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of Alternative Technologies for Freshwater Augumentation
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3.5 Rainwater Harvesting for Irrigation Water Supply
In Bangladesh, two types of agricultural water storages are observed.
One type is used to store water on plots which are slightly inclined;
water accumulates in the low lying portions of the fields or in a low
lying areas nearby. Water stored using this method is used for both land
preparation for aman paddy cropping and during the growing/milking stage
of paddy farming when the water requirement is most critical. In
Bangladesh, aman is transplanted in June/July and harvested in
October/November. The other type of water storage involves the storage of
rainwater in ditches or depressions located outside bunds or in land
depressions beside road embankments. Water is carried from these
depression to the fields in buckets, pitchers or traditional dhoon
whenever it is needed. In some cases, if the waterbody is large enough,
water may be used to irrigate a rabi crop or for fishing during the period
of monsoonal inundation. In some upland areas of Bangladesh (North
Central zone), rainwater is stored in low lying plots between two hills
for use in times of necessary.
Figure 10. Stagnant Water on the Lower Slope of a Plot
Rainwater stored using this technology may be transferred
between fields by overflowing successive plots and may be collected in the
lowest fields in a given area. In the West-Cental region, rainwater is
harvested from lands situated at higher elevations and conveyed to storage
ponds through culverts. In this region, because farm lands are situated at
lower elevations than the storage ponds, stored rainwater may also be used
for irrigating farm fields during the dry season. The specific location of
the catchment area and its elevation relative to the fields to be
irrigated are important factors in determining the potential for using
these types of rainwater harvesting technologies.
Figure 11. Irrigation of Crops with Rainwater in
Extent of Use
Rainwater storage in low lying portions of farms or in neighbouring
plots is possible only when the locations and elevations of the plots are
suited to such storage. No detailed data on the extent of use of this
technology were identified, but the field survey suggested that, if such
opportunities exist, farmers made use of these technologies. In upland
areas, nearly all farms having access to rainwater stored in depressions
within hills made use of such water for irrigating aman paddies. In saline
areas, this practice was observed on lands located within polders or
embankments erected to obstruct the intrusion of saline water. In these
areas, there is a conflict between aquacultural (saline water-based shrimp
culture) and agricultural (freshwater-based crop) production, which has
led to violent confrontations. During the field visit, the murder of a
local womens' leader, named Korunamoey Sardar and aged around 40 years,
allegedly by shrimp growers has caused continued deep resentment among the
local farmers and has strengthened the resolve of the local people to
continue fresh water cultivation within the polder in defiance of the
threats by shrimp cultivators.
Figure 12. Irrigation of Crops with Rainwater Using
Operation and Maintenance
The use of natural depressions does not eliminate the maintenance
requirements. Repair work, such as repairing bunds, maintaining slopes,
etc. involve about two person-days of family labour per year at an
equivalent cost of $2.50, based upon a rate of $1.25 per day. Local
agricultural equipment is used for this purpose.
Level of Involvement
This technology is implemented at the household level, although it has
been implemented sometimes at the community level.
Construction costs are minimal since this system of rainwater harvesting
is practised only when the land is naturally sloped, when the farmer has a
plot nearby with a low enough elevation, or when there is an existing
ditch or depression available where rainwater can be stored.
Effectiveness of the Technology
Data from the North Central zone of Bangladesh shows that the use of
this technology increases paddy crop yields by about 32%. In order to
achieve similar yields as can be achieved through irrigation using
rainwater harvesting techniques, farmers would have to incur additional
expenses in transporting water from other sources. The cost of
transporting water would be the equivalent of five to six person-days of
family labour and one to two days of hired labour.
This technology is suitable in areas where natural depressions are found
and where there is adequate rainfall to produce runoff.
The advantages of this technology are that it is a locally implemented
technology, which can be used at little additional cost.
The disadvantage of this technology is that rainwater cannot be stored
for long time due to seepage losses. The method also lacks scientific
This technology is very well accepted and has no known cultural
Further Development of the Technology
This is a fully developed technology. However, development of criteria
for sizing storage areas would make this technique more rigorous.
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,