http://danvillesanramon.com/print/story/print/2008/01/11/storm-sewers-strained-during-deluge


DanvilleSanRamon.com

Newsfront - January 11, 2008

Storm sewers strained during deluge

Neighbor wants catch basin to stop Blackhawk Road runoff

by Natalie O'Neill

Pooling and minor flooding in older Danville neighborhoods - aggravated by last weekend's downpour - drove homeowners to the town engineering department to resolve rain accumulation dilemmas this week.

Wet socks, soggy yards and large puddles prompted a handful of phone calls with concerns about storm sewers and gutters.

For Diablo Creek Place resident John Schembri, the problem has to do with a lack of catch basins - the metal grate where rain water is designed to flow from streets.

Whenever it rains, he can expect a 2-foot-wide stream to run from Blackhawk Road in front of his house, to the nearest storm drain, he said.

"If I wanted to cross from my driveway to the street I'd have to step in it," the 20-year resident said. "There is a tremendous amount of water."

Town Engineer Steve Lake said Schembri's problem is not uncommon for a subdivision built in 1978. The street and its adjacent cul-de-sac rest on the border of Blackhawk and have six catch basins and a piping system that is 15 inches in diameter.

"There are occasions where we have storms that are larger than what the system can handle," Lake said.

After a storm system is built, he said, the town rarely goes back and adds to it, aside from maintenance or significant design problems, which typically only occur in systems designed before 1950.

"In the case of a modern subdivision like Diablo Creek, there's very little work that needs to be done," Lake said. "It has a curb gutter and sidewalk. That gutter is designed to handle those types of flows."

Up to 5 inches deep of rain on occasion is still considered normal, he said; abnormal is when the water raises above the curb.

But Schembri, who lives four houses down from Blackhawk Road, says another catch basin should be added closer to the road to prevent the water from streaming heavily in front of his home.

There is so much water that algae grows on the storm sewer, which causes a slippery safety issue, he said.

"I think they should fix it," he said.

From Jan. 1-8, the town of Danville accumulated 5.93 inches of rain, taken from a measuring station at the Danville Library at 1 p.m. Tuesday, according to the County Flood Control District.

Those were the highest numbers of the 24 county measuring stations and nearly half of the town's total rain accumulation since July. Measuring stations are in areas like Mt. Diablo State Park, Martinez, Orinda and Richmond.

Mayor Candace Andersen said the drain system in the Diablo Creek neighborhood is functioning as it was designed to and that the town had been in communication with Schembri.

"Drainage (problems) are rare - usually it's when we have these big storms," Andersen said.

When Town Council looks into whether storm drain improvements are necessary, members consider if people or property are in danger, if the draining is functioning, if there is anything they can do to improve it, and if changes have occurred since the area was designed.

"As uses of property have changed, you aren't finding the original design as effective as it was," Andersen said.

Recently, neighbors on La Questa Drive off Diablo Road in central Danville complained and filed a lawsuit against the town about a storm sewer issue on their street, which had been designed in the 1940s. The town settled out of court and completed the project for approximately $800,000.

"What we get there is water that ponds in front yards and enters garages. That's a serious problem that affects people's livelihood," Lake said.

After some research of the Diablo Creek area, he said there is a difference between the La Questa Drive project and what's going on in Schembri's neighborhood.

"I don't want to minimize his issue, because honestly I haven't seen it," he added.

The storm sewer system on La Questa Drive was designed to flow in dirt ditches to the creek. But over the years the ditches have been blocked by trees and landscape.

"Technology wasn't quite as good in the 1940s," said Michael Stella, senior civil engineer for the town of Danville. "It's true of neighborhoods of that vintage - they rely on roadside ditches."

Storm sewers are repaired and upgraded with the town's capital improvement funds and are usually reviewed in the summer months, Stella said. Engineers present projects they deem important and the Town Council prioritizes them.

When engineering storm sewers, developers take into account how much hard surface, like concrete or asphalt, there is in the area compared to soft surface like grass and dirt. Soft surface absorbs rainfall and the more soft surface, the fewer storm drains are needed.

Designers also take into account the slope of the road, elevation of the neighborhood and climate.

"Once the system is designed, we very seldom go back and change it," Lake said.

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