recharge, annual rainfall, and proximity to surface water bodies. These thematic
layers were studied by principal component analysis techniques to select the most
influential layers for groundwater prospecting. Seven thematic layers were selected,
and their features were assigned suitable weights according to their relative importance with regard to groundwater occurrence. The selected thematic maps were
integrated by weighted linear combination methods in a GIS environment to
generate the groundwater potential maps [58].
A recent example of successfully combining traditional geology and cuttingedge digital tools to reveal underground aquifers in drought-stricken areas is
described by Gramling [59]. Accordingly, a scientific team led by geologist Alain
Gachet, head of Radar Technologies International (RTI), found large water aquifers
in northwestern Kenya where a drought was devastating the land, causing crops to
collapse, livestock to die, and prompting a food crisis that affected millions of
inhabitants in Kenya, Somalia, South Sudan, and Ethiopia. The team is part of the
UNESCO Groundwater Resources Investigation for Drought Mitigation in Africa
Program.
The area explored by Gachet’s team, Turkana County, Kenya, is bordered in the
east by Lake Turkana, a water-filled depression that is part of the East African Rift,
a region having a stretched and fractured crust. Between the fractures, sunken
blocks of land called grabens form sediment-filled troughs that are several kilometers deep. The troughs were a primary target, because they are potential traps for
groundwater. To identify them, RTI used powerful computer programs to merge
refined geological knowledge with large samples of data from ground sensors and
space-based remote sensors. The data used included traditional geologic maps,
hydrologic data, satellite images, and gravity and seismic survey data. Gachet’s
team also used commercial satellite radar images to detect soil moisture. RTI
developed image-processing technology, WATEX, which “erases” obstacles,
such as rocks and villages that can obscure the images, to reveal traces of moisture
that can suggest the presence of an aquifer. WATEX helped identify five likely
aquifers under the desert, each more than 100 m below the surface, containing water
resources totaling at least 250 billion cubic meters. So far, drilling has confirmed
existence of two of the aquifers. The RTI team expects to find many more deeply
buried groundwater aquifers in arid regions, such as South Sudan and Sudan’s
Darfur state [59].
5 Detecting Freshwater Springs and Biomass
Freshwater springs can occur on dry land, in wetlands, and along the coast. Springs
occur when groundwater is confined by a low-permeability geologic formation,
which constrains water to a focused discharge point. Fractures in hard rock and
confining clay units are typical conduits for spring flow [60]. Springs may discharge
at the land surface or below the open water surface. In arid areas, freshwater springs
and irrigated areas induce the growth of a dense vegetation cover, including trees,
44
V. Klemas and A. Pieterse
layers were studied by principal component analysis techniques to select the most
influential layers for groundwater prospecting. Seven thematic layers were selected,
and their features were assigned suitable weights according to their relative importance with regard to groundwater occurrence. The selected thematic maps were
integrated by weighted linear combination methods in a GIS environment to
generate the groundwater potential maps [58].
A recent example of successfully combining traditional geology and cuttingedge digital tools to reveal underground aquifers in drought-stricken areas is
described by Gramling [59]. Accordingly, a scientific team led by geologist Alain
Gachet, head of Radar Technologies International (RTI), found large water aquifers
in northwestern Kenya where a drought was devastating the land, causing crops to
collapse, livestock to die, and prompting a food crisis that affected millions of
inhabitants in Kenya, Somalia, South Sudan, and Ethiopia. The team is part of the
UNESCO Groundwater Resources Investigation for Drought Mitigation in Africa
Program.
The area explored by Gachet’s team, Turkana County, Kenya, is bordered in the
east by Lake Turkana, a water-filled depression that is part of the East African Rift,
a region having a stretched and fractured crust. Between the fractures, sunken
blocks of land called grabens form sediment-filled troughs that are several kilometers deep. The troughs were a primary target, because they are potential traps for
groundwater. To identify them, RTI used powerful computer programs to merge
refined geological knowledge with large samples of data from ground sensors and
space-based remote sensors. The data used included traditional geologic maps,
hydrologic data, satellite images, and gravity and seismic survey data. Gachet’s
team also used commercial satellite radar images to detect soil moisture. RTI
developed image-processing technology, WATEX, which “erases” obstacles,
such as rocks and villages that can obscure the images, to reveal traces of moisture
that can suggest the presence of an aquifer. WATEX helped identify five likely
aquifers under the desert, each more than 100 m below the surface, containing water
resources totaling at least 250 billion cubic meters. So far, drilling has confirmed
existence of two of the aquifers. The RTI team expects to find many more deeply
buried groundwater aquifers in arid regions, such as South Sudan and Sudan’s
Darfur state [59].
5 Detecting Freshwater Springs and Biomass
Freshwater springs can occur on dry land, in wetlands, and along the coast. Springs
occur when groundwater is confined by a low-permeability geologic formation,
which constrains water to a focused discharge point. Fractures in hard rock and
confining clay units are typical conduits for spring flow [60]. Springs may discharge
at the land surface or below the open water surface. In arid areas, freshwater springs
and irrigated areas induce the growth of a dense vegetation cover, including trees,
44
V. Klemas and A. Pieterse