Flood Warning

By Madeline Bodin​

As Hurricane Matthew lashed the coast of Georgia in October, the rain came down in Augusta, about 120 miles inland. Locals wondered, would it be like the flood of 1990, when some roads were under six feet of water and the Augusta National Golf Club's notorious "Amen Corner" washed away? Or would it be like the flood of 2000, when just four inches of rain created flash flooding in west side neighborhoods and over-topped a vital interstate highway?

It wasn't just Augusta. It was hard to ignore floods and their damage in 2016. On April 18, thunderstorms flooded Houston. Several people died, freeways became flumes, schools and businesses were closed, and properties in nine counties were inundated.

On August 11, the rain started falling on the Baton Rogue region of Louisiana. Eventually, a flood caused 13 deaths and damaged more than 100,000 homes. On August 26, shoppers at the Castleton Square Mall in Indianapolis found their cars submerged nearly to their windows. It was just one in a series of little-reported flash floods that swept the country that day, from the Midwest to the Rocky Mountains. And on September 21, flooding began in northeastern Iowa. Over the next week, flooding was so widespread in the state that one-quarter of Iowa's counties qualified for state disaster relief.

It's not a fluke. There are more damaging floods these days and they're becoming more frequent, thanks in part to climate change. According to the Third National Climate Assessment, a federal report put together by a team of 300 experts, "The heaviest rainfall events have become heavier and more frequent, and the amount of rain falling on the heaviest rain days has also increased."

Add to the mix more development in floodplains and coastal regions and you have a recipe for increased property-damaging floods.

Huge bands of rain are seen in this satellite image of Hurricane Matthew just before it made landfall in South Carolina last October. Photo by Jesse Allen, courtesy NASA Earth Observatory.

Even areas deep in drought are not immune. In January 2016, parts of both central and southern California flooded during storms, but the rainfall was not enough to erase the drought that persists throughout the region.

Planning tools can help keep communities safe from floods. APA's Planning Advisory Service recently updated its report Subdivision Design and Flood Hazard Areas, PAS 584, with detailed information on how that can be accomplished.

The report's editor, James Schwab, FAICP, manager of APA's Hazards Planning Center, says that a planner's most important tool for preventing flood damage is a map with more information and detail than what's available from a Federal Emergency Management Agency Flood Insurance Rate Map, known as a FIRM.

He says that a planner's most important skill is encouraging creative subdivision design. He adds that research for the report revealed a surprising flood risk in subdivisions where home owners associations manage flood-control infrastructure.

Although its winds had weakened as it moved north, Hurricane Matthew delivered record-breaking rainfall to parts of the Southeast. NASA's Terra satellite captured this image of floodwaters laden with sediment pouring out from several rivers in North Carolina and South Carolina. Dissolved organic matter may have contributed to the dark color of the river water as it spilled into the Atlantic Ocean. Photo by Jeff Schmaltz and Adam Voiland, NASA.

Mapping your way

In August 1995, Tropical Storm Jerry dumped up to nine inches of rain on Charlotte and Mecklenburg County, North Carolina, creating one of the most damaging floods on record for the region. Residents had barely recovered when Hurricane Danny struck in July 1997. This time 13 inches of rain fell and three people died.

Charlotte-Mecklenburg was ready to take action. The first thing they did was turn to the FIRMs, says Timothy Trautman, manager of Charlotte-Mecklenburg Storm Water Services' engineering and mitigation program. The maps were 20 years old, but that was not the only problem.

Many municipalities rely on FIRMs from FEMA for flood planning. And why not? These maps provide so much: base flood elevations, flood zones, and floodplain boundaries. "The flood maps that the United States has are the best in the world, bar none, as far as being detailed and comprehensive," says Chad Berginnis, executive director of the Association of State Floodplain Managers.

Berginnis, a contributor to the PAS report, makes it clear that he's not bashing the maps when he says they are not sufficient for effective planning in floodplains. First, FIRMs primarily map areas that are already developed. When a new subdivision is being built in a cornfield 10 miles out of town, there may not be an existing FIRM for the area. But that doesn't mean there's no flood risk.

Second, FIRMs represent past information and they are not updated frequently. New development in the floodplain means new risks downstream that are not reflected on old maps. FIRMs also don't reflect future conditions, such as shifts in rainfall patterns because of climate change. That's because FIRMs are as much an insurance tool as a land-use tool, says Berginnis.

"The planning horizon is different than the insurance horizon," says Marc Rosenberg, senior casualty policy analyst with the American Academy of Actuaries. "While planners look 20 years into the future, the insurance industry looks back at the last 15 years for the risk in the next year, but doesn't reflect the risk 20 years from now." FIRMs mirror the insurance industry perspective.

Third, FIRMs focus on the 100-year floodplain, which is the area where there is a one percent risk of flooding each year. Many Planners find the 500-year floodplain, which reflects a 0.2 percent annual risk (or one in 500 chance), to be a more valuable measure. FIRMs also don't map flooding from dam failures, which like floods, are something that seems to be happening more frequently. For example, more than 40 dams failed in South Carolina in one October 2015 storm.

"Depending on the resources of the community, that FEMA map may be the best they can do," says Schwab. Communities that choose to invest in better maps will see better results, he says. It wouldn't be unreasonable, he adds, to ask the developer to pay for floodplain mapping for that subdivision in the cornfield without a FIRM.

Charlotte-Mecklenburg saw their maps could be better. "We realized that if we simply updated the maps, they would still be inadequate," Trautman says. A pilot project in a single watershed compared updating the maps to reflect the current level of development to creating a map that showed what the floodplain would look like once the area was fully developed as zoned and planned.

"There was a five-foot difference in flood heights for a hundred-year event," Trautman says. In other words, they could follow all of FEMA's rules and still wind up with subdivisions that were five feet underwater a few decades down the road. "That was an eye-opener."

The city and county's combined stormwater agency took the lead, Trautman says. Funding came from FEMA and the state. The maps, created by local engineering firms, continue to be updated. The maps were digital, even in their first appearance in 2003.

Today, Trautman says, a real estate agent can pull up the maps while showing a property and see instantly what the insurance needs will be and whether flood development rules will apply to expanding the kitchen, for example.

"The mapping has paid off phenomenally," Trautman says. "I haven't seen a building flood that has been built since we had the new maps. It still could happen, but we've just reduced the risk so much more."

Charlotte-Mecklenburg 3-D Interactive Floodzone Mapping

After multiple rounds of flooding, the North Carolina region initiated an extensive mapping program that shows flood risk far better than FIRMs do. It helps property owners understand their flood risk, assess flood insurance needs, and know whether a renovation would trigger flood development rules. Here's a map showing an older neighborhood, developed before the new flood regulations. Blue indicates high risk and green medium risk.

Map courtesy CMSWS.

Creative solutions

In 2011, Cedar Falls, Iowa, created an ordinance that banned any platting in the 500-year floodplain and restricted the amount of fill that could be used, says Stephanie Houk Sheetz, AICP, interim director of community development there.

Ordinances that ban development in the floodplain are the simplest way to get developers to take topography into account when designing subdivisions. But there are other methods that encourage developers to be resourceful in meeting municipal goals.

Recently, Cedar Falls decided that not allowing even an inch of a new lot within the 500-year floodplain was too restrictive.

The 100-year floodplain is still completely restricted, says Sheetz. But, she says, as long as less than 25 percent of a lot is in the 500-year floodplain and the building envelope is completely outside it, the lot can be created.

Other communities have been even more creative. In Licking County, Ohio, large-lot zoning means that any newly-created lot must have enough buildable natural ground outside the floodplain for the main structure. (See the case study on page 30.) Thirty years ago, Augusta, Georgia's floodplain ordinances conformed to the National Flood Insurance Program's standards of the time, which said buildings needed to be at or above the 100-year floodplain.

But after the flood of 1990, when "Amen Corner" washed away, the city approved a new ordinance that required new buildings to be two feet above the 100-year floodplain, says Terri Turner, AICP, the floodplain manager in the Augusta Planning and Development Department. (Turner also contributed chapters to the PAS report.)

After the 2000 flood submerged basements and an interstate, regulations shifted to require that new buildings be three feet above the floodplain. Still, in a survey, residents named flooding as the number one natural hazard faced by the community.

Since then, Augusta has taken many steps to reduce its flooding risk, Turner says. It bought out flood-prone properties — an important tool in many flood-prone cities.

It adopted a "No Adverse Impacts" ordinance, which prohibits development that will increase flooding elsewhere. But perhaps its most creative effort was the establishment of a conservation subdivision ordinance.

Developers in Augusta may choose to build under the conservation subdivision ordinance, which requires that at least 40 percent of the acreage of the tract is green space. (If more than half of that green space could have been developed otherwise, the requirement is just 30 percent.)

In return, the ordinance lets the developer create the same number of lots in the subdivision that it would have been allowed if the green space had been developed. (An exemption is required if the lots are less than 60 percent of the otherwise allowed minimum.)

There are other benefits to the developer, Turner points out. With the lots concentrated in an area outside of the floodplain, costs for roads and sewers are lower. Plus, she says, home buyers love having access to all that green space.

In October, Augusta escaped the wrath of Hurricane Matthew with no flooding. Today, Turner says, residents name high winds as the community's greatest natural hazard. Flooding has dropped to second.

South Carolina 2015 Floods: Forty-Seven Failed Dams and Counting

The confluence of a frontal system and Hurricane Joaquin resulted in prolonged heavy rain and significant flooding during the first week of October 2015. With up to 31 inches of rain falling over several days (see map below), the storm caused the failure of at least 47 dams. Very few of the dams had inundation mapping associated with them. Emergency action plans associated with dam failures were not understood by home owner associations and not communicated to residents of the developments adjacent to the dams.

Storm Totals in Inches, South Carolina, September 30 to October 7, 2015

From Subdivision Design and Flood Hazard Areas, PAS Report 584, Chapter 5. Map By South Carolina Department of Natural Resources.

What home owners associations are hiding

Craig Wilson is the CEO of a home owners association management company in Maryland with 35 years of experience in the business. Twice in the last 18 months he's heard something he's never heard in his career before: that his management company would be responsible for monitoring a high-hazard dam.

Home owners associations are also called community associations. Special districts created to fund levees and water districts are closely related, in that they are funded only by the residents that live there. "Home owners associations come in all sizes," says Dawn Bauman, senior vice president of government and public affairs for the Falls Church, Virginia-based Community Associations Institute. "Thirty-five to 40 percent are managed just by volunteers."

From coast to coast, flood prevention infrastructure is in the hands of home owners associations. This includes small, relatively easy-to-manage stormwater retention ponds, but also includes levees along rivers, sea walls, and dams and weirs of all sorts.

It may seem like a good deal at first. Let the developer build and maintain the flood infrastructure that lets development occur in a floodplain. In the long term, though, it's a home owners association that takes on the developer's responsibilities.

"After 40 years of representing these associations," says Tyler Berding of the California law firm Berding|Weil, "I can tell you, it doesn't work. The home owners associations don't raise enough money to maintain this infrastructure. These communities have a hard time running this infrastructure."

Berding has sued municipalities on behalf of home owners associations to get the municipality to take over management of vital infrastructure or perform emergency maintenance when a structure is on the verge of failure.

"This is hugely important," says Chad Berginnis. Even as planners and floodplain managers are increasingly working together to protect their communities from flooding, he says, home owners associations are left out and their role in flood prevention is not so much overlooked as completely unknown.

Laws vary by state on what responsibilities home owners associations can take on. In Maryland, for example, home owners associations can't manage dams, Wilson says. So, he was surprised by the monitoring requirement. The ultimate solution is not tougher negotiations between municipalities and developers, but better subdivision design.

"In most communities the floodplain manager is not in the planning department," says Turner, who knows her situation in Augusta as a planner and floodplain manager is unusual. But that doesn't mean that floods should ever be far from planners' minds.

"Flood risks need to be addressed by all the talent in the community," says Berginnis. Planning for floods is a process, Berginnis says. Your community's first steps may not be perfect, he adds, but it's important to take them.

Madeline Bodin is a freelance science and environmental journalist who writes frequently about floods.

Resources

 This NASA video shows the amount of rainfall dropped by Hurricane Matthew over the life and track of the storm. Real-time data covers the period from September 28 through October 10, 2016: youtu.be/TeWKdFobabg