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62 Chapter Two

Fig. 2.26 Diagram showing the influence of hummocky topography in producing local, intermediate and regional groundwater flow
systems. After Tòth (1963).

is superimposed on the incline to represent hum- of regional-scale and continental-scale groundwater
mocky topography. Freeze and Witherspoon (1967) flow systems are given in Boxes 2.10 and 2.11 and
developed this mathematical approach further by illustrate the combined influence of geology and
employing numerical simulations to examine the topography on groundwater flow.
effects of topography and geology on the nature of
regional groundwater flow patterns.
As illustrated in Fig. 2.26, Tòth (1963) proposed 2.14 Groundwater and geology
that it is possible to differentiate between local, inter-
mediate and regional groundwater flow systems. The occurrence of groundwater and the extent and
Tòth (1963) further showed that as the ratio of distribution of aquifers and aquitards in a region are
depth to lateral extent of the entire aquifer system determined by the lithology, stratigraphy and struc-
becomes smaller and as the amplitude of the hum- ture of the geological strata present. The lithology
mocks becomes larger, the local flow systems are refers to the general characteristics of the geological
more likely to reach the aquifer base, thus creating a strata in terms of mineral composition and texture
series of small groundwater flow cells. In general, of the formations present. The stratigraphy describes
where the local topography is subdued, only regional the character of the rocks and their sequence in time
systems develop compared to areas of pronounced as well as the relationship between various deposits
local relief where only local flow systems develop. in different localities. Structural features, such as folds
Groundwater flow in the local and intermediate and faults, determine the geometric properties of the
systems moves relatively quickly along short flow- formations that are produced by deformation and
paths and discharges as baseflow to streams at the fracturing after deposition or crystallization. In un-
local scale and rivers at the intermediate scale. The consolidated strata, the lithology and stratigraphy
regional component of groundwater flow has a relat- comprise the most important controls.
ively long residence time and follows long flowpaths In any hydrogeological investigation, a clear
before discharging to major rivers. Field examples understanding of the geology of an area is essential if