Chisolm: Assessing the risk of glacial lake outburst floods, Palcacocha Lake, Peru
1
(a) (b) (c) Avalanche Model Impulse Wave Model The RAMMS avalanche module (Bartelt, et al. 1999) was used to simulate avalanches into Lake Palcacocha from the Palcaraju Glacier for three different scenarios: small, medium and large events. The characterisHcs for the simulated avalanches and the results of the avalanche simulaHons are given in Table 1. Empirical equaHons are used to determine the iniHal characterisHcs of the avalancheLgenerated impulse wave according to the method outlined by Heller and Hager (2009). The avalanche characterisHcs presented in Table 1 are used as inputs to this empirical model along with the dimensions of the lake and the densiHes of the slide material and water (Table 2). Variable Value SHll water depth at slide impact 64 m Slide width 350 m Density of slide material 900 kg/m 3 Slide impact angle (α) 30˚ Table 2: Values of input variables in the impulse wave model gh The characterisHcs of the avalancheLgenerated impulse wave are determined as a funcHon of the impulse product parameter (P), which is based on the slide Froude number (F = slide velocity/ ), relaHve slide mass (M), and the relaHve slide thickness: P = FS 1 2 M 1 4 cos 6 7 α ( ) ! " # $ { } 1 2 The empirical impulse wave model produces characterisHcs for the iniHal impulse wave that can then be used as inputs to the hydrodynamic lake model. The iniHal impulse wave characterisHcs for each of the three scenarios are presented in Table 3. Avalanche Volume (m 3 ) Avalanche Thickness (m) Avalanche Velocity (m/s) Small Event 500,000 6 20 Medium Event 1,000,000 15 32 Large Event 3,000,000 20 50 Maximum Wave Height (m) Wavelength (m) Downstream distance to maximum wave heightG x m (m) Small Event 9 253 147 Medium Event 21 468 254 Large Event 42 793 392 Table 3: Results of impulse wave model for three scenarios. Table 1: CharacterisLcs of simulated avalanches at Lake Palcacocha for three scenarios. The avalanche thickness and velocity are given at the point of impact with Lake Palcacocha. Figure 4: ThreeGdimensional representaLon of the maximum height (leQ) and maximum velocity (right) for the large avalanche scenario Figure 3: Profiles of the maximum avalanche velocity for the small (a), medium (b) and large (c) event scenarios Research Objec,ves Study Area Figure 2: Loca,on of Lake Palcacocha in the Cordillera Blanca, Peru The overall goal of this research is to study the flood risk for communi7es living downstream from glacial lakes in the Cordillera Blanca, Peru. As these lakes con7nue to grow, they pose an increasing risk of catastrophic glacial lake outburst floods (GLOFs). For many decades Lake Palcacocha has posed a threat to ci7zens living in the watershed below and was the source of the deadly 1941 GLOF that nearly destroyed Huaraz. The most common GLOF triggers are avalanches or ice calving into the lake, which result in a large wave that is propagated across the lake, causing moraine overtopping. This work focuses on the upper part of the glacial watershed system, from the glacier to the terminal moraine damming the lake, but it is part of a broader effort to assess the GLOF risk from Lake Palcacocha. The results from this work will be used as input to a downstream GLOF and risk assessment model. A flow hydrograph for each scenario of moraineMovertopping events is produced through the following: • Run avalanche simula7ons for three scenarios • Determine ini7al characteris7cs of the avalancheMgenerated impulse waves • Model wave propaga7on and moraine overtopping with a hydrodynamic lake model Avalanche Simula7on Ini7al Impulse Wave Hydrodynamic Lake Model Moraine Breach Model Downstream GLOF Model Lake Palcacocha lies at the base of the Palcaraju Glacier and the head of the Paria River basin. Palcacocha contains approximately 17.3 million m 3 of water and has a maximum depth of 73 m. The average water surface eleva7on is 4562 m. The steep slope of the Palcaraju glacier directly above Lake Palcacocha and the small amount of freeboard make the lake suscep7ble to outburst flooding. There have been efforts to control the lake level using siphon tubing, and there is a permanent drainage pipe that maintains the current lake level. Figure 1: Schema,c diagram of the processes to be studied at Lake Palcacocha Peru Cordillera Blanca Lake Palcacocha Palcaraju Glacier Lake Palcacocha Terminal Moraine distance (m) distance (m) 250 500 750 1000 1250 1500 1750 2000 100 200 300 400 500 4560 4565 4570 4575 4580 distance (m) distance (m) 250 500 750 1000 1250 1500 1750 2000 100 200 300 400 500 4500 4550 4600 Loca%on of Slide Impact Terminal Moraine Hydrodynamic Lake Model Conclusions The Fine Resolu%on Environmental Hydrodynamics (FREHD), a descendent of the PC2 Matlab model (Hodges and Rueda 2008) is used to model the wave propaga%on across Lake Palcacocha and the overtopping of the moraine. The model is run at a 5 m grid resolu%on with square grid cells. The lake bathymetry data were taken from a bathymetric survey done by UGRH (2009). The model domain extends downstream of the terminal moraine to the point where the original terminal moraine was destroyed by the 1941 GLOF. The wave characteris%cs of the ini%al impulse wave for the medium event (Table 3) are reflected in the ini%al free surface eleva%on (Figure 6), and the FREHD model simulates the wave propaga%on from its ini%al posi%on. A threeYdimensional hydrodynamic lake model will allow for more accurate representa%on of an outburst flood event than has previously been possible. The work presented here will give a reasonable es%mate of the flow hydrograph and total volume for a moraineYovertopping event and will also give an idea of the response %me available aZer an avalanche occurs. AZer the ini%al moraineYovertopping, the moraine will likely begin to erode, allowing for complete lake drainage. This event will be modeled through a separate process, but the results of the hydrodynamic lake model will influence the modeling of the ensuing moraine breaching event. While the work presented here will provide the ini%al flow hydrograph for a GLOF event, it can also be used to determine the %me to begin applying the model of the moraine erosion and lake drainage to determine the subsequent flood hydrograph. The two hydrographs can then be combined to be used as inputs to the downstream GLOF model. The downstream communi%es that could be affected by a GLOF event are the mo%va%on for this research, and the ul%mate goal is to determine what effect a GLOF event may have on these communi%es. Because each process in the chain of events leading to a GLOF affects the end result, it is important to represent all the physical processes accurately. Improved representa%on of the upstream processes, such as the avalanche model, impulse wave model, and lake model presented here will be^er inform the models of downstream processes, such as moraine breaching, GLOF propaga%on downstream, and risk assessment for affected communi%es. Bo^om Eleva%on (m) Figure 5: Bathymetry data for Lake Palcacocha used in the hydrodynamic simula=on and terrain data for the downstream area located below the terminal moraine Figure 6: Free surface eleva=on of ini=al impulse wave for mediumCsized avalanche Water Surface Eleva%on (m) Assessing the Risk of Glacial Lake Outburst Floods in the Cordillera Blanca, Peru: A Case Study at Lake Palcacocha Rachel Chisolm, Daene McKinney, Marcelo Somos, Ben Hodges Center for Research in Water Resources The University of Texas at Austin: Department of Civil, Architectural and Environmental Engineering [email protected] , [email protected] References Bartelt, P., B. Salm, U. Gruber; 1999; Calculating dense-snow avalanche runout using aVoellmy- fluid model with active/passive longitudinal straining; Journal of Glaciology; vol. 45; no. 150; pp. 242-254. Heller, V., Hager, W. H., and Minor, H.-E; 2009; Landslide generated impulse waves in reservoirs—Basics and computation; VAW-Mitteilung; Vol. 211; R. Boes, ed.; ETH Zurich; Zurich. Hodges, B.R., and F.J. Rueda; 2008; Semi-implicit two-level predictor-corrector methods for non-linearly coupled, hydrostatic, barotropic/baroclinic flows; International Journal of Computational Fluid Dynamics; 22:9: 593-607. UGRH (2009). Unidad de Glaciologia y Recursos Hidricos, Autoridad Nacional de Agua (ANA) de Peru.
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Poster presented at the High Mountains Adaptation Partnership conference in Huaraz, Peru, July 2013.
Transcript of Chisolm: Assessing the risk of glacial lake outburst floods, Palcacocha Lake, Peru
(a)$ (b)$ (c)$
Avalanche)Model)
Impulse)Wave)Model)
The$RAMMS$avalanche$module$(Bartelt,$et$al.$1999)$was$used$to$simulate$avalanches$into$Lake$Palcacocha$from$the$Palcaraju$Glacier$for$three$different$scenarios:$small,$medium$and$large$events.$The$characterisHcs$for$the$simulated$avalanches$and$the$results$of$the$avalanche$simulaHons$are$given$in$Table$1.$$ $ $$
Empirical$equaHons$are$used$to$determine$the$iniHal$characterisHcs$of$the$avalancheLgenerated$impulse$wave$according$to$the$method$outlined$by$Heller$and$Hager$(2009).$The$avalanche$characterisHcs$presented$in$Table$1$are$used$as$inputs$to$this$empirical$model$along$with$the$dimensions$of$the$lake$and$the$densiHes$of$the$slide$material$and$water$(Table$2).$$$
Variable) Value)SHll$water$depth$at$slide$impact$ 64$m$Slide$width$ 350$m$Density$of$slide$material$ 900$kg/m3$
Slide$impact$angle$(α)$ 30˚$
Table)2:)Values)of)input)variables)in)the)impulse)wave)model)
gh
The$characterisHcs$of$the$avalancheLgenerated$impulse$wave$are$determined$as$a$funcHon$of$the$impulse$product$parameter$(P),$which$is$based$on$the$slide$Froude$number$(F$=$slide$velocity/$$$$$),$relaHve$slide$mass$(M),$and$the$relaHve$slide$thickness:$$
$$ P = FS12M
14 cos 6
7α( )!"
#${ }12
The$empirical$impulse$wave$model$produces$characterisHcs$for$the$iniHal$impulse$wave$that$can$then$be$used$as$inputs$to$the$hydrodynamic$lake$model.$$The$iniHal$impulse$wave$characterisHcs$for$each$of$the$three$scenarios$are$presented$in$Table$3.$$
)$Avalanche)Volume)(m3)$
Avalanche)Thickness)(m)$
Avalanche)Velocity)(m/s)$
Small$Event$ 500,000$ 6$ 20$Medium$Event$ 1,000,000$ 15$ 32$Large$Event$ 3,000,000$ 20$ 50$
)$Maximum)Wave)
Height)(m)) Wavelength)(m))Downstream)distance)to)
maximum)wave)heightG)xm)(m))Small$Event$ 9$ 253$ 147$
Medium$Event$ 21$ 468$ 254$Large$Event$ 42$ 793$ 392$
Table)3:)Results)of)impulse)wave)model)for)three)scenarios.)))
Table)1:)CharacterisLcs)of)simulated)avalanches)at)Lake)Palcacocha)for)three)scenarios.))The)avalanche)thickness)and)velocity)are)given)at)the)point)of)impact)with)Lake)Palcacocha.))
Figure)4:)ThreeGdimensional)representaLon)of)the)maximum)height)(leQ))and)maximum)velocity)(right))for)the)large)avalanche)scenario)
Figure)3:)Profiles)of)the)maximum)avalanche)velocity)for)the)small)(a),)medium)(b))and)large)(c))event)scenarios)
Research(Objec,ves(
Study(Area(
Figure(2:(Loca,on(of(Lake(Palcacocha(in(the(Cordillera(Blanca,(Peru(
The$overall$goal$of$this$research$is$to$study$the$flood$risk$for$communi7es$living$downstream$from$glacial$lakes$in$the$Cordillera$Blanca,$Peru.$As$these$lakes$con7nue$to$grow,$they$pose$an$increasing$risk$of$catastrophic$glacial$lake$outburst$floods$(GLOFs).$For$many$decades$Lake$Palcacocha$has$posed$a$threat$to$ci7zens$living$in$the$watershed$below$and$was$the$source$of$the$deadly$1941$GLOF$that$nearly$destroyed$Huaraz.$$
The$most$common$GLOF$triggers$are$avalanches$or$ice$calving$into$the$lake,$which$result$in$a$large$wave$that$is$propagated$across$the$lake,$causing$moraine$overtopping.$This$work$focuses$on$the$upper$part$of$the$glacial$watershed$system,$from$the$glacier$to$the$terminal$moraine$damming$the$lake,$but$it$is$part$of$a$broader$effort$to$assess$the$GLOF$risk$from$Lake$Palcacocha.$The$results$from$this$work$will$be$used$as$input$to$a$downstream$GLOF$and$risk$assessment$model.$$
A$flow$hydrograph$for$each$scenario$of$moraineMovertopping$events$is$produced$through$the$following:$$• Run$avalanche$simula7ons$for$three$scenarios$• Determine$ini7al$characteris7cs$of$the$avalancheMgenerated$impulse$waves$• Model$wave$propaga7on$and$moraine$overtopping$with$a$hydrodynamic$lake$model$
Avalanche$Simula7on$
Ini7al$Impulse$Wave$
Hydrodynamic$Lake$Model$
Moraine$Breach$Model$
Downstream$GLOF$Model$
Lake$Palcacocha$lies$at$the$base$of$the$Palcaraju$Glacier$and$the$head$of$the$Paria$River$basin.$$Palcacocha$contains$approximately$17.3$million$m3$of$water$and$has$a$maximum$depth$of$73$m.$The$average$water$surface$eleva7on$is$4562$m.$$The$steep$slope$of$the$Palcaraju$glacier$directly$above$Lake$Palcacocha$and$the$small$amount$of$freeboard$make$the$lake$suscep7ble$to$outburst$flooding.$There$have$been$efforts$to$control$the$lake$level$using$siphon$tubing,$and$there$is$a$permanent$drainage$pipe$that$maintains$the$current$lake$level.$$
Figure(1:(Schema,c(diagram(of(the(processes(to(be(studied(at(Lake(Palcacocha(
Peru$ Cordillera$Blanca$Lake$Palcacocha$
Palcaraju$Glacier$
Lake$Palcacocha$
Terminal$Moraine$
distance (m)
dist
ance
(m)
250 500 750 1000 1250 1500 1750 2000
100
200
300
400
500
4560
4565
4570
4575
4580
distance (m)
dist
ance
(m)
250 500 750 1000 1250 1500 1750 2000
100
200
300
400
500
4500
4550
4600
Loca%on'of'Slide'Impact'
Terminal'Moraine'
Hydrodynamic+Lake+Model+
Conclusions+
The'Fine'Resolu%on'Environmental'Hydrodynamics'(FREHD),'a'descendent'of'the'PC2'Matlab'model'(Hodges'and'Rueda'2008)'is'used'to'model'the'wave'propaga%on'across'Lake'Palcacocha'and'the'overtopping'of'the'moraine.'The'model'is'run'at'a'5'm'grid'resolu%on'with'square'grid'cells.'The'lake'bathymetry'data'were'taken'from'a'bathymetric'survey'done'by'UGRH'(2009).'The'model'domain'extends'downstream'of'the'terminal'moraine'to'the'point'where'the'original'terminal'moraine'was'destroyed'by'the'1941'GLOF.''
The'wave'characteris%cs'of'the'ini%al'impulse'wave'for'the'medium'event'(Table'3)'are'reflected'in'the'ini%al'free'surface'eleva%on'(Figure'6),'and'the'FREHD'model'simulates'the'wave'propaga%on'from'its'ini%al'posi%on.''
A'threeYdimensional'hydrodynamic'lake'model'will'allow'for'more'accurate'representa%on'of'an'outburst'flood'event'than'has'previously'been'possible.'The'work'presented'here'will'give'a'reasonable'es%mate'of'the'flow'hydrograph'and'total'volume'for'a'moraineYovertopping'event'and'will'also'give'an'idea'of'the'response'%me'available'aZer'an'avalanche'occurs.'AZer'the'ini%al'moraineYovertopping,'the'moraine'will'likely'begin'to'erode,'allowing'for'complete'lake'drainage.'This'event'will'be'modeled'through'a'separate'process,'but'the'results'of'the'hydrodynamic'lake'model'will'influence'the'modeling'of'the'ensuing'moraine'breaching'event.''While'the'work'presented'here'will'provide'the'ini%al'flow'hydrograph'for'a'GLOF'event,'it'can'also'be'used'to'determine'the'%me'to'begin'applying'the'model'of'the'moraine'erosion'and'lake'drainage'to'determine'the'subsequent'flood'hydrograph.'The'two'hydrographs'can'then'be'combined'to'be'used'as'inputs'to'the'downstream'GLOF'model.''''The'downstream'communi%es'that'could'be'affected'by'a'GLOF'event'are'the'mo%va%on'for'this'research,'and'the'ul%mate'goal'is'to'determine'what'effect'a'GLOF'event'may'have'on'these'communi%es.''Because'each'process'in'the'chain'of'events'leading'to'a'GLOF'affects'the'end'result,'it'is'important'to'represent'all'the'physical'processes'accurately.''Improved'representa%on'of'the'upstream'processes,'such'as'the'avalanche'model,'impulse'wave'model,'and'lake'model'presented'here'will'be^er'inform'the'models'of'downstream'processes,'such'as'moraine'breaching,'GLOF'propaga%on'downstream,'and'risk'assessment'for'affected'communi%es.''
Bo^om'Eleva%on'(m)'
Figure+5:+Bathymetry+data+for+Lake+Palcacocha+used+in+the+hydrodynamic+simula=on+and+terrain+data+for+the+downstream+area+located+below+the+terminal+moraine+
Figure+6:+Free+surface+eleva=on+of+ini=al+impulse+wave+for+mediumCsized+avalanche+
Water'Surface'Eleva%on'(m)'
Assessing the Risk of Glacial Lake Outburst Floods in the Cordillera Blanca, Peru: A Case Study at Lake PalcacochaRachel Chisolm, Daene McKinney, Marcelo Somos, Ben HodgesCenter for Research in Water Resources The University of Texas at Austin: Department of Civil, Architectural and Environmental [email protected], [email protected]
ReferencesBartelt, P., B. Salm, U. Gruber; 1999; Calculating dense-snow avalanche runout using aVoellmy- fluid model with active/passive longitudinal straining; Journal of Glaciology;
vol. 45; no. 150; pp. 242-254. Heller, V., Hager, W. H., and Minor, H.-E; 2009; Landslide generated impulse waves in reservoirs—Basics and computation; VAW-Mitteilung; Vol. 211; R. Boes, ed.; ETH
Zurich; Zurich.Hodges, B.R., and F.J. Rueda; 2008; Semi-implicit two-level predictor-corrector methods for non-linearly coupled, hydrostatic, barotropic/baroclinic flows; International Journal
of Computational Fluid Dynamics; 22:9: 593-607.UGRH (2009). Unidad de Glaciologia y Recursos Hidricos, Autoridad Nacional de Agua (ANA) de Peru.
