The annual rainfall is 1,650 mm in Hanoi; around 70–80 % of the precipitation
occurs from May to October. From July to October, the coastal area of the Red
River Delta is affected by low pressure systems from the South China Sea. The low
pressure systems result in inclement weather ranging from tropical storms to
typhoons. The storm surges resulting from those typhoons or tropical depressions
cause severe coastal erosion and flood damage.
Typhoons often attack coastal regions. The typhoon season lasts from June to
September. The average number of typhoons which yearly hit the northern coastal
region in Vietnam is between 1 and 2. In the Red River Delta, typhoons cause
enormous damage to both the national economy and society. The maximum wind
speed exceeds a scale of 12. High winds generated by strong typhoons directly
approach the coastline of Hai Phong, Ninh Binh and Thanh Hoa (Cao et al. 2007).
10.2.3 Floods and Reservoirs
The Red River is characterized by its seasonal variation of water level. Floods occur
almost every year when typhoons come. When floods occur, the water level of the
river rises 188 cm per day. Because the Red River is a raised bed river, the river
water sometimes overflows its banks. The fluctuation band of the river’s water level
is 1,141 cm in a year. At the Son Tay, the flood records are as follows, 25,100 m
3 /s
in 1915, 33,500 m
3 /s in 1945, 28,300 m
3 /s in 1969, 37,400 m
3 /s in 1971 (Haruyama
2004). The flood of 1971 exhibited a discharge rate of 37,400 m
3 /s. Dangerous
water levels continued for 36 days. The flood disaster lasted for more than 1 month
in the Red River and the Day River Basins (Haruyama and Van 2002). Booij (2004)
described the flood situation of 26 provinces in the Red River Delta for the period
1990–2001. The flood in 1996 was extremely severe, and the flood damage was
enormous in Ninh Binh Province.
The Red River that flows through Hanoi, the capital city of Vietnam, is comprised of three major tributaries: the Da, Thao, and Lo rivers, which bring annual
floods threatening the capital and the delta. Upstream reservoirs, namely Hoa Binh,
Thac Ba, Tuyen Quang, and Son La, have a total storage capacity of 8.5 billion m
3
for flood control (Dang et al. 2011).
The reservoir system in the Red River Basin plays a very important role in the
socio-economic development of Vietnam. The major reservoirs include:
1. Thac Ba reservoir (since 1964). It has the following features: high water level:
59 m; total storage: 3.6 billion m
3 ; flood regulation storage: 0.45 billion m
3 ; and
installed capacity: 120 MW.
2. Hoa Binh reservoir (since 1994): It is the biggest in Vietnam in 2007. Main
features: high water level: 120 m; total storage: 9.45 billion m
3 ; flood regulation
storage: 5.6 billion m
3 , and installed capacity: 1,920 MW.
10 Mapping Coastal Erosion Risk in the Southern Red River Delta, Vietnam
201
occurs from May to October. From July to October, the coastal area of the Red
River Delta is affected by low pressure systems from the South China Sea. The low
pressure systems result in inclement weather ranging from tropical storms to
typhoons. The storm surges resulting from those typhoons or tropical depressions
cause severe coastal erosion and flood damage.
Typhoons often attack coastal regions. The typhoon season lasts from June to
September. The average number of typhoons which yearly hit the northern coastal
region in Vietnam is between 1 and 2. In the Red River Delta, typhoons cause
enormous damage to both the national economy and society. The maximum wind
speed exceeds a scale of 12. High winds generated by strong typhoons directly
approach the coastline of Hai Phong, Ninh Binh and Thanh Hoa (Cao et al. 2007).
10.2.3 Floods and Reservoirs
The Red River is characterized by its seasonal variation of water level. Floods occur
almost every year when typhoons come. When floods occur, the water level of the
river rises 188 cm per day. Because the Red River is a raised bed river, the river
water sometimes overflows its banks. The fluctuation band of the river’s water level
is 1,141 cm in a year. At the Son Tay, the flood records are as follows, 25,100 m
3 /s
in 1915, 33,500 m
3 /s in 1945, 28,300 m
3 /s in 1969, 37,400 m
3 /s in 1971 (Haruyama
2004). The flood of 1971 exhibited a discharge rate of 37,400 m
3 /s. Dangerous
water levels continued for 36 days. The flood disaster lasted for more than 1 month
in the Red River and the Day River Basins (Haruyama and Van 2002). Booij (2004)
described the flood situation of 26 provinces in the Red River Delta for the period
1990–2001. The flood in 1996 was extremely severe, and the flood damage was
enormous in Ninh Binh Province.
The Red River that flows through Hanoi, the capital city of Vietnam, is comprised of three major tributaries: the Da, Thao, and Lo rivers, which bring annual
floods threatening the capital and the delta. Upstream reservoirs, namely Hoa Binh,
Thac Ba, Tuyen Quang, and Son La, have a total storage capacity of 8.5 billion m
3
for flood control (Dang et al. 2011).
The reservoir system in the Red River Basin plays a very important role in the
socio-economic development of Vietnam. The major reservoirs include:
1. Thac Ba reservoir (since 1964). It has the following features: high water level:
59 m; total storage: 3.6 billion m
3 ; flood regulation storage: 0.45 billion m
3 ; and
installed capacity: 120 MW.
2. Hoa Binh reservoir (since 1994): It is the biggest in Vietnam in 2007. Main
features: high water level: 120 m; total storage: 9.45 billion m
3 ; flood regulation
storage: 5.6 billion m
3 , and installed capacity: 1,920 MW.
10 Mapping Coastal Erosion Risk in the Southern Red River Delta, Vietnam
201