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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 flow (Halley 1691). Over 100 years later, the famous chemist John Dalton (1766–1844) made further observations of the water cycle, including a consideration of the origin of springs (Dalton 1799).

One of the earliest applications of the principles of geology to the solution of hydrological problems was made by the Englishman William Smith (1769–1839), the ‘father of English geology’ and originator of the epoch‐making Map of England (1815). During his work as a canal and colliery workings surveyor in the west of England, Smith noted the various soils and the character of the rocks from which they were derived and used his knowledge of rock succession to locate groundwater resources to feed the summit levels of canals and supply individual houses and towns (Mather 1998).

Fig. 1.6 Baroque‐style depiction of the interlaced systems of air, fire and water within the Earth as conceived by the German Jesuit scholar Athanasius Kircher (1602–1680) in his book Mundus Subterraneus (1664).

Source: AF Fotografie/Alamy Stock Photo.

In Britain, the industrial revolution led to a huge demand for water resources to supply new towns and cities, with Nottingham, Liverpool, Sunderland and parts of London all relying on groundwater. This explosion in demand for water gave impetus to the study of the economic aspects of geology. It was at this time that Lucas (1874) introduced the term ‘hydrogeology’ and produced the first real hydrogeological map (Lucas 1877). Towards the end of the nineteenth century, William Whitaker, sometimes described as the ‘father of English hydrogeology,’ and an avid collector of well records, produced the first water supply memoir of the Geological Survey (Whitaker and Reid 1899) in which the water supply of Sussex is systematically recorded.

The drilling of many artesian wells stimulated parallel activity in France during the first half of the nineteenth century. The French municipal hydraulic engineer Henry Darcy (1803–1858) studied the movement of water through sand and from empirical observations defined the basic equation, universally known as Darcy's Law that governs groundwater flow in most alluvial and sedimentary formations (Freeze 1994). The equation was published in one of eight appendices in a volume that is partly a consulting report on the water supply for the City of Dijon, France, and partly an encyclopaedia of mid‐nineteenth century water knowledge (Bobeck 2006) and can be found in the entire translation of Darcy's report by Bobeck (2004). Darcy's Law is the foundation of the theoretical aspects of groundwater flow and his work was extended by another Frenchman, Arsène Dupuit (1804–1866), whose name is synonymous with the equation for axially‐symmetric flow towards a well in a permeable, porous medium.

The pioneering work of Darcy and Dupuit was followed by the German civil engineer, Adolph Thiem (1836–1908), who made theoretical analyses of problems concerning groundwater flow towards wells and galleries, and by the Austrian Philip Forchheimer (1852–1933) who, for the first time, applied advanced mathematics to the study of hydraulics. One of his major contributions was a determination of the relationship between equipotential surfaces and flow lines. Inspired by earlier techniques used to understand heat flow problems, and starting with Darcy's Law and Dupuit's assumptions, Forchheimer derived a partial differential equation, the Laplace equation, for steady groundwater flow. Forchheimer was also the first to apply the method of mirror images to groundwater flow problems; for example, the case of a pumping well located adjacent to a river.

Much of Forchheimer's work was duplicated in the United States by Charles Slichter (1864–1946), apparently oblivious of Forchheimer's existence. However, Slichter's theoretical approach was vital to the advancement of groundwater hydrology in America at a time when the emphasis was on exploration and understanding the occurrence of groundwater. This era was consolidated by Meinzer (1923) in his book on the occurrence of groundwater in the United States. Meinzer (1928) was also the first to recognize the elastic storage behaviour of artesian aquifers. From his study of the Dakota sandstone (Meinzer and Hard 1925), it appeared that more water was pumped from the region than could be explained by the quantity of recharge at outcrop, such that the water‐bearing formation must possess some elastic behaviour in releasing water contained in storage. Seven years later, Theis (1935), again using the analogy between heat flow and water flow, presented the ground‐breaking mathematical solution that describes the transient behaviour of water levels in the vicinity of a pumping well.

Two additional major contributions in the advancement of physical hydrogeology were made by Hubbert and Jacob in their 1940 publications. Hubbert (1940) detailed work on the theory of natural groundwater flow in large sedimentary basins, while Jacob (1940) derived a general partial differential equation describing transient groundwater flow. Significantly, the equation described the elastic behaviour of porous rocks introduced by Meinzer over a decade earlier. Today, much of the training in groundwater flow theory and well hydraulics, and the use of computer programmes to solve hydrogeological problems, is based on the work of these early hydrogeologists during the first half of the twentieth century.

The development of the chemical aspects of hydrogeology stemmed from the need to provide good quality water for drinking and agricultural purposes. The objective description of the hydrochemical properties of groundwater was assisted by Piper (1944) and Stiff (1951) who presented graphical procedures for the interpretation of water analyses. Later, notable contributions were made by Chebotarev (1955), who described the natural chemical evolution of groundwater in the direction of groundwater flow, and Hem (1959), who provided extensive guidance on the study and interpretation of the chemical characteristics of natural waters. Later texts by Garrels and Christ (1965) and Stumm and Morgan (1981) provided thorough, theoretical treatments of aquatic chemistry.

By the end of the twentieth century, the previous separation of hydrogeology into physical and chemical fields of study had merged with the need to understand the fate of contaminants in the sub‐surface environment. Contaminants are advected and dispersed by groundwater movement and can simultaneously undergo chemical processes that act to reduce pollutant concentrations. More recently, the introduction of immiscible pollutants, such as petroleum products and organic solvents into aquifers, has led to intensive research and technical advances in the theoretical description, modelling and field investigation of multi‐phase systems. At the same time, environmental legislation has proliferated, and has acted as a driver in contaminant hydrogeology and in the protection of groundwater‐dependent ecosystems. Today, research efforts are directed towards understanding natural attenuation processes as part of a managed approach to restoring contaminated land and groundwater and also in developing approaches to manage groundwater resources in the face of global environmental change.

Hence, hydrogeology has now developed into a truly interdisciplinary subject, and students who aim to become hydrogeologists require a firm foundation in Earth sciences, physics, chemistry, biology, mathematics, statistics and computer science, together with an adequate understanding of environmental economics and law, and government policy. Indeed, the principles of hydrogeology can be extended to the exploration of water on other planetary systems. Finding water on other planets is of great interest to the scientific community, second only to, and as a prerequisite for, detecting evidence for extraterrestrial life. As an example, a discussion of the evidence for water on Mars is given in Box 1.2.