Accepted Papers - 3.pdf - UNESCO

Modern Structures
During the last 100 years there has been
considerable technological development, interalia,
in the design and construction of water harvesting
structures for various purposes. In areas where
source of water is only rainfall, entire efforts of water
conservation are to be concentrated on insitu
rainfall.. Gully plugging , Contour bunding, Bench
terracing and Gabbion structures are the common
water conservation structures applicable in run off
zone. They are also part of watershed improvement
works. These measures are multipurpose, mutually
complementary and conducive to soil and water
conservation. They help to increase forestation and
agriculture productivity.
Gully Plugging : These are the smallest soil and
water conservation structures built across gullies in
hilly areas carrying drainage of tiny catchments
during rainy season. These are built with locally
available materials like stone boulders, earth,
weathered rock brushwood etc. Sand bags or
brickwork may also be used to strengthen the bund.
Gully plugs may be chosen wherever there is local
break in slope to permit accumulation of adequate
water behind the bund. The height of individual plug
depend upon land slope may be between 2 to 3 m
above nala bed and progressively taper off on side
slope. A number of gully plugs may be provided on
the same gully or nala, one below the other at every
hundred-meter separation.
Contour Bunding :
These are small structures earthen bunds
built horizontally in parallel rows across the hill
slope. These help in augmenting soil moisture and
prevent erosion of topsoil. This technique is suitable
in low rainfall area where monsoon runoff can be
impounded by constructing bunds on the slopping
ground all along the contour of equal elevation. The
434
flowing water is intercepted before it attains the
erosive velocity by keeping suitable spacing
between the bunds. The Spacing of between two
contour bunds depends on the slope of the area and
the permeability of the soil. Contour bunding is
suitable on land with moderate slope without
involving terracing..
Bench Terracing :
Sloping land with surface gradient up to 8%
having adequate soil cover can be leveled through
bench terracing for bringing under cultivation. It
helps in soil conservation and holding runoff water
on terraced area for longer duration giving rise to
increased infiltration recharge. The width of
individual terrace should be fixed depending upon
the slope of the land. The upland slope between two
terraces should not be more than 1;10 and the terrace
should be leveled.
Gabbion Structure
This kind of check dam commonly
constructed across small streams to conserve stream
flow with practically no submergence beyond
stream course. Small bund across the stream is made
by putting locally available boulder in a steel of
mesh wires and anchored to the stream banks. The
height of such structures is around 0.5 m and is
normally used in the stream with width of less than
10.0 m. The excess water overflows this structure
storing some water to serve as source at recharge.
The silt content of stream water in due course and
with growth of vegetation, the bund becomes quite
impermeable and helps in retaining surface water
runoff for sufficient time affect rain to recharge the
ground water body.