14 Groundwater
321
same expectation alignments of sinkholes attract the attention. The study of
fractures on imagery of limestone terrain has attracted early attention (Bouche and
Poulet, 1971; see also a discussion in Waters, 1990).
Because lineaments based on surface features, need not necessarily have a
hydrogeologic significance, additional information is welcome, such as derived
from airborne geophysics. Colour Plate l4.C shows an example.
A part of an aquifer in a semi-arid environment is shown. The aquifer consists of
sandstones, with interbedded basalts and is overlain by fossil eolian sands. The
aquifer is broken up by faults. The location and offsets have to be known for input
in a groundwater model. Data of airborne magnetic surveys (along lines at regular
spacings) have been processed to produce a continuous image and to show fault
traces. That image has been added to a false colour image of Thematic Mapper, as
shown in the Colour Plate. It can be observed that some major faults can be traced
further into the region for which no geophysical data was available, showing
evidence that lineaments on imagery can be associated with existing faults,
covered by overburden. In the part covered by geophysics, nearly all faults are
expressed as lineaments on the TM image, but a few additional lineaments have
been interpreted, which could not be supported by the subsurface data.
14.5 Groundwater management and conclusions
Apart from the contribution which remote sensing can make to understanding
regional hydrogeology - necessary for managing groundwater resources - perhaps
the strongest application for the management is the evaluation of the recharge, the
groundwater drafts for irrigation and the identification of flow systems in areas
where there is a paucity of geohydrological data. Surface conditions,- soils,
weathered zones, geomorphology and vegetation - determine the recharge,
suitability for artificial recharge and soil and water conservation measures which
can affect the recharge (see also Chap. 15).
Groundwater vulnerability to pollution is also directly related to surface
conditions. Indexing methods such as the one described by (Aller et aI., 1987) and
similar methods, group Depth to water table, net Recharge, Aquifer media, Soil
medium,Topography, Impact ofthe vadose zone media and hydraulic Conductivity
of the aquifer (leading to the acronyme DRASTIC) into a relative ranking scheme
that uses a combination of weights and ratings to produce numerical values. In
most areas in the world, many of the factors are derived by analytical
(physiographic or geomorphological) image interpretation.
The limitation of the indexing and ranking methods is, that lateral flows or flow
systems are not considered. This can be remedied, to a certain extent, by including
simple 2-D modelling in the vulnerability, provided the sections are properly
selected, again using images. Furthermore, up-to-date land use classifications
provided by remote sensing are essential for determining the pollution by
agriculture and many point pollution sources can be interpreted on high resolution
imagery, such as aerial photography.
321
same expectation alignments of sinkholes attract the attention. The study of
fractures on imagery of limestone terrain has attracted early attention (Bouche and
Poulet, 1971; see also a discussion in Waters, 1990).
Because lineaments based on surface features, need not necessarily have a
hydrogeologic significance, additional information is welcome, such as derived
from airborne geophysics. Colour Plate l4.C shows an example.
A part of an aquifer in a semi-arid environment is shown. The aquifer consists of
sandstones, with interbedded basalts and is overlain by fossil eolian sands. The
aquifer is broken up by faults. The location and offsets have to be known for input
in a groundwater model. Data of airborne magnetic surveys (along lines at regular
spacings) have been processed to produce a continuous image and to show fault
traces. That image has been added to a false colour image of Thematic Mapper, as
shown in the Colour Plate. It can be observed that some major faults can be traced
further into the region for which no geophysical data was available, showing
evidence that lineaments on imagery can be associated with existing faults,
covered by overburden. In the part covered by geophysics, nearly all faults are
expressed as lineaments on the TM image, but a few additional lineaments have
been interpreted, which could not be supported by the subsurface data.
14.5 Groundwater management and conclusions
Apart from the contribution which remote sensing can make to understanding
regional hydrogeology - necessary for managing groundwater resources - perhaps
the strongest application for the management is the evaluation of the recharge, the
groundwater drafts for irrigation and the identification of flow systems in areas
where there is a paucity of geohydrological data. Surface conditions,- soils,
weathered zones, geomorphology and vegetation - determine the recharge,
suitability for artificial recharge and soil and water conservation measures which
can affect the recharge (see also Chap. 15).
Groundwater vulnerability to pollution is also directly related to surface
conditions. Indexing methods such as the one described by (Aller et aI., 1987) and
similar methods, group Depth to water table, net Recharge, Aquifer media, Soil
medium,Topography, Impact ofthe vadose zone media and hydraulic Conductivity
of the aquifer (leading to the acronyme DRASTIC) into a relative ranking scheme
that uses a combination of weights and ratings to produce numerical values. In
most areas in the world, many of the factors are derived by analytical
(physiographic or geomorphological) image interpretation.
The limitation of the indexing and ranking methods is, that lateral flows or flow
systems are not considered. This can be remedied, to a certain extent, by including
simple 2-D modelling in the vulnerability, provided the sections are properly
selected, again using images. Furthermore, up-to-date land use classifications
provided by remote sensing are essential for determining the pollution by
agriculture and many point pollution sources can be interpreted on high resolution
imagery, such as aerial photography.