Largest ancient dam built by Maya in Central America

That dam -- constructed from cut stone, rubble and earth -- stretched more than 260 feet in length, stood about 33 feet high and held about 20 million gallons of water in a human-made reservoir.

These findings on ancient Maya water and land-use systems at Tikal, located in northern Guatemala, are scheduled to appear this week in the Proceedings of the National Academy of Sciences (PNAS) in an article titled "Water and Sustainable Land Use at the Ancient Tropical City of Tikal, Guatemala." The research sheds new light on how the Maya conserved and used their natural resources to support a populous, highly complex society for over 1,500 years despite environmental challenges, including periodic drought.

The paper is authored by Vernon Scarborough, UC professor of anthropology; Nicholas Dunning, UC professor of geography; archaeologist Kenneth Tankersley, UC assistant professor of anthropology; Christopher Carr, UC doctoral student in geography; Eric Weaver, UC doctoral student in geography; Liwy Grazioso of the Universidad de San Carlos de Guatemala; Brian Lane, former UC master's student in anthropology now pursuing doctoral studies at the University of Hawaii; John Jones, associate professor of anthropology, Washington State University; Palma Buttles, technical staff senior member, SEI Carnegie Mellon University; Fred Valdez, professor of anthropology, University of Texas-Austin; and David Lentz, UC professor of biology.

Starting in 2009, the UC team was the first North American group permitted to work at the Tikal site core in more than 40 years.

Detailed in the latest findings by the UC-led efforts are

• The largest ancient dam built by the ancient Maya of Central America

• Discussion on how reservoir waters were likely released

• Details on the construction of a cofferdam needed by the Maya to dredge one of the largest reservoirs at Tikal

• The presence of ancient springs linked to the initial colonization of Tikal

• Use of sand filtration to cleanse water entering reservoirs

• A "switching station" that accommodated seasonal filling and release of water

• Finding of the deepest, rock-cut canal segment in the Maya lowlands

An example of the thick vegetation common in the area where a UC-led team worked in and around Tikal.

According to UC's Scarborough, "The overall goal of the UC research is to better understand how the ancient Maya supported a population at Tikal of perhaps 60,000 to 80,000 inhabitants and an estimated population of five million in the overall Maya lowlands by AD 700."

He added, "That is a much higher number than is supported by the current environment. So, they managed to sustain a populous, highly complex society for well over 1,500 years in a tropical ecology. Their resource needs were great, but they used only stone-age tools and technology to develop a sophisticated, long-lasting management system in order to thrive."

Water collection and storage were critical in the environment where rainfall is seasonal and extended droughts not uncommon. And so, the Maya carefully integrated the built environment -- expansive plazas, roadways, buildings and canals -- into a water-collection and management system. At Tikal, they collected literally all the water that fell onto these paved and/or plastered surfaces and sluiced it into man-made reservoirs. For instance, the city's plastered plaza and courtyard surfaces and canals were canted in order to direct and retain rainwater runoff into these tanks.

In fact, by the Classic Period (AD 250-800), the dam (called the Palace Dam) identified by the UC-led team was constructed to contain the waters that were now directed from the many sealed plaster surfaces in the central precinct. It was this dam on which the team focused its latest work, completed in 2010. This gravity dam presents the largest hydraulic architectural feature known in the Maya area. In terms of greater Mesoamerica, it is second in size only to the huge Purron Dam built in Mexico's Tehuacan Valley sometime between AD 250-400.

Said Scarborough, "We also termed the Palace Dam at Tikal the Causeway Dam, as the top of the structure served as a roadway linking one part of the city to another. For a long time, it was considered primarily a causeway, one that tourists coming to the site still use today. However, our research now shows that it did double duty and was used as an important reservoir dam as well as a causeway."

Another discovery by the UC-led team: To help purify water as it sluiced into the reservoir tanks via catchment runoff and canals, the Maya employed deliberately positioned "sand boxes" that served to filter the water as it entered into the reservoirs. "These filtration beds consisted of quartz sand, which is not naturally found in the greater Tikal area. The Maya of Tikal traveled at least 20 miles (about 30 kilometers) to obtain the quartz sand to create their water filters. It was a fairly laborious transportation effort. That speaks to the value they placed on water and water management," said UC's Nicholas Dunning.

According to UC's Ken Tankersley, "It's likely that the overall system of reservoirs and early water-diversion features, which were highly adaptable and resilient over a long stretch, helped Tikal and some other centers survive periodic droughts when many other settlement sites had to be abandoned due to lack of rainfall."

UC paleoethnobotanist David Lentz explained that the sophisticated water management practiced by the ancient Maya impacted the availability of food, fuel, medicinal plants and other necessities. He said, "Water management by the Maya included irrigation, which directly impacted how many people could be fed and overall population growth. Accordingly, it is essential to understand the array of canals and reservoirs at Tikal, which conserved water during the annual dry season and controlled floodwaters during the rainy months. These practices allowed the Tikal Maya to sustain relatively high population densities for several centuries. As it evolved, this system of reservoirs was largely dependent on rainfall for recharging. With the onset of the 9th century droughts however, water supplies dwindled, causing the resource base and social fabric of the Tikal Maya to come under considerable stress. These developments may well have contributed to the abandonment of the city."

Of significance to Scarborough and the entire team are the potential lessons that can be gleaned from identifying a water system like that at ancient Tikal. Said Scarborough, "Water management in the ancient context can be dismissed as less relevant to our current water crisis because of its lack of technological sophistication. Nevertheless, in many areas of the world today, the energy requirements for even simple pumping and filtering devices -- to say nothing about replacement-part acquisition -- challenges access to potable sources. Tropical settings can be especially difficult regions because of high infectious disease loads borne by unfiltered water schemes. The ancient Maya, however, developed a clever rainwater catchment and delivery system based on elevated, seasonally charged reservoirs positioned in immediate proximity to the grand pavements and pyramidal architecture of their urban cores. Allocation and potability were developmental concerns from the outset of colonization. Perhaps the past can fundamentally inform the present, if we, too, can be clever."

UC's research at Tikal is supported by the Alphawood Foundation, by the National Science Foundation and by the university.