This article was contributed by Charles Ortloff, Research Associate, Anthropology Department at University of Chicago
The use of software for engineering problems in fluid dynamics is now common practice. While computational tools are available for present-day hydraulic engineering applications, how did engineers of the ancient world produce remarkable and sophisticated water conveyance structures using hydraulic technologies as yet unknown to the present day? A method to discover the hydraulic engineering knowledge base used in design and operation of ancient hydraulic conveyance systems is to first recreate water flows in aqueducts, canals, pipelines and water distribution networks using FLOW-3D models and next, using the solutions for water flow patterns, observe the hydraulic and civil engineering knowledge base underlying the design intent and operation of their water systems.
Through involvement in archaeological projects in Peru, Bolivia, Guatemala, Turkey, Egypt, Jordan, Israel and Cambodia in association with archaeologists from major US and foreign universities, the discovery of ancient hydraulic science continued over many years with findings now detailed in my 2009 Oxford Press book “Water Engineering in the Ancient World: Archaeological and Climate Perspectives on Ancient Societies of South America, the Middle East and South East Asia.” As many of the ancient water systems are quite modern in design, current hydraulic nomenclature is used to describe the accomplishments of their hydraulic engineers.
Included in the book are examples derived from FLOW-3D calculations that show that the Chimu society (800-1400 AD) of north coast Peru invented and used a form of open channel hydraulics in their 50 mile long Moche-ChicamaValley Intervalley Canal involving streamwise channel cross-section shape variations to produce water flows in the Froude number (Fr) range of 0.8 < Fr < 1.2 . This is necessary to achieve a stable, maximum flow rate in the water transport canal – this was done much in the same manner as modern practice dictates. FLOW-3D discoveries at 100 BC-AD 300 Petra (Jordan) show the use of pipeline designs to ensure the maximum flow rate for critical, partial flow conditions that prevented pipeline joint leakage by ensuring atmospheric pressure in the airspace above the partial flow. For typical five kilometer long pipelines with individual pipe elements of one half meter length, 10,000 pipeline joints would otherwise be subject to pressurized, full flow leakage without this design feature. FLOW-3D investigations of the Roman Pont du Garde aqueduct (in southern France) analyze a terminal aqueduct castellum design that provided stable, near critical flow to the multiple (10) pipelines emanating from the castellum that ensured maximum flow rates to the fountains, baths, reservoirs, gardens and housing structures in Roman Nimes.
Independent FLOW-3D analysis of the castellem confirms the ~40,000 m3/day water delivery rate delivered to Nimes made by earlier investigators. In Cambodia, FLOW-3D groundwater aquifer flow calculations reveal the source of dry season rice harvests for the ancient city of Angkor (800-1400 AD) derived from rainy season water capture and storage and subsequent groundwater seepage from a large (5 miles long by 1.5 miles wide) reservoir. Here the groundwater height is maintained by reservoir seepage sufficient to sustain dry season rice farming. A FLOW-3D example of a major ancient Peruvian Chimu canal system shows use of a dual opposing stone choke to limit canal flow rate excess from an El Niño flood event- here excess water over the permissible choke flow rate was diverted into an elevated side weir connected to a separate canal system to limit destructive over-bank flow in the main canal. Additional FLOW-3D investigations at 100 BC-AD 400 Roman Ephesos (Turkey) illustrate the use of pipeline top holes to eliminate partial vacuum regions resulting from full to partial flow transitions resulting from a mild to steep pipeline slope changes. This use of distributed top holes on pipelines is shown to stabilize the delivery flow to major fountains within Ephesos.
An example from 300 -1100 AD Tiwanaku (Bolivia) uses FLOW-3D groundwater aquifer and surface canal flow calculation capabilities to demonstrate the basis for optimizing food production in Tiwanaku’s 2,000 km2 raised-field agricultural systems- some of the ancient fields have been brought back into use by present day inhabitants of altiplano Bolivia to enhance food resources. Here FLOW-3D provided the hydraulic science underlying use of these fields by the Tiwanaku society. An ancient pre-classic period Maya canal system at Kaminal-juyu in Guatemala was also analyzed. This unusual early Maya canal had a steep slope over its kilometer length that relied on a terminal hydraulic jump to elevate water to irrigate associated field systems. Further analyses performed at the early Nabataean site of Mamshish in Israel showed use of a dam to collect sparse rain water which was then diverted to large circular pits to enhance groundwater height for agriculture. These illustrative cases, together with many other examples from the ancient world described in the current Oxford Press book and a forthcoming new University of Chicago Press book, now contribute to describe and supplement the history of hydraulic science through use of FLOW-3D’s superior free surface and aquifer water transport capabilities and bring into view for the first time what ancient hydraulic engineers in different parts of the Old and New worlds accomplished.