Environmental Engineering Reference
In-Depth Information
bodies are called jalmahals or fishing grounds.
The annual flooding and post-flooding standing
of water in the floodplains plays a vital role in the
sustenance of fish stocks and the maintenance of
species diversity in the open water fishery of the
jalmahals. The floodplains comprise a rich eco-
systemproducing biomass that supports themajor
biological activities of fish. During the monsoon
season, fish movement increases throughout the
floodplain and fromrivers into distributaries. Fish-
ing seasons in the haor areas include the monsoon
and post-monsoon months from mid-June to No-
vember, and also the dry and pre-monsoonmonths
from December to early June. Fishing catch is
highest during the monsoon when the migration
andmovements of fish take place. DuringNovem-
ber and December, dams are placed in the drainage
canals to stop recession of floodwaters. Converse-
ly, in February water levels in the beels are
reduced through drainage to maximize the catch
(Paul 1997).
summer fruits and vegetables are grown, or dry
season rice varieties called boro. All Rabi crops
need irrigation and can be grown on a variety of
land types. Even in the permanently wet F4 lands,
boro is grown locally.
The different cropping seasons usually overlap.
As a result, farmers usually go for double cropping,
i.e. two crops in one calendar year. Figure 24.3
shows a generalized cropping calendar for the
entire country. But the schedule of plantation and
harvesting differs slightly within the different
hydroecological regions. The monsoon starts ear-
liest in the northeast andmoves towards the west,
starting latest in the western part of the country.
Similarly, the flooding pattern varies as the flood
peak arrives earliest in the northern areas, and
recedes latest in the southern coastal areas.
It is important to understand that the timing
and duration of floods plays a major role in the
cropping pattern. Early floods (in April/May) gen-
erally cause severe damage to boro crops. Severe
damage to mature boro rice from flash floods is
reported in the eastern foothill regions virtually
every year.Moreover, excessivefloods in June/July
can harm standing aus crops and delay transplan-
tation of aman. Impeded drainage of floodwaters
causingwater to stay in agricultural lands formore
than five consecutive days can seriously reduce
yield. Therefore, F0 (high land) and F1 (medium-
high land) provide a wider range of options for
intensification of cropping than the more deeply
flooded land types. In very deeply flooded land
types (F3 and F4) productivity is very low and
cropping choices are also limited. However,
pulses, oilseeds and other dry-land Rabi crops can
be grown provided floodwaters recede before
December.
Although agriculture receives the highest pri-
ority in water and land management in Bangla-
desh, fisheries are also given some consideration
especially in beel and haor (perennial wetland)
areas. Inland water bodies can be differentiated
into open water bodies such as rivers, canals,
beels, haors and floodplains, which produce cap-
ture fisheries, and closed water bodies such as
ponds and lakes, which are increasingly being
used for culture fisheries. The perennial water
Flood Management Practices in Bangladesh:
Impacts on Land Use
In present-day Bangladesh, the FCD or FCDI
projects dominate land and water management
practices. The implementation agency for these
projects is the Bangladesh Water Development
Board. From an agricultural perspective the
FCD/FCDI schemes are designed to:
.
protect standing crops (aus, planted in March/
April) against river floods;
.
expand the area under monsoon rice (aman,
planted in August/September) by excluding flood
waters from the scheme;
.
retain water in the schemes during the post-
monsoon period.
Typical projects have three major components:
.
embankments to control overbank spills;
.
khal (or canal) closures to control entry of river
floodwater;
.
khal (or canal) regulators to control entry and
drainage of floodwater.
Embankment construction has been the major
activity in these FCD projects as part of the
