Chapter
9:
Case
studies
in
Ta’izz
meters
below
the
ground
surface.
The
smaller
depth
to
water
makes
this
aquifer
exploitable
by
dugwells,
which
are
found
in
abundance
in
the
area.
In
many
zones,
the
alluvial
aquifers
are
prone
to
over
exploitation.
The
quality
of
the
water
is
generally
good
(Van
der
Gun
&
Riaz,
2004).
In
addition
to
the
alluvium
deposits,
water
is
also
found
in
fractures
in
the
volcanic
rocks
that
dominate
the
sub-‐surface
in
the
study
area.
The
thickness
of
these
rocks
in
the
study
area
is
estimated
to
be
600-‐700
meters.
The
volcanics
are
generally
not
a
very
productive
source
and
yields
of
wells
dug
in
these
strata
are
low.
The
water
is
also
of
poor
quality.
This
is
specially
the
case
where
the
fractures
are
connected
to
overlying
alluvial
aquifers
in
the
polluted
zones,
although
poor
water
quality
in
the
volcanics
also
has
natural
causes
(e.g.,
naturally
occurring
salinity
in
some
zones)
(Van
der
Gun
&
Riaz,
2004).
Another
major
source
of
groundwater
in
the
area
is
the
deep-‐seated
sandstone.
This
formation
has
proven
very
productive
elsewhere
in
Yemen
and
is
the
focus
of
exploratory
efforts
in
the
Ta’izz
region
too.
However,
the
sandstone
aquifer
in
the
planning
area
has
not
yet
been
fully
exploited
except
in
Dhi
Sufal
zone
where
NWSA
wells,
in
addition
to
some
farmers’
wells,
tap
into
this
aquifer.
These
wells
have
high
yields
and
quality
of
water
is
also
good
(Van
der
Gun
&
Riaz,
2004).
Table
9.1
illustrates
the
1993
dugwells
and
306
boreholes
that
had
been
constructed
up
until
1996.
Some
of
which
have
become
dry
due
to
high
rate
of
abstractions.
Table
9.1:
Wells
and
springs
in
Ta'izz
region.
Well
type
Number
of
wells
Springs
88
Dugwells
1993
Boreholes
306
Source:
Data
files
of
NWRA
well
inventory
1996
Nearly
all
of
the
streams
in
the
Upper
Wadi
Rasyan
catchment
that
flow
for
at
least
six
months
of
the
year
are
polluted
by,
or
entirely
comprise,
domestic
and
industrial
waste
water.
Domest