3.3 Watershed Responsiveness, Water Retention and Dam
Construction: Irrigation and Flood Risk Management
3
This section summarizes and reviews the key findings made from a field study we
conducted (Schad et al. 2012) in a mountainous watershed of north-west Vietnam.
The aim of the study was to explore and analyze the causes and impacts of an
exceptional flood event that occurred in 2007. Based on an interdisciplinary
research approach comprising both socio-economic and biophysical data evaluation, the emphasis of the study was to examine how local people perceived the
flooding in terms of its causal relations and impact assessment, and how these
perspectives related to a scientific analysis of the causes and effects of the flooding
event. Finally, we identified options for the mitigation/minimization of the risk of
future flood events, and also the prospects of these measures working.
The field study was conducted in the commune of Chieng Khoi, Son La province
in the north-west of Vietnam (Chap. 1, Fig. 1.1). The commune is located on a midlevel plateau at an altitude of 350 m.a.s.l., and is bounded by steep karstic mountains
to the south and by the valley of Yen Chau to the north. In this mountainous area,
subsistence-oriented agriculture systems dominate. The flat valley plateau is exclusively used for paddy rice (Oryza sativa) cultivation, accounting for a total rice crop
area of 60 ha. The peripheral upland fields on the steep hill slopes are mainly cropped
with cassava and maize. Many of the rice farming systems in Chieng Khoi include
fish ponds in which farmers raise fish to produce additional food and generate
income. The subtropical climate (see Sect. 3.2) entails a wet season which lasts
from April/May to September/October each year, and relatively dry, cold winters
which run from November to April. Regarding both land use and topography, the
structure of the Chieng Khoi watershed can be considered as being generally representative of the mountainous regions of northwest Vietnam (Anyusheva et al. 2012;
Lamers et al. 2011; Schad et al. 2012).
In general, paddy rice cultivation uses large quantities of water, and as a rule of
thumb, up to 5 m
3 of running water is required to produce 1 kg of paddy rice.
Taking into account the total rice crop area in Chieng Khoi commune, the entire
water demand over a typical paddy rice growing season amounts to approximately
1.0 million m
3 . In Chieng Khoi there are two rice crop seasons per year, a spring
season from February to June and a summer season from July to November. During
the summer crop season, irrigation water is only provided in order to supplement
rainfall, while during the spring crop season, most of the demand for water is
achieved through irrigation. In order to meet the high demand for water and
guarantee two rice crop seasons per year, a reservoir was built in Chieng Khoi
between 1962 and 1968, damming up a stream that originates in the nearby karstic
mountains. In the mid-1970s, this dam was heightened, yielding a reservoir which
covers a total area of 26 ha (Schad et al. 2012).
3 Written by Marc Lamers and Iven Schad.
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
121
Construction: Irrigation and Flood Risk Management
3
This section summarizes and reviews the key findings made from a field study we
conducted (Schad et al. 2012) in a mountainous watershed of north-west Vietnam.
The aim of the study was to explore and analyze the causes and impacts of an
exceptional flood event that occurred in 2007. Based on an interdisciplinary
research approach comprising both socio-economic and biophysical data evaluation, the emphasis of the study was to examine how local people perceived the
flooding in terms of its causal relations and impact assessment, and how these
perspectives related to a scientific analysis of the causes and effects of the flooding
event. Finally, we identified options for the mitigation/minimization of the risk of
future flood events, and also the prospects of these measures working.
The field study was conducted in the commune of Chieng Khoi, Son La province
in the north-west of Vietnam (Chap. 1, Fig. 1.1). The commune is located on a midlevel plateau at an altitude of 350 m.a.s.l., and is bounded by steep karstic mountains
to the south and by the valley of Yen Chau to the north. In this mountainous area,
subsistence-oriented agriculture systems dominate. The flat valley plateau is exclusively used for paddy rice (Oryza sativa) cultivation, accounting for a total rice crop
area of 60 ha. The peripheral upland fields on the steep hill slopes are mainly cropped
with cassava and maize. Many of the rice farming systems in Chieng Khoi include
fish ponds in which farmers raise fish to produce additional food and generate
income. The subtropical climate (see Sect. 3.2) entails a wet season which lasts
from April/May to September/October each year, and relatively dry, cold winters
which run from November to April. Regarding both land use and topography, the
structure of the Chieng Khoi watershed can be considered as being generally representative of the mountainous regions of northwest Vietnam (Anyusheva et al. 2012;
Lamers et al. 2011; Schad et al. 2012).
In general, paddy rice cultivation uses large quantities of water, and as a rule of
thumb, up to 5 m
3 of running water is required to produce 1 kg of paddy rice.
Taking into account the total rice crop area in Chieng Khoi commune, the entire
water demand over a typical paddy rice growing season amounts to approximately
1.0 million m
3 . In Chieng Khoi there are two rice crop seasons per year, a spring
season from February to June and a summer season from July to November. During
the summer crop season, irrigation water is only provided in order to supplement
rainfall, while during the spring crop season, most of the demand for water is
achieved through irrigation. In order to meet the high demand for water and
guarantee two rice crop seasons per year, a reservoir was built in Chieng Khoi
between 1962 and 1968, damming up a stream that originates in the nearby karstic
mountains. In the mid-1970s, this dam was heightened, yielding a reservoir which
covers a total area of 26 ha (Schad et al. 2012).
3 Written by Marc Lamers and Iven Schad.
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
121