Geology Reference
In-Depth Information
Table 3:
Data on optimum depth of wells in different regions and rock types
Region
Rock type
Optimum depth (m)
Cyprus
Gabbro
170-200
Satpura hills, India
Granite gnesiss and schist
45-60 and 45-75
Northern Carolina, USA
Granite
75-90
Kararnoja, Uganda
Gneiss and schist
30-92
Zimbabwe
Greenstone and gneiss
40-80
Norway
Granite and gneiss
40-60
fracture systems are generally hydraulically connected with the weathered
saturated residuum. The yield potential of the crystalline and meta-sedimentary
rocks shows wide variations. Through 10 cm to 15 cm diameter bore-wells,
the fractured system generally yields from 10 m
3
/hour and up to 100 m
3
/
hour in the vicinity of structurally disturbed areas (Table 4).
Studies in different parts of the world indicate that the following factors
can be related to well yields (Banks et al., 1996; Singhal and Gupta, 1999;
Moore et al., 2002, Faillace, 2003; Henriksen, 2003).
Rainfall regime and intensity.
Size of the drainage area up-gradient of the well.
Distance to the nearest water body.
Well proximity to major fractures and lineaments.
Narrow alluvial valleys in hard rock terrain and underlying weathered and
fractured hard rocks can be a potential source of water supply.
Table 4:
Yield of bore-wells in crystalline rocks
Well yield (m
3
h
-1
)
Rocks type
Region
Well depth (m)
Granite-gneiss
Southern and
eastern India
3-10
15-80
Granite-gneiss,
Tamilnadu,
Charnockite
South India
6-18.3
0-70
Granite and gneiss
Kwara, Nigeria
9.5
50-75
Granite and gneiss
Victoria, Zimbabwe
4.1
20-30
Gneiss (fractured)
Maharashtra, India
48
164
Granodiorite and
Gabbro (fractured)
Lee Valley, USA
3.5-23
60-150
Pegmatite (fractured)
Karnataka, India
110
42
Quartz vein (fractured)
Bihar, India
55
137
Marble
Sri Lanka
2.4-24
Quartzite
Sri Lanka
6-28.8
Schist
Connecticut, USA
4.16
33.4
Slate
Slate Maine, USA
3.42
