Hydrogeology. Kevin M. Hiscock

institutions in cities, towns and villages. Ultimately, as mains water was introduced across Britain from the nineteenth century onwards following the Public Health (Water) Act of 1878, the village pump was superseded by the communal outdoor tap or water pillar, itself made redundant when piped water was provided to individual houses.

Fig. 1.3 Longitudinal section of a qanat (Beaumont 1968 and Biswas 1972).

      (Sources: Based on Beaumont, P. (1968) Qanats on the Varamin plain, Iran. Transactions of the Institute of British Geographers 45, 169–179; Biswas, A.K. (1972) History of Hydrology. North‐Holland, Amsterdam.)

Fig. 1.4 Irrigation canal supplied with water by a qanat or falaj in Oman.

      (Photograph provided courtesy of M.R. Leeder.)

Box 1.1 The aqueducts of Rome

      The aqueducts of ancient Rome are often associated with Roman expertise in civil engineering, and the fact that most of the aqueducts are supplied by springs is a tribute to the importance of groundwater in sustaining human civilization (Deming 2020). The remarkable organization and engineering skills of the Roman civilization are demonstrated in the book written by Sextus Julius Frontinus and translated into English by Bennett (1969). In the year 97 AD, Frontinus was appointed to the post of water commissioner, during the tenure of which he wrote the De Aquis. The work is of a technical nature, written partly for his own instruction, and partly for the benefit of others. In it, Frontinus painstakingly details every aspect of the construction and maintenance of the aqueducts existing in his day.

For more than 400 years, the city of Rome was supplied with water drawn from the River Tiber, and from wells and springs. Springs were held in high esteem, and treated with veneration. Many were believed to have healing properties, such as the springs of Juturna, part of a fountain known from the south side of the Roman Forum. As shown in Fig. 1.5 and illustrated in Plate 1.2, by the time of Frontinus, these supplies were augmented by several aqueducts, presumably giving a reliable supply of good quality water, in many cases dependent on groundwater. For example, the Vergine aqueduct brought water from the estate of Lucullus where soldiers, out hunting for water, were shown springs which, when dug out, yielded a copious supply. Frontinus records that the intake of Vergine is located in a marshy spot, surrounded by a concrete enclosure for the purpose of confining the gushing waters. The length of the water course was 14 105 paces (20.9 km). For 19.1 km of this distance the water was carried in an underground channel, and for 1.8 km above ground, of which 0.8 km was on substructures at various points, and 1.0 km on arches. The source of the Vergine spring, located approximately 13 km east of Rome in the small town of Salone, is shown on a modern hydrogeological map (Boni et al. 1986) as issuing from permeable volcanic rocks with a mean discharge of 1.0 m³ s⁻¹ (Fig. 1.5). Frontinus also describes the Marcia aqueduct with its intake issuing from a tranquil pool of deep green hue. The length of the water‐carrying conduit is 61 710½ paces (91.5 km), with 10.3 km on arches. Today, the source of the Marcia spring is known to issue from extensively fractured limestone rocks with a copious mean discharge of 5.4 m³ s⁻¹.

Fig. 1.5 Map of the general geology in the vicinity of Rome showing the location of the spring sources and routes of Roman aqueducts (Bennett 1969 and Boni et al. 1986).

      (Sources: Based on Bennett, C.E. (1969) Frontinus: The Stratagems and the Aqueducts of Rome. Harvard University Press, Cambridge, Massachusetts; Boni, C., Bono, P. and Capelli, G. (1986) Hydrogeological Scheme of Central Italy. Sheet 1 (A. Hydrogeological Map). Memoir of the Geological Society of Italy XXXV, Geological Society of Italy, Rome.)

      After enumerating the lengths and courses of the several aqueducts, Frontinus enthuses: ‘with such an array of indispensable structures carrying so many waters, compare, if you will, the idle Pyramids or the useless, though famous, works of the Greeks!’ To protect the aqueducts from wilful pollution, a law was introduced such that: ‘No one shall with malice pollute the waters where they issue publicly. Should any one pollute them, his fine shall be 10 000 sestertii’ which, at the time, was a very large fine. Clearly, the ‘polluter pays’ principle was readily adopted by the Romans! Further historical, architectural and engineering details of the ancient aqueducts of Rome are given by Bono and Boni (2001) and Hodge (2008).

      The Vergine aqueduct is one of only two of the original aqueducts still in use. The name derives from its predecessor, the Aqua Virgo, constructed by Marcus Agrippa in 19 BC. The main channels were renovated and numerous secondary channels and end‐most points (mostre) added during the Renaissance and Baroque periods, culminating in several fountains, including the famous Trevi fountain completed in 1762 (Plate 1.3). The total discharge of the ancient aqueducts was in excess of 10 m³ s⁻¹ supplying a population at the end of the first century AD of about 0.5 million. Today, Rome is supplied with 23 m³ s⁻¹ of groundwater, mainly from karst limestone aquifers, and serving a population of 3.5 million (Bono and Boni 2001). Many of the groundwater sources are springs from the karst system of the Simbruini Mountains east of Rome.

1.4 History of hydrogeology

It is evident from the examples mentioned previously that exploitation of groundwater resources long preceded the founding of geology, let alone hydrogeology. Western science was very slow in achieving an understanding of the Earth's hydrological cycle. Even as late as the seventeenth century it was generally assumed that water emerging from springs could not be derived from rainfall, in that it was believed that the quantity was inadequate and the Earth too impervious to permit infiltration of rain water far below the surface. For example, Athanasius Kircher (1602–1680) erroneously considered in his publication Mundus Subterraneus of 1664 that the tides were caused by water moving to and from a subterranean ocean (Fig. 1.6). In contrast, Eastern philosophical writings had long considered that the Earth's water flowed as part of a great cycle involving the atmosphere. For example, ancient China had explicit concepts about water circulation as early as the mid‐fourth to early‐third centuries BC and also documented relationships between topography, soil type and groundwater depth in the book Guan Zi authored in the early Warring States Period (475 BC–221 BC) (Zhou et al. 2011). Even earlier, about 3000 years ago, the sacred Hindu Vedas texts of India explained the Earth's water movements in terms of cyclical processes of evaporation, condensation, cloud formation, rainfall, river flow and water storage (Chandra 1990).

      A clear understanding of the hydrological cycle was achieved by the end of the seventeenth century. The English experimentalist Robert Hooke (1635–1703) made a number of observations on whether precipitation was sufficient to fully account for terrestrial stream flow (Deming 2019) and the French experimentalists Pierre Perrault (1611–1680) and Edme Mariotte (ca. 1620–1684) recorded measurements of rainfall and runoff in the River Seine drainage basin. In addition, the English astronomer Edmond Halley (1656–1742) demonstrated that evaporation of seawater was sufficient to account for all springs and stream