Southwestern Lakes Ancestral Puebloan Water Handling Kenneth R. Wright, P.E. Ancestral Puebloans, Table 1. Mesa Verde Storage Structures. Climate and Reservoirs Structure Identification Location Time Span (AD) he ancient Ancestral Puebloan people of Mesa Verde, popularly known as Morefield Reservoir 5MV1931 Morefield Canyon 750-1100 Tthe Anasazi, reconciled their lifestyle Far View Reservoir 5MV833 Chapin Mesa 950-1180 to the semi-arid and changeable climate. These dryland farmers who lived at Mesa Sagebrush Reservoir 5MV1936 Unnamed Mesa 950-1100 Verde from about AD 550 to about AD Box Elder Reservoir 5MV4505 Prater Canyon 800-950 1300 contended with periods of drought and occasional cool growing seasons. Mug House Cistern 5MV1586 Wetherill Mesa 1200-1290 Dealing with climate variability was tough for people living in an already harsh environment with few resources. One of the ways the Ancestral Puebloans adapted to their difficult surroundings was by becoming reservoir builders. Wright Paleohydrological Institute, a team of scientists, engineers, and archaeologists devoted to the study of prehistoric water use, began investigating Ancestral Puebloan water handling in 1995. Over the past 13 years, we have studied five Ancestral Puebloan water storage facilities at Mesa Verde (Table 1) and learned that these people were good engineers and hard workers who persevered in spite of the variable climate. Mesa Verde Climate Mesa Verde is located near the Four Corners region of Southwest Colorado (Figure 1). Average annual rainfall is about 18 inches, while the average annual maximum temperature is about 62° F. The terrain is semi-arid, with many flat mesas and steep, rocky canyons. The people who lived in this environment did not have an easy life, even during times when the climate was favorable. Paleo climate evaluations using dendrochronology (tree rings) provide estimates of precipitation and temperature Figure 1. Mesa Verde National Park is located in the Four Corners area of southwestern going all the way back to AD 500 (Figure Colorado. Winter 2008 / LAKELINE 23 Mesa Verde Paleohydrological Survey Project - Site 5MV1931 Morefield Canyon Mesa Verde Dendroclimatic Reconstruction of Annual Precipitation 481 A.D. - 800 A.D. 1201 A.D. - 1600 A.D. 45 35 40 30 35 25 inches inches 30 8 20 25 on [inches] rage- 18 erage- 1 on [inches] i i v e 20 15 Precipitat Precipitat year av 15 year a 0 0 0 10 15 150 10 5 5 0 0 481 501 521 541 561 581 601 621 641 661 681 701 721 741 761 781 1201 1221 1241 1261 1281 1301 1321 1341 1361 1381 1401 1421 1441 1461 1481 1501 1521 1541 1561 1581 Year Year 801 A.D. - 1200 A.D. 1601 A.D. - 1988 A.D. 35 35 30 30 25 25 inches inches 20 20 n [inches] rage- 18 rage -rage 18 on [inches] o i e e 15 15 Precipitat Precipitati year av year av 0 0 10 10 150 150 5 5 0 0 801 821 841 861 881 901 921 941 961 981 1001 1021 1041 1061 1081 1101 1121 1141 1161 1181 1601 1621 1641 1661 1681 1701 1721 1741 1761 1781 1801 1821 1841 1861 1881 1901 1921 1941 1961 1981 Year Year Source: Dr. Jeffrey Dean, Dept. of Dendrochronology, Univ. of Arizona Wright Water Engineers, Inc. Figure 2. The dendrochronology record by Dr. Jeffrey Dean shows periods of drought at Mesa Verde. 2). This climate record includes the years Background on and several thousand occupants. With of the Ancestral Puebloans’ inhabitancy Ancestral Puebloans 130 years of somewhat reliable rainfall, of Mesa Verde, from about AD 550 to AD The residents of Mesa Verde and an agricultural lifestyle was begun in 1300. The records show that the ancient their time frames are shown in Table 2. southwest Colorado that still exists today. people of Mesa Verde could not rely on Starting about AD 550, Basketmaker There was a population expansion consistent weather patterns. One of the III farmsteads sprang up in southwest by AD 750. By this time, the resident worst drought periods at Mesa Verde Colorado wherever there were good soils, population of southwestern Colorado within the dendroclimate record started in streams and relatively adequate rainfall. was well over 3,000 people, known as AD 1135 and ran to AD 1180. Then, in They were lucky; between AD 570 and Pueblo I. For the Pueblo I community, the AD 1275, another major drought struck 700, southwestern Colorado had decent biggest challenge in Mesa Verde was its that lasted until AD 1300. climate conditions, and this area took on change to relative aridity. Their dryland Cooling trends may also have had a decided agricultural character. Their farming atop mesas and in canyons an impact on the Ancestral Puebloans. homes – pit houses – were half dug into relied on soil moisture, snowmelt, and Kenneth Peterson and others have the soil and half above ground (Figure 3). occasional summer rains. The people of estimated that the southwestern United By the end of the period, southwestern Mesa Verde were accomplished dryland States experienced its own “Little Ice Colorado was the home of many villages farmers with a record of success. We Age” beginning around AD 1200 until know there was no irrigation at Mesa about 1850 (Peterson 1988). Average Verde (Wright 2006). Fortunately, maize, temperatures of 2–4° F cooler are thought Table 2. Periods of Mesa Verde. their staple, is adaptable to a wide variety to have caused shorter growing seasons of environmental conditions. and less successful crops at Mesa Verde. Period Time Span (AD) The Pueblo I people started building Tree ring expert Matthew Salzer noted Basketmaker III 550-750 rooms aboveground, and their pit houses “significant volcanic activity” in AD transitioned into kivas (Figure 4). This 1259, which likely chilled the atmosphere Pueblo I 750-900 allowed a larger grouping of people and shortened the growing season (Salzer Pueblo II 900-1100 into communities with organized social 2000). order and its related benefits. Over the Pueblo III 1100-1300 next century, the Mesa Verde population 24 Winter 2008 / LAKELINE 3:1 slope. Starting in 1995, Wright Paleohydrological Institute performed excavations and paleohydrologic analyses on the mound, establishing that it was actually a reservoir (Figure 5). When we analyzed and dated the reservoir, we realized that its commencement predated the Great Kiva by 80 years, indicating that a water supply was the first priority. With the water supply secured, the Pueblo I then used their organizational and building skills to create a more developed and well-rounded society. Morefield Reservoir began with the digging of a shallow pond in Morefield Canyon about AD 750, in the canyon’s normally dry bottom, the thalweg. The land cover had changed over the years because of forest fires, considerable clearing of timber for building and fuel, Figure 3. A Basketmaker III pit house shows their use of wooden poles. They entered through a and the planting of maize in the upper part hole in the top. of the valley. The result of these changes was that the earth absorbed much less water, and there was more runoff than in earlier days. This worked well for filling their pond, although erosion increased. The rains that came, especially late summer rains from the monsoon phenomenon, now flowed down the canyon bottom, or thalweg, filling the pond. This flow also brought the silt and sand from hillside erosion into the water hole, which the people dredged using sticks, antlers, stones, and baskets. These dredged sediments eventually formed a berm. Dredging took a lot of organization and energy, but was necessary for maintaining this water resource. Pretty soon the elevation gain meant that water would no longer flow into the pond. Rather than digging another pond, the early settlers did a smart thing – they built an inlet canal to bring in water by gravity flow. Addressing and finding a solution Figure 4. The Great Kiva of Morefield was built about AD 860. to this hydraulic challenge required creativity, leadership, and organized increased to about 1,000. Housing between AD 829 and 865, left almost community effort. These and similar improvements and kivas made life intact for modern scientists to study, technological developments led to an somewhat easier, but the relative scarcity measures 55 feet in diameter and 7 overall southwest Colorado population of water remained. Community life meant feet deep. It is carefully designed and increase to about 9,000 by the mid-850s. that amenities could now be developed constructed and must have made a fine The success of the technology of that had been impossible for small place for religious rituals, meetings, the Morefield Canyon people inspired isolated groups. and winter shelter. It is an extraordinary their “cousins” in Prater Canyon one accomplishment of many people striving mile to the west. Box Elder Reservoir in Water Harvesting toward a common goal. Prater Canyon was started in AD 800, The Pueblo I people of Mesa Verde Near the Morefield kiva is a using precisely the same technology as clearly knew how to excavate. A Great mound about 200 feet in diameter at Morefield Reservoir. The Prater Canyon Kiva they built in Morefield Canyon the base, about 16 feet high, with a community grew to about 300 residents Winter 2008 / LAKELINE 25 without interruption despite periodic did work. We know this because our field water shortages. This Pueblo II culture, investigations show that the silt, sand, even with fewer people, kept operating and maize pollen left in the two mesa-top and maintaining the reservoirs like their reservoirs were waterborne, carried in by predecessors had done. By AD 950, ditches that intercepted water harvested Morefield Reservoir stood much higher from packed down areas.