Special
Reports/Water Crisis |
Planning for efficient water delivery
By F.H. Mughal
ALL five dams, Bhasha, Munda, Kalabagh, Akori and Kurrum
Tangi, would be built by 2016. The building of water
reservoirs in the upstream reaches of a river will impact
the volume of water flowing in the downstream areas.
To
avoid this problem, there are a number of alternatives which
can be used quite often in combinations as substitutes of
dams. Water diversions can be achieved by alternatives like
infiltration galleries. These are structures which are used
for diverting water.
There are two types of infiltration galleries: vertical
wells and horizontal infiltration galleries. Through gravity
flow or pumping, water is drawn from the rivers gravel
substrate through perforated pipes.
Vertical wells draw water through perforated pipes, which
are placed vertically into the stream. The water table is
maintained by the surface flow of water in the stream.
Location of vertical wells is dependent on river conditions.
They can be located near or away from the river.
Horizontal infiltration gallery concept is simple and
convenient. The infiltration gallery structure typically
involves locating perforated pipes in the riverbed and,
these pipes discharge to a sump. Water seeps in the
perforated pipes and flows to sump. Water collected in sump
flows by gravity (or is pumped, in some cases) to a point
where it is used or stored.
Location of perforated pipes and its diameter is governed by
the factors like rate of diversion of water, type of gravel
at the site, the depth to which bed scouring is likely to
occur during high flows in the river, and the size of river
itself.
Infiltration galleries may face problems if armoured gravels
are on the riverbed as that would reflect low percolation
rates. Fine-grained soils such as the clay, silt and sand
would cause logging. Absence of gravel substrate may prevent
the placement of perforated pipes at depths sufficient to
protect them from scouring.
Seasonal dams are temporary and relatively small structures
that can be erected for water diversion. They raise the
river water level allowing water to be diverted through a
channel or pipe. Flashboard and inflatable dams are the
common types of seasonal dams. Despite their smaller size,
seasonal dams can affect rivers negatively by increasing
water temperatures, harbouring predator species, reducing
downstream water flows and associated aquatic life, inducing
erosion of the bed and banks of rivers, causing fluctuations
in upstream water levels, and impacting biota and aquatic
vegetation. The magnitude of negative impacts is small and
easily manageable.
Agriculture is the largest user of water. Irrigation-purpose
water supply dams are common worldwide. In this case,
alternative diversions need to be coupled with irrigation
practices. Rational irrigation practices which can even
obviate the need for a dam, include efficient water
distribution (land levelling), achieving better soil
moisture retention (furrow dykes to prevent runoff),
dry-land farming (coordinating seeding to ideal soil
moisture, choosing crops more suited to water-deficit
conditions and fallowing), land retirement (temporary
suspending farming on a particular unit of land in exchange
for financial incentives) and, land chiselling (allowing
land to absorb water more efficiently).
Management strategies help in ensuring efficient water
delivery. The strategy components are scheduling irrigation,
determining soil moisture, measuring rainfall and, checking
pumping efficiency.
It requires the education of irrigation staff through
agriculture extension services. Use of drip irrigation or
micro-sprinklers, solid set systems, and constructing a
tail-water recovery system has the potential to further
improve the water efficiency.
Alternate arrangement for use of water attempts to seek out
sustainable management and can provide additional water for
use. Rain is the major source of water. Concrete and other
impervious surfaces are increasing in peri-urban areas. This
prevents natural infiltration and interferes with hydrologic
cycle of nature. Aging pipes and infrastructure give rise to
water loss. In Karachi, the local water agency loses 33 per
cent of water supplied to city due to pipe leakage and water
vandalism.
Groundwater is a major water resource in Sindh, but its
potential use is reducing due to pollution. Sustainable use
of groundwater can reduce reliance on surface water supplies
and dams.
Rainwater harvesting is an old trusted practice of
collecting rainwater from rooftops and storing it in drums.
Water can be used in lawns, or for drinking after passing it
through filters. It reduces storm-water runoff; prevents
flooding, erosion and pollution of surface water bodies.
Recycling and re-use of water has the potential of entailing
large savings and can decrease the amount of freshwater
required. Recycled water can be used for irrigation and in
industries. Water pricing is a useful way of conserving
water. Seawater desalination is an attractive alternative of
avoiding use of freshwater. There are many technologies of
separating salt from water but the two most common are
reverse osmosis and thermal distillation.
There is no separate department for freshwater management in
Sindh. The set-up of Sindh Freshwater Management Department
is suggested with staff qualified in water engineering. The
Sindh government should take the matter seriously.
The case of Aral Sea should be an eye-opener. Decline of the
Aral Sea started in the 1960s as increasing amounts of water
were diverted from the Amu Darya and Syr Darya mainly for
irrigation. Between 1960 and 1996 the surface area of the
sea declined by some 50 per cent (from 67,000 square km to
30,000 square km) and, the sea level dropped by 16 meters.
The desiccation of the Aral Sea and the damage to the river
deltas resulted in serious economic, social and
environmental consequences such as (i) elimination of fish
production in the delta as well as hay production along
streams, lakes and wetlands; (ii) extremely high levels of
salinity and pollution; (iii) dust and salt storms occur
often and climatic changes take place around the sea; (iv)
non-availability of adequate and safe drinking water
supplies; (v) increase in human health problems resulting in
reduced life expectancies in the areas near the sea; (vii)
elimination of tens of thousands of jobs in fishing,
agriculture and service sectors, and; (viii) degradation of
agricultural lands, soil, surface waters and groundwater
and, wetlands.
Courtesy :
The DAWN
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Pakissan.com;
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