Geology Reference
In-Depth Information
Topography and geomorphology have distinct influence on transmissivities
and well yields. Steep slopes and sites on hill tops should be avoided for
constructing bore-wells.
Lithology doesn't appear to have any appreciable influence on well yield
(Fig. 8)
Experience of water well drilling in hard rock terrains indicate that even
in geologically promising areas, the yield of bore-wells may not be satisfactory.
Proper design and development of bore holes is very important. A bore hole
should be oriented so that it intercepts the maximum number of fractures,
preferably perpendicular to the hydraulically open fractures. Further,
techniques of artificial yield enhancement such as hydraulic fracturing or
explosives will greatly improve well yield by creating a network of
interconnected fractures (Singhal and Gupta, 1999).
Figure 8.
Distribution of well yields for different rock types in the Central
Scandinavian area (after Banks et al., 1996) 1: syn-orogenic granites. 2: post-
orogenic granite. 3: post-orogenic gabbros and dolerites. 4: gneisses.
5: Caledonian mica schists.
ESTIMATION OF AQUIFER RECHARGE
Quantitative estimates of recharge to aquifers and changes in groundwater
storage is important to manage the development of groundwater resources
and to know the amount of groundwater that can be withdrawn without
exceeding recharge.
