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Glacial Flooding & Disaster Risk Management Knowledge Exchange and Field Training July 11-24, 2013 in Huaraz, Peru

Reducing Lake  Water  Level  in  Thorthormi  Glacial  Lake  in   Bhutan:  An  Adaptation  Project  to  the  Adverse  Impact  of   Climate  Change   Karma   Department  of  Geology  and  MinesBhutan   Introduction   Bhutan,  a  tiny  little  country  located  in  the  eastern  part  of  the  Himalayas  surrounded  by   China  in  the  north,  India  to  the  east,  west  and  south  (fig.1)  has  677  glaciers  and  more   than  2500  glacial  lakes  (ICIMOD  2001).  Out  of  2500  glacial  lakes  24  of  them  has  been   classified   as   potentially   dangerous   lakes   which   has   the   potential   of   outburs.   Later   in   2006,   Department   of   Geology   and   Mines   (DGM)   again   in   collaboration   with   ICIMOD   has   found   an   additional   lake   which   has   capacity   to   outburst   in   the   future,   thus   taking   the   number  of  potentially  dangerous  lake  to  25.  Subsequent  studies  carried  out  by  DGM  in   collaboration   with   the   scientists   from   University   of   Vienna,   Austria   and   Nagoya   University,   Japan   thereafter   in   Lunana   region   in   northern   part   of   the   country   (fig.1)   found   out   that   the   risk   of   GLOF   from   Thorthormi   lake   is   ever   increasing.   Accordingly,   during  the  formulation  of  first  National  Adaptation  Plan  of  Action  (NAPA)  in  Bhutan,  a   proposal   to   reduce   the   risk   of   GLOF   from   Thorthormi   Tso   was   proposed.   Considering   the  facts  based  on  the  results  of  intensive  scientific  investigations,  the  proposal  received   the  highest  priority  and  was  approved  for  funding  under  the  UNFCCC  funding  scheme.   The   project   had   three   main   components:   reducing   water   level   Thorthormi   lake,   installation   of   GLOF   Early   Warning   System   along   the   river   Pho   Chu   and   Public   Awareness.   The   first   component   was   implemented   by   Department   of   Geology   and   Mines,   second   by   the   Department   of   Hydromet   Services   and   the   third   component   by   Department  of  Disaster  Management  respectively.  As  the  main  implementing  agent  for   the   first   component,   this   paper   is   focussed   primarily   on   reducing   water   level   of   Thorthormi  Lake.  

Figure 1:  Location  map  of  Bhutan  and  Project  Site     Glacial  Lake  Outburst  history  in  Bhutan   Before  1950  there  are  no  information  on  any  incidences  of  GLOF  happenings  but  field   evidences  suggest  that  there  had  been  several  GLOF  incidences  in  different  river  basins.   Through   some   verbal   communication   with   the   elders   in   villages   there   were   cases   of   GLOFs   in   1957   along   Punakha-­‐Wangdue   valley   in   which   the   historical   Punakha   dzong   was   partially   damaged.   Again   in   1960   an   outburst   from   a   lake   in   eastern   lunana   damaged  the  same  historical  structure  partially.  There  were  cases  of  damages  by  flood   in   Punakha,   Thimphu   and   Paro   dzongkhags   in   1967.   The   most   recent   and   well   documented  GLOF  event  occurred  on  7th  October  1994  from  a  glacial  lake  called  Lugge   in  Lunana  region  along  Pho  chu  river  in  Punakha-­‐Wangdue  valley.  This  GLOF  has  caused   severe   damages   to   infrastructures   such   as   houses   and   bridges,   agricultural   land,   livestocks  and  17  human  lives  were  lost.   The  project   The  project  was  designed  for  four  years  with  four  working  seasons  (4  months)  per  year.   This  is  mainly  based  on  the  accessibility  in  the  project  site.  Thorthormi  Lake  is  located   in   Lunana   which   takes   9   walking   days   from   the   nearest   motorable   road   and   need   to   cross  three  high  passes,  the  highest  being  Gangla  Karchung  with  a  height  of  5220  masl.   Since   these   passes   will   not   be   accessible   till   April-­‐May,   the   working   season   was   proposed   from   June-­‐September   coinciding   with   the   peak   monsoon   season   which   makes   it  a  challenging  one.   The  objective  of  the  project  is  to  reduce  the  water  level  in  this  growing  Thorthormi  lake   by  5  m.  In  doing  so  approximately  17  million  cubic  meters  of  water  was  being  release   artificially   from   the   Lake   Thorthormi.   This   volume   is   almost   equivalent   to   the   1994   GLOF  which  was  18  million  cubic  meters  of  water.  

Identification of  risk  on  Thorthormi  Lake   Several  factors  were  considered  in  identifying  GLOF  risk  from  Thorthormi  glacial  lake.   The  following  are  some  of  the  main  factors  and  scenarios  considered:   a. Rapid  expansion  of  Thorthormi  supra  glacial  ponds  on  the  glacier  

Photo 1:  Recent  and  rapid   expansion  of  supra  glacial   ponds  on  Thorthormi  glacier  

Thorthormi   glacier   has   been   melting   at   an   accelerated   rate   since   1950s.   The   average   annual  rate  of  glacier  retreat  in  Bhutan  for  the  debris  covered  glacier  was  reported  as   high  as  30-­‐35  meters  per  year  (Ageta  et  al  2001).  Photo  1  shows  the  changing  surface  of   Thothormi  glacier  from  2008  to  2012  and  drastic  expansion  in  terms  of  surface  area  of   the  water  bodies  (lake)  can  be  observed.   b. Size  of  glacier  and  future  glacial  lake  

Photo  2:  Size  of  probable  future  lake  on  Thorthormi  glacier  

The above   satellite   image   shows   the   most   probable   size   of   lake   to   be   developed   on   Thorthormi   glacier.   If   whole   glacier   ice   melts   on   Thorthormi   glacier   a   lake   with   a   surface  area  of  3.42  square  kilomenter  will  be  formed.  During  a  bathymetric  survey  in   2008,   it   was   found   that   the   depth   of   supra   glacier   ponds   varies   from   23   m   to   76   m.   The   average  glacier  ice  thickness  was  found  to  be  about  150  m.   c. Weakened  moraine  wall  on  the  left  lateral  moraine  of  Thorthormi  glacier  

Photo  3:  weakened  left  lateral  moraine  of  Thorthormi  glacier  and  direction  of  1994  GLOF   (black  arrow)   During  the  1994  GLOF  from  Lugge  lake  located  in  the  upstream  of  Thorthormi  glacier,   the   left   lateral   moraine   of   Thorthormi   was   severely   damaged   due   to   erosion   on   the   outer  side  (photo  3,  marked  by  red  boundary).  Due  to  this,  the  left  lateral  moraine  wall   has   become   so   thin   that   at   some   point   on   the   moraine   crest   people   can   hardly   walk   across.  In  case  a  full  lake  develops  inside  this  moraine  by  melting  of  ice,  this  stretch  of   moraine  wall  may  not  be  able  to  stand  the  hydrostatic  pressure  of  the  water  in  the  lake.    

d. Seepage from  the  lake  

 Photo  4:  Seepages  from  Thorthormi  Lake   The   above   satellite   image   (photo   4)   shows   several   seepage   points   around   the   lake.   Atleast  there  are  4  seepage  points  which  are  confirmed  to  be  coming  out  from  the  lake.   e. Active  sliding  on  the  moraine  wall  separating  Thorthormi  and  Rapstreng   lake    

Photo  5:  Slide  on  both  sides  of  maraine  wall  between  Rapstreng  and  Thorthormi  lake   The   two   lakes   Rapstreng   and   Thorthormi   are   separated   by   a   complex   moraine   wall   formed   by   left   lateral   moraine   of   Rapstreng   and   right   lateral   moraine   of   Thorthormi   glacier.  As  the  wall  facing  both  the  lakes  have  high  gradient,  active  sliding  is  a  common  

phenomenon. This   sliding   activities   on   both   sides   as   shown   in   photo   5   is   resulting   in   thinning  of  this   moraine  barrier  between  the  two  lakes  which  ultimately  will  result  in   weakening  of  the  moraine  wall  surrounding  Thorthormi  lake.   f. Rock  and  snow  avalanches    

Photo  6:  snow  avalanche  from  the  accumulation  zone  of  Thorthormi  glacier   Due   to   high   slope   in   the   accumulation   zone   of   Thorthormi   glacier,   avalanches   which   take   place   frequently   can   directly   fall   into   the   lake   which   can   generate   a   surge   wave.   Apart   from   that   with   the   retreat   of   glacier   more   rock   faces   are   exposed   which   are   quite   fragile   (brittle)   and   result   in   mass   movement   and   impact   the   lake   directly   in   generating   surge  waves  from  the  lake.   g. Ice  cored  moraine  barrier  between  Rapstreng  and  Thorthormi  Lakes   The  moraine  barrier  between  Rapstreng  and  Thorthormi  lake  is  not  only  getting  thinner   due  to  mass  movement  but  as  per  the  result  of  the  resistivity  carried  along  this,  shows  a   presence  of  huge  ice  body  inside  at  a  depth  of  around  80  m  from  the  surface  (photo  7).   Now  considering  the  increasing  global  temperature,  the  ice  body  inside  the  moraine  has   a   high   chance   of   melting   faster   which   may   result   in   destabilizing   the   whole   moraine   wall.   This   can   again   result   in   weaken   of   the   moraine   wall   surrounding   the   future   Thorthormi  lake.      

Photo 7:  Result  of  the  resistivity  profile  along  the  moraine  barrier  between  Rapstreng  and   Thorthormi  lakes.   The  Risk   Considering  the  above  7  factors,  the  risk  in  the  present  context  is  shown  in  the  following   section  diagrammatically.  The  total  volume  estimated  in  this  scenario  is  53  million  cubic   meters  of  water  which  is  approximately  3  times  the  one  occurred  in  1994.  


X Thorthormi

Thorthormi Rapstreng



Failure of  moraine  barrier between   Rapstreng and Thorthormi

Over topping   of  water  from  Thorthormi lake  into  Rapstreng lake.  Water  level  in Thorthormi lake  is  higher   than  Rapstreng lake  by  74  m

Finally resulting  in  an  outburst  with   combination  of  water  from   Thorthormi &  Rapstreng.  Estimated volume  is  53  million  cubic  meter.

Need for  lake  mitigation  work    

Figure  2:  Settlement  map  of  Bhutan   Fig.   2   shows   settlement   pattern   of   Bhutan   and   it   can   be   seen   from   the   figure   that   major   settlements  are  all  along  major  river  basins.  Infact,  as  per  the  survey  it  is  said  that  about   70%  of  settlements  in  Bhutan  are  located  along  the  fertile  valley  bottoms  where  major   river   systems   run   through.   With   the   settlements   comes   the   developmental   activities.   Along   Puna   Tsang   Chu   basin   in   which   Thorthormi   Lake   drains,   there   are   number   of   mega  hydro  power  projects  coming  up  which  are  still  in  constructions  phases.  Beside,   Khuruthang   town   of   Punakha   district   is   located   right   on   the   bank   of   this   river.   Therefore,  the  mitigation  work  was  required  considering  the  following:   1. There   are   vast   areas   of   agricultural   land   with   number   of   settlements   located   close  to  the  river.   2. Many   developmental   activities   are   taking   place   along   this   river   including   construction  of  mega  hydro  power  plants.   3. Numerous  historical  monuments  are  located  on  the  low  lying  bank  of  this  river   such  has  Punakha  Dzong  (old  fortress)     Method  Adopted  to  lower  lake  water  level  in  Thorthormi  lake   Basically  three  methods  were  considered  for  lowering  water  level  in  Thorthormi  lake.   The  three  methods  are  

1. Construction of  spillway  channel  (through  the  natural  existing  outlet  channel)   2. Siphoning   3. Pumping   Considering   number   of   uncertainties,   workability   of   equipments,   environment   and   location   of   lake   Thorthormi,   transportation   of   heavy   equipments   for   9   days   on   foot,   siphoning  and  pumping  were  considered  not  feasible.  The  best  option  was  found  to  be   construction   of   spillway   channel   along   the   existing   outlet   channel   by   deepening   and   widening   the   existing   natural   outlet   channel.   The   width   of   the   finished   channel   was   designed  to  be  10m.  A  2%  bed  gradient  was  adopted  for  the  final  channel  bed  which  is   based  on  the  existing  channel  gradient.   Constraints   Implementing   such   a   huge   project   in   a   place   which   is   located   9   days   trek   from   the   nearest   motorable   road   head,   situated   at   an   altitude   of   about   4300   m   is   a   challenging   task.   Due   to   harsh   weather   conditions   and   high   working   environment   there   were   various   difficulties   faced   by   the   project   management   team.   The   following   are   some   of   the  main  problems  encountered  during  the  implementation  phase  of  the  project.   a. Unpredictable  weather  system   As   the   working   season   coincides   with   peak   monsoon   season   in   Bhutan,   weather   conditions   can   be   an   important   impeding   factor   for   the   project.   Most   of   the   time   the   workers   had   to   work   in   wet   condition   where   the   water   temperature   can   be   near   to   freezing  point.  Combining  this  with  torrential  down  pour  all  day  impacts  work  output  to   a   great   extent.   Not   only   the   excavation   work   at   the   site   is   affected   but   really   bad   weather  can  also  impact  the  transportation  of  rations  on  the  way  due  to  landslides  and   swelling  rivers  blocking  them  from  reaching  the  project  site  on  time.   b. Health  Issues  (medical  issues)   To  reach  the  project  site  the  workers  need  to  trek  for  9  days  crossing  high  passes.  This   makes   them   vulnerable   to   high   altitude   sickness.   Although   there   is   a   medical   team   to   cater   to   such   situation   but   due   to   accessibility   reason,   providing   medical   attention   to   those   needed   on   time   is   a   huge   challenge.   During   the   entire   four   years   of   the   project,   three   lives   were   lost   to   high   altitude   sickness.   Incase   of   emergencies,   evacuation   from   the   project   site   by   helicopter   was   a   big   problem   mainly   due   to   weather   condition   and   also  beauracratic  procedure  involved  in  arranging  the  helicopters.   c.  Transportation  of  materials   In  each  phase  of  the  project  approximately  60  MT  of  materials  including  rations  need  to   be   transported   at   the   site   by   horses   and   yaks.   The   whole   logistic   arrangement   for   the   transportation  of  such  quantity  of  material  on  yaks  and  horses  was  a  challenging  task.   d. Recruiting  and  managing  large  workforce  

In a  place  like  Lunana  which  is  located  in  a  remote  corner  of  Bhutan,  9  days  trek  from   any   place   with   modern   amnesties,   recruiting   and   managing   about   400   people   is   a   big   task.   First,   in   the   later   part   of   the   project   period   it   was   difficult   to   recruit   workers   despite  paying  about  4  times  the  normal  daily  wage  and  other  incentives  like  food  and   cloth.   Even   if   enough   work   forces   are   found,   taking   them   to   the   project   site   involves   number   of   life   threatening   risk   (on   the   way   due   to   mountain   sickness).   Once   they   are   at   the   project   site,   various   management   issues   comes   up   starting   from   maintaining   discipline  in  the  camp  and  relation  with  the  local  communities.  The  management  had  to   face   unnecessary   social   issues   from   a   simple   brawl   in   the   camp   to   serious   problems   with  the  locals.     Acknowledgement   I   would   like   to   acknowledge   the   support   I   and   my   other   colleagues   in   the   multidisciplinary  team  received  from  the  following  individuals,  organizations,  agencies   and  institutions  during  the  entire  project  period  including  the  opportunity  given  to  me   to  attend  the  workshop  in  Peru.   Firstly,  I  on  behalf  of  the  project  management  team  like  to  extend  my  gratitude  to  the   main   donor   of   the   project   which   is   UNFCCC/LDCF   and   other   co-­‐financers   such   as   Austrian  Government,  WWF,  UNDP  and  Royal  Government  of  Bhutan  for  their  generous   contribution  in  terms  of  budget  for  this  important  project.   Secondly,   I   would   like   to   thank   the   Royal   Bhutan   Army   for   their   kind   support   in   whatever   we   requested   from   them   especially   for   their   readiness   to   participate   in   the   last   phase   of   the   project   in   2012   when   the   project   management   had   huge   problem   in   recruiting  work  force.   Thirdly,  the  project  management  would  like  to  acknowledge  the  kind  support  received   from   Gasa   Dzongkhag   in   providing   the   logistic   support   especially   transportation   of   project   materials   using   horses   and   yaks.   More   importantly,   the   kind   support   and   cooperation  received  by  the  project  team  from  the  local  communities  including  the  gup   of  lay  and  lunana  are  also  highly  acknowledge.   Lastly,   our   sincere   gratitude   goes   to   UNDP   Bhutan   for   their   unfailing   support   throughout   the   project   including   the   opportunity   and   support   provided   to   Mr.   Karma,   Chief  Glaciologist  from  DGM  to  attend  an  important  workshop  in  Peru.    

Karma: Reducing lake water level in Thorthormi Glacial Lake in Bhutan  

Bhutan, a tiny little country located in the eastern part of the Himalayas surrounded by China in the north, India to the east, west and sou...

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