CD-ROM Volume @

Proceedings of the 9th International Conference on

HYDROINFOR TICS 2oJo edited by Jianhua Tao

. Qiuwen Chen . Shie-Yui Liang

@ Chemical Industry Press

IV

Development of Real-Time Flood Forecasting Method in Urban Drainage Areas 1802 Makoto Kimura, Yoshinobu Kido, Eiichi Nakakita

Use of Artificial Neural Network in Quantitative Rainfall Prediction for Flood

Forecast in Central Vietnam Do Hoai Nam, Keiko Udo, Akira Mano

Freshwater Ice Fixed-Point Ice Thickness Measurement Sensor and Its System

Based on Electric Field Sensor Yinke Dou, Xuechun Li

Using UML Models for Flood Disaster Management System Designfocus on 3D

1811

1819

Spatial Information Dissemination 1825 Xuan Zhu, Arthur E. Mynett

Evaluation of Real-Time Flood Forecasting over the Huaihe River Basin of China for

the Flooding Seasons of2005-2009 1833 Zhiyong Wu, Guihua Lu, Lei Wen , Charles A. Lin

Sustainable Water Integrated Management (Swim) for South-To-North Water Transfer Project 1841 Augusto Pretner, Gan Hong

A Forecasting System for Storm Surge and Flood Inundation in Low-Lying Coastal Zone 1849 Jung Lyul Lee, Joo-Yong Lee, Kun-Young Park

Modelling of Most Adaptive Early Warning System Against Dam Failure Applying

Geo-Hydrotechnical Approach 1856 D. Legono, T. Faisal Fathani, A. Pamudji Rahardjo, 1. Prabowo, M Fujita

An Flooding Warning System Framework Study Based on the Online Model 1864 Yuwen Zhou, Lei Wang

The Early Warning and Secondary Disaster Mitigation of Urban Water Distribution

Network Leakage and Pipe Burst Liguo Sun, Yuwen Zhou

3-D Visualization ofFload Routing Caused by Barrier Lake Breach Yuntao Ye, Yunzhong Jiang, Lili Liang

Comprehensive Analysis of the Regional Drought in Haihe Basin Guixia Yan, Guihua Lu, Zhiyong Wu

An Analysis of the 500-Hpa Height Signal Fields for Heavy Rainfall over the

Huaihe River Basin During Flood Season Jian He, Guihua Lu, JiayouHuang, Yang Yang

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gil> International Conference on Hydroinformatics HIC 2010, Tianjin, CHINA

MODELLING OF MOST ADAPTIVE EARLY WARNING SYSTEM AGAINST DAM FAILURE APPLYING

GEO-HYDROTECIlNICAL APPROACH

O. LEGONO, 1'. FA ISAL FATI-I ANl, A. PAMUDJI RAHARDJO Civil & Em'immmmral Eng. Department, Unil'ersillls Gadjall Mac/a

),ogyakarta. 551281, Illc/ollesia

I. PRABOWO {'hJ'.\"ics Depa/'{melll. Ulli\'er~'il(L~ G(ldja/t Mac/a

I'ogyakar/a, 5.'i128I,llIdOlle.~i(/

M. FUJITA

RC'.~l>(lrdl CClller/or F!I/I'jal (/Ild Coastal Disaster. DPR). Kyoto Unil'ersilY

}.:yolo. Japall

T he dam development requires su Oieicllt I;]~· tor of safet), against failure. where in ~rnc

cxh:nl, tl\er1opping condition is tll la lly 1I0t "upposed 10 take pl ace al any :.ituati(Jn . A

eUIl:\u.krably high au ... ntioll should be p.tid not onl} durlllg the :'Uf'\ey, irl\c:.tlgation, and

~'I)l1'tntctlon, but abo \\ilhin lhe p ... riod of operation and Illaintcnance. The IndOIll'sian

nc\\ w,tem of deel'ntr..lli/~lIion apparently needs to be antH:lpatcd In su ... h a way that the dam management i!'> s imple but meets lhe optimum bcndki;IT),. O'IC hand. optimum

hl:llcliclaT) ml'ans economically feas ibk III the other hand. means aecept .. blc.

Accountabi lity of the dam management i!'> therefore need 10 be m:ldc a\ailablc. and till'

t·untiml{lIL:. c\aluation necd to be carried OUI thoroughly. This paper cvahtatcs the

catilstrllphic diSilst

1857

Gintung (irrigation gates, spi llway structures, spi ll way gates, etc.), as well as the

additional facil ities such as jogging truck, were evaluated to underst.and the historical aim

of the dam development. Recommendations are presented in respect w ith the necessary

monitoring techniques in both hydraulics-hyd rology and gcoleclmical parameters, which

is aimed at reducing risk due to simi lar d isaster.

INTRODUCfION

A ll TIle Situ Gintung dam failure is a specific phenomenon that happened rarely in the case. but it should be reali zed that it may be occurred anytime and anywhere. The era of

mi tigation efforts as a part of disaster managcmcnt cycle requires various parties to

understa nd the dam failure phenomenon. These includc the understanding 0 11 the mechani sm of the S itu Gintung tnilurc such as the hydro logy process (particu larly to

identify its extra-ordinary characterist ic, the hydraulics process in conjunction with the

dam structural integrity (geotechnical characteristic dynamics), as well as it'> abnlpt of the

dischargc during thc failure process. However, unless suffi cient sign ificant monitoring

data (based on the Sta ndard Operating Procedure being implemented) is obtained, il is

ralher difficult to confinn the failure mcchanism. The early morn ing dam fai lure of Situ

Gintu ng of 27th March 2009 has awakencd the lndones iall 11ydntulician, especially those involved in the dam development including situ (s itu is the colllmon name of smull natural reservoi r in West Jav:l). More then 80 casualties died from a tsunami as caused by more than 10 lll/sccond now velocity resulted from the f,lilure of the cmbankment in only

less than 2 hours. From thc hydro logical point of view, the rainfall characteristic should have been into mlcd whether or no t thc rainfall condition was abnonn:ll. Prior to the dam

failure occu rrence, 11 relatively high intcnsity of minfall (more th,l11 70 nun/hrs) occurred during the afternoon of Ihe 26110 March 2009 at the catchment area of Situ Gilllung [I].

Another report said that structurally, the embankmen t condition is far than at fair

condition. These were indicated by apparent physical conditions such as too narrow

spillway, insuffic ient width of spillway crest , impertect intcrfllce between spillway

structure and soil embankment, utilization of downstream embankment for housi ng, etc.

These of course contributed the Situ Gintung darn fa ilure phenomenon wh ich needs to be studied thoroughly.

I'OSSIIILE MECI-IAN ISM OF SITU C INTUNG DAM FA ILURE

Hydraulics Vicw Po ints T he analysis of dam failu re has been studied and modelled as the growth of dam opening

which was simplified similar to the trapezoidal form (Brunner and Gary [2n. In the implementation , thi s model may be extended not only for the earth fill type dam, but also

for the concrete mass dam as well as concrete arch dam (by modify ing several

parameters). The process or overflowing of water from the reservoir during the growth of the dam openiilg is used as the basic of the mathematical governing equation of the dam

L

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failure (sec Figure I). The dClcnnination of parameters affecting the dam failure involves time of failure process (f), width of failure opening (b), depth of failure opening (h), slope o f failure opening (z) , non-linearity of the growth of the failure opening (P) and coefficient of type of failure reason (k). Apart from those mentioned parameters, reservoir characteristic will also be utilized to develop the failure model, i.c. the storage volume (II) and the inuqdation area (A).

h.

Pattern of Dam Failure

, , , ~

b

},~ •

••• J ~

, ...... '- ____ 1

b

, , . , , , ,

,

•

Figure I. Model of the growth or dam failure opening

Crest of Dam

I"

Foundation (Abutment)

h

Hydrologic issues for dam safety based on FEMA workshop report (2005) arc risk analysis, standards, and meteorological needs. Risk analysis focuses on items relating to ullcertainty fCictors Ihal inl1uence reservoir inflow values and the computation of the Annual Exceedancc Pro:'ability (AEP) of eX lremc floods. Standards issues include

physical fac tors Ihal influence the mcthodology for thc computation of extreme floods. including the Prob:lble Maximum Flood (I)M F). Metcorological needs focus on rainfall

analysis from bolh the standards base an:llysis and a risk-based analysis. including precipitation analysis, rainfall frequency analysis, and real-time storm analysis. Thc modelling of the growth of opening of lhe dam failure utilizes the following equation

(F"ad [3]).

(I)

Wh ile for the growth offailure opening width is as the following:

(2)

The modelling of water flow from the reservoir to the opening of the dam failurc is

adopted utilizing the dynamic of unsteady flow model. However, whcn the length of the reservo ir is relati vciy short, or the inundation area is relatively small, the approach of

1859

pool-level storage is justified. The unsteady flow model is also uti lized to analyze the propagation of fl ush-flood at the downstream of the dam. The duration of the flush flood is a func tion of not only the duration of the dam failure, but also the duration of the

drainage mechanism of the water storage in the reservoir after the flood reaches the its maximum hydrograph. Following (Figure 2) is the sketch of the dam failure mechanism.

reservoir

-- --... :------... ....... '---'-.......................... \ , '. . , ..... '-.-failure opening

flood propagation

Figurc 2. Sketch of Flood propngation due to dam failure

Rcsults ur hydru lilie analysis highli ght the understandin g that unless su fficient and reliable d(lta is available, both overlapping and/or breaching arc slill possible to cause the cataslrophic disaster. From the hydrological point of view, the rainfall characteristic should havc bcen informed whether or not thc rainfa ll condition was abnorma l. Prior 10 the d(llll fai lu re occllrrens;e, a relali vely high intensi ty of rainfall (more than 70 mm/hrs) occ urred duri ng the afiemoon of the 26'b March 2009 at the

catchment arca of Situ Gintung. Another report sa id that structura lly, the embankment co ndition is far than :It fair condition. These were indi cated by apparent phys ical cond itions such as too narrow spillway, insufficient width of spillway crest, imperfect interface betwccn spillway structure and soi l embankment, utilization of

downstream embankment for hOll sing, etc. The analysis of dam f"ilure was carried out through the modelling of growth of dam opening which WliS simplified similar to

the trapoziodal fo rm (Rahardjo (41). Based on the hidrograf inflow. out now and the res ult of maximum water level s imulation shown in Figure 3. the peak discharge at the time of fai lure reach 56,26 1 m'/sec and the max imum ve locity of 1,107 mJsec, and the inundation area at the dowllstream is 9,5 ha.

1860

(a) Hydrograph inflow, oulflow (without breach) dan oUlflow (with breach)

- -"-

_gon ,. " \ . _ .. WS 'J'M.I.R'2OOQ~~

, -c~i 17MARi0090.0ClS --.--- I

~~ - _._. - - - -•

! coo

'/ - - - - - - - -"" "'" v _)r~

~---1-, -

-.....,~o.-.~ (b) Maximum water level althe time offaiiure

Figure 3. Hydraulics rouling orSilu Gintung

Geotcchnic View I~oints It is difficult 10 detennine the causative factors triggering the embankment failure of Situ Gintuog, since it needs a forensic engineering analysis. In general, the embankment failure of Silu Ginlung could happen due 10 several causative factors as described below.

a) The increase of driving forces and decrease of resistance forces on the embankment structure. Figure 4 shows external forces acting on the slope of embankment. The conslmclion of houses and road yields the existence of defects on embankment structure. The discontinuity plane appearance due to these defects could grow to be a critical slope surroce with a minimum sa fety factor. Based on the result of intcrview with local

1861

community, there was a report of Ihe occurrence of slope damages at the upstream around two years ago. This report needs to be evaluated carefully in order to clearly explore the causative factors of the embankment failure.

Figure 4. House and road constmction on the slope of embankment

b) Landslide due 10 the raising of reservoir level (reservoir- induced landslide). It is difficult to decide whether the embankment fllilUl'c at Situ Gintung occurs due to the raisin&. of reservoir level, since there was no monitoring instrumentation such as Automatic Rai nfa ll Recordcr (ARR) and Automatic Water Level Recorder (AWLR) at Situ Gintung. To begin the anal ysis of reservoir induced landslide, there is a necessity to collect the claw such as: hourly rainllill intensity, hourly water level fiuctuli li on, and geotechnicOl l properties of soil.

c) The existence of suft soil layer with high pl asticity and low sl u.:ar strength at the cmbankment base. The ex istence of soft soil layer wi th the thickness of 50 em at the base of embankment may also affect the liLilure phenomenon considerably [5]. This soft soi l has low shear strength, high plasticity and strongly affected by the nuctuation of pore water pn:ssure. The damages of embankment structure affe::t the stabil ity of the slope, particul arly when the sliding surface passes through this soft soil. A detail investigation is necesS3ry to explore this soft soil lllycr below the embankment structure. Further geotechnical analysis indicates that interaction between the dynam ic of water elevation and the cutting slope of earth fill darn plays a significant role in the occurrence of Situ Gintung darn fa ilure . The appurtenances of Situ Gintung and the cutting slope due to the houses construction were eva luated to und'!rstand the historical aim of the dam develupment. A two-dimensional stress-stmin lInal ysis has been perfonlled to figure out the distribution ofrc!alive shear stress and plastic points on the dam emh

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Section A: Section B:

Failure!'! b,mk with slope culling and huuses E~isling bank

Figure 5. Layollt showing the dam sections being investigated

Section B Def '" 83.72 X IO-J III FS = 1,426

~~~m

Section C Dcr ", 82,28X IO·Jm FS = J

Figure 6. Defonnation (Del) and Factor of Safety (FS) at Section B and C

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Figure 7 shows the increase of defonnation and decrease of safety factors in conjunction with the increase of upstream water surface elevation at various sections. Further necessary recommendations arc presented in respect with the development of monitoring techniques in both hydraulics-hydrology and geotechnical parameters.

" ,

"'~"- -00 " ,

g f

j" • , .. ~ • M ,.

•• " • : '" . -.j •.. -to ~

" ,., " 00 " " "" Wal ..... ",1""" eI ...... lion (m) Figure 7. Decrease of dam integrity due to rise in upstream waler surface elevat ion.

ACKNOWLEDGMENTS

The authors wish 10 express their gratitude's and thanks to all parties involved in the field investigation due to Situ Gintung Dam failure, and to all staff at both hydmulics and gcotcchnics labomtories of Universitas Gadjah Mada (UGM) for the necessary laboratory investigations.

REFERENCES

[I] Research Center and Development for Water Resources, Ministry of Public Works, Indonesia, "Geotechnical fln-estigatiol1 of Situ Ginfllflg. Report of Dam Failllre", (2009).

[2] Brunner and Gary W., ·'!IEC·RAS River Analysis System User's Mall/llIf', US Army Corps of Engineers, Hydrologic Engineering Center, (2008).

[3] Fread, "NWS FLDWAV Model: The Replacement of OAMBREAK for Dam-Breuk Flood Prediction", Proceedings: 10th Ann1lal Conference of the Association of State Dam Safety Officials, Inc., Kmlsas City, Missouri , (1993), pp 177 - 184.

[4] A.P. Rahardjo, 2009, "Simulation ofa Dam Break Triggered Flood, the Case of Situ Gintung Disaster on March 27, 2009", international Conference all Sustainable Development for Water alld Wastewater Treatment, Yogyakarta, (2009).

[5] D. Legono. " Disaster Risk Reduction of Dam Failure through Development of Hydro·Geotechnical Monitoring Technique", Asia-Pacific Symposium 011 New Techllologiesfor PredictiOfl alld Mitigation of Sediment Disasters, Tokyo, (2009).

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