown to properties like the one at Columbia and College and new residential, there’s lots of potential.
Can anyone explain (seriously) why a swimming pool is considered an impervious surface? I get it, if the pool is covered, but for an open pool this has always just confused me.
Seems like that would depend on the goal. If you are concerned about groundwater recharge, the concrete pool is a negative. If you are concerned about runoff and flooding issues, the pool should be positive or neutral.