Tumacácori National Historical Park contains remarkable examples of adobe architecture that are now threatened by increasingly severe rain events/Michael Newberry
Water Worries: Threatened And Endangered Cultural Sites
Cascading effects of climate change, including increasing rain events and rising seas, are challenging cultural resource managers throughout the National Park System.
By Kim O’Connell
In the American Southwest, water is essential but often scarce. Ancient and Indigenous people learned to work with the water that was available, to follow the natural courses and cycles of water as it moved across the landscape. Today, climate change has disrupted those natural patterns, creating drought conditions that have brought the Colorado River and other Western waterways to historically low levels.
But too much water, not the lack of it, is also causing problems in the Southwest, particularly at historic sites such as Tumacácori National Historical Park in Arizona and Pecos National Historical Park in New Mexico, which both maintain historically significant adobe structures. Here, climate change has caused increasingly severe rainstorms that have had profound impacts on the historic earthen walls found in these two parks.
Other water-related issues, such as storms, flooding, and sea level rise, have wreaked havoc on cultural and historic sites elsewhere in the park system, too, including Statue of Liberty National Monument, Colonial National Historical Park and the Jamestown Settlement, and Castillo de San Marcos National Monument.
In the coming months and years, preservation of historic resources at these and other cultural parks will require not just traditional restoration but also possible relocation of park resources or total replacement of lost historic artifacts and features.
Attention On Adobe
Adobe is an ancient building material, made by combining sand, straw or grass, clay, and water in rectangular frames and letting them dry in the sun. In an arid climate, adobe is durable and abundant, which has allowed some adobe structures to last for hundreds of years.
Located about 50 miles south of Tucson, where the annual rainfall barely tops 11 inches, Tumacácori National Historical Park preserves three historic Spanish missions dating to the 17th and 18th centuries, with outstanding examples of earthen adobe architecture. Since 2010, however, park buildings have had four wall collapses, due to long-duration storm events that have allowed rain to penetrate beneath the protective lime plaster that covers the adobe to saturate the bricks beneath.
“Adobe is an unstabilized mud brick that’s dried in the sun, so if you add water it turns back to a mud,” says architect Mark Chalom, an adobe expert who recently gave the keynote address on earthen architecture at the Earth USA conference in Santa Fe, New Mexico. “Climate change is really affecting the erosion of these structures, so [park managers] have to work harder to maintain and protect them. One rainstorm is not going to take them away. It’s slow. But it’s happening, and it’s happening at a faster rate.”
In a research paper published in Heritage Science in November 2021, a group of preservationists, archaeologists, and masonry experts from the National Park Service, U.S. Department of Agriculture, and the University of Arizona noted that intensifying rainfall is likely to cause increasing damage to earthen architecture at Tumacácori and similar sites in the future.
The authors recount a series of tests conducted at the park in 2018 to determine how adobe test walls reacted to a range of conditions that simulated high- and low-intensity rainstorms. A LiDAR (laser imaging, detection, and ranging) scan then measured the test walls before and after the rainfall simulations. What they found was a nearly exponential increase in wall degradation with increasing rainfall intensity.
“Balancing the preservation of earthen architecture and visitor enjoyment is a difficult task and, throughout the history of the NPS, these two factors have led to a sense of overwhelming urgency: we must protect architecture now, before any more is lost,” the authors conclude. “Couple that with limited testing on the mechanisms that cause structural damage, and NPS cultural resource specialists are left to manage fragile resources with assumptions made from anecdotal observations.”
The study adds significant data to the parks’ preservation arsenal, but more work needs to be done before more historic adobe is lost for good. “Adobe is a material that will last thousands of years if it’s taken care of,” Chalom says, “and it’s worth taking care of because it’s our past and it’s our future.”
Strengthening Walls
On the East Coast, with increasingly brutal weather and flooding at several cultural sites, improving the resiliency of historic resources in the face of climate change is paramount. At the iconic Statue of Liberty, for example, which was forced to close temporarily after Hurricane Sandy pummeled coastal New York in fall 2012, workers are now focused on restoring Fort Wood, the 11-pointed, star-shaped fort on which the statue stands.
Built between 1808 and 1811 as part of the early defenses of New York Harbor, the fort features some 35,000 square feet of granite that now needs extensive and varied repairs, from mortar installation to replacement of disintegrating stones. With funding from the Great American Outdoors Act, the restoration project is designed to provide for long-term protection of the fort’s terreplein (horizontal structure) and vertical surfaces against exposure to weather and the marine environment.
And yet, the iconic park could still be vulnerable to the effects of climate change: According to the National Parks Conservation Association, the monument still has an estimated $1.5 billion in assets within three feet of the current sea level. And scientists now say that the sea level around New York is rising by one inch every seven to eight years.
Increasing flooding around the historic Tidal Basin in Washington, D.C., has prompted new plans for rehabilitation of the seawalls there. / NPS
Similarly, at the Tidal Basin in Washington, D.C., part of the National Mall and National Capital Park group, the Park Service is now collecting public comments on the planned rehabilitation of the site’s historic seawalls, which have been increasingly flooded and sinking as the Potomac River rises. According to a Potomac Conservancy report, the Potomac River and Chesapeake Bay region are expected to sink 6 inches in the next 100 years due to land subsidence, which could mean disaster for the low-lying historic sites and monuments of the nation's capital, when coupled with sea level rise.
Castillo de San Marcos National Monument in St. Augustine, Florida, which dates to the 17th century and is the oldest masonry fort in the continental United States, is a historically important example of building with coquina—a rare form of limestone composed of the shell fragments of ancient mollusks and invertebrates. As with other marine parks, the increasing frequency and severity of storms has led to degradation of the coquina walls, and the park is now working on reinforcing the walls so they are better protected against storm surge and weathering. Recently, the Conservation Research Laboratory at Texas A&M University also restored the park’s 25 historic cannons, whose cast iron surfaces have deteriorated in the salty Florida air.
"The main issue driving corrosion on the cannon was the presence of chloride ions, which came from either the depositional environment that they were found, or from the salty sea air that they are displayed in," says Dr. Christopher Dostal, director of the Conservation Research Laboratory. "Though storms and rain associated with climate change might seem like they would be a threat to the cannon, in reality they have much less of an effect than the thousands of visitor hands that touch them every year. By preparing for the latter, we are by default protecting for the former."
Whether all the cultural and historic sites within the Park Service’s domain get the same level of attention and funding for similar work remains to be seen. Such projects also point to another ongoing need—adequately trained trades workers who are skilled in historic preservation.
This is especially true when it comes to using modern additives and materials to bolster historic stone, plaster, adobe, or wood, according to Hugh Miller, former chief historical architect for the Park Service and a preservation technology expert.
“The technical issues still haunt us in terms of determining best practices [for these restoration projects],” Miller says. “The hand teaches the mind—trade skills are important and will remain so in the future.”
Saving Artifacts
At the Jamestown settlement at Colonial National Historical Park in tidewater Virginia, the site of the first permanent English settlement in America, archaeologists are in a race against time. Excavations have occurred there for years, and researchers believe they have uncovered about 85 percent of the early 17th-century fort. More than 3 million artifacts have been found, providing important clues to the many layers of history that have occurred on the site, from the earliest Indigenous peoples through the 20th century.
Due to the rising James River, the Pitch and Tar Swamp on Jamestown Island is swallowing more and more of the land, inundating possibly significant archaeological sites. / NPS
But rising seas, increasing storms, and recurrent flooding have repeatedly inundated the site, with some historic areas already permanently underwater and others getting uncomfortably close to that reality. NOAA monitoring stations nearby have shown that the adjacent James River has risen nearly 18 inches in the last century.
According to a November dig report posted by the Jamestown Rediscovery Foundation, a private nonprofit that works in partnership with Colonial National Historical Park, archaeologists are focused on digging near the Pitch and Tar Swamp that spreads across Jamestown Island and is slowly swallowing more and more of it. Excavations in 1941 indicated a possible palisade near a current footbridge over the swamp, but archaeologists are concerned that the ground there may already be too saturated for digging.
“In general, any groundwater inundation will affect archaeological resources,” says Jamestown Rediscovery spokesperson Angel Johnston via email. “Repeated inundation and drying out periods (i.e. what happens during flood and high tide events) are especially damaging, because the repeated effects of soaking and drying accelerate any decay process.”
Within the next five years, one major goal is to improve drainage in the swamp to ease flooding and tidal impacts, Johnston says. “By slowing down the worst of the impacts, we can continue doing archaeology in these areas and uncover the history lying beneath the surface before it disappears.”
At Jamestown and elsewhere in the park system, the clock is ticking.
