Opinion

How Raleigh manages flooding. A big test awaits.

One vehicle lies stranded by the bridge leading into the back side of Crabtree Valley Mall off Crabtree Ave. in Raleigh, NC, on Tuesday morning, April 25, 2017. Heavy rains all day Monday and through the night caused a lot of flooding in the area as creeks and rivers overflowed. The mall was closed Tuesday due to the floods.
One vehicle lies stranded by the bridge leading into the back side of Crabtree Valley Mall off Crabtree Ave. in Raleigh, NC, on Tuesday morning, April 25, 2017. Heavy rains all day Monday and through the night caused a lot of flooding in the area as creeks and rivers overflowed. The mall was closed Tuesday due to the floods. cseward@newsobserver.com

Hurricane Florence could provide a difficult test for how Raleigh manages flooding.

As urban development increases in Raleigh, concrete and asphalt prevent rainwater from soaking into the ground and directs it towards streams and creeks instead. This rainwater also washes items such as soapy water, leaves and litter into drains and ditches, which lead to local streams and creeks. This increases the chance that local waterways will flood, and causes greater pollution and erosion in streams.

“We can only manage flooding, we can’t prevent it. What we try to do is understand where it can happen, and how often,” said Wayne Miles, stormwater program manager for the City of Raleigh.

Raleigh residents and commercial properties’ monthly stormwater fee — on average $5 per 2,260 feet of impervious surface — funds stormwater programs to decrease runoff and manage flooding, such as improvements to dams and underground pipes that manage stormwater. Raleigh has adopted several measures to manage flooding and stormwater. Here are a few of the most effective:

1. Computer modeling and analysis. Raleigh’s Stormwater Management Division works with with the U.S. Geological Survey to place gauges along Raleigh waterways to monitor water levels. This includes places such as Pigeon House Branch Creek near Cameron Village, Crabtree Creek near Old Wake Forest Road, and Walnut Creek, off Fayetteville and Wilmington streets. The city also sends surveyors to measure water levels when flooding occurs. The data from these water gauges and surveys help the city develop computer models. “The computer models give us the freedom to simulate impacts and decide what improvements (we need to make),” Miles said.

2. Green stormwater infrastructure. This form of landscaping makes a property more attractive and treats stormwater runoff. It incorporates vegetation that helps keep the air clean and holds soil together or uses rainwater to water plants. Planting inside medians along city streets is one way that Raleigh has promoted green infrastructure; Sandy Forks Road is one example. The city also included a green roof and rain garden at the new Union Station downtown.

“More stormwater infrastructure puts water back into streams slowly (as opposed to a torrent). For a long time, stormwater infrastructure was only gray. The whole purpose was to get water away from houses as fast as possible. We realized that wasn’t the best route and that we need to merge gray and green together,” said Peter Raabe, a conservation expert with American Rivers who has assisted.

Residents can help the city manage stormwater runoff by taking advantage of Raleigh’s Rainwater Rewards Program. The city gives residents up to 90 percent reimbursement for costs when they add cisterns, rain gardens, green roofs, and other green options on their property.

3. Public education. The police department plays a role in educating residents about the dangers of flooding in an urban area. “We’re very fortunate in the city that we live in that we do not experience (flooding and major storms) on a regular basis, so folks have time to research (what to do),” said Capt. K.S. Anderson of the Northwest Raleigh police district.

During major storms, the police department checks on neighborhoods where there is major flooding, directing residents away from flood sites, monitoring flood levels, and helping other city services, such as the fire department or utility companies, access neighborhoods.

Police recommend that residents avoid driving through standing water, and if unable to evacuate or leave their home, to stock up on supplies such as flashlights, bottled water, and phone batteries. “(The best advice I have is) do not attempt to drive through standing water. It looks (still), but there is a current there. You never know how much your car can take before it stalls,” Anderson said.

4. Development regulations. Last year, the city changed its unified development ordinance to make it easier for developers to add green stormwater infrastructure, such as cisterns, rain barrels, and rain gardens, to construction sites. “The changes make (green stormwater infrastructure) more accessible, and shifted stormwater from waste into a resource,” said Raabe.

City employees ensure that developers and builders incorporate measures to manage flooding and stormwater runoff in their commercial and residential designs. They meet with contractors before construction and inspect sites during and after construction. They also ensure that stormwater runoff is controlled during construction.

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