Watershed-Scale Hydrogeologic Analysis and Paleohydrologic Modeling With Applications for Predicting Abandonment of Prehistoric Settlements, Mesa Verde Region, Southwest Colorado Kenneth E. Kolm and Schaun M. Smith, Washington State University and Colorado School of Mines Y. Eugene Yan, Argonne National Laboratory NSF Biocomplexity Conference April 2003

ACKNOWLEDGEMENTS National Science Foundation Biocomplexity Grant # “Coupled Human/Ecosystems Over Long Periods, Mesa Verde Region Prehispanic Ecodynamics” Dr. Timothy Kohler – PI Dr. Kenneth Kolm - Co-PI Dr. Robert G. Reynolds - Co-PI Dr. Mark Varien - Co-PI

RESEARCH PURPOSE AND OBJECTIVES Perform hierarchical analysis of environmental system, including watershed-scale hydrogeologic & hydrologic systems. Develop conceptual and mathematical models of the hydrologic system.

RESEARCH PURPOSE AND OBJECTIVES (cont.) Model lagged response of water resources to historic and prehistoric (AD ) climatic changes and environmental stresses. Develop understanding of impacts to prehistoric settlements by coupling human and hydrologic systems modeling and analysis.

Detail of Four-Corners Region and Study Area

Mesa Top Environment Eolian Deposits/Farming/Infiltration/Gw Recharge Sage/Yellow Jacket Settlement Site Sleeping Ute Tertiary Intrusion Canyon Rim - K Dakota & Burro Canyon Ss/Water Supply/Gw Discharge

Upper Canyon Rim Environment Eolian/Farming/Gw Recharge K Dakota & Burro Canyon SS Aquifer Water Supply/Gw Discharge/Springs & Seeps J Morrison Units Settlement/Sage Pinyon/Juniper Scrub Alluvium Colluvium

Lower Canyon Environment Sleeping Ute Tertiary Intrusion McElmo Creek J Morrison Units Pinyon/Juniper Scrub Few Settlements J Junction Creek Ss J Entrada & Navajo Aquifer

Settlement Ruins Hovenweep Towers

TWO BROAD HYPOTHESES Prehistoric (AD ) groundwater quantities were controlled by long-term lagged hydro- geologic response, not by direct climate forcing. This lagged hydrogeologic response to prehistoric climatic changes significantly contributed to depopulation of the Mesa Verde region by reducing the drinking water supply.

SITE-SPECIFIC HYPOTHESES As the sole variable, climate forcing is not system- limiting. Van West 1994, has shown soil moisture was adequate for sustaining agriculture during prehistoric time periods. Infiltration functions of eolian deposits are not system limiting. Size of local recharge areas for groundwater subsystems is limiting variable. Lagged hydrogeologic response is directly related to hydrologic properties of Dakota and Burro Canyon SS. Variability of prehistoric water supply will not match frequency of climatic cycles.

RESEARCH APPROACH 1). Conceptualize and characterize the modern hydrologic system, using integrated, multidisciplinary hierarchical systems analysis. 2). Develop solid and mathematical models to visualize and quantify the modern hydrogeology and hydrologic system on a watershed-scale, and on selected site- specific areas. 3). Test mathematical models by incorporating known hydrologic system stresses which occurred within historic times.

RESEARCH APPROACH (cont.) 4). Develop scenarios of the paleohydrologic system based on paleoclimate records (such as tree ring data) for identifying the relative roles of climate and human-induced stresses. 5). Compare the dynamics of the paleohydrologic system with the cultural activities, population shifts, and abandonment of cultural centers.

Problem Definition: Systems Scale Sustainability Basic Data Gathering and Preparation: Surface, Geomorphic, and Geologic Characterization Atmospheric System Surface Water System and Components Hillsides Channels Lakes and Reservoirs Valley Bottoms and Wetlands Ground Water System and Components Unsaturated Zone Saturated Zone Recharge and Discharge Storage and Movement Terrestrial Ecosystem Aquatic Ecosystem Socioeconomic System Structure and Function Physical Chemical Citizen Input Citizen Involve- ment Decision Support System Citizen Decisions Structure and Function Physical Chemical Biological Structure and Function Physical Chemical Geomorphologic System BIOCOMPLEXITY LOGIC DIAGRAM FOR CHARACTERIZING ECOSYSTEM (after Kolm and Langer, 2000)

Upper Canyon Rim Environment Conceptual Model Eolian/infiltration/Gw Recharge K Dakota & Burro Canyon SS Aquifer Water Supply/Gw Discharge/Springs & Seeps Settlement Location Climate: Precip/ET Colluvium AlluviumPinyon/Juniper Scrub

Hovenweep Canyon and Spring Conceptual Model Gw Discharge/Springs & Seeps Phreatophytes (ET) K Dakota & Burro Canyon Ss Aquifer Gw Flow System Mesa Top Infiltration/GwRecharge Climate: Precip/ET

General Hydrogeologic & Hydrologic System Conceptual Model Canyon Rim Mesa Top Lower Canyon

Distribution of Hydrogeologic Units

Preliminary 3-D Block Model – Bedrock (w/o Quaternary) 400 meter resolution K Dakota Aquifer K Mancos Sh J Morrison Units Tertiary Intrusion J Junction Creek Ss & N Aquifer

Preliminary 3-D Block Model – Bedrock (w/Quaternary) 400 meter resolution K Dakota Aquifer K Mancos Sh Tertiary Intrusion J Junction Creek Ss J Morrison Units Q Eolian Recharge Zone Q Alluvium & N Aquifer

REGIONAL SYSTEM CROSS-SECTIONS

REGIONAL SYSTEM CROSS-SECTION

EXPECTED RESULTS Hierarchical Systems Analysis of Watersheds - approach transferable to any Colorado Plateau watershed Couple GMS, Hydrogeologic Solid Block Model, and Mathematical Models - intigration of systems analysis w/3-D hydrogeologic block models, and steady-state modern system models Paleohydrologic System Mathematical Models - series of transient models as snapshots through prehistoric time using paleoclimate records (tree-ring, paleo-jet streams) Correlate groundwater models with locations of settlements spatially and temporally

SUMMARY OF PROGRESS TO DATE Continued analysis of surface, geomorphic, geologic and hydrogeologic data on watershed- scale. Continued development of 3-dimensional hydrogeologic solid block models (regional and site-specific). Continued development of modern hydrologic system conceptual models.

SUMMARY OF PROGRESS TO DATE (cont.) Continued development of modern steady-state mathematical groundwater flow system models. Conceptualization of prehistoric human settlements placed in landscape based on hydrologic system analysis.

Why Did They Leave? Lowry Settlements

Why Did They Leave? Phreatophytes/Spring Hovenweep Tower Dakota Aquifer

Questions ? Hey, where’s everybody going?