Monday, August 16, 2010

Engineer lists plans to thwart flooding

More excuses for bad planning.
Chad Christian says we are having "Excessive" rain events.
Chad is getting almost as good as Joe Robinson at making excuses...

Engineer lists plans to thwart flooding

Dusty Compton | Tuscaloosa News
8th Ave. in Tuscaloosa was flooded by the torrential rain in Tuscaloosa, Ala. Friday, June 25, 2010. Urban flooding often has its roots in development. Rain runs rapidly off asphalt, concrete and rooftops as opposed to soaking into the ground and being slowed on its way to drainage basins by vegetation.
By Robert DeWitt Senior Writer
Published: Monday, August 16, 2010 at 3:30 a.m.
Last Modified: Sunday, August 15, 2010 at 11:25 p.m.
TUSCALOOSA | Urban flooding often has its roots in development. Rain runs rapidly off asphalt, concrete and rooftops as opposed to soaking into the ground and being slowed on its way to drainage basins by vegetation.

Engineer To-Do List
Inspect storm water retention systems at developments in the area where flooding has been reported.
Make changes such as adding inlets or realigning pipes in neighborhoods that have problems.

Click to enlarge

STAFF GRAPHIC | Anthony Bratina

So after the city's recent flooding problems, fingers have been pointing at the Woodlands of Tuscaloosa, the new apartment complex on Hargrove Road built in what had previously been an open pasture. Serious flooding in nearby neighborhoods sprang up after the development neared completion.
But Chad Christian, the city's storm drainage engineer, said he believes most of the flooding was due to extraordinarily large rain events. And he points to flooding in areas with no new development, saying much of the flooding from recent storms occurred in a drainage basin that flows through the Cedar Crest subdivision.
“If you look at that drainage basin for any new development to point a finger at, you just don't see it,” Christian said.
But enough questions have been raised about the Woodlands project that the city issued a conditional certificate of occupancy. The city called for some changes to the complex's storm drainage system and put other conditions on the development.
Most of the focus will be on keeping the water from overflowing Hargrove Road, Christian said, since the overflow not only impedes traffic, but it also causes the water to flow into the houses and yards downstream as it attempts to get back into the stream.
“If we can keep it out of Hargrove Road, we don't have the issues on the south side of Hargrove Road,” he said.

Flooding has also occurred upstream from the apartment complex in the Carriage Lane and St. Charles subdivisions and in drainage basins that are unrelated to the development. In some areas that flooded, the water simply did not flow to or through the Woodlands, Christian said. In all, 81 homes have reported some flood damage, said Robin Edgeworth, the city's contact person for flood damage.
The Woodlands is not the only development in the area. University Mall, Midtown Village, Home Depot and Target all have large rooftops and asphalt parking lots.
All of those developments have storm water retention systems. Christian said that to his knowledge, those are all functioning as they should, and he plans to make certain of that.
“I have on my to-do list to check all of those systems to make sure they're functioning properly,” he said. “The one at Target is above ground, and you can inspect it visually.”
Christian has inspected the retention system below Home Depot, which has pipes large enough for a man to stand in. They hold large amounts of water and lead to two 16-inch pipes. The large pipes hold water as it is gradually released through smaller pipes.
“I've got plans on all of those except maybe the mall, due to its age,” Christian said. “To be thorough, we have to go back and review them.”
He said he isn't sure how the retention system for the 30-year-old mall works.
Aronov Realty, the mall's owner, referred inquiries about its water retention system to mall manager Roger Gregg, who could not be reached for comment.
Christian said he has seen no indication of anything amiss with the retention systems at any of the major established developments. Most evidence points to huge rain events that overwhelmed the drainage system.
“The Highlands is one of the oldest subdivisions in the city,” Christian said. “Two hundred feet from there, we had five feet of water in McFarland Boulevard.”
That drainage basin runs back through Alberta, and there has been no recent development in that area.

On July 26, houses flooded in Southern Gardens, Lynnwood Park, Kennedy Park and Candlelight Terrace, subdivisions north of University Mall. In Alberta, Arlington Square Apartments suffered damage to 14 units. None of the water that goes through that area comes from major new developments, Christian said.
The city has had four major rain events this summer, on May 20, June 15, June 25 and July 26. At least three — May 20, June 15 and July 26 — may have been extraordinary.
On May 20, the Emergency Management Agency rain gauge at Kaulton in southwest Tuscaloosa recorded 2.44 inches of rain, which fell within a very short period. At times that day, rain fell at a rate of 5.24 inches an hour. On June 15, the total was 2.14 inches, and at one point, rain fell at a rate of 7.89 inches an hour.
The most intense rain fell on July 26, when 2.40 inches of rain fell at a rate of 8.23 inches an hour at one point. Data indicates the May 20 and July 26 storms were between 50- and 100-year one-hour rain events, Christian said.
He noted that the rain gauge was not located in the areas that flooded, so the rainfall could have been greater there. Some indications are that more rain, up to 4 inches in some cases, fell in east Tuscaloosa.
After the July 26 storm, Christian measured a debris line on McFarland Boulevard that indicated the water was 59 inches deep at that point, 1 inch short of 5 feet. The water swamped a car and a fire truck.
One common feature in most areas is that witnesses say the water disappeared almost as soon as the rain stopped. Christian said that indicates that the sudden rush of rain overwhelmed inlets and pipes.
Mayor Walt Maddox inspected some of the flooded areas.
“The majority of the cases we're seeing, the rainfall exceeded the drainage basin's ability to handle it,” Maddox said.
He said some improvements can be made that will help the situation.
Most of the improvements are simple, Christian said, such as adding another inlet in a neighborhood or realigning a pipe so that it flows into a ditch with the water flow, instead of against it.

“You can do some really inexpensive things to help your existing infrastructure function better,” Christian said. “Ideally, city forces could do most, if not all, of them.”
But he said the drainage system can't be constructed to handle the flow from the most extraordinary rain events, likening it to building Tuscaloosa's roads to handle all of the traffic on a University of Alabama game day.
“The taxpayers just can't afford it,” Christian said.

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