Historical Perspectives of Urban Drainage
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Historical Perspectives of Urban Drainage Steven J. Burian* and Findlay G. Edwards* *Assistant Professor, Dept. of Civil Engineering, University of Arkansas, 4190 Bell Engineering Center, Fayetteville, AR 72701 USA, Phone: (479) 575-4182; [email protected] / [email protected] Abstract Historically, urban drainage systems have been viewed with various perspectives. During different time periods and in different locations, urban drainage has been considered a vital natural resource, a convenient cleansing mechanism, an efficient waste transport medium, a flooding concern, a nuisance wastewater, and a transmitter of disease. In general, climate, topography, geology, scientific knowledge, engineering and construction capabilities, societal values, religious beliefs, and other factors have influenced the local perspective of urban drainage. For as long as humans have been constructing cities these factors have guided and constrained the development of urban drainage solutions. Historical accounts provide glimpses of many interesting and unique urban drainage techniques. This paper will highlight several of these techniques dating from as early as 3000 BC to as recently as the twentieth century. For each example discussed, the overriding perspective of urban drainage for that particular time and place is identified. The presentation will follow a chronological path with the examples categorized into the following four time periods: (1) ancient civilizations, (2) Roman Empire, (3) Post-Roman era to the nineteenth century, and (4) modern day. The paper culminates with a brief summary of the present day perspective of urban drainage. Introduction The relation of modern engineering to ancient engineering is difficult to comprehend considering that modern engineering is so highly specialized and technologically advanced. Design rules-of- thumb, empirical equations, physics, numerical methods, computer simulators, and other engineering tools taken for granted today were not available to ancient engineers. Despite the supreme technological advantage today’s engineer has over the ancient engineer, fantastic engineering feats rivaling those of today were achieved throughout history. For example, several ancient civilizations built magnificent cities of stone, brick, and wood and equipped the cities with sophisticated infrastructure systems including roads, water supply and distribution systems, wastewater collection, and stormwater drainage. Further, in some instances infrastructure systems were integrated, as was often the case with wastewater collection and stormwater drainage. Urban drainage is defined to include two types of fluids: wastewater and stormwater (Butler and Davies 2000). Wastewater is water that after use for life support, industrial processes, or life enhancement must be collected and disposed of appropriately to prevent nuisances and polluted conditions from developing in urban areas. Stormwater is runoff produced by precipitation. Both wastewater and stormwater must be considered during urban drainage system planning. Historically the two waters have either been combined into a single conduit (i.e., combined 1 sewers), or have been kept separate during collection and disposal (i.e., separate sewers). Both combined and separate urban drainage systems will be discussed in this paper. This paper will explore the perspectives of urban drainage that have prevailed throughout history. According to the Merriam-Webster Dictionary, perspective is defined as the interrelation in which a subject or its parts are mentally viewed. Using this definition we reviewed historical accounts of urban drainage systems and formed an opinion of the prevailing perspective of urban drainage for that time period and location. We found that urban drainage has been viewed as a vital natural resource, a convenient cleansing mechanism, an efficient waste transport medium, a flooding concern, a nuisance wastewater, and a transmitter of disease. Urban drainage systems were planned, designed, built, and retrofitted in response to the prevailing view of urban runoff. Ancient Urban Drainage Systems "The history of man is reflected in the history of sewers…" -Victor Hugo, Les Misérables Historical accounts of ancient civilizations (e.g., Indus and Minoan) suggest urban drainage systems were constructed with great care and that the objectives of the systems were to collect rainwater, prevent nuisance flooding, and convey wastes. The systems that eventually met their objectives likely did so after trial-and-error modifications. In general, planning and design were limited. Few numerical standards existed for urban drainage and engineering calculations were not used during design. Despite the lack of optimization and the use of trial-and-error construction methods, numerous ancient urban drainage systems can be rated very successful. Lewis Mumford summarized the state of ancient urban infrastructure when he stated that ancient sewer systems were an “uneconomic combination of refined technical devices and primitive social planning” (Mumford 1961). The Indus civilization flourished in the Indus River Valley during the beginning of the third millennium BC. Webster (1962) and Kirby et al. (1956) described the technologically advanced urban drainage systems that the Indus civilization constructed for several of their more important cities. Ruins from two cities in particular provided a detailed glimpse of the Indus urban drainage systems. The ruins from Harappa and Mohenjo-Daro, two Indus cities separated by about 350 miles, suggest that they were arranged according to a plan and that the urban drainage system was coordinated with the layout of the town sites. Connections were built from most residences to open channels constructed in the center of the streets. The channels were either excavated into the ground or constructed above ground of burnt brick (see Figures 1 and 2). Although houses were connected to the drainage channels, wastewater was not permitted to flow directly to the street sewers. First, the wastewater was passed through tapered terra-cotta pipes into a small sump. Solids settled and accumulated in the sump, while the liquids overflowed into the drainage channels in the street when the sump was about three-fourths full. The drainage channels could be covered by bricks and cut stones, which likely were removed during maintenance and cleaning activities. Another interesting feature of the channel was the inclusion of a cunnette (Webster 1962). The cunnette was probably constructed to convey the smaller 2 flows associated with daily wastewater discharges, while the entire channel would only be used during wet weather events. Overall, the Indus civilization viewed urban drainage systems as providing the dual purposes of waste and stormwater conveyance. Figure 2. Picture of Harappan above ground sewer channel constructed of burnt brick (Kirby et al., 1956) Figure 1. Picture of Mohenjo-Daro excavated sewer channel (Hodge, 1992) The Persians were another ancient civilization that constructed urban drainage systems. Niemczynowicz (1997) explained that ancient Persians considered urban runoff sacred and enacted laws to protect it from pollution. Polluting water in Persia was considered a sin. Moreover, rainwater and urban runoff were collected in cisterns for potable uses. Deep wells injected urban runoff into the underlying aquifer. The Persian perspective of urban runoff was clearly as a vital natural resource. Unfortunately, as time passed changes in the Persian attitudes and behavior contributed to water pollution problems and the eventual downfall of the civilization (Niemczynowicz 1997). The Mesopotamian Empire states of Assyria and Babylonia marked great advances in civilization during the second millennium BC. The ruins from Mesopotamian cities contain well-constructed storm drainage and sanitary sewer systems. For example, the ancient cities of Ur and Babylon, located in present day Iraq, had effective drainage systems for stormwater control (Jones 1967). The systems contained vaulted sewers and drains for household waste and gutters and drains specifically for surface runoff (Maner 1966). The material of choice was baked brick with an asphalt sealant. Rainwater was also collected for household and irrigation uses. The Babylonians were partially motivated to construct urban drainage systems by their desire to remain clean. The Babylonians, like other ancient civilizations, viewed uncleanliness as a taboo, not because of the physical uncleanness but the moral evil it suggested (Reynolds 1946, pp. 198-204). In retrospect, the Mesopotamians viewed urban runoff as a nuisance flooding concern, waste conveyor, and a vital natural resource. 3 The Minoan civilization flourished on the Island of Crete from about 2800 BC to 1100 BC. The ruins from this civilization located on the Aegean Sea revealed elaborate systems of well-built stone drains (see Figure 3), which carried sanitary sewage, roof runoff, and general surface drainage (Gray 1940). The drains emptied into a main sewer that disposed of the sewage a considerable distance from the origin of the wastes. The frequent and torrential rains in Crete resulted in excellent flushing of the system. Ruins from the palace-city of Knossos indicate that a two-conduit system was installed, where one conduit collected sewage and the other rainwater. The efficient separate urban drainage system integrated with rainwater collection devices suggests that the Minoans viewed urban runoff as a nuisance