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Roanoke maps parcels for storm water runoff

A team is cataloging the information to determine what residents would pay if a fee is approved.

STEPHANIE KLEIN-DAVIS | The Roanoke Times

Roanoke GIS specialist David Dearing (left) and Justin DiProsperis evaluate a parcel of property in an aerial photograph looking for impervious areas that will be the basis for a possible storm water management fee.

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Storm water fee

Roanoke officials have proposed a fee to finance badly needed drainage and water quality work. The city council could vote on it later this year.

What’s the proposed charge?

Ninety cents a month for each 500 square feet of impervious surface — so, for a modest 3-bedroom house, with front and back porches, no driveway but a 10-foot-long front walk and a total impervious surface of 1,255 square feet the charge would be $1.80 a month or $21.60 a year. The city will round up or down to the nearest 500.

How will it be billed?

Probably with the property tax bill.

What’s impervious?

Anything that keeps rain from soaking into the ground — roofs, driveways, concrete or overhead structures like decks or awnings.

What’s the bottom line?

The charge should generate about $4.8 million a year, specifically for managing storm water. That kind of money could allow the city to borrow a larger sum to make faster progress on a backlog of needed work that now exceeds $70 million.

What’s next?

The city will post maps showing impervious area for roughly 10,000 commercial parcels this month and 35,000 residential parcels in October.

What’s still to be decided?

The city council will consider whether or not go ahead with a storm water fee later this year. At that time, it will formally set a rate, set a date to begin levying the charge, consider phasing it in over time and approve a system of credits for property owners who take steps to reduce runoff.

David Ress | 981-3253

Wednesday, September 11, 2013

After peering through thick tree cover on the aerial photos of parts of Raleigh Court, the 2600 block of Roanoke’s Derwent Drive almost seemed like a breeze to mapping technician Justin DiProsperis.

He’s a member of the four-person team measuring the roofs, driveways and other impervious surfaces on Roanoke’s 35,000 residential lots so that the city will know how much to bill for a storm water fee — if, that is, the city council approves the new charge later this year.

City officials have proposed a fee based on the amount of a parcel’s surface that rainwater can’t soak through. The larger that area, the larger the cost to the city of making sure the runoff can drain properly and isn’t picking up pollutants on its way to the nearest stream.

New federal rules will soon set tougher water quality standards for runoff, while Roanoke’s backlog of drainage work already exceeds $70 million.

The mapping team members hope to finish their work in October, and will post it on the city’s website, so residents can check and see what the team measured.

“We want people to call us if they have questions about what we’ve done or think we’re wrong or don’t understand what we’ve done,” City Engineer Phil Schirmer said.

DiProsperis’ job is to map and measure impervious surfaces in southwest Roanoke. He uses aerial photographs — mainly but not only from 2012, 2011 and 2009 — and holds the current record for the team: 285 parcels mapped onto the city’s online Geographic Information System in a day.

“I didn’t even want to look at a [computer] mouse after that,” he said.

When the recent Virginia Western engineering technology graduate can click his computer cursor around a simple rectangular roof and driveway, the work goes fast.

On Derwent, it went a bit more slowly.

At one corner was a house with a complicated footprint and a curving driveway, the outline of which he had to trace carefully. Next door, a pale, beige colored patch around a shed popped up on his main computer screen. Dirt? Cement?

DiProsperis glanced to the smaller screen to his left. On that, instead of the directly overhead view he’d been looking at, he could see the house from a bit of an angle, and could check all four sides. After a moment, he pretty much decided it was paved, but he called up the 2009 and 2012 aerial photos as well. The space was grass in 2009, while the 2012 image showed the beige. He mapped the area as impervious.

Two houses down, he has another dirt or paving question. The 2011 photos that he is mapping onto show a paved area next to a carport, but a shadow cast by the house means he can’t tell if the walk goes all the way to the house or not. The 2009 photo doesn’t help too much, but there’s more light in the 2012 photo and the area’s color is darker than the walk.

“Looks like dirt,” DiProsperis says. City GIS specialist David Dearing steps close, peers and nods. Rain can soak into dirt. That area won’t be part of what the city will bill to that property owner, if the council approves a storm water fee.

Continuing along the block, he pauses when he thinks he sees a shed under a tree, but can’t confirm it by looking at an aerial shot when the leaves were down. Another couple of houses down, he spots an odd grayish square patch on the 2011 photo that shows up in the 2009 and 2012 images as well.

“Could be an old foundation,” Dearing says. But the photos also show a faintly green something sticking up – they aren’t quite sharp enough to tell what it is. If you’re not certain, Dearing says, don’t map it.

But there is a black square in the middle of the shadow cast over the back yard by a large tree. Peering at the oblique view, the two decide there is some kind of platform up in the tree. Since it blocks light, it would block rain. It gets mapped.

The swimming pool a few houses down that shows up in the 2012 photo but not the base 2011 series is not.

When the first two members of mapping team started back in April, they began with the 2011 aerial photos since they were already loaded into the city’s GIS system. The team can map impervious areas accurately by tracing their outlines with their computer cursors, but a freehand sketch from the 2012 image would not be as accurate, Dearing said.

The team will capture it next year, when the 2012 photos or the brand-new 2013 series become the base in the GIS system, and the outline can be traced exactly, Dearing said.

“We don’t want to charge people for something we shouldn’t,” he said.

Saturday, September 14, 2013