New Discoveries and Perspectives on Water Management at 300 Bc-Ad 1100 Tiwanaku’s Urban Center (Bolivia)

摘要

Introduction The 300 BCE- CE 1100 pre-Columbian site of Tiwanaku located on the high altiplano of Bolivia demonstrated an advanced use of hydrologic and hydraulic science for urban and agricultural applications that is unique in the Andean world. From recently discovered aerial photos taken of the site in the 1930’s, new perspectives of the water system of the ancient city, beyond previous interpretations of a major drainage canal as a dividing ‘moat’ between ceremonial and secular parts of the city, are now possible from new discoveries of a network of water channels not previously known. Surrounding the ceremonial core structures of urban Tiwanaku was a large encompassing drainage canal that served as the linchpin of an intricate network of spring-fed supply and drainage channels to control both surface and groundwater aquifer flows. The drainage canal served to: collect and drain off rainfall runoff into the nearby Tiwanaku River to limit flood damage; accelerate post-rainy season ground drying by collecting aquifer seepage from infiltrated rainwater into the drainage canal to promote health benefits for the city’s population; provide water from a newly discovered spring-fed channel to two subterranean channels to flush human waste from elite structures to the nearby Tiwanaku River, maintain the groundwater level constant through both rainy and dry seasons to stabilize the foundation soil underneath massive pyramid structures to limit structural deformation; facilitate rainy season water accumulation drainage from the floor of a semi-subterranean temple into the stabilized, groundwater layer to rapidly dry the temple floor and Provide drainage water to inner city agricultural zones. The sophistication of the water control network in Tiwanaku city is analyzed by computational fluid dynamics (CFD) modeling of transient surface and groundwater aquifer flows to illustrate the function of the drainage canal in both rainy and dry seasons. The hydrological regime of Tiwan Of interest to present-day engineers are the engineering accomplishments of ancient civilizations. In the discussion to follow, the pre-Columbian 300 BC- AD 1100 city of Tiwanaku located in the high altiplano (~4500 masl) region of Bolivia demonstrates use of advanced hydrologic principles to maintain city drainage during the long rainy season through a complex network of surface and subsurface channels. This water control system involves both groundwater stability control coupled to spring-supplied surface channels to perform health and monument maintenance benefits to city inhabitants and, as such, is a unique demonstration of hydrologic engineering not seen at any other pre-Columbian South American site. Research at the site of Tiwanaku has revealed that the city’s ceremonial center, composed of monumental architecture and elite residential compounds, is circumscribed by a large drainage channel (Figures 1-5 W-D-V-X). While previous researchers correctly interpreted its main purpose as a boundary separating sacred and secular urban areas of the city, the encircling channel additionally served as a hydraulic regulator enhancing aquifer drainage to promote rapid post-rainy season soil dry-out as the dry season progressed. Water collecting in the drainage channel from aquifer drainage, rainy season runoff and flow from canals intersecting the drainage channel rapidly exited through connecting canals to the Tiwanaku River to limit groundwater recharge during the rainy season; during the dry season, continued aquifer seepage and flow from adjacent canals recharged the groundwater to maintain and stabilize its height through seasonal changes. One net effect was to stabilize the groundwater layer through rainy and dry seasons to maintain the bearing strength of soil under large monuments within the?ceremonial center to limit structural distortions [1]. Water accumulating in the drainage channel from aquifer drainage and channeled spring water flow provided flow through dual subterranean channels to flush human waste delivered into the subterranean channels from elite structures to maintain hygienic conditions in the residential compounds. The multi-faceted hydrological aspects of the drainage channel thus served city environmental and hygienic conditions through rapid soil drying in city living areas while promoting structural stability for its many monuments as well as aiding in rainy season drainage from the Sunken Temple (Figure 5,F) floor. While groundwater control mastery is apparent in the urban setting, additional research on Tiwanaku raised field agriculture indicates similar advances in use of groundwater control technology not previously reported in the literature. To demonstrate the seasonal interaction of surface and aquifer water flows, a porous media aquifer model is utilized for computational fluid dynamics analysis to demonstrate the inland drainage channel’s role as a hydrological control element?vital to the city’s sustainabilit