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run was carried out for 30 minutes. The model was design and
made of reinforced cement concrete with the
working section of 300 cm IP length and 111.5 cm
in width including a floodplain and a river channel
with the same length of 300 cm and widths of 90
cm and 21.5 cm respectively and an embankment
made of wooden plate with the thickness of 10 mm
made in-between the floodplain and the river
channel. Different lengths and depths of breaches
were made in the embankment as per requirement.
The mid points of the embankment breaches
during model runs were kept fixed at X-100 cm.
Medium sand (0.6-0.2 mm) with d 50=0.23 mm with
the thickness of 6 cm was used as bed materials of
the floodplain of the model. To have the similarity
ratio the vertical and horizontal scale of the model
were selected to be 100 and 1000 respectively. The
velocity scale ratio was calculated based on the
Froudian Similarity. Different L b of 5 cm, 10 cm,
20 cm & 30 cm in the model corresponded to 50
m, 100 m, 200 m & 300 m in the prototype
respectively. The average discharge in the river
channel at the upstream of the embankment breach
3
at X=50 cm was observed to be 7606 cm /s in
model runs 1-16. The scour depth formed on the
c/s floodplain due to embankment breach was
measured at 2 cm interval along both longitudinal
(X) and lateral (Y) directions. The results of the
analyses showed that the mean velocities and
discharges into the floodplain through the
embankment breach and the mean velocities at the
scouring location decreased with the increase of
the water depth and increased with the increase of
the length and depth of embankment breaches. The
area of scour formed in the c/s floodplain due
increased with the increase of length of breach and
decreased with the increase of depth of breach in
the embankment. The volume and maximum depth
of scour formed in the c/s floodplain increased
with the increase of length and depth of
embankment breaches. A line joining the mid point
of the embankment breach at X=100 cm and the
location of maximum scour depth in the c/s
floodplain formed an angle of scour α with the d/s
portion of the failure embankment due to the effect
of different length and depth of embankment
breaches. The α decreased with the increase of
length and depth of embankment breaches. To
mitigate any disaster caused due to embankment
failure every embankment in Bangladesh is
recommended to be constructed following proper
101
construction procedure. As
embankment failure is a frequent natural disaster in
Bangladesh, further in depth study of this
phenomenon would be useful & may result in less
economic losses incurred due to embankment
failure and contribute to the growth of the national
economy of this disaster prone country.
329 ISLAM, M.Z. & DATTA, A.R.
(Institute of Water and Flood Management
(IWFM), Bangladesh University of Engineening
and Technology (BUET), Dhaka). A STUDY ON
DRAINAGE CONGESTION IN BEEL
KURALIA AND ITS MITIGATION
APPROACH. IWFM Res. Bull., 2001-2002, 3, 39-
61.
Beel Kuralia, a part of greater Chalan Beel lies in
Pabna district of Bangladesh. Out of its gross area
of 6,000 ha about 5,000 ha remains under water
almost throughout the year due to drainage
congestion. Once the people could grow
abundance of agricultural crops here. But recently
developed unplanned human activities like the
construction of cross bunds, sluice gates etc. across
the River Baral, the River Chiknai and their
siltation have totally stopped the water flow
resulting in degradation of environment,
agriculture, fisheries, health, employment and
consequently socio-economical conditions of the
people of the region. In this regard A Study on
. ‘
Drainage Congestion in Beel Kuralia and Its
Mitigation Approach' was under taken in July 1999
with the objectives to identify the causes of
drainage congestion in Beel Kuralia and to assess
its positive and negative impacts on agriculture,
fisheries, hydrology, health and socio-economical
conditions and to recommend mitigation measures
for the negative impacts caused due to drainage
congestion in Beel Kuralia. For the study
questionnaires were formulated and interviews
were held with four hundred people including 200
farmers, 100 fishermen "and 100 persons of
different occupations. Impact assessment was
made based on the methodology, Environmental
Evaluation System (EES) developed by Battelle
Columbus Laboratories in the United States. The
negative impacts as identified in the agricultural
sector were decrease in agricultural lands, change
in cropping areas for different harvests, reduction