Town Planners Look To New Designs to Control Floods

Nat sound: rain…1049
A light rain is falling on an employee parking lot in back of New London Hospital.
Lori Underwood, the Director of Planning and Projects at the hospital, smiles as she looks at the concrete lot.
“It’s really impressive, we have had some pretty heavy storms, we’ve had people coming over to take a look at it and see how it’s working but there is no pooling anywhere, and it’s really an amazing thing”
It may seem a bit odd to be impressed by a concrete parking lot – but this is no ordinary lot.
It’s porous concrete, designed to absorb and treat stormwater where it falls.
Underwood says before they learned about the new surface, the hospital was in a quandary over how to decrease flooding while adding parking to an area that’s already a sea of asphalt.
“we were trying to come up with other solutions that would decrease the runoff, increase the treatment of the water that would runoff of this lot and started looking at some alternative models of doing that”
In planning lingo, those alternatives are called Low Impact Development designs.
The New London Planning board now requires developers to use low impact development techniques such as porous concrete to infiltrate, filter and detain stormwater runoff in new developments.
That’s because stormwater runoff is the single greatest threat to water quality not only here, but nationwide.
New London Zoning Administrator Peter Stanley says all communities in the state should be looking at the best way to manage it.
“everybody has had to deal with the effects of runoff at one point or another here in the last five years especially, we’ve had road washouts and power outages and people unable to come and go from their properties and plumes and sandbars created in lakes where there weren’t any before and all kinds of issues that I think people understand and want to solve.”
Researchers at the University of New Hampshire Stormwater Center have been trying to solve stormwater problems since 2004.
Research scientist James Houle says traditional techniques like detention ponds and swales that collect water and re-channel it don’t work well.
25 when we have a huge parking lot and we take all the runoff and put it into one singular pipe and into one singular treatment, we’re enhancing the sheer volume of water that’s coming into a certain location as opposed to decentralizing it over the land and let the natural contours of the land deal with the runoff 4:13
Houle says not only can centralized systems make flooding worse, they also have the tendency to trap pollutants like car fluids, oils, and trash coming off city streets and parking lots.
1007 :25 for various contaminants the quality of the water leaving the system was worse than what was coming into it, so these systems, as far as water quality is concerned were not performing very well, in some instances were actually adding contaminants to the water stream.
Low impact development mimicks the land’s natural hydrology, using vegetation, soils, and even porous pavement to filter store and detain the stormwater where it falls.
Nat sound HUGE GUSH OF WATER
A mixing truck dumps 15-hundred gallons of water onto a porous concrete parking lot at UNH.
A group of engineers, architects and contractors are standing right next to it and aren’t getting wet.
The pavement looks and feels like regular concrete, but it’s soaking up the water like a sponge.
UNH Researchers are demonstrating that the porous concrete works better at absorbing water than the ground next to it.
“We’re probably in the two to three thousand inches per hour range to give you an idea, the soil right next to it, right over there is probably half an inch per hour”
That’s Rob Roseen, Director of UNH’s Stormwater Center.
He says there are drawbacks to this porous concrete – for instance it has to be cleaned once or twice a year so it won’t clog.
But he says even if you let it clog, it will work better than natural soil, and far better than regular asphalt or concrete.
“At two to three thousand inches per hour we can clog greater than 99-percent and still have an infiltration rate that’s exceeds a hundred year storm in terms of intensity and is still far better than the soils right next door.”
Roseen says they’ve found that pervious pavements –whether concrete or asphalt - hold up better and longer.
And even in winter months not as much sand or salt is needed to clear the lot.
“Standard pavement is a very good cap, it seals out the subsurface, it keeps the vapor exchange from going back and forth, so that’s how you explain that it clears on a day that it’s below freezing out you have the warming from the subsurface that’s happening.”
Rob Hithcock watched the demonstration with a bit of skepticism – he’s with the engineering firm SVE Associates.
1036 :18 it looks pretty slick but I’m not convinced on the cost benefit yet, it seems like it’s definitely beneficial but I have a hard time believing it’s cost competitive.
And there is an added cost – conventional concrete for example, costs around 90 dollars a yard – pervious concrete costs about 20-percent more, around 110 dollars.
But Roseen says while the upfront cost may be higher, there are cost-savings from not having to build detention basins or lay storm pipes.
Landscape Architect Ken Costello, with Keastle Boos Associates, says it may be awhile before this type of stormwater technology is widely used.
1029 :55 we’re getting engineers, town engineers that are pushing us to look at this, but it’s an education process I think throughout the whole construction industry, you have to have a good contractor out there to do it and there’s not a lot of people out there who have done it to date.
But Costello says it’s long overdue.
Town planners in New London think so too – and are hoping that new regulations will push those in the construction industry to move toward more environmentally-friendly stormwater systems.
For NHPR news, I’m Amy Quinton.