Environmental Engineering Reference
In-Depth Information
Box 24.2
Case study: the Dhaka-Narayanganj-
Demra project
has experienced a progressive change in land
use from a potential agricultural area to an
urban development area. Numerous industries
of different categories have also sprung upwith-
in this project area. In 1990, a land use study by
the Flood Action Plan (8A) found that 21.7 km
2
(38%) of the DND project area was urbanized
with 31.7 km
2
(56%) land being used for agri-
culture (Japan International Co- operation
Agency 1991). The present land-use pattern
shows that 60%of the project area is urbanized
while land used for agriculture has decreased to
only 20%. Furthermore, the rapid urbanization
and industrialization have caused an un-
checked increase in population. Moreover, al-
though the land is free from river floods,
unplanned urbanization impedes drainage of
rainwater, causing drainage congestion every
year and forcing changes in land management
practices.
The Dhaka Narayanganj Demra (DND) project
demonstrates the impact of increased flood
protection on land use and land management
practices in Bangladesh. The project was orig-
inally designed as an irrigation project by the
Bangladesh Water Development Board (BWDB)
in the early 1960s tomeet national objectives of
achieving self-reliance in food grain produc-
tion. The project was also conceptually
identified to accelerate agricultural production
by providing comprehensive Flood Control,
Drainage and Irrigation (FCDI) facilities cover-
ing 56.79 km
2
of the Greater Dhaka District.
The area is situated in close proximity to the
capital Dhaka adjacent to a major national
highway.
As a result, with the increase in flood-free
land, over the last two decades the DND area
the flood-protected areas. The dominance of paddy
in cropping patterns increased; however, cropping
intensities were rarely increased. Because of the
more secure growing conditions in high (F0) and
medium-high (F1) lands, a shift from B (broadcast)
aman or aus/aman to TL (local transplanted)
aman and transplanted HYV (high-yielding varie-
ty) aman was recorded. The change from F2 to
shallow-flooded F1 has allowed the introduction
of T aman in place of B aman (deepwater).
Conversion of shallow-flooded F2 to very-shal-
low-flooded F0 allowed the introduction of
HYV varieties (Brammer 2002). Boro expansion
occurred where protection from early flash floods
(mainly in the northeast) or irrigation was provid-
ed. Paddy yields improved as a result of the shift
to higher yielding paddy types. As a result, data
analysis shows that FCD schemes have been suc-
cessful in raising agricultural production by 35%
(Datta 1999).
In contrast, drainage congestion has been the
most serious technical problem, reducingmuch of
the efficiency of the FCD schemes and in many
cases lowering agricultural productivity. Accord-
ing to NWMPP (2000), most projects concentrated
on flood protection, with drainage receiving
less attention. Drainage congestion has basically
stemmed from inadequate planning and design of
drainage canals and sluices. Appropriate consider-
ationwas not given to external impacts (e.g. higher
flood levels outside polders, reduction of river
flows downstream of cross-dams) and adverse
internal impacts (such as siltation), and to the
inclusion of mitigation measures (e.g. structural
floodproofing to mitigate higher external flood
levels). Inaccurate maps and other data deficien-
cies have also contributed to ineffective drainage.
Modern flood management practices have, on
the whole, resulted in strongly negative impacts
on thefisheries sector, with capturefisheries being
the worst affected. Reductions in perennial beels
and natural water bodies in deeply and regularly
flooded areas due to late or controlled flooding
have decreased fish habitat. In addition flood pro-
tection infrastructure has caused blockage of
fish migration routes limiting reproduction. The
production of culture fisheries has seen a slight
improvement, but capture fisheries losses have far
outweighed culture fishery gains. Moreover, such
gains have not benefited the mostly poor capture
