Page 83 - Hydrogeology Principles and Practice

HYDC02 12/5/05 5:38 PM Page 66

66 Chapter Two

BO X
Continued
2.11

Fig. 3 Simplified cross-section of the Great Artesian Basin showing the position of major aquifer and confining units (see Fig. 2 for
location of section A–A′). After Habermehl (1980).

of sand and silt-size sediment and carbonate which range in height groundwater development since the 1880s. Groundwater levels in
and diameter from a few metres to tens of metres, some with water- the confined aquifer in the upper part of the Cretaceous sequence
filled craters (Habermehl 1980). The location of many springs have always been below ground level throughout most of the
appears to be fault-controlled with others present where aquifers Basin area and development of these non-flowing artesian aquifers
abut low permeability basement rocks or where only thin confining requires the installation of pumping equipment. Transmissivity
beds are present. Diffuse discharge also occurs from the artesian values of the main aquifers in the Lower Cretaceous–Jurassic
aquifers near the Basin margins where the overlying confining beds sequence, from which most overflowing artesian groundwater is
2
−1
are thin. obtained, are typically several tens to several hundreds of m day .
The potentiometric surface of the Triassic, Jurassic and Lower Average groundwater flow rates in the eastern and western parts
Cretaceous confined aquifers is still above ground level in most areas of the Basin range from 1 to 5 m a −1 based on hydraulic data and
(Fig. 3) despite considerable lowering of heads due to extensive radiometric dating using carbon-14 and chlorine-36 radioisotopes,