With better imaging and better maps, it’s easier than ever to see the effects of sea level rise on the Chesapeake.
by Marty LeGrand
The very first map of the Chesapeake Bay, drawn by guess which bushy-bearded English explorer, was published 400 years ago. Reasonably accurate, it was also designed to introduce the recently scouted, resources-rich estuary to prospective settlers.
Well, we’re here. Seventeen million and counting, some three million living in areas less than about three feet above seal level. Now we can contemplate the latest in Chesapeake cartography: computer-enhanced renderings of Captain John Smith’s “faire Bay” circa 2100, by which time, scientists estimate, sea level could be anywhere from two to five feet higher. If these modern “maps” prove to be reasonably accurate simulations, this is what a supersized Bay portends:
• The disappearance of Smith, Tangier, Hooper and Deal islands like 13 other once-charted Chesapeake islands before them.
• Storm-induced flooding in downtown Annapolis, Baltimore, Norfolk, Virginia Beach and Washington D.C., where iconic national memorials could be submerged by ill-timed storm surges.
• Loss of waterfront businesses and homes throughout the Bay, including Rock Hall, Oxford and Deltaville.
• Potential isolation of communities such as St. Michaels, Tilghman Island, Deale and Shady Side, Md., and/or costly infrastructure projects to elevate the roads, bridges, water and sewer lines that serve them.
• Submersion of many low-lying parks and wildlife refuges, including the 26,000-acre Blackwater National Wildlife Refuge.
• Loss of valuable tidal wetlands that buffer coastal communities from the effects of erosion, storm surge and saltwater intrusion into aquifers.
And what of the good captain’s home port, Jamestown? Gone. If estimates are anywhere close to the worst-case scenario, the island and its historical parks will be entirely submerged by the 22nd century.
Warmer oceans and melting glaciers are causing sea level rise. But not all sea level rise is created equally. In the Chesapeake Bay, sea level is rising at double the global rate, making our sprawling estuary one of the most vulnerable regions in the country. And that’s because here not only are the seas rising; the land is sinking. A study by the Army Corps of Engineers and the Virginia Institute of Marine Science, using 30 years worth of measurements, shows that sea level alone is rising at a rate of 1.8 millimeters per year. That would add up to about 7 inches in a century’s time. But the same study shows that land around the Bay is sinking nearly as fast—and in some places much faster, up to 4 millimeters per year. When you add that to the equation you get a “relative” sea level rise of up to two feet in that same 100 years. And of course that’s only if the changes continue to happen at exactly that rate. If the rate of sea level rise accelerates, as some predict it will, the problem will of course only be worse.
Blame the subsidence problem, or at least most of it, on the last ice age. When glaciers formed over North America they stopped just north of what would become the Chesapeake. Lands along the glacial periphery were forced upward as the ice nestled in—much as the surface of an air mattress rises on each side of you when you lie down on it. When you get up off the mattress, the smooshed area (we believe that’s the scientific term for it) rises and the surrounding surfaces fall. Now all you have to do is imagine that happening in glacial (and post-glacial) slow motion, over thousands of years, and you have the idea.
The causes of global warming and the attendant sea level rise are still debated politically (man’s need for fossil fuels or Mother Nature’s inevitable cycles, pick a side). Scientists disagree about whether and how much global rates will accelerate as more ice melts and fills the Earth’s big bathtub higher. But virtually nobody disputes that sea level is rising. To paraphrase at least one Bay scientist, we can stop arguing about whether or not it’s happening; it’s happening. Now it’s time to argue about what we should do about it.
The Chesapeake Bay and its tidal tributaries have over 11,000 miles of shoreline, none of which will look exactly the same by the middle of this century and certainly not by its end. That’s nothing new. Nature and development happen. But the contours of the estuary are also being imperceptibly redrawn as the Bay rises an average of 3 to 4 millimeters per year historically. At that rate, by 2023 the Bay’s relative sea level will have risen by at most 1.5 inches. Hardly a hair-raising prospect unless you plan to live another century or two.
Yet some effects are already being felt. Sea level rise acts like an energy drink for destructive natural processes such as shoreline erosion and storm surge, which gulp the excess water and intensify. Take Tropical Storm Isabel in 2003, viewed by many as the Chesapeake’s climate change wake-up call. Isabel’s storm surge caused massive coastal and urban flooding that exceeded predictions because previous forecast models no longer applied in one crucial respect, relative sea level.
But nearly a decade later, memories are fading. It’s human nature to move on. So in the absence of tempests like Isabel on a regular basis, federal and state officials are trying to convey the importance of planning now for rising waters decades to come. They’ve found an effective tool in an ancient medium gone digital: maps. In the last five years, improvements in mapping technology (known broadly as GIS, for geographic information systems), data collection and computer modeling have allowed scientists to “see” the Bay’s future shorelines in progressive stages of retreat. Increasingly available to the public, these forecast maps have heightened awareness like never before about sea level rise and its primary impacts: increased erosion, greater flooding from storm surge and lowland inundation. With the click of a mouse, policy makers and urban planners, emergency responders, marina operators, waterfront homeowners and recreational boaters can get a virtual glimpse of the climate-altered future they and succeeding generations must accommodate.
Sea level rise poses a different set of threats to every corner of the Chesapeake. Large portions of the low-lying Eastern Shore face inundation. Heavily urbanized Hampton Roads, filigreed with rivers, bays and canals, is prone to chronic flooding and storm surge. Rivers that have sustained historic port cities for centuries now threaten to drown them when powerful storms roll up the Bay. Here we’re going to break it down into the three fundamental threats: erosion, storm surges and inundation. Erosion can make the effects of storm surge and inundation worse, and of course storm surges can greatly accelerate erosion. How many inlets over the years have been created by erosive storm surge from a nor’easter or tropical storm? And history tells us that islands generally submerge from a combination of erosion and rising seas. So it helps to keep in mind that none of these threats operates in complete isolation from the other two.
Threat 1: Erosion
David Welser doesn’t need a map to see what’s becoming of his waterfront property on Turkey Point Island on the South River below Annapolis. When Welser and his wife Carol moved into their two-story house in 1976 their beach extended about 35 feet outward. Situated near the river’s mouth and boat traffic from Selby Bay’s numerous marinas, the sandy beach was nonetheless sheltered from waves and wakes by small barrier islands that formed a roughly 20- by 40-foot lagoon. For years it made an idyllic spot for gatherings of family and friends.
But on a warm morning this August, the river slapped against the Welsers’ bulkhead at high tide. A pair of tropical storms did in the islands and the lagoon in 1999. There’s no beach to speak of now, even at low tide, Welser says as he tosses a handful of dried corn to a flock of ducks out for a snack. Fifty years ago four large sewer pipes were installed here on the island’s east side as makeshift jetties. They’re barely visible now, clogged with sand and powerless to halt the inevitable. Eroding at a rate of about one foot per year, the Welsers’ beach eventually migrated northward around Turkey Point and into Selby Bay.
Minus the islands the couple’s waterfront is subject to greater fetch now. Minus the sloping beach there’s little to absorb the high-energy waves. Welser dreads two things: strong storms, which have pushed water in massive waves over their bulkhead, and poker runs. “When the big boats rev up heading out of [Selby] Bay it’s like a tsunami coming in,” says Welser, who owns a 32-foot powerboat. Elsewhere on the island, a private community of peaceful streets and about 45 homes, erosion has claimed two communal beaches since the land was first subdivided in the 1940s. It has also submerged 12 undeveloped riverfront lots.
Coastal erosion removes a shoreline’s natural defenses (barrier islands, beaches, trees and other stabilizing vegetation), allowing storm surge and high tides to reach farther onshore. Chronic flooding can then lead to inundation of lowlands. Islands are the poster children for this destructive cycle.
Over the past half-century, erosion and storms have dramatically reshaped Turkey Point Island, part of the Edgewater/Mayo peninsula, blunting the island’s point and allowing the South River to breach Ramsay Lake (now Ramsay Bay). Erosion vulnerability models suggest further shoreline retreat on the island’s east side in the next 50 years, which could affect several homes. Even conservative estimates of sea level rise show that portions of the island’s only access road (and some sewer lines) could be under water by 2100.
Baywide, island dwellers are at more immediate risk from sea level rise, but mainlanders will be impacted too. For example, a vulnerability assessment two years ago by Anne Arundel County determined that if sea level rises another one to two feet by the end of the century (a conservative estimate) it would endanger nearly $3 billion worth of property. Not surprisingly, the most at-risk business sector is the marine industry, where 208 of 221 marinas and yacht clubs could be impacted, the study shows.
Local governments face difficult choices ahead. Can they afford to protect all public infrastructure? Should zoning ordinances allow coastal property owners to rebuild in flood-prone areas? Should policies discourage new development in such zones at the risk of a drop in tax revenues? In Maryland, the adaptation-and-response portion of the state’s Climate Action Plan, adopted in 2008, offers some guidance. It promotes such measures as increased elevation (“freeboard”) standards for new structures in floodplains and non-structural shore stabilization (“living shorelines”) to preserve natural resources.
Public policy doesn’t budge without supporting data, however. The Coastal Zone Management Division of Maryland’s Department of Natural Resources (DNR) pulled together information on sea level rise, erosion rates, storm surge vulnerability, historic shoreline positions, current shoreline features and more. Then the agency added a new twist to make the data more persuasive and user friendly: high-resolution topographic maps produced by an airborne imaging technology called lidar (light detection and ranging). Now incorporated into DNR’s Coastal Atlas (dnr.maryland.gov/ccp/coastalatlas), an interactive mapping tool, the information provides users with compelling visuals of the potential impacts of rising seas and receding shorelines. More than half of the state’s 16 coastal counties and several flood-prone cities have begun to assess their vulnerabilities thanks in part to the atlas.
“You can show [local officials] a series of screens with statistics and graphs and numbers, but once they see the map that’s when they fully engage,” says Chris Cortina, a DNR natural resources planner who provides technical assistance to local governments addressing sea level rise and coastal hazards.
Awareness has filtered to the community level as well. Two years ago the Turkey Point Property Owners Association purchased a five-acre marsh in perpetuity to spare it from development. Community leaders now encourage the use of living shorelines where feasible (they are not in the Welsers’ case), rather than traditional rip-rap, which holds erosion at bay but can redirect the vulnerability elsewhere and amplify it.
Threat 2: Flooding
If erosion is a slow-speed menace, attacking islands and beaches in particular, flooding is the fast and furious nemesis of urban areas. When Isabel swept across the Bay a decade ago, the storm unleashed a 6- to 8-foot storm surge on Baltimore, flooded downtown Annapolis, where residents chose kayaks over cars to get around, and prompted mandatory evacuations in Norfolk, one of the most hurricane-vulnerable cities on the Bay.
Imagine flooding post-Isabel as a preview of inundation and then consider Hampton Roads’ plight. Low elevation, flat topography and a greater rate of relative sea level rise than other parts of the Chesapeake put the region in harm’s way when storms approach. Even now, low-intensity storms and unusually high tides flood parts of Norfolk, which is spending millions on flood protection each year and wondering where it all will end.
A 2011 study by the Hampton Roads Planning District Commission estimated that even today 65,000 Norfolk residents could be impacted by a Category 2 storm (Isabel’s strength when it made landfall) and more than 200,000 by a major Category 4 hurricane. For all of Hampton Roads, current potential storm surge exposure ranged from 100,000 people in a Category 1 storm to more than 1 million in a Category 4.
Planners are taking these storm surge snapshots seriously. Coastal management officials have a mantra for how to adapt to sea level rise and impacts such as storm surge. Protect. Accommodate. Retreat. Protective measures might include building living shorelines. Accommodation could mean elevating streets and sewer lines to keep them from flood damage. But no one really wants to say the “r” word just yet.
Norfolk mayor Paul Fraim came closest last April when he conceded that officials could one day be forced to vacate chronically flooded parts of the city. “I think I’m one of the first mayors anywhere to say we may have to retreat somewhat from the sea,” he told the PBS TV and webzine Need to Know. “In the next twenty to thirty years,” the mayor said, “there will be places in the city that will contain water all the time and so we need to be prepared for that inevitability.”
Flooding has been a catalyst for planning in Maryland, too. State officials released a response plan in 2000, but it took Isabel to rivet local governments’ attention. “Isabel gave us an opportunity to focus in on coastal hazards,” says Zoe Johnson, author of Maryland’s Sea Level Rise Response Strategy and program manager for Climate Change Policy at DNR. “We moved forward from a hazard planning perspective, not [just] with sea level rise.”
Several cities are getting proactive about the prospect of heightened storm surge. Annapolis and Cambridge have adopted building elevation standards that exceed current National Flood Insurance Program requirements. Annapolis is factoring in sea level rise as it plans to redesign City Dock. The U.S. Naval Academy, which suffered extensive damage in Isabel, is determining how high to build a flood wall to protect its campus. What impresses Johnson about the Naval Academy’s deliberations is their planning horizon. “They were talking about three hundred years in the future,” she says. “They’re going through that thought process in that [long-term] way.”
Competing constituencies, limited budgets and more urgent needs prevent local governments from emulating “the Navy way” to prepare for encroaching seas and storms of uncertain magnitude. Preparedness remains a complex process involving multiple departments within local government.
“Planning for sea level rise is a long-term process,” Johnson says. “You don’t just go in and do it and then you’re done with it. It keeps evolving.” She sees it happening piece by piece over time as local officials, for example, revise their zoning laws or update emergency response plans.
Meanwhile, however, coastal communities grow larger and larger. Coastal planners warn of the “moral hazard” of accommodating such growth and allowing property owners to keep returning to flood-prone areas at the expense of other taxpayers. Johnson calls it the “build-insure-rebuild” syndrome.
The recourse, then, is to keep people out of harm’s way. Mayor Fraim acknowledged that Norfolk’s citizenry may not be ready to accept “retreat zones” as a necessary measure, but the dialogue has begun.
Threat 3: Inundation
Bordering Maryland’s Rhode River lies what may be the most well studied marsh in the nation, where scientists are trying to divine the future of the Chesapeake’s wetlands. A village of clear plastic chambers, linked by a zigzagging boardwalk, rises from the marsh grasses at the Smithsonian Environmental Research Center’s (SERC’s) Global Change Research Wetland. For nearly three decades researchers have been filling the chambers with carbon dioxide to test the effect on the grasses inside. If the plants are able to flourish—which research to date has indicated—there’s hope that increasing CO2 levels will actually help the marshes outpace future sea level rise and continue to perform their beneficial functions.
Healthy tidal marshes buffer shorelines from storm surge, slow erosion, filter sediments and provide habitat for fish, birds and other wildlife. They’re in jeopardy, however, from inundation due to sea level rise, shoreline development, land subsidence and invasive plants and animals. Among the areas most at risk:
• The peninsula surrounding Cambridge, including Blackwater National Wildlife Refuge, which could lose two-thirds to nearly 100 percent of its marshes by 2100 depending on the rate of water rise.
• Tangier Sound, where losses could range from 12 to 49 percent, exposing undeveloped dry land to inundation as well.
• The upper Tidewater region, including Mobjack Bay and the Hampton peninsula, which could see an 85 percent decline in brackish marsh and a 30 percent decline in tidal swamp.
An interactive website and map produced by National Geographic in partnership with the Conservation Fund (www.chesapeakeadaptation.org) vividly illustrates the extent of potential land submersion along the Eastern Shore. Marshlands and islands from Trappe Bay to the Pocomoke Sound—including Hooper, Deal, Smith and Tangier islands—will likely be inundated if sea level rises one meter (3.28 feet) or less.
The U.S. Army Corps of Engineers built offshore breakwaters to protect Smith Island, and Crisfield, Md., which sits a few feet above sea level, sought state help to install tide gates. But officials concede ultimately that won’t be enough. Communities will have to come to grips with rising waters as their own resources and political will dictate.
“Smith Island, Crisfield, Annapolis. We as a state don’t need to step in and say you need to do this,” Johnson says. “There are short-, medium- and long-range decisions that are going to need to be made within these communities. And no community is going to make a big decision now about what’s going to be let go.”
Conservation groups advocate several strategies for protecting land vulnerable to sea level rise, including negotiating conservation easements or acquiring homes and businesses in areas adjacent to wetlands. The strategies will protect coastal ecosystems while providing owners with an alternative to costly improvements or forced relocation, says the Chesapeake Conservancy’s Jeff Allenby. But it’s been a tough sell to many homeowners who fear acknowledging the vulnerability will affect their property value. “People are going to experience the effects of sea level rise, such as flooding during storms or seasonally high tides, long before they are permanently flooded,” Allenby says, “and they need to plan accordingly.”
The group has had greater luck negotiating conservation easements with owners whose properties flood repeatedly. “We look at climate change as both a challenge and an opportunity,” says the conservancy’s executive director, Joel Dunn. “Based on the best science available we help stakeholders decide where to protect land, where to protect Bay access and how to find new ways to finance conservation projects.”
The best science available at the Global Change Research Wetland shows that at least portions of the ecosystem might be able to fend for themselves. Patrick Megonigal, deputy director of SERC’s biogeochemistry lab, said that on their carbon dioxide diet the test plants have produced enough soil-trapping roots over the past three decades to keep the marsh 3 to 4 millimeters above the pace of sea level rise. Storms, erosion, sea rise, colonists; for 6,000 years this wetland has adapted to them all.
There is no Virginia equivalent to the Maryland DNR’s Coastal Atlas, but the Virginia Department of Emergency Management has a series of downloadable storm-surge maps, broken down by region and county and showing four levels of vulnerability in the affected areas. Go to www.vaemergency.gov/readyvirginia/stay-informed/hurricane/storm-surge.