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Rhode Island Researchers Predict, Map Future Flooding

The maps are the product of what experts say is one of the most sophisticated models to project future damage from storm surges and sea level rise.

(TNS) - On his laptop computer, Grover Fugate, director of the Rhode Island Coastal Resources Management Council, opens up a 3D map of the potential flooding damage to buildings on Conimicut Point in Warwick if a storm like Hurricane Carol in 1954 were to strike again.

The buildings are color-coded in shades starting with green, depicting no impact from the 15-foot surge of water that storm winds would drive up Narragansett Bay, through yellow, orange and finally red, a near-total or total loss.

The most vulnerable houses on the narrow, triangular point that juts into the Bay are colored red, but the more sheltered shoreline neighborhoods to the north and south fare better, with swathes of yellow and only scattered dabs of orange.

Then, as Malcolm Spaulding, a professor emeritus of ocean engineering at the University of Rhode Island, looks on, Fugate clicks to the next slide in his presentation, showing a map of the same neighborhoods in the event of the same type of 100-year storm. But this one also takes into account seven feet of sea level rise, which the National Oceanic and Atmospheric Administration predicts could occur by the end of this century.

In the new map, dozens of structures are already gone, swallowed up by the higher seas that have pushed inland, and hundreds of the remaining buildings are now awash in broad bands of red and orange in a wave of destruction that stretches from the point and runs west along both sides of Mill Cove and up the banks of Buckeye Brook.

In this scenario, more than twice as many buildings sustain damage.

“A bad day,” Spaulding remarks.


These maps are the product of what experts say is one of the most sophisticated models to project future damage from storm surges and sea level rise.

They are among the first to result from a new tool created by the CRMC and URI as part of a continuing effort to better predict the effects of climate change on Rhode Island’s 400 miles of coastline. Fugate and Spaulding call the mapping tool CERI, short for Coastal Environmental Risk Index.

CERI builds on an existing computer mapping program called StormTools that was created nearly two years ago, also at the request of the CRMC and under the direction of Spaulding.

StormTools marries Google Earth-like satellite images of Rhode Island with projections of sea level rise and storm surge to predict the reach of floodwaters in a variety of future conditions. It is interactive and online, allowing a user to zoom in on any area of the state.

The new program goes even further by depicting, street by street and building by building, the extent of damage from flooding under a pair of extreme conditions: during a 100-year storm — one that has a 1-percent chance of happening in any given year and the norm used by the federal government for coastal planning; and with seas that are seven feet higher than today — the upper estimate by 2100 put forward by NOAA.

The maps incorporate information on housing structures from Rhode Island’s E-911 emergency response database, which not only pinpoints houses using satellite information but also divides them into general categories: with basement or without, elevated or not, one story or two, and so on.

CERI then integrates generic projections of storm damage for those different house types that were developed by the Army Corps of Engineers. Those projections, known as damage functions, were adapted to break down the loss to a structure’s value by tiers: 0, 0 to 25 percent, 26 percent to 50 percent, 51 percent to 75 percent, and 76 percent to 100 percent.

And for the three-dimensional renderings created by URI's Marine Affairs Visualization Lab, like the one of Warwick that Fugate shows in his presentation, each tier is assigned a color, running from green to red, so the viewer can easily assess the level of damage.

So far, CERI maps have been created for sections of Charlestown and Warwick as part of a federally funded pilot project to demonstrate the potential impact of a serious storm on the two broad categories of coastline in Rhode Island: along the ocean in the southern part of the state and to the north within Narragansett Bay.

Surprising results for Warwick

Some of the results so far have been surprising. It’s reasonable to think that Warwick, located in the middle reaches of the Bay, is more protected than Charlestown, which is exposed to the open ocean. But the CERI projections show that the risks in the two communities are nearly the same.

That’s true for a couple of reasons. One, the shoreline neighborhoods in Warwick are much more densely developed than those in Charlestown. And two, the wind-driven storm surge that would spread out horizontally in Charlestown, affecting wide geographic areas, would actually amplify as it traveled up the Bay, meting out significant damage in isolated pockets. In other words, as the Bay narrows towards its head in Providence, the surge would grow higher, increasing the potential impact to places like Warwick along the way.

“I didn’t quite believe that until I started taking a look at the numbers, but sure enough,” Spaulding told coastal planners from around the state at a recent meeting. “It turns out there’s a 40-percent amplification from the mouth of the Bay to the head of the Bay ... and almost no amplification as you go along the [southeastern] coast.”

Not surprisingly, the CERI projections also show that higher seas would without question exacerbate the effects of an extreme storm. Simply put, as seas rise, flooding will spread inland and affect many more structures that would otherwise remain untouched. Wave damage would also extend its reach.

Six percent of residential structures within Rhode Island's 21 coastal communities are currently vulnerable to some level of flooding in the event of a 100-year storm, according to calculations made by URI graduate student Nicole Leporacci as part of the CERI project. That number nearly doubles to 12 percent if seven feet of sea level rise is factored in.

Leporacci also pinpointed hot spots for flooding based on the density of affected structures — the number per square mile. In the event of seven feet of sea level rise, the worst-hit areas would include large chunks of Warren and Barrington, eastern Warwick, Misquamicut in Westerly, downtown Newport and, assuming the Fox Point Hurricane Barrier would be inundated, downtown Providence.

As would be expected, elevated houses fare best in the CERI projections. Houses with basements generally fare the worst, because their boilers, hot water heaters and other costly mechanical systems are installed below ground level, where even a small amount of water can cause significant damage.

It turns out that most of the houses on the Charlestown and Warwick coasts are ill-suited to a future of higher seas. Two-thirds of homes in the study area in each community have basements, while only a small percentage in Charlestown and a tiny fraction in Warwick are elevated.

The projections look several decades ahead because most homes are built to last that long. Taking such steps as elevating them can make them much more resilient in the future.

But the maps can also apply to businesses and municipal projects, such as building roads or schools and laying sewer lines, helping to determine the level of investment in infrastructure that should be made in what could eventually be part of a flood zone.

The CERI maps provide essential information as Rhode Island’s coastal cities and towns plan for a changing climate, Fugate says.

“It allows the community to see what the future is,” he says. “The question is, ‘What are they going to do about it?’”

Planning underway

William DePasquale, director of planning in Warwick, says the city is already using the maps developed by Fugate and Spaulding to look ahead.

The projections are worrying for a city with shoreline neighborhoods like Conimicut that are primarily low-lying and separated from the water by narrow barrier beaches or salt marshes that are being worn away over time.

“When I saw some of those scenarios, my jaw hit the ground,” DePasquale says of the CERI maps.

Of the 34,479 structures in Warwick, 2,504 would receive some damage from a 100-year storm, according to the projections. With seven feet of sea level rise, that figure doubles to 5,304 — 15 percent of the city’s buildings.

And the extent of damage to any structure increases dramatically when higher seas are factored in. The number of buildings that would sustain 50 percent or greater damage more than quadruples, to 2,192, with seven feet of sea level rise.

The 50-percent benchmark is important because under CRMC rules, any building with damage greater than that cannot simply be repaired but must be rebuilt in conformity with the latest building standards.

In the short term, DePasquale says, the city is looking at ways to station more emergency response vehicles on Warwick Neck, the peninsula that runs south from Conimicut. The maps show that the surge from a 100-year storm would inundate the strip of land between Mill Cove and Warwick Cove, cutting the residential areas of Warwick Neck off from the rest of the city and effectively creating a temporary island in the Bay.

City officials are also considering changes to the building code to bump up the “freeboard” requirement — the minimum height a home must be elevated above projected flood elevations. An increase would affect new construction, but it could also apply to extensive renovations of an existing structure, DePasquale says.

And looking further into the future, he says there are discussions about having the city buy up properties that are most at-risk, akin to what happened in the 1980s in the city’s Belmont Park neighborhood, where the federal government paid to move or tear down 61 homes prone to flooding from the Pawtuxet River.

A similar project on the coast could include both vacant land and developed lots that have grown more vulnerable as waters have risen and the shoreline has eroded.

“Do we rebuild on the coast only to have them wiped out again?” DePasquale says.

Retreat, regrade, remove

On a sunny morning, as she walks through Warwick’s Riverview neighborhood, Wenley Ferguson, director of habitat restoration for the environmental group Save the Bay, answers that question.

“We should really look at retreat, regrading and removal of infrastructure,” she says.

She stands on a sandy path where the end of Mill Cove Road used to be. With extreme high tides washing over the road and eroding the earth underneath, the city agreed to have a 140-foot-long strip removed in 2014 and replaced with a rocky swale and plantings to control drainage and a walking path that leads to a beach on the Bay.

Save the Bay has carried out similar projects on three other roads in Riverview and one in Conimicut Village as part of a NOAA-financed project to help the area better withstand storms and flooding. The long-term hope is that the little protection the beach offers can be enhanced by a buffer of native plants and salt marshes.

There are at least half a dozen other roads in this stretch of coastline that dead-end near the Bay and are slowly being undermined by encroaching waters. The city is considering removing sections of those roads, too, and has even closed down one street in Conimicut because of frequent tidal flooding.

As she walks on the beach near Mill Cove, Ferguson points across to vacant house lots with “For Sale” signs and shakes her head.

“We have enough vulnerable infrastructure in our coastal zone,” she says. “We don’t want to add more.”

This section of coastline has been eroding for decades — in places, as much as 200 feet in the last 80 years, according to CRMC maps based on historical aerial photos. In one 1939 photo, a north-south road is visible running a few blocks along the Riverview shore. That road is gone, subsumed by the Bay.

Riverview Beach is littered with wooden pilings, broken concrete and other remnants of houses, commercial buildings and seawalls that were destroyed in the Hurricane of 1938 or Hurricane Carol or have been abandoned as the water has gradually moved in.

Stephanie Van Patten lives with her husband and their two daughters in an 1890 house that looks out over Mill Cove. The house sits higher than much of the surrounding neighborhood, but the first floor was still flooded on Aug. 31, 1954, during the 14.4-foot storm surge from Carol, which flattened much of Conimicut.

Van Patten and her family have no plans to move away from the coast, but she worries about the next hurricane that will hit Warwick.

And she knows that higher seas will magnify the impact of a surge.

“We’re kind of expecting it with sea level rise,” she says. “We keep our basement unfinished for a reason.”

©2016 The Providence Journal (Providence, R.I.) Distributed by Tribune Content Agency, LLC.