Page 20 - Hydrogeology Principles and Practice

HYDC01 12/5/05 5:44 PM Page 3

Introduction 3

of water on and over the Earth’s surface independent
of the seepage of groundwater and springs which
sustain river flows during seasonal dry periods. How-
ever, too strict a division between the two subjects
is unhelpful, particularly when trying to decipher
the impact of human activities on the aquatic envir-
onment. How well we respond to the challenges
of pollution of surface water and groundwater, the
impacts of over-exploitation of water resources, and
the possible impact of climate change will depend
largely on our ability to take a holistic view of the
aquatic environment.
Fig. 1.2 Lady’s Well in Coquetdale, northern England (National
Grid Reference NT 953 028). Groundwater seeping from glacial
1.3 Early examples of groundwater exploitation
deposits at the foot of a gently sloping hillside is contained within
an ornamental pool floored with loose gravel. The site has been
The vast store of water beneath the ground surface used since Roman times as a roadside watering place and was
has long been realized to be an invaluable source of walled round and given its present shape in either Roman or
medieval times. Anglo Saxon Saint Ninian, the fifth century
water for human consumption and use. Throughout
apostle, is associated with the site, and with other ‘wells’ beside
the world, springs fed by groundwater are revered for
Roman roads in Northumberland, and marks the spot where Saint
their life-giving or curative properties (Fig. 1.2), and Paulinus supposedly baptized 3000 Celtic heathens in its holy
utilization of groundwater long preceded under- water during Easter week, 627 ad. The name of the well, Lady’s
standing of its origin, occurrence and movement. Well, was adopted in the second half of the twelfth century when
the nearby village of Holystone became the home of a priory of
Groundwater development dates from ancient
Augustinian canonesses. The well was repaired and adorned with
times, as manifest by the wells and horizontal tunnels
a cross, and the statue brought from Alnwick, in the eighteenth
known as qanats (ghanats) or aflaj (singular, falaj), and nineteenth centuries. Today, groundwater overflowing from
both Arabic terms describing a small, artificial chan- the pool supplies the village of Holystone.
nel excavated as part of a water distribution system,
which appear to have originated in Persia about
3000 years ago. Examples of such systems are found arid plain at its lower end (Fig. 1.4). The depth of the
in a band across the arid regions extending from mother well (Fig. 1.3) is normally less than 50 m, with
Afghanistan to Morocco. In Oman, the rural villages discharges, which vary seasonally with water-table
3 −1
and aflaj-supplied oases lie at the heart of Omani cul- fluctuations, seldom exceeding 3 m s .
ture and tradition. The system of participatory man- Such early exploitation of groundwater as part of
agement of communal aflaj is an ancient tradition in a sophisticated engineered system is also evident in
Oman by which common-property flows are chan- the supply of water to feed the fountains of Rome
nelled and distributed to irrigation plots on a time- (Box 1.1).
based system, under the management of a local
community (Young 2002).
Figure 1.3 shows a cross-section along a qanat with 1.4 History of hydrogeology
its typical horizontal or gently sloping gallery labori-
ously dug through alluvial material, occasionally As is evident from the above examples, exploitation
up to 30 km in length, and with vertical shafts dug of groundwater resources long preceded the founding
at closely spaced intervals to provide access to the of geology, let alone hydrogeology. Even as late as
tunnel. Groundwater recharging the alluvium in the the seventeenth century it was generally assumed that
mountain foothills is fed by gravity flow from water emerging from springs could not be derived
beneath the water table at the upper end of the qanat from rainfall, for it was believed that the quantity was
to a ground surface outlet and irrigation canal on the inadequate and the Earth too impervious to permit