Page 65 - Hydrogeology Principles and Practice

HYDC02 12/5/05 5:38 PM Page 48

48 Chapter Two

/
divided by a change in strain). The compressibility of −dVV T
=
T
α eq. 2.27
water, β, is defined as: d σ
e
/
=
w
β −dVV w eq. 2.26 where V is total volume of aquifer material and
dP T
w dV /V is volumetric strain for an induced change in
T T
where P is porewater pressure, V is volume of a effective stress dσ .
e
w w
given mass of water and dV /V is volumetric strain Now, with reference to equation 2.27, for a reduc-
w
w
for an induced stress dP . For practical purposes, β tion in the total volume of aquifer material, dV , the
T
w
2
can be taken as a constant equal to 4.4 × 10 −10 m N −1 amount of water produced by compaction of the
−1
(or Pa ). aquifer, dV , is:
w
The compressibility of aquifer material, α, is de-
fined as: dV =−dV = αV dσ eq. 2.28
w T T e
BO X
The thermal springs of Bath, England
2.7
The thermal springs at Bath in the west of England are the principal
occurrence of thermal springs in the British Isles and have been
exploited for at least the past 2000 years. The springs have temper-
−1
atures of 44–47°C with an apparently constant flow of 15 L s .
Three springs, the King’s (Fig. 1), Cross and Hetling Springs, issue
from what were probably once pools on a floodplain terrace on the
River Avon, in the centre of Bath. A succession of buildings has been
constructed over the springs, beginning with the Roman Baths and
temple of the first century ad (Fig. 2). Further details and an account
of the hydrogeology of the thermal springs are given by Atkinson
and Davison (2002).
The origin of the thermal waters has been subject to various
investigations. Andrews et al. (1982) examined the geochemistry of
the hot springs and other groundwaters in the region, and demon-
strated that they are of meteoric origin. The silica content indicates

Fig. 1 The King’s Spring (or Sacred Spring) emerging into the Fig. 2 The overflow of thermal spring water adjacent to the
King’s Bath at the Roman Baths, Bath, England. King’s Bath shown in Fig. 1.