598
Climatic Geomorphology
144,836 kn] 2 and more than 110 million inhabitants, of which a greater part live upon
floodplains and have a per capita income of about 140 dollars (Brammer, 1990; Khalil,
1990). The Ganges-Brahmaputra delta is located in the southern region, and it is also fed
by the Meghna River (Figure 22.12). The delta contains numerous islands where
population density is up to 1000 people/km 2, and agricultural land exploitation is very
intense (Carter, 1988). About 60% of the country presents a flooding hazard. Two great
closed and shallow structural depressions develop on those wide deltaic plains and
floodplains. Elevated zones correspond to Pleistocene fluvial terraces and Tertiary hills
(Rasid and Pramanik, 1993). Maximum annual precipitation is 11,615 mm, recorded at
Cherrapunji, to the NE of the country. Rainfall decreases from this region towards the
west, where it reaches an average value of 1250 mm (Brammer, 1990). In their low
courses, the Ganges, Brahmaputra and Megna rivers have valley widths of about 10 km
and during floods maximum discharge is 160,000 m3/s, three times the average value of
the Mississippi River. These rivers transport a sediment load of 2.5 x 109 t/year (Coleman,
1969) and have a marked seasonality. They record high levels from the beginning of spring
to the end of summer, due to the Himalayan snow melting and to the June-July monsoon
rains, which can give rise to important flooding.
The Bay of Bengal has a tropical cyclone frequency of 20% (Barry and Chorley, 1987).
When cyclones approach the coast they produce a sudden sea level rise due to strong winds
and low atmospheric pressure (storm surge), and high storm waves. These waves can reach
6 to 7 m in height and penetrate deeply into the coastal fringe, which is constituted by
deltaic zones of very low height, and hence houses and crops get flooded. Sea penetration
effects are emphasised when the cyclone passing coincides with high tide conditions, as
happened in November, 1970 (Smith and Ward, 1998). Strong destructive winds that can
exceed 200 km/h and strong cyclonic precipitation adds to the marine flooding (Reading
et al., 1995).
The Bangladesh territory has suffered nearly 20 important floods since the middle-20th
century (Brammer, 1990). Some have only produced material damage, but in most of them
the number of deaths has been very high. The biggest catastrophe happened on the 12th of
November, 1970, and it is considered as the worst natural disaster of the 20th century. It
was generated by a cyclone that arrived at the coast at 11 p.m. and produced 300,000
deaths (Burton et al., 1978; Carter, 1988). In successive years new catastrophes also took
place. In 1987 and 1988 fiver floods were caused by strong monsoonal precipitation and,
according to official data, they produced 1657 and 2379 deaths, respectively
(Brammer, 1990). On 30 April 1991, as a consequence of a new catastrophic cyclone,
70,000 people lost their lives in SE Bangladesh and millions lost their homes (Davis, 1992;
Reading et al., 1995).
Protection measures against these natural catastrophes have been quite scarce due to the
great poverty of the country. Earth walls and tree fences have been constructed, although
the former are designed for fighting against salinization. During the 1970 cyclones, some
5% of people were saved in official refuges and about 38% by climbing into the trees. This
cyclone was identified 3 days before and monitored by satellite, although no intensity was
calculated (Burton et al., 1978). Despite alarms, very few people were evacuated and most
of them remained on their lands, perhaps due to religious reasons (Carter, 1988). In the
1991 cyclone, however, meteorological predictions and alarms led to a major evacuation.
Climatic Geomorphology
144,836 kn] 2 and more than 110 million inhabitants, of which a greater part live upon
floodplains and have a per capita income of about 140 dollars (Brammer, 1990; Khalil,
1990). The Ganges-Brahmaputra delta is located in the southern region, and it is also fed
by the Meghna River (Figure 22.12). The delta contains numerous islands where
population density is up to 1000 people/km 2, and agricultural land exploitation is very
intense (Carter, 1988). About 60% of the country presents a flooding hazard. Two great
closed and shallow structural depressions develop on those wide deltaic plains and
floodplains. Elevated zones correspond to Pleistocene fluvial terraces and Tertiary hills
(Rasid and Pramanik, 1993). Maximum annual precipitation is 11,615 mm, recorded at
Cherrapunji, to the NE of the country. Rainfall decreases from this region towards the
west, where it reaches an average value of 1250 mm (Brammer, 1990). In their low
courses, the Ganges, Brahmaputra and Megna rivers have valley widths of about 10 km
and during floods maximum discharge is 160,000 m3/s, three times the average value of
the Mississippi River. These rivers transport a sediment load of 2.5 x 109 t/year (Coleman,
1969) and have a marked seasonality. They record high levels from the beginning of spring
to the end of summer, due to the Himalayan snow melting and to the June-July monsoon
rains, which can give rise to important flooding.
The Bay of Bengal has a tropical cyclone frequency of 20% (Barry and Chorley, 1987).
When cyclones approach the coast they produce a sudden sea level rise due to strong winds
and low atmospheric pressure (storm surge), and high storm waves. These waves can reach
6 to 7 m in height and penetrate deeply into the coastal fringe, which is constituted by
deltaic zones of very low height, and hence houses and crops get flooded. Sea penetration
effects are emphasised when the cyclone passing coincides with high tide conditions, as
happened in November, 1970 (Smith and Ward, 1998). Strong destructive winds that can
exceed 200 km/h and strong cyclonic precipitation adds to the marine flooding (Reading
et al., 1995).
The Bangladesh territory has suffered nearly 20 important floods since the middle-20th
century (Brammer, 1990). Some have only produced material damage, but in most of them
the number of deaths has been very high. The biggest catastrophe happened on the 12th of
November, 1970, and it is considered as the worst natural disaster of the 20th century. It
was generated by a cyclone that arrived at the coast at 11 p.m. and produced 300,000
deaths (Burton et al., 1978; Carter, 1988). In successive years new catastrophes also took
place. In 1987 and 1988 fiver floods were caused by strong monsoonal precipitation and,
according to official data, they produced 1657 and 2379 deaths, respectively
(Brammer, 1990). On 30 April 1991, as a consequence of a new catastrophic cyclone,
70,000 people lost their lives in SE Bangladesh and millions lost their homes (Davis, 1992;
Reading et al., 1995).
Protection measures against these natural catastrophes have been quite scarce due to the
great poverty of the country. Earth walls and tree fences have been constructed, although
the former are designed for fighting against salinization. During the 1970 cyclones, some
5% of people were saved in official refuges and about 38% by climbing into the trees. This
cyclone was identified 3 days before and monitored by satellite, although no intensity was
calculated (Burton et al., 1978). Despite alarms, very few people were evacuated and most
of them remained on their lands, perhaps due to religious reasons (Carter, 1988). In the
1991 cyclone, however, meteorological predictions and alarms led to a major evacuation.