Effect of sea-dykes on tsunami run-up. Tainan Hydraulics Laboratory National Cheng-Kung University Tainan TAIWAN.

Transcription

1 Effect of sea-dykes on tsunami run-up Kao-Shu Hwang Chen-Chi Liu Hwung-Hweng Hwung Tainan Hydraulics Laboratory National Cheng-Kung University Tainan TAIWAN.

2 Outline Introduction tsunami research in THL after the 24 Indian Ocean tsunami The motivation and the objectives of present study Preliminary results Ongoing experiments Future works 2

3 run up sensor 3.5 m 1.5 m wave generator 1:6 197 m 6 1 MEASURE 2 6 PROCESS 3 wave gages No. 51~78 spacing 2. m 88 m plane view of the flume wave gages No. 79~96 spacing.4~.8 m GENERATE 4 5 AD/DA 5. m wave gages No. 4~47 spacing 4.~6. m 15m 6 1:2 side view of the flume.4 m 1:4 5.2 m : : : : : : : configuration file instruments database measured signals processing results AD/DA instruction file wave board control signals command file IPC1 MNDAS Experimental set-up 3

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5 Surface wave profiles after breaking

6 R/h vs. H/h.5 c o tβ = 1 9 r u n u p la c o tβ = 2 E B M c o tβ = 1 9 c o tβ = , S y n o la k is ( ) w, 4, 6, L i( 2 3 ). 8 5, S y n o la k is ( ), h = 3. 5 m, r a m p tr a je c to r y R /h c o tβ = 4, h = 2. 5 m, r a m p tr a je c to r y c o tβ = 6, h = 2. 5 m, r a m p tr a je c to r y.2 c s c s c s.1.1 H /h.2 o o o o o o tβ = 6, lita r y -w tβ = 6, lita r y -w tβ = 6, lita r y -w h av h av h av = e = e = e 2.5 tr a 3.2 tr a 1.5 tr a m, je c to r y m, je c to r y m, je c to r y.3 6

7 .2.4 x*= x*= x*= breaking at x*= x*= η* η* and u* (cotβ=2, H/h=.12) x*= u* t* 4 5 7

8 .6 x*= x*= x*=.9.6 η*.2 x*= x*= η and u* above shoreline (cotβ=2, H/h=.12) u* 7 t* 8

9 .2.4 x*= x*= x*= η* x*= t* 7 breaking at x*= η and u* (cotβ=4, H/h=.12) u* 8 9

10 .3.6 x*= x*= x*= η* -.1 breaking at x*= x*=-1..2 η and u* (cotβ=4, H/h=.23) -.2 x*= u* t* 8 1 1

11 x*= x*= x*= x*= η* η and u* above shoreline (cotβ=4, H/h=.23) x*= u* 12 t* 11

12 About 1/3 coastline is protected coast length 1,141 km with km protected by sea-dykes or revetments design wave conditions:??????????????????????????? West coast??? H1/3 :4-6 m, T1/3:8-1 s East coast H1/3 :1-14 m, T1/3:1-16 s crown levels of sea dykes or????????????????????????????????? revetments West coast???????????? E.L. +4~ +6 m East coast E.L. +8~+1 m 12

13 A typical coastal landscape of Taiwan Seafloor bathymetry source: NCOR, TAIWAN

14 A report about the role of sea-dykes (revetments) in the 24 tsunami attack.. However, on Male Island, which is the national capital of the Republic of Maldives, revetments and other structures have been constructed around the island. The island was relatively unaffected by the Sumatra tsunami because these revetments helped protect the island from inundation. National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, Japan 14

15 State of tsunami wave runup with and without revetment National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, Japan 15

16 The objectives Tsunami run-up and overflow when there are sea-dykes (revetments) protecting the coast Hydrodynamics around the sea dykes (revetments) and the overflow field in a tsunami attack 16

17 Preliminary results by taking advantage of consulting projects that originally aimed to investigate the stability of sea-dykes under storm wave conditions

18 s o lita r y w a v e -fo r m x / h = η /η m ax θ The flume 2 m 2 m 2 m The wave maker Servo-electrical piston type Stroke: 1. m Max..4 m solitary wave height under 1. m water depth 18

19 A typical sea-dyke profile of the east coast 19

20 The mean overflow rate 25 m ean overtopping rate (m ^3/s/m ) Y am am oto (25) 5 w ith detached breakw ater w ithout detached breakw ater over flow height (m ) 2

21 The mean overflow rate h H q =.55 gh h (m 3 /m/s) Where h is the overflow height by Takanashi and Yamamoto (25) 21

22 Computation domain 3 dx =.5 m B oundary particle = 648 Fluid particles = On fixed boundary, boundary force is used to prevent penetration X (m)

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27 Ongoing experiments

28 Considerations in test program tsunami heights the tsunami heights (H) are the same order to the sea-dyke height above the sea level (Hc) The sea-dyke front and rear slopes The slope behind the sea-dyke Hc H 28

29 Disaster cases of coastal structures by tsunamis (Yamamoto et. al.,26) Date of disaster Coastal name Structure type Damage level Type of destructive force Crown height (m) Tsunami height (m) Mean overflow rate (m3/m/s) Hokkaido Prefectur e (1993 July 12) Hirahama, Taisei-cho Revetment (crown covered with concrete) Complete destructio n Umikurimae, Okushiricho Self-supported dike Complete destructio n Monai, Okushiricho Self-supported revetment Complete destructio n Aonae, Okushiricho Self-supported revetment Complete destructio n By incident tsunami pressure By incident tsunami pressure By incident tsunami pressure By tsunami pressure from back coast

30 Date of disaster Coastal name Structure type Damage level Type of destructive force Crown height (m) Tsunami height (m) Mean overflow rate (m3/m/s) Akita Prefectur e facing the Nihon sea (1983 May 26) Kodomari fishery harbor Block-type revetment (crown not covered) Complete destruction By return flow Todoroki fishery harbor Self-supported revetment Partial destruction By return flow Iwadate fishery harbor Self-supported revetment Partial destruction By incident tsunami pressure Iwadate fishery harbor Self-supported revetment Partial destruction By incident tsunami pressure Minehama Self-supported revetment Partial destruction By incident tsunami pressure Kotohama Reinforced concrete revetment (the crown was covered) Complete destruction Destruction of front face and outflow of back filling

31 2m NDV.5m.76m.5m 1 :2 1 m.1 8m Piston-type W avem aker Synchronizer A D C ard Am plifier A D system W avem aker system A solitary wave propagate on an inclined beach & a sea-dyke The run-up heights, mean overflow rate The pressure distribution on the structure The flow field 31

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33 .8 d2 d18 d16 d2 Dike d18 Dike d16 Dike Synolakis (1987) R/h The run-up heights.1.2 H/h

34 d2h71t25 (cm) H (cm) P (cm/s) V Time(1/5 s) Time series of the overflow depth, pressure and velocity on top of the sea-dyke 34

35 M e a n o v e r f l o w r a te ( m ^ 3 /m /s ). 8 T a k a n a s h i a n d Y a m a m o to ( 2 5 ) d2 d18 d T s u n a m i o v e r f lo w h e ig h t ( m ) The overflow 35

36 Future works To use the super tank for larger scale tests on 36

37 Thank you!

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39 Seafloor bathymetry around TAIWAN (source: NCOR, TAIWAN) 39

40 The worries Can it happen here? How bad can it be if it can happen here? How about the defense capability of the existing coastal defense works? 4

41 h 堤重 weight of the passive ground sea wall pressure 被動土壓 H static water pressure incident tsunami pressure q =.55 gh h (m 3 /m/s) Where h is the overflow height by Takanashi and Yamamoto (25) u = 1.1 gh Where H is the tsunami height by Iizuka and Matsutomi (2) 41

42 h H 42

43 .8 d2 d18 d16 d2 Dike d18 Dike d16 Dike R/h H/h.3.4.5

44 South China.6 Sea Tsunami workshop 27 d2 d18 The run-up height d16.55 d 2 D ik e d 1 8 D ik e d 1 6 D ik e R /h H /h

45 青草崙海堤改善斷面示意圖 青草崙海岸地形示意圖 A typical sea-dyke profile of the west coast 45

46 Design Wave condition VS. solitary waves sea level: E.L m crown level: E.L. +5. m Design wave H1/3=6. m, T1/3=12. s overflow:.45 m3/s/m Solitary wave H=6. m overflow:.987 (2.41) m3/s/m H=4.8 m.673 (1.237) m3/s/m H=3.6 m.23 (.827) m3/s/m H=2.4 m.173 (.67) m3/s/m tolerance:.5 m3/s/m H=1.2 m.162 (.297) m3/s/m 46

47 η u (z u (z b = 5 c m b =.5 c m ) ) η (m ) x = 4m η (m ) x = 3 m x = m. η(m ) u ( m /s ) u ( m /s ) u ( m /s ) 1. 1 s q r t( g H ) t1 ( s )