306
A.M.J. Meijerink
land use. Hard rock terrain, such as a basement complex, has its own
characteristics and is discussed in a separate section.
14.2 Conceptualization of the hydrogeology
14.2.1 The three dimensional hydrogeologic situation
The 3-D hydrogeologic situation is compiled by merging results of image
interpretations and available field data, such as drilling logs, geophysical data, etc.
Within the scope of this text it is not possible to treat the interpretation of the
abundance of hydrogeologic situations encountered in nature. The reader is
referred to the texts on photo-geology (e.g. Ray,1960; Miller and Miller,1961;
Sabins, 1987; Drury,1993). The examples included here illustrate the principles.
The aerial photo of Fig.14.l of an semi-arid area shows folded rocks consisting
of slate (with cultivated fields) and of quartzitic sandstone/quartzite with thinly
interbedded siltstone and slate (outcrop areas with poor shrub and grasses/herbs).
The interpreted structure is illustrated by the N-S geologic section. The gentle
folds and normal -tensional- faults of the upper part of the photo are flanked by
imbricated structures with steep dips and high angle reverse faults in the lower
part. On the right hand comer remnants of a gravelly cover (quartzites) resting on
a pediment surface can be seen. The vegetation resembles that of the outcrop
areas, but the pattern is different and some agricultural fields have been made by
clearance of the boulders and pebbles. Minor valleys traverse the area and they
have been widened and partly blocked by walls along the fields. The geologic
cross-section, as derived by photo-geologic interpretation and a field traverse is
shown.
Hydrogeological mapping and updating the Quaternary geology. Various
studies have shown how image interpretation can contribute to hydrogeological
mapping and qualitative evaluation (e.g. Meijerink,1974; Moore and Deutsch,
1975; Kruck, 1979, Sahai et al., 1985; Dutartre et al., 1990a,b; Waters et al. 1990;
Anon. 1990; Li Botao et al.,1990).
The Quaternary is often poorly differentiated on existing geologic maps. This is
regrettable because recharge, shallow flow systems and water quality are related to
these non- or little-consolidated deposits. Quaternary deposits can often be
distinguished and mapped on imagery, especially in dry regions.
In the false colour (T.M) image of Colour Plate l4.A, three Quaternary units can
be differentiated; (a) the slightly dissected fanglomerate with lime crusts (generally
light tones) where little recharge occurs,(b) the younger gravel beds and splays
(dark grey to bronwnish colours) with high recharge and (c) the clayey, lower
alluvial fan deposits (blocky red fields and the light yellow colours corresponding
to a groundwater fed grassland) with little recharge. It is difficult to map such
relevant differences without imagery.
A.M.J. Meijerink
land use. Hard rock terrain, such as a basement complex, has its own
characteristics and is discussed in a separate section.
14.2 Conceptualization of the hydrogeology
14.2.1 The three dimensional hydrogeologic situation
The 3-D hydrogeologic situation is compiled by merging results of image
interpretations and available field data, such as drilling logs, geophysical data, etc.
Within the scope of this text it is not possible to treat the interpretation of the
abundance of hydrogeologic situations encountered in nature. The reader is
referred to the texts on photo-geology (e.g. Ray,1960; Miller and Miller,1961;
Sabins, 1987; Drury,1993). The examples included here illustrate the principles.
The aerial photo of Fig.14.l of an semi-arid area shows folded rocks consisting
of slate (with cultivated fields) and of quartzitic sandstone/quartzite with thinly
interbedded siltstone and slate (outcrop areas with poor shrub and grasses/herbs).
The interpreted structure is illustrated by the N-S geologic section. The gentle
folds and normal -tensional- faults of the upper part of the photo are flanked by
imbricated structures with steep dips and high angle reverse faults in the lower
part. On the right hand comer remnants of a gravelly cover (quartzites) resting on
a pediment surface can be seen. The vegetation resembles that of the outcrop
areas, but the pattern is different and some agricultural fields have been made by
clearance of the boulders and pebbles. Minor valleys traverse the area and they
have been widened and partly blocked by walls along the fields. The geologic
cross-section, as derived by photo-geologic interpretation and a field traverse is
shown.
Hydrogeological mapping and updating the Quaternary geology. Various
studies have shown how image interpretation can contribute to hydrogeological
mapping and qualitative evaluation (e.g. Meijerink,1974; Moore and Deutsch,
1975; Kruck, 1979, Sahai et al., 1985; Dutartre et al., 1990a,b; Waters et al. 1990;
Anon. 1990; Li Botao et al.,1990).
The Quaternary is often poorly differentiated on existing geologic maps. This is
regrettable because recharge, shallow flow systems and water quality are related to
these non- or little-consolidated deposits. Quaternary deposits can often be
distinguished and mapped on imagery, especially in dry regions.
In the false colour (T.M) image of Colour Plate l4.A, three Quaternary units can
be differentiated; (a) the slightly dissected fanglomerate with lime crusts (generally
light tones) where little recharge occurs,(b) the younger gravel beds and splays
(dark grey to bronwnish colours) with high recharge and (c) the clayey, lower
alluvial fan deposits (blocky red fields and the light yellow colours corresponding
to a groundwater fed grassland) with little recharge. It is difficult to map such
relevant differences without imagery.