their traditional involvement in water management issues (Schad et al. 2012).
The main duties and responsibilities of the Lake Manager are manifold. He
regulates the discharge from the outlet of the lake, services and operates the
lake’s infrastructure, and continuously adapts the water management schemes
implemented in response to weather forecasts. The residents of the villages in
Chieng Khoi have to pay moderate fees directly to the Provincial Department for
using the irrigation water derived from the lake.
In 2007, the Chieng Khoi catchment was hit by an unprecedented and unforeseen
flood event, as in early October 2007, a tropical typhoon named Lekima made
landfall in Vietnam, triggering 3 days of heavy rainfall. On October 4th, the
typhoon caused a rainfall event in the Chieng Khoi region lasting 36 h, with
maximum intensities reaching 20 mm/h
À1 . It should be noted that the total amount
of rain that fell during the typhoon was 166 mm, equivalent to five times the
average monthly rainfall for October. During Lekima, most of the rainwater was
drained from the surrounding mountains into the reservoir through surface run-off,
since the soil had already been saturated due to previous rainfall. As a consequence,
the water level in the reservoir rose rapidly, reaching a rate of 2.5 cm/h. It is worth
noting that the Lake Manager had previously heightened the overspill during the
wet season of 2006 by piling sandbags on top in order to store extra water during the
next dry season. This action was triggered by the extraordinary dryness of 2006,
during which time the reservoir did not refill until the end of July (Fig. 3.6).
According to the Lake Manager, this activity was carried out after consultation
with both the Department of Dyke Management and the Provincial Department of
Irrigation (Schad et al. 2012). Unfortunately, 24 h after the onset of the typhoon, the
water level in the reservoir exceeded the critical level, causing the sandbags to be
flushed away and initiating an overflow. As a result of this overflow, stream
discharge increased sharply within a few hours, from less than 0.5 m
3 s
À1 to a
maximum of 45 m
3 s
À1 (Fig. 3.7).
This combination of environmental and man-made conditions caused one of the
most severe flood events within living memory in Chieng Khoi (Schad et al. 2012).
Figure 3.8 shows a paddy field located slightly below the dam at the onset of the wet
season and during the flood event of 2007. Shortly after the flooding occurred, an
Uplands Program team and some co-workers conducted a series of structured
interviews in Chieng Khoi, mainly discussing the economic consequences of the
event, local responses during the flood and people’s personal views on the factors
that had led to the flood (Schad et al. 2012).
Although the people we interviewed who owned a TV said they had heard about
the typhoon and the intensive rainfall in the daily weather forecast at least 1 day in
advance, the flooding itself took people by surprise, as most people underestimated
the severe weather alert. They told the team that due to the fact that diverse weather
is typical for northern Vietnam, they often do not expect the weather forecast to be
that precise, though they attributed the flood event to general weather changes that
had been observed in the area in terms of rainfall patterns and frequencies over the
previous decade (Schad et al. 2012).
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
123
The main duties and responsibilities of the Lake Manager are manifold. He
regulates the discharge from the outlet of the lake, services and operates the
lake’s infrastructure, and continuously adapts the water management schemes
implemented in response to weather forecasts. The residents of the villages in
Chieng Khoi have to pay moderate fees directly to the Provincial Department for
using the irrigation water derived from the lake.
In 2007, the Chieng Khoi catchment was hit by an unprecedented and unforeseen
flood event, as in early October 2007, a tropical typhoon named Lekima made
landfall in Vietnam, triggering 3 days of heavy rainfall. On October 4th, the
typhoon caused a rainfall event in the Chieng Khoi region lasting 36 h, with
maximum intensities reaching 20 mm/h
À1 . It should be noted that the total amount
of rain that fell during the typhoon was 166 mm, equivalent to five times the
average monthly rainfall for October. During Lekima, most of the rainwater was
drained from the surrounding mountains into the reservoir through surface run-off,
since the soil had already been saturated due to previous rainfall. As a consequence,
the water level in the reservoir rose rapidly, reaching a rate of 2.5 cm/h. It is worth
noting that the Lake Manager had previously heightened the overspill during the
wet season of 2006 by piling sandbags on top in order to store extra water during the
next dry season. This action was triggered by the extraordinary dryness of 2006,
during which time the reservoir did not refill until the end of July (Fig. 3.6).
According to the Lake Manager, this activity was carried out after consultation
with both the Department of Dyke Management and the Provincial Department of
Irrigation (Schad et al. 2012). Unfortunately, 24 h after the onset of the typhoon, the
water level in the reservoir exceeded the critical level, causing the sandbags to be
flushed away and initiating an overflow. As a result of this overflow, stream
discharge increased sharply within a few hours, from less than 0.5 m
3 s
À1 to a
maximum of 45 m
3 s
À1 (Fig. 3.7).
This combination of environmental and man-made conditions caused one of the
most severe flood events within living memory in Chieng Khoi (Schad et al. 2012).
Figure 3.8 shows a paddy field located slightly below the dam at the onset of the wet
season and during the flood event of 2007. Shortly after the flooding occurred, an
Uplands Program team and some co-workers conducted a series of structured
interviews in Chieng Khoi, mainly discussing the economic consequences of the
event, local responses during the flood and people’s personal views on the factors
that had led to the flood (Schad et al. 2012).
Although the people we interviewed who owned a TV said they had heard about
the typhoon and the intensive rainfall in the daily weather forecast at least 1 day in
advance, the flooding itself took people by surprise, as most people underestimated
the severe weather alert. They told the team that due to the fact that diverse weather
is typical for northern Vietnam, they often do not expect the weather forecast to be
that precise, though they attributed the flood event to general weather changes that
had been observed in the area in terms of rainfall patterns and frequencies over the
previous decade (Schad et al. 2012).
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
123