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3.9 Rainwater Harvesting in Ponds
In the southern region of Bangladesh, the salinity of both
surface and ground waters is beyond the tolerable limits for human and
agricultural uses, including watering of animals as well as plants. From
time immemorial, pond water, replenished by rainfall, is used for drinking
and other purposes, including for fish cultivation. The ponds are
specially constructed with bunds so that surface water cannot enter the
ponds. This feature keeps the bed of the pond relatively free of sediment.
Traditionally, trees have been planted on all four sides of the ponds to
provide additional protection of the pond area. In the Sunderban region,
animals are permitted to drink from the ponds during the night.
Extent of Use
In southern portion of Hatya Island (Figure 18), and other remote
islands in the Bay of Bengal, rainwater, collected in ponds, meets nearly
80% of the drinking water requirements during the monsoon season. The
water levels in the ponds fall during the dry season, and the water
becomes turbid and more saline due to the deposition of marine aerosols,
but the water continues to be used by the local people who have no other
source of water, although some households bring water from distant areas.
The pond water is used for bathing, washing of clothes and other household
purposes through out the year. Where tubewells exist, women are generally
carry the water from the wells to the point of use. In contrast, even in
areas where religious norms are strictly adhered to, men may be found to
carry water from the ponds.
Operation and Maintenance
Maintenance of the ponds involves repairing the bunds, cleaning and
removing sediment, and general upkeep of the surrounding area.
Level of Involvement
This technology is generally implemented at the community level.
Capital costs depend on the materials and methods used in constructing
and lining the ponds. Typical pond construction costs range between $350
and $500 for a 15m x 15m pond. Maintenance costs are typically about $12
Effectiveness of the Technology
In Bangladesh, the ponds fill with rainwater during the monsoon season,
which, on Hatya Island, extends from April to August. At the conclusion of
the monsoons, the water level in the ponds falls rapidly during January
and February, and the water becomes salty. Nevertheless, a large number of
people depend on the ponds for their domestic water supply. Hence, this
technology appears to be very effective in meeting local needs.
This technology is suitable in areas with abundant rainfall to fill the
This technology is relatively inexpensive and can be implemented using
local technological skills and community cooperation.
There is a potential for the pollution of the pond water by animals.
Also, if the ponds are poorly maintained, there may be seepage losses.
Because the ponds are open, they are subject to evaporative losses.
Some communities do not drink water from this type of storage pond
because it is considered unholy and contaminated.
Further Development of the Technology
This technology may be considered to be fully developed. However, cost
effective methods need to be introduced to reduce water losses and
pollution to improve its effectiveness.
Mohammed Aslam, Saleh Ahmed Chowdhury, Alamgeer Faridul Hoque,
and S.R. Sanwar, Intermediate Technology Group, House 32,
Road 13A, Dhanmondi, Dhaka, Bangladesh, Tel. 880 2 811 934, Fax: 880 2 813
134, E-mail: email@example.com.