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American Society of Landscape Architects

 

March 2008 Issue

Managed Retreat:
Coastal Development in an Era of Climate Change
Can coastal communities survive rising sea levels? One Virginia town struggles to find an answer.

By Mary H. Cooper Ellis, Student ASLA

Managed Retreat: Coastal Development in an Era of Climate Change

Of all the havoc wreaked by global warming, rising sea levels may pose the biggest immediate threat. More than one-third of the globe’s 2.4 billion human inhabitants reside within 60 miles of an oceanic coast, and coastal populations are increasing faster than the rate of population growth worldwide.

Some coastal communities are beginning to consider one or more of three basic approaches to deal with rising sea levels:

  • hardscape—protecting land to maintain existing uses with dikes, levees, seawalls, and the like
  • softscape—restoring and expanding wetlands, coastal marshes, dunes, and beaches
  • adjustments—accommodating current uses by raising structures on pilings and cultivating flood- and salt-tolerant plants and food crops

Policy makers in Britain have adopted an innovative strategy of purposeful abandonment of vulnerable coastal areas before disaster strikes. Under the moniker of “managed retreat” or “managed realignment,” local governments are identifying sites that are likely to be inundated by rising seawater and banning all construction on these lands.

The British approach has not received widespread attention in the United States, but a few states have begun to examine this strategy. In 1995 state agencies in Maine drew up a blueprint for identifying vulnerable coastal areas and recommended two options for managed retreat.

One involved the prohibition of all new development within areas expected to experience flooding due to sea-level rise over the next century. The other involved adoption of the “rolling easement,” a regulatory tool that bars construction of bulkheads and other hard structures to impede the natural flow of water and requires removing all structures and restoring sites to their natural state as the shoreline moves inland. Clearly written into the deeds of affected waterfront properties at the time of sale, rolling easements would be reflected in the properties’ value and preclude charges of adverse possession that have figured in several recent lawsuits involving eminent domain.

Maine, Rhode Island, and South Carolina subsequently adopted forms of rolling easements, while North Carolina prohibits construction of new houses in areas deemed likely to be eroded by wave action in coming decades. Common law in Texas recognizes rolling easements along its Gulf Coast beaches.

High Stakes: The Chesapeake Bay

The Chesapeake Bay, where there has been little discussion of such policy changes, is especially vulnerable to rising sea levels. The largest estuary in the United States, the bay is a vast, brackish water body where freshwater from several major rivers mixes with saltwater from the Atlantic Ocean, ebbing and flowing with the ocean tides. The bay is a unique habitat for myriad plant and animal species, serves as an essential nursery for spawning marine fish, and supports a vital fishing industry. At the same time, the Chesapeake is drawing new residents in search of waterfront homes.

The Chesapeake Bay’s water level is rising twice as fast as the global average, mostly owing to sediment compaction as a result of the removal of groundwater through wells serving the bay’s growing coastal population. Another factor is isostatic adjustment, as the land is still shifting in the wake of the retreat of ice sheets to the north many millennia ago.

Whatever the cause of the bay’s rapid rise in water level, the impacts are becoming increasingly apparent. Several islands have slipped underwater, forcing residents to relocate to the mainland, a fate that now threatens the inhabitants of Smith Island, Maryland, and Tangier Island, Virginia. Bay shore communities are reporting more frequent flood events from storm surges and extreme high tides, flooding houses, destroying septic systems, and washing caskets out of centuries-old graveyards. Many communities reported unprecedented flooding in September 2003 in the wake of Hurricane Isabel, a mild storm by historical standards. Large numbers of dead trees along the bay front bear witness to salt incursion, which kills many plant species and may render low-lying coastal agricultural land useless for cultivation.

Public concern about the bay’s health has focused on the harmful effects of polluted runoff from urban storm sewers and fertilized croplands on the aquatic vegetation, fish, and shellfish that comprise this unique ecosystem. But efforts to improve the bay’s “water quality” have not been matched by concern over its “water quantity.” Even in the wake of Hurricane Katrina’s devastation of the Gulf Coast in September 2005, there has been little sign that bay-side residents perceive the need to protect their communities and plan for the day when they, too, may face the ocean’s inexorable force.

The need to prepare is all the more urgent in light of development pressure. According to the National Oceanic and Atmospheric Administration, the counties of Virginia and Maryland fronting the Chesapeake Bay drew more than two million new residents from 1980 to 2003. With the impending retirement of millions of Baby Boomers beginning in 2008, this trend seems certain to intensify.

Cities on the Chesapeake Bay and their tidal tributaries, such as Baltimore and Annapolis, Maryland, have long defended themselves from high water with seawalls. Although floodgates may conceivably be an additional option for cities like Washington, D.C., or Richmond, Virginia, which lie along narrow stretches of tidal rivers flowing into the Chesapeake Bay, such barriers would be of limited value to the most vulnerable cities—Norfolk, Virginia Beach, and neighboring communities near the broad mouth of the bay.

Amid burgeoning development, armoring the Chesapeake Bay’s 8,000 miles of shoreline with bulkheads or riprap also would be prohibitively expensive. In any case, rising sea levels would overtop such structures in a matter of decades.

A more realistic strategy to deal with rising sea levels on the bay would reserve hardscape solutions like seawalls for the most vulnerable and valuable urban centers while employing innovative land-use policies and tax incentives to enable property owners to use their properties as long as possible but also allow nature to take its course. But coastal communities may wish to turn to planners, landscape architects, and architects rather than structural engineers for solutions to the problem. The regulatory vehicles that permit innovative land use, such as easements, have to be approved by local or state legislatures. Planners can draw up these vehicles, while landscape architects and architects can provide the design ideas for the interim use of land that is threatened by eventual inundation—such as parks, cultivation of salt-tolerant plants, or structures on stilts. Though still in its infancy, Britain’s pioneering strategy of managed retreat offers an intriguing model for forward-thinking state and local governments.

A Thought Experiment: Kilmarnock, Virginia

How might such a policy look if put into practice here? The town of Kilmarnock, Virginia, is a useful model for considering the potential impacts of and responses to rising seas on the Chesapeake Bay because it includes the agricultural, residential, and industrial uses typical of the region and because it is sufficiently undeveloped to accommodate design and planning tools for dealing with sea-level rise. Located at the tip of the Northern Neck—a 100-mile-long peninsula stretching from Fredericksburg to the bay between the Potomac and Rappahannock rivers—Kilmarnock is a rural community of 1,200 residents that is surrounded by low-lying fields and woodlands stretching to the water’s edge at Indian Creek, a mile east of town.

Kilmarnock’s relationship with the bay was traditionally purely utilitarian, as a watery highway for transporting grain and other farm products and a fertile ground from which local watermen extracted the oysters, crabs, and fish for which the bay became famous. But over the past several decades, changing economic forces have affected the area. Farmers have switched from truck-farming produce shipped to buyers in Richmond and Washington to the more lucrative and larger-scale growing of wheat, corn, and soybeans for poultry and industrial buyers on the Eastern Shore and beyond. Small waterfront landowners have cashed in on the growing demand for residential parcels by second-home owners and retirees. The water is now valued as an amenity.

Unlike many communities here, Kilmarnock lies not at the water’s edge but inland, atop an escarpment marking an ancient beachfront that runs down the western side of the bay. At about 90 feet above current sea level at its highest point, Kilmarnock illustrates the impacts of rising seas at multiple stages because the town itself would survive most plausible future increases in water level. However, the low-lying area that stretches eastward from town to the waterfront is vulnerable to sea-level rise, and changes in land use there will affect Kilmarnock proper.

The 660-acre study site lies east of Kilmarnock, from the town boundary to the shores of Indian Creek, a branch of the Chesapeake Bay. Lancaster County records place the total value of the land and its structures in 2005 at $27,611,800.

Residential property occupies just over 20 percent of the area but accounts for almost three-quarters of its total value, making private residential development by far the most valuable use of the site. Most of these properties lie on the waterfront, however, making residential use especially vulnerable to sea-level rise.

Like most of the residential areas, all of Kilmarnock’s industrial sites are vulnerable to early-stage rises in sea level. The town sewage treatment plant, the Southern States grain storage facility, the Chesapeake Boat Basin (Kilmarnock Wharf), and two adjoining gas and oil facilities occupy less than 5 percent of the land but account for 20 percent of the site’s total value.

Three-quarters of the site is undeveloped or marginally developed. The largest single parcel is the 95-acre Alexandria Police Department’s Boys Camp, valued at more than $2 million for its waterfront location.

The rest of the marginally developed land—more than 60 percent of the site—is cultivated farmland or woodland, much of which is harvested for timber. Located mostly inland, these parcels are the least valuable.

The prospect of rising sea levels could prompt a series of events along these lines: After a heated debate, Virginia joins other coastal states in adopting rolling easements and other policies to discourage waterfront development as sea levels rise. From the ridge, the town of Kilmarnock barely perceives a five-foot rise in sea level. Although it is somewhat broader and deeper, Indian Creek still provides a safe haven away from the rough waters of the open bay, and most of the site would remain above high tide. But the peninsula that provides that essential buffer, Bluff Point, already is undergoing a radical loss of dry land, and the open water has captured much of the point’s vast wetlands, exposing the site to flooding from storm surge.

The grain facility shuts down two of its silos, which have been contaminated by high tides.

The town wharf raises its boathouses on piers to provide adequate clearance for vessel traffic.

The small community of 1960s-era houses adjacent to the silos is subject to periodic basement flooding, prompting several residents to sell their houses at a loss.

Encroaching saltwater is killing many of the hickories, loblolly pines, and oaks that comprise the densely wooded buffer along the low-lying shoreline of the Boys Camp.

When water overtops existing bulkheads and riprap, all illusions that the previous way of life on the waterfront could endure are put to rest. At 10 feet, much of Bluff Point is underwater, and most of its luxury waterfront houses must be abandoned. Floating houses are options at this stage, as long as roadways to town remain above water. But many waterfront residents are newcomers to the area, retirees with no family roots in Kilmarnock and little stomach for the arduous task of rebuilding sustainable housing on an unpredictable waterfront. Most will retreat from the area.

As the region’s farmland falls to inundation and salt incursion, demand for grain storage has plummeted. Forced to move farther inland or shut down because of flooding, Southern States dismantles its silos and closes the facility for good.

The Boys Camp has lost about half its dry land. Virtually all the trees that once covered much of the site have died, and most of the property is covered by wetlands. The Alexandria Police Department reluctantly closes the facility to campers.

As bulkheads and riprap fail, virtually all waterfront properties have been abandoned. A new federal program helps property owners pay for the removal of structures, cleanup of septic systems, and remediation of their land.

The bright side of rising sea levels is the spread of wetlands and the wildlife they support. Long degraded by development and shoreline armoring, wetlands thrive at a sea level of 15 feet above the 2007 mark. Thanks to the site’s almost level topography at this elevation, the seawater stretches over a vast, shallow substrate, creating ideal conditions for wetland plants and animals.

About one-third its former size, the site is dominated by woodlands, with a few small open fields.

All former waterfront development has been destroyed. Former residents have moved to town or left the area altogether.

Newly exposed to the open bay by the inundation of Bluff Point, the town dock and marina services have sought a safer harbor at the town of Irvington, six miles away on the Rappahannock River.

With more than half the site under a relatively shallow sheet of water, local watermen try their hand at farming oysters and crabs, once mainstays of the region’s economy.

Blessed with ample high ground for new construction and viable highway connections to inland cities, Kilmarnock’s remaining residents decide to hold their own. Taking a cue from Gulf Coast communities that have decided to adapt to the menacing water instead of retreating from it, Kilmarnock identifies sites that are suitable for accommodating new residents and businesses while maintaining its historic core. The town has expanded its boundaries to encompass undeveloped areas in its immediate vicinity that lie at least 70 feet above 2007 levels. These sites have been targeted for cluster development, supplanting the old suburban pattern and offering mixed commercial and residential uses. The ultimate town boundary is the encroaching water, accentuated by a deep vegetated buffer, held in the public trust as parkland.

Speculating about the future based on current and likely ephemeral conditions is a risky business. Using existing topographic maps to envision future landforms under conditions of rising sea levels further clouds the picture: A single Katrina-like storm surge could reshape a coastal site. Many years of surge and wave action would surely alter the topography. Add to all that the unpredictability of human response to a creeping crisis like widespread flooding and waves of environmental refugees from coastal cities, and the picture is blurred beyond recognition.

So the scenarios envisioned in this article are speculative. But the message is not. “Sea level rise under warming is inevitable,” the Intergovernmental Panel on Climate Change flatly concluded in November 2007. Managed retreat implies a revolution in current thinking about climate change and its impacts. But we would be well served to assume the worst in order to better protect our descendants from its outcome.

Mary H. Cooper Ellis, Student ASLA, received her master of landscape architecture and master of urban and regional planning degrees from Virginia Tech in 2007. She lives in Kilmarnock, Virginia.

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