41

Scenario Analysis on Risks of Glacial Lake Outburst Floods on
the Mangde Chhu River, Bhutan
Toru KOIKE* and Shuhei TAKENAKA
Earth System Science Co., Ltd.,
1-23-1, Shinjuku, Shinjuku-ku, Tokyo 160-0022, Japan*e-mail: koike@ess-jpn.co.jp

Abstract
Three glacial lakes, Zanam B, Zanam C and Metatshota, upstream on the Mangde Chhu River, central
Bhutan, were selected to be studied as potentially hazardous in the generation glacial lake outburst floods(GLOFs). Disaster risks were analyzed by numerical simulation of a glacial lake outburst using the
NWS-BREACH model with the adjusted parameters for reproducing the event of the Lake Luggye outburst in
1994, considering the possible scenario of a moraine dam breach, followed by an analysis of consequent floodrisk occurrence using the FLO-2D model, hazard mapping of the flood inundation and risk identificationreflecting the vulnerability of communities and facilities in downstream areas.
The results showed that in the uppermost village along the Mangde Chhu River the peak discharge of a
GLOF would arise three hours after the outburst under a possible scenario of a breach of Lake Metatshota, andthe flood would affect some houses and farmland situated on the lower terrace plain. The calculated hydrograph shows the flood level sharply rising to the peak within tens of minutes so that residents could hardly
escape from the flood if they had taken no precautions. Community based disaster management, including
early warning and awareness raising, would therefore be effective for GLOF disaster risk mitigation.
Key words: Bhutan Himalayas, breach potential, flood analysis, GLOF, hazard map, Mangde Chhu

1. Introduction

2. Study Area

Unlike storm floods, GLOFs are virtually unpredictable events since it is difficult to monitor and detect any
precursory phenomena of bursting of moraine dams
which are located in high altitude remote areas. The
hazard of a GLOF is characterized by a rapidly risingflood wave in a short time, causing downstream disasters
without sufficient preparedness against the risks.
The most recent GLOF event in Bhutan occurred in
1994 in the Po Chhu River, assaulting the ancient capital
city of Punakha, 90 km downstream from the Luggye
glacial lake, and destroying buildings and claiming 21
lives in total. Despite this experience, many glacial lakes
in Bhutan remain uncertain in stability and probability ofgenerating GLOFs.
In this study, we estimated the breach potential of
glacial lakes in the Mangde Chhu River basin based on
geotechnical and hydrological approaches, and simulateda GLOF occurrence and its hydrograph. We also analyzed the disaster risks of GLOFs downstream, comparing them to the case of flooding from Cyclone Aila in2009 and identifying hazard areas reflecting the vulnerability of communities and facilities.

The Mangde Chhu River runs through central Bhutan,
from the Himalayan ridge-line in the north toward theIndian plain in the south, joining together with the adjacent Chamkhar Chhu River (Fig. 1a). The total basin area
is approximately 3,800 km2. Although most residential
areas are located on land highly elevated from theriverbed, there are two major villages, Bjizam andThingtibi, along the river. A national highway crosses theriver at both of these villages. A hydroelectric power
plant with 720 MW output is now under construction
27 km downstream of Bjizam village. Electric power is amajor export industry of Bhutan.
Cyclone Aila hit the country of Bhutan in May 2009,
bringing serious damage to various regions (Komori et al.
2010a). Most of the gauging stations in the country,
excluding the Tangza station in the high mountains,
recorded maximum water levels since observations
began according to the Hydo-Met Service Division,
Department of Energy of Bhutan. There are two gauging
stations along the Mangde Chhu River at Bjizam andThingtibi. The Bjizam station was destroyed by the heavy
flooding from Aila, whereas the Thingtibi station
recorded 2,243 m3/s in maximum discharge, approx-

Global Environmental Research
16/2012: 41-49
printed in Japan©2012 AIRIES

42

T. KOIKE and S. TAKENAKA

imately corresponding to the 30-year probable flood at
the station (JICA, 2000). A large amount of debris was
supplied from a tributary at a point near the site of thehydroelectric power plant during Cyclone Aila, dammingup the main channel of the Mangde Chhu River andwashing out a part of the national highway.

3. Breach Model
3.1 Target lakes
There are three main tributaries upstream on the
Mangde Chhu River, viz. the main stream of the Mangde
Chhu, the Sacha Chhu River and the Tampe Chhu River(Fig. 1b). There are 127 glacial lakes of more than
0.1 km2 in surface area distributed in the basins. Lake

Metatshota in the Tamape Chhu sub-basin is the largest,with a surface area of 1,23 km2, comparable to Lake
Luggye (1.34 km2 currently). It is followed by Lake
Zanam D (0.88 km2), Lake Zanam B (0.86 km2) and Lake
Zanam A (0.51 km2), which are all located in the Sacha
Chhu sub-basin (Fig. 2).
According to bathymetric surveys by Komori et al.
(2010b), lakes Zanam A and D have a typical shelving
bathymetry, and the physical breach potential of themoraine dam seems to be infinitely low. In this study,
therefore, we refined the target into the two lakes ofMetatshota and Zanam B. Additionally we targeted Lake
Zanam C, which is rather small but was predicted to havethe highest potential due to the steep slope of the moraine
dam in our preliminary study.

Fig. 1 Location of study area.
(a) Overview of the Mangde Chhu River basin and villages to be protected. TR: Trongsa, ZM: Zhemgang,
GY: Gyelephu, JK: Jakhar town. The red square frames the area shown in b. (b) Locations of glacial lakes
upstream in the Mangde Chhu River basin (blue: glacial lakes, red: target lakes in this study)

Fig. 2 Surface areas of glacial lakes upstream in the Mangde
Chhu River basin.

Fig. 3 Concept of the NWS-BREACH model(revised from Fread, 1988).

Scenario Analysis on Risks of Glacial Lake Outburst Floods on the Mangde Chhu River, Bhutan

3.2 Method
In this study, the NWS-BREACH model (Fread,1988) mounted in the FLO-2D model (O’Brien, 2009)
with some modification was employed to examine thebreach potentials and hydrographs of the target lakes.
The NWS-BREACH model, which has often beenutilized in previous studies (e.g., Bajracharya B. et al.
2007; Wang X. et al. 2008), simulates the channel-bed
erosion process of the dam outlet using a sedimenttransportation equation, as well as the horizontal widening process of the breach channel using a slope stability
equation (Fig. 3).
The erosion rate of a channel-bed is mainly dependent
on the flow discharge running through the channel. In thecase that the flow discharge is small and the erosion rateis slow, the lake water level is gradually lowered according to the eroding crest height, where no catastrophic
breach phenomenon is generated. If the erosion rate isfaster, on the contrary, the lake water level cannot follow
the lowering crest height, and the outlet discharge will
increase due to the expansion of the channel. The increased flow will lead to further erosion of the channel
and eventually it is going to breach.
An overtopping breach is thought to occur as theresult of a sudden increased flow due to any impulsive
wave, which may be triggered by an ice avalanche and/or
slope mass failure in and around the lake. The magnitudeof the impulsive wave and resulting increased flow may
fluctuate greatly. In this study, we assume some kind of“constant inflow” pouring in from upstream of the lakes,
estimate the breach potential for each inflow and simulate the hydrograph for each specific condition.
Considering the heterogeneity of the constituent
materials in the moraine dam, it may not be appropriate
to apply soil parameters obtained from a piece of themoraine dam to the breach model. In this study, we
determine the necessary parameters by case analysis of amoraine dam that had an outburst in the past, reproducing
the observed inflow and discharge during the breach
event. The parameters are then applied to the target
moraine dams. It should therefore be noted that theobtained breach scenario and discharge of the target
moraine dams are relative consequents compared to thereproduced outburst moraine dam.
The GLOF in 1994, generated by an outburst of Lake
Luggye in the Po Chhu River basin, is the only such an
event physically recorded from a phenomenal andhydrological viewpoint. In contrast to the Po Chhu Riverbasin, no recorded GLOF event in the Mangde Chhu
River basin has been reported in previous studies. In thisstudy, therefore, we reproduced the outburst event of
Lake Luggye in 1994 by adjusting the soil parameters ofthe moraine dam, and then applied the obtained
parameters to the moraine dams of our target glacial lakes
in the Mangde Chhu River basin.
3.3 Parameter generalization from the 1994 GLOF
from Lake Luggye
In 1994 a GLOF with a total flood volume of43

18 million m3 was measured at the Wangdue Rapid
gauging station, 100 km downstream of Lake Luggye(Leber et al., 2000). Several previous studies have tried
to estimate the breach hydrograph of the Lake Luggye
outburst by reproducing the event using models. They
reported the peak discharge as approximately 1,800 2,500 m3/s (e.g., JICA, 2001). Yamada et al. (2004)
measured the outlet discharge of Lake Luggye as 2.5 5.0 m3/s during the period of September - October, 2000
which corresponds to the 1994 GLOF event (7 October1994). Since no rainfall was reported at the time of the
GLOF, the same amount of constant flow discharge could
have been streaming. Although the direct trigger of the1994 GLOF is unknown, the moraine dam was deemed to
be at a critical level for breaching under a constant flowof 5.0 m3/s. Accordingly, we arranged the parameters ofthe moraine dam so that it didn’t breach under flows lessthan 5.0 m3/s, but it breached when the outlet constantflow exceeded 5.0 m3/s resulting in about 18 million m3
in total flood volume and 1,800 - 2,500 m3/s in peak discharge.
The original profile of the moraine dam of Lake
Luggye was duplicated from an adjacent moraine figureusing ALOS/PRISM DSM (Fig. 4a) showing slopes of
1/1.5 on both sides of the moraine dam and 28 m of crest
width. The basic soil characteristics such as grain size
and unit weight measured at our target lakes are almost
identical to those from Lake Imja in Nepal (Umemura &Dangol, 2000). Thus, we basically employed the same
soil constants, but adjusted Manning’s N to reproduce the1994 Luggye outburst well, satisfying the above conditions.
As a result of the trial commutations, the Luggye
moraine started to breach under the soil parameters
shown in Table 1, with 17.0 million m3 in total volume
and 2,200 m3/s in peak discharge released over the
5.0 m3/s inflow/outflow discharge (Fig. 5). Accordingly,
we generalized these parameters and applied them to ourtarget moraines in the Mangde Chhu River basin as
follows.
3.4 Breach potentials & hydrographs
3.4.1 Lake Zanam B
Lake Zanam B has the third largest surface area,
0.85 km2, among lakes in the Mangde Chhu River basin.
According to a bathymetric survey by Komori et al.
(2010b), the lake is divided into two sub-basins as shownin Fig. 4b. The maximum depth of the rear basin isapproximately 100 m and the one of frontal basin is 15 m.
However, due to the threshold between two basins, which
is at 7 m depth, the maximum possible runoff must be
limited. The upstream and downstream slopes of themoraine dam are 1/6.0 and 1/8.5 respectively, and thecrest width is 20 m as shown in Fig. 4b.
The results of our computation (Fig. 6) show theactual runoff by a breach would be 2.0 million m3 of thetotal reservoir capacity of 28 million m3. The breach peakdischarge, excluding the constant inflow from upstream
would only be 170 m3/s. When the constant inflow was44

T. KOIKE and S. TAKENAKA

Fig. 4 Topographical features and profiles of the target lakes, compiled from ALOS/PRISM DSM and bathymetric surveys by
Komori et al. (2010b). (a): Lake Luggye, (b): Lake Zanam B, (c): Lake Zanam C, (d): Lake Metatshota.

3

Discharge (m /s)

Table 1 Soil parameters for the breach model of the 1994 Luggye
outburst.

Time (hr)Fig. 5 Breach hydrographs of the reproduced Lake Luggye
outburst.

45

3

3

Discharge (m /s)

Discharge (m /s)

Scenario Analysis on Risks of Glacial Lake Outburst Floods on the Mangde Chhu River, Bhutan

Time (hr)Time (hr)3Discharge (m /s)

3

Discharge (m /s)

Fig. 6 Simulated breach hydrographs from Lake Zanam B.

Time (hr)Time (hr)Fig. 7 Simulated breach hydrographs from Lake Zanam C.

less than 40 m3/s, no breach was observed. As the catchment area of Lake Zanam B is about one-fourth that ofLake Luggye, the regular outlet discharge can be expected to be less than 5 m3/s even in the monsoon season.
Consequently, it can be concluded that the breach potential of Lake Zanam B is relatively lower than that of Lake
Luggye, but it may breach if the outlet discharge is temporarily increased over 40 m3/s due to an ice avalanche orslope mass failure into the reservoir. Indeed, the lake has
several hanging glaciers and steep cliffs behind it.
3.4.2 Lake Zanam C
Lake Zanam C is elevated about 200 m above themain stream of the Sacha Chhu River (Fig. 4c). Becauseof the steeply sloping moraine dam with less vegetation,
it seems to have a high potential topographically forbreaching. Similarly to Lake Zanam B, however, the lake
is composed of two sub-basins, a frontal basin of 10 m
depth and rear basin of 28 m depth as shown in Fig. 4c.
According to a geophysical exploration by Ohashi et al.
(2012) in this issue, the actual thickness of the moraine
dam was estimated at only 20 m of the total height of
200 m, and deeper than that it seems to be base-rock. The
topographic profile of the moraine was set as in Fig. 4c,based on a bathymetric survey and ALOS/PRISM DSM.
In this geometric condition, the outlet discharge wascomputed under constant inflows which were varied
from 30 to 70 m3/s. The results showed a breach to startwhen the constant inflow exceeded 40 m3/s, the same as

Fig. 8 Simulated breach hydrographs from Lake Metatshota,
using moraine features of (a): the original moraine, (b):a modified moraine (crest width: 0 m, downslope: 10
degrees).

at Lake Zanam B. The total runoff and peak discharge
were 0.9 million m3 and 140 m3/s respectively (Fig. 7). It
can be said that the flood magnitude of both of the twolakes, Zaman C and B, under this assumption would bemuch smaller than the case of the Lake Luggye breach,and they may not affect the downstream area.
3.4.3 Lake Metatshota
Lake Metatshota has the largest surface area of any
lake in the Mangde Chhu River basin and has a numberof hanging glaciers on the cliff behind it, which could
trigger a GLOF. The total reservoir capacity is estimatedat 41 million m3. The deepest part of the lake reaches
120 m depth, but the frontal basin near the outlet is lessthan 40 m depth. The moraine dam near the outlet has
been deeply eroded so the actual height of the dam crest
from the frontal plain is only 25 m as shown in Fig. 4d.
The downstream slope of the moraine dam is as gentle as
1/12 and the crest width is 110 m.
Figure 8a shows the calculated hydrographs at 1.7 km
downstream of the outlet. Under this geometric conditionof the moraine dam, no breach event could be generated
for any amount of inflow up to 5,000 m3/s. Due to thegentle downstream slope and the large crest width of themoraine dam, the erosion rate of the outlet channel was
small enough to sustain itself, so that the lake water level
could follow, corresponding to a lowering crest height,
and not lead to a rapid increment of discharge. Consequently, the breach potential of Lake Metatshota is defi-

46

T. KOIKE and S. TAKENAKA

nitely low at the moment.
However, the existence of such a huge natural reservoir upstream still remains a threat for the residents settled in the downstream area. In consideration of futuredestabilization due to continuous erosion of the moraine
dam, we repeated the calculation assuming that the crest
width is going to be reduced by recession of the downstream slope of the moraine. Figure 8b shows ourrecalculated hydrographs at various inflows, with theconditions of 0 m crest width and 10 degrees of downslope. When the inflow exceeded 50 m3/s, the moraine
dam drastically started to breach with a total runoff
volume of 20.5 million m3 and peak discharge of
2,750 m3/s, which are comparable with the 1994 GLOF
from Lake Luggye. In the flood analysis which follows,
we regard this breach hydrograph as a probable largescale scenario of a GLOF in the Mangde Chhu Riverbasin.

4. Flood Analysis
4.1 Flood routing
Given the probable large-scale scenario of a GLOF
generated by the breaching of Lake Metatshota, we conducted a flood analysis using the FLO-2D model to pre-dict the flood’s arrival time and hydrograph downstream.
The FLO-2D, which is a flood routing model using
dynamic wave approximation, computes a one dimensional unsteady flow along the river channel and a twodimensional overbank/floodplain flow when the channel
capacity is exceeded. An interface routine calculates theexchange between the channel flow and floodplain flow
based on the computational grid’s elevation at the riverbanks (O’Brien, 2009).
The channel cross-sections were extracted from
ALOS/PRISM DSM at 1 km intervals, and were interpolated by 100 m computational grids. A two-year
probable flood (nearly equal to the average of the yearlymaximum flood) measured at two gauging stations at
Bjizam and Thingtibi, was applied for the base flow.
Likewise, the lateral inflows into the main river channel
were estimated by specific discharges based on the
two-year probable flood.
Figure 9 shows the resulting hydrographs at eachlocation along the Mangde Chhu River. The peakdischarge generated from the outburst of Lake Metathota
quickly decays from 2,700 m3/s to 2,000 m3/s before
reaching Bjizam village, 62 km downstream. However
it maintains a peak flow of approximately 1,800 2,000 m3/s due to the lateral inflows from tributaries. The

3

Discharge (m /s)

Fig. 9 Calculated hydrographs at areas to be protected along the Mangde
Chhu River.

Fig. 10 Hydrological profiles along the Mangde Chhu River(gray area: supercritical flow zone).

Scenario Analysis on Risks of Glacial Lake Outburst Floods on the Mangde Chhu River, Bhutan

times it takes the flood to reach areas to be protected arethree hours at Bjizam village, four hours at the site of
the hydroelectric power plant and about six hours atThingtibi village, 123 km downstream from the source of
the GLOF. The average flood velocity from Lake
Metatshota to Bjizam is calculated as 5.7 m/s, which isfaster than the 4.4 m/s of the Po Chu River estimation
based on Meyer et al. (2006). This may be due to thesteep riverbed gradient of the Mangde Chhu River (1/20)
compared to the Po Chhu River (1/28).
Figure 10 shows calculated hydrological profiles of
the GLOF’s peak discharge (blue dotted line), base flow
(blue dash-dot line) and the total peak discharge (bluesolid line). The GLOF, generated at Lake Metatshota,
starts the torrent in the tributary with a peak flow of
2,750 m3/s and continues to run for 30 km without thepeak flow receding until it reaches the confluence with
the Mangde Chhu main stream. The flood then decays
rapidly to 1,500 m3/s until a point 70 km downstream
from the Lake. It keeps running with a relatively stablepeak flow until the point near the power plant site 90 km
downstream. The flood’s peak flow again decays gradually as it continues further downstream. At Thingtibi, thepeak of the GLOF and the total peak discharge are
estimated at 1,000 m3/s and 1,750 m3/s, respectively.
The riverbed profile of the Mangde Chhu River has
two discontinuous steep gradient sections, upstream andin the middle stretch, the same as the other main rivers in
Bhutan (Motegi, 1998). Reflecting this character of theriverbed profile, there are two supercritical flow zones, at
0-36 km and 70-80 km, according to our analysis results(grey-colored area in Fig. 10), which almost correspondto the discharge profile sections where the flood peakdischarge has not attenuated. Accordingly, it has been
proven that the flood discharge keeps its high peak in the
supercritical flow zone in the river, whereas it rapidly
decays in subcritical flow zone.
4.2 Disaster risk analysis
GLOF inundation maps in Bjizam and Thingtibi villages were prepared based on the hydrograph assuming
the probable large-scale scenario of a Lake Metatsota

47

outburst (Fig. 11). The computational grid size is 5 m for
Bjizam and 10 m for Thingtibi, which were generated
from ALOS/PRISM DSM with modifications of riverprofiles using cross-sections at the gauging stations andbridge design specifications.
Bjizam village is located on an alluvial fan deposit
from a tributary. There are at least two terrace plains. The
higher terrace plain, where Bjizam Primary School issituated, is at 10 to 12 m relative height above theriverbed. The lower terrace plain is 6 to 8 m above thebed. The computed results show that the peak water level
would reach the lower terrace plain within tens ofminutes, and several houses with more than ten residents
would be directly affected by the flood. The primaryschool is not at risk from the assumed GLOF inundation.
The Bjizam Bridge across the Mangde Chhu River,which is designed for high water levels comparable to3,200 m3/s, would be safe in the assumed flood.
The main village of Thingtibi lies on a higher terrace
plain, over 50 m above the riverbed, so it would not beaffected by the assumed GLOF under the estimated peakdischarge of 1,750 m3/s at this point. However the farmland around Takabi settlement, located 800 m northwestof Thingtibi village, on the lowest terrace plain would be
affected. This settlement experienced flood inundation asa result of Cyclone Aila in 2009 (Takenaka, 2012, in thisissue), with a recorded discharge of 2,243 m3/s.

5. Discussion
Figure 12 elucidates the differences between the peakdischarge profiles of a storm flood (Cyclone Aila in 2009
and 100-years probable flood) and the GLOF estimatedin this study. In a storm flood, the peak discharge
increases accordingly from upstream toward downstream
by merging with lateral inflows from tributaries. In contrast, a GLOF event produces a huge discharge at thebreaching point, most upstream, and gradually decays
toward downstream. In a GLOF event, considering its
nature of only rare occurrence, the rapidly rising discharge flows down, involving a huge amount of drift
trees uprooted from the river bank slope, especially from

Fig. 11 Flood depth at Bjizam village (left) and Thingtibi village (right) in a provable large-scale scenario of a GLOF.

48

T. KOIKE and S. TAKENAKA

Distance from Lake Metatshota (km)Fig. 12 Peak discharge profiles of storm floods and GLOFs.

upstream, where a storm flood discharge is comparatively smaller than that of a GLOF.
These differences between storm floods and GLOFs
suggest that the GLOF risk is higher upstream, whereas
the storm flood risk is comparatively higher downstream.
Assuming a 100-year probable flood in the Mangde Chhu
River, for example, the level of inundation risks of a
GLOF and a storm flood may be equivalent around thesite of the hydroelectric power plant, as shown in Fig. 12.
It is helpful for understanding GLOF risk to compare
their hydrographic characteristics with those of storm
floods. The observed hydrograph of the GLOF in 1994 at
the Wangdue Rapid gauging station on the Po Chhu River,as well as the simulated hydrograph of a probablelarge-scale scenario of a GLOF at the Thingtibi station on
the Mangde Chhu River, are both comparatively smaller
in peak discharge and total flow than those observed
during the storm flood of Cyclone Aila in 2009 (Fig. 13).
The rate of rise of an approaching GLOF’s water level,
however, is much higher than that of a storm flood. The
maximum flood rising rates of GLOFs, for example, are2.55m and 3.55m in 30 minutes on the Po Chhu Riverand the Mangde Chhu River, respectively.
Unlike a storm flood, the sudden rising of the GLOF
water, in addition to the condition of no precursor
phenomena, makes it difficult for people to quickly andsafely evacuate themselves, even if they notice the risingwater and start to take action. In fact, most of the
21 victims of the 1994 GLOF in the Pusaka district weresaid to have been killed by sudden hydraulic assault, eventhough their settlement area along the riverbank was justbeside a safe place, according to the administrative
officers of the district. This means that some early warning measures could mitigate GLOF disaster risks.

6. Conclusion
Breach potentials and hydrographic characteristics
were studied targeting glacial lakes in the Mangde Chhu
River basin. To simulate breach scenarios of hetero-Fig. 13 Comparison between a GLOF and cyclone Aila
observed at (a) the Wangdue Rapid station downstream
on the Po Chhu River, and (b) the Thingtibi station on
the Mangde Chhu River, compiled from HMSD (2009).

geneous moraine material, the soil parameters weregeneralized, reproducing the Lake Luggye outburst in
1994, and applied to glacial lakes in the Mangde Chhu
River basin. From the results, we concluded that: (1) the
breach potentials of the target lakes are relatively lower
than that of Lake Luggye, (2) Lake Zanam B and C havea possibility of breaching assuming an ice avalanche
and/or slope mass failure into the lake, (3) the breachpotential of Lake Metatshota, the largest glacial lake inScenario Analysis on Risks of Glacial Lake Outburst Floods on the Mangde Chhu River, Bhutan

the basin, is low because of its wide crest and the gentle
slope of moraine dam, and (4) a possible breach scenario
of Lake Metatshota considering future destabilizationshows a flood volume of 20.5 million m3, which iscomparable to that of the 1994 GLOF from Lake Luggye.
In terms of disaster risks downstream, under theassumption of Lake Metatshota breaching, the destructive GLOF would arrive in Bjizam village, affecting
several houses and some farmland situated on the lower
terrace plain. Since the GLOF water level would rise very
quickly and there would be no precursor phenomenon,
people in the affected areas could not safely evacuate
themselves. Some early warning measures could be
effective at mitigating GLOF disaster risks.

Acknowledgements
This study was implemented as a part of the “Study on
Glacial Lake Outburst Floods in the Bhutan Himalayas”
under the Science and Technology Research Partnershipfor Sustainable Development (SATREPS) supported by
the Japan Science and Technology Agency (JST) and theJapan International Cooperation Agency (JICA). We are
deeply grateful to Department of Geology & Mines andDepartment of Energy, Royal Government of Bhutan forsupporting and providing valuable data for our study. We
greatly appreciate the constructive and valuable review
from Dr. Hitoshi Baba, JICA Senior Adviser. We also
thank Prof. Shuji Iwata for giving us the opportunity tojoin this project and for his warm encouragement.
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Toru KOIKE
Toru KOIKE is a Deputy General Manager of theEnvironmental & Disaster Management Department at Earth System Science Co., Ltd. He has
been working in the field of disaster management,
including geological and river engineering under
Official Development Assistance funding fromthe Japanese government. During 2000-2002, he lived in Bhutan andworked for the Department of Geology & Mines. Currently he is working
in disaster related projects in Thailand, Vietnam, Bhutan, Bolivia andCaribbean countries.

Shuhei TAKENAKA
Shuhei TAKENAKA is dedicated staff of Earth
System Science Co., Ltd., for the JICA/JST
Bhutan GLOFs project. Although he got his
M.Sc. in Glaciology from Nagoya University 30
years ago, prior to joining the project, he worked
as a manager at an electronic device company.
Some five years ago, he decided to return from “cyber space” to “the realworld” looking for a chance to perform field work and more directly
contribute to the human community. On Himalayan trails, he feels happy
with his decision despite the aches in his back and knees. In addition to
glaciers, he is interested in how local communities in remote areas arebeing changed by modern technologies like TVs and cell phones.

(Received 15 November 2011, Accepted 13 February 2012)