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Reflection on Typhoon Morakot – Facing the Challenges of Compound Disasters

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Reflection on Typhoon Morakot – Facing the Challenges of Compound Disasters ___________________________________________________________________________ 2009/TFEP/WKSP/023 Reflection on Typhoon Morakot – Facing the Challenges of Compound Disasters Submitted by: Chinese Taipei Workshop on the Framework of Long-Term Capacity Building for Disaster Risk Reduction in APEC Taipei, Chinese Taipei 30 November – 1 December 2009 Director of Disaster Prevention Research Center, National Cheng Kung University Professor Chjeng Lun Shieh Chinese TiTaipe i Genesis of Typhoon Morakot Path of the center of the Typhoon Morakot On August 2, 2009 a tropical depression formed on the sea, northwest to Philippines. It strengthened gradually into a tropic storm and was gave a name, Morakot. Typhoon Morakot made its landfall on at 23:50 on August 7, 2009. The storm turned into a typhoon on August 5. It started raining on Aug 6, 2009 in Chinese Taipei. The eye of the typhoon left Chinese TiTaipe i from Taoyuan at 14:00 on August It affected Chinese Taipei on Aug 6, 2009 8, 2009. The track data is from the UniSys Weather (2009). http://weather.unisys.com/hurricane/w_pacific/2009/MORAKOT/track.dat Characteristics of the rainfall‐Long duration At the rain gauge 160 Typhoon Morakot (2009) YhYuyushan(御油山站, Typhoon Kalmaegi (2008) Typhoon Aere (2004) C1V330), the record Typhoon Toraji (2001) Typhoon Winnie (1997) shows that it rained 120 Typhoon Herb (1996) continuously from Typhoon Isewan (1959) August 6, 2009 to th(mm) p August 10, 2009. 80 The duration is 91 Rainfall de hours. 40 The dtiduration of the rainfall during Typhoon Morakot is 0 siifilignificantly longer 0 20406080100 Time (hour) than those of other typhoons. Characteristics of the rainfall‐High intensity The intensity‐duration curves shows that the intensity of rainfall of Typhoon Herb, except the initial 160 Typhoon Morakot (2009) part of the curve, is larger than Typhoon Kalmaegi (2008) others, but the duration of the Typhoon AREA (2004) rainfall of Typhoon Herb is only 44 Typhoon Toraji (2001) hours. Typhoon Winnie (1997) 120 Typhoon Herb (1996) The peak intensity of rainfall of Typhoon Isewan (1959) Typhoon Kalmaegi is the largest but the intensity rapidly decreases /hr) m with the increasing of duration. 80 The intensity of rainfall of Typhoon Kalmaegi is smaller than that of Intensity(m Typhoons Herb and Morakot when the duration exceeds 13 hours. 40 The comparison reveals that the rainfall intensity of Typhoon Morakot remained high for 91 hours. 0 The maximum intensity was 123 0 20406080100mm/hour at Alishan. Duration (hour) Characteristics of the rainfall‐ Large accumulated rainfall depth 3000 The accumulated rainfall depth of Typhoon Morakot 2000 is far larger than epth (mm) that of others. Typhoon Morakot (2009) Typhoon Kalmaegi (2008) Rainfall d Rainfall 1000 Typhoon Aere (2004) Typhoon Toraji (2001) The largest Typhoon Winnie (1997) Typhoon Herb (1996) accumultdlated Typhoon Isewan (1959) rainfall depth was 0 0 20406080100 Time (hour) obdbserved 3079 mm at Alishan. Characteristics of the rainfall‐ Broad extent Most of Chinese Taipei was covered under the heavy rainfall. Two storm centers can be found in the Isohyet. The values of accumuldlated rainfllfall depth at these two points approach 3000 mm.。 Characteristics of the rainfall Long duration High intensity Large accumulated rainfall depth Broad extent Compound disaster More than two different disasters concurrently strike an area. Regions for different kinds of disasters in Typhoon Morakot A,, B(Plain area) Flood C, D(Mountainous area) Sediment‐related disasters, including ldlidlandslides, dbidebris flows, and landslide dams, etc. Relation between the accumulated rainfllfall dhdepth and the sediment reldlated disasters The regions in which the values of accumuldlated rainfall depth are larger than 800 mm are surrounded with red lines. Compound disasters occurred in the area where the accumulated rainfall depth are larger than 1000 mm. The more the accumulated rainfllfall dhdepth, the more types of disasters. DevastationDevastation of Siaolin village More than 500 people were killed by the landslide BfBefore ThTyphoon MktMorakot After Typhoon Morakot (2008/11) (2009/08) The only remaining building in Siaolin village after the landslide Environment of Siaolin village The Siaolin villagg,e, which is a small mountainous region, is southwest of Chinese Taipei. It is located in a terrace plilain, fifacing Chis han River, with Mt. Shiandu in its back. The Siaolin village is conventionally divided into two parts which are resppyectively called the northern village and the Wulipu. The landslide occurred at the northern village. Compound disaster in Siaolin village Disasters Flood Bridge collapse Landslide Formation of a landslide dam Break of the landslide dam These disasters almost occurred concurrently. Such disasters are called the compound disaster. The process of the compound disaster in Siaolin village 4 8 8 9 8 5, 6 *CWB: Central Weather Beureau; SWCB: Soil and Water Conservation Bureau 7 Inhabitants evacuated to shelters #1 4 and #2 according to the evacuation plan. The landslide fell on the two shelters. Locations of monitoring stations Three kinds of gauges are illdinstalled around Siao lin village. Water level stations 1730H046 was installed on Nanfong Bridge. 1730H8H058 was ins ta lle d on Sunlin Bridge which is at the downstream of Nanfong Bridge. Rain gauges Five gauges Seismic meters Four meters Occurring time of the landslide 06:16:31 06:16:59 06:16:38 06:16:28 Four seismic meters dddetected the signal of a earthkhquake at the same time. The location of the earthquake was in Siaolin village. This is perhaps the evidence of the occurring time of the landslide devastating Siaolin village. Accumulated rainfall depth 5000 4000 World's greatest observed point rainfall C0V150 3000 C0V250 C1V230 2000 C1V240 C1V300 1000 900 800 700 600 (mm) 500 400 Depth Depth 300 200 100 90 80 70 60 50 2 3 4 5 6 7 8 9 20 30 40 50 60 70 1 10 Duration (hour) Rainfall data of five rain gauges which are in the vicinity of Siaolin village are collected and compared with the world’s greatest observed point rainfalls (WMO, 1994). 2‐day and 3‐day values of the accumulated rainfall depth are close the world’s greatest observed point rainfalls. Evidence of the landslide of Mt. Shiandu 376 375 374 373 372 level (m) level r e 371 Wat 370 369 368 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 Aug 06, 2009 Aug 07, 2009 Aug 08, 2009 Aug 09, 2009 Aug 10, 2009 Date and time A water level station (1730H046) was installed on Nanfong Bridge. The record stopped at 6:00 Aug 9, 2009. Rainfall‐runoff simulation 377 Dam break 2500 Water level 376 Discharge 375 2000 ) ) s 374 / 3 1500 373 ge (m r level (m r 372 a e 1000 h 371 Wat Disc 370 500 369 368 0 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 Augg, 06, 2009 Augg, 07, 2009 Augg, 08, 2009 Augg, 09, 2009 Augg, 10, 2009 Augg, 11, 2009 Date and time The rainfall‐runoff process of the watershed whose outlet is at Nanafong Bridge is modeled using the NCUC model (Lin and Wang, 2007). The result shows that the peak disc harge at NfNanfong Bridge 2184 m3/s. Historical maximum peak discharge observed at Nanfong Bridge DDtate PPkeak disch arge RRkemark (m3/s) The peak discharge during Typhoon Morakot 8/9/2009 2184 Typhoon Morakot was (estimated) estimated 2184 m3/s which 8/29/1997 286 Typhoon Amber 6/8/1998 660 is the historical maximum 8/9/1999 488 value. 8//3/23/2000 520 Typhoon Bilis Wee belie ve ttathat ttehe 7/30/2001 2030 Typhoon Toraji landslide dam was flushed 8/6/2002 148 away under this large 6/12/2003 199 discharge. 7/4/2004 1641 Typhoon Mindulle 7///19/2005 718 ThTyphoon HiHaitang 6/9/2006 1080 8/19/2007 840 Typhoon Sepat 7/18/2008 713 Typhoon Kalmaegi Evidence of the formation and the break of the landslide dam 3 124 06:00 08:00 1 123 122 121 120 level (m) r 119 Wate 118 117 07:00 116 2 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 Aug 06, 2009 Aug 07, 2009 Aug 08, 2009 Aug 09, 2009 Aug 10, 2009 Aug 11, 2009 Aug 12, 2009 Date and time Another water level station is installed on Sunlin Bridge (1730H058) in the downstream of NfNanfong BidBridge. The arrow 1 points out a significant drop of the water level, from 121 m to 181.1 m at 06:00 on Aug 9, 2009. Then the water level soon arose to 123. 1 m at 8:00 on Aug 9, 2009. Comparing this phenomenon with the statements of survivors, it can be inferred the landslide dam broke at around 6:00 on Aug 9, 2009 Events versus Accumulated rainfall depth 100 3000 Hyetograph Accumulated rainfall depth 6 80 1. Yellow warning for debris flow was issued 5 (138.5 mm). m) 2. Br idge # 8 co llapse d (de br is flow, 413 mm ). m 3. Red warning for debris flow was issued (506.5 2000 60 mm). 4. Bridge #9 was flooded (2023 mm). fall ( fall depth pth pth (mm) 5. Landslide occurred (2060. 5 mm). n ai 6. Landslide dam broke (2098 mm) r 40 3 Rainfall de Rainfall 1000 mulated 2 u 1 4 Acc 20 0 0 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 6:00 12:00 18:00 Augg, 05, 2009 Augg, 06, 2009 Augg, 07, 2009 Augg, 08, 2009 Augg, 09, 2009 Augg, 10, 2009 Augg, 11, 2009 Date and time Summary of the devastation Bridges #8 and #10 collapsed ((9//2009/08/08 199,:00, debris flow).
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