GEO Brasil - UNEP

the state of water resources
the state of the environmet in Brazil
of calcareous rocks, whose porosity, permeability or interstitial or fissure
characteristics were locally and occasionally expanded by rock dissolution
processes by meteoric water which infiltrates
In alluvial deposits and dunes, underground waters are fundamentally healthy,
free, freatic and really vulnerable The use and occupation conditions of the
based rocks, covered by an altered
rock mantle on average 50 meters
thick The permanent total revenue of
underground water in Brazil is about
112,000 km3, and about 90 percent of
these waters are in sedimentary
basins (Rebouças, 1988)
On the other hand, the most frequent
supply rate obtained by already
opened wells varies less than 1!!m3/h
in underground water areas of
fractured rocks, which are virtually
water proof of geological base of Pre-
Cambrian age of semi-arid Northeast,
up to more than a thousand 1,000m3/
h in sedimentary basins in humid
climate conditions
Considering the generalized level of
these estimates, it is fundamentally
important to carry out basic studies
in the different hydro - geological
contexts, in scales compatible to the
problems to be solved and their
complexities and magnitudes, to
develop monitoring, and constitute
basic hydro - geological databases
which should be fed in a permanent
way
In Brazil, the hydro - geological
potentials referred to in terms of
specific capacity [(m3/h) m-1], in other
words, the flow (m3/h) which is
obtained of each well by lowering
meter (m-1) of the respective healthy
water level is presented in Figure 4
environment fundamentally affect the quality of drawn waters, above all through
shallow wells (3 to 10 m, mainly), nailed and dug
26 Underground Water Potentials in Brazil
The data in table 1 indicates that permanent underground water reservoirs of
main hydro geological contexts in Brazil vary from 80 km3 in the 600,000 km2 of
semi-arid Pre-Cambrian age rock domain in the Northeast mainly; it reaches
10,000 km3 in almost 4,000,000 km2 of crystalline and metamorphic Pre-Cambrian
It is observed, therefore, that
underground water potentialities in the
national territory are really varied In
the most promising domains, the
specific capacities of wells vary from
5 to 10 and superior to 10 m3/hm-1
In these areas, there is a possibility of
obtaining flows from 250 to 500 m3/h
in each well, with the lowering of 50
meters of respective static level or
water level (WL)
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