Journal of Natural Disaster Science, Volume 25, Number 1, 2003, pp1-6

Characteristics of the Heavy Rainfall Disaster in Central Taiwan, July 29 to 30, 2001.
Motoyuki USHIYAMADisaster Control Research Center, Graduate School of Engineering, Tohoku University
Keiichi TODA and Hajime NAKAGAWA
Disaster Prevention Research Institute, Kyoto University(Received for 1. Feb., 2002 and in revised form 20 May., 2003)

ABSTRACT
Typhoon No.0108 (Toraji) struck central Taiwan July 29 to 30, 2001, and caused a heavy rainfall disaster. In
Hualien and Nanto prefectures hourly precipitation of more than 100mm lasted 3 hours, and the total precipitation
was more than 500 mm. As a result heavy debris flows occurred in many places in both prefectures, and severe
flooding occurred due to both overtopping flow and bank breaches, in Nanto Prefecture. Owing these flood andsediment disasters, more than 210 persons were killed or missing and severe damage was done throughout thecountry. Typhoon No. 9608 (Herb) had struck this same area in July 1996, and rainfall stronger than that of the2001 event was recorded. The damage done by typhoon No.0108, however, was greater than that done bytyphoon No. 9608.

1. INTRODUCTION
Heavy rainfall that occurred in the central area of Taiwan
from July 29 to 30, 2001, caused extensive damage in Nanto and
Hualien prefectures and surrounding areas, and 214 persons were
killed or reported missing. Because this event was one of theseverest rainfall disasters in Taiwan in resent several decades, weinvestigated the area from Aug. 13 to 17, 2001. The characteristicsof this disaster are here discussed based on our field survey findings.

they have international names, assigned them by the Japan
Meteorological Agency based on the table of the ESCAP/WMO
Typhoon commission. Its international name was Toraji, and its
Taiwanese name 桃芝 (peach turf). Here we refer to it as

2. PRECIPITATION CHARACTERISTICS
2.1 Outline
The heavy rainfall was caused by typhoon No. 0108.
Typhoons usually are identified by numbers in Japan, althoughFig. 1 The course of typhoon No.0108

Fig. 2 Isoheytal map of cumulative precipitation in Taiwan from
July 29 to 31.

KEY WORDS: Typhoon No.0108 (Toraji), heavy rainfall, sediment disaster, Nanto Prefecture, Hualien Prefecture, Taiwan.

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M. USHIYAMA, K. TODA AND H. NAKAGAWA

Fig. 3

Hourly and cumulative precipitation at Hsini (Nanto P.) and Fenglin (Hualien P.).

typhoon No. 0108.
It appeared in the Philippines Sea at 9 a.m., July 27, 2001 andmoved north west, striking the east coast of Taiwan at 12 a.m.,
July 30. After crossing central Taiwan, it had changed into a tropical storm when it reached southern China at 9 a.m., July 31(Fig.1). When the typhoon struck Taiwan, its central pressure was
965 hPa, central wind speed 35m/s, and radius of wind speeds
15m/s was 300km. This typhoon ranked as a strong typhoon of
medium size in the classification system of the Japan
Meteorological Agency.
2.2 Precipitation during the typhoon
As typhoon No. 0108 approached on July 29, rain began tofall in Taiwan, heaviest on July 30 and stopping on July 31. An
isohyetal map for precipitation accumulated from July 29 to 31,
based on records of surface observatories is shown in Fig. 2. The
heaviest rainfall occurred in the central mountain area, the highest
recorded precipitation was 758 mm at Alishan observatory (alt.
2406 m).
Heavy rainfall (100mm/h or more) lasted for about 3 hours in
Hualien and Nanto prefecture in central Taiwan (Fig. 3). The 1hour precipitation high was 149 mm (Kuangfu), and the 3-hour
precipitation high 390 mm (also Kuangfu).
For several days before the typhoon's approach, there had been
hardly any rain in Taiwan. Until May 2001, the precipitation
recorded at Alishan was approximately the same as in a normal
year, but there was very little rain after June, the accumulated precipitation from July 1st to 28 being 54% that of a normal year; i.e.,there had been very little precipitation preceding the typhoon.
2.3

Comparison with normal precipitation
Normally, the western plain area of Taiwan receives little
annual rainfall, whereas the north and central mountainous areas
have high rainfall. (Fig.5, Taiwan Central Weather Bureau, 2001).
In the central and southern areas, the rainy season is from May to
September, and the difference in precipitation between the rainy
and dry seasons is high (Figs. 4, 5).
Nanto Prefecture, which had heavy rain from typhoon No.
0108 is a high rainfall area in Taiwan; e.g., the highest normalmonthly precipitation (September) at Alishan is 820 mm. Hualien
Prefecture is a lower rainfall area than Nanto Prefecture, the normal highest monthly precipitation at Hualien City is 385 mm andFig. 4Yearly mean precipitation in Taiwan, 1961 to 1990.

at Chengkung 366 mm (both, September). The highest accumulated precipitation from typhoon No. 0108 in Hualien Prefecture was
565 mm, recorded at Fenglin. The normal precipitation at Fenglin
is unknown, but the normal precipitation at Hualien City can beassumed to be similar because of their being in proximity and having similar topographies. Given this assumption, the recorded 3day precipitation (565 mm) is equivalent to an amount much higher than the normal highest monthly precipitation.
2.4

Comparison with recent heavy rainfall events
The highest 2-day precipitation at Alishan per month from1997 to 2001 is shown in Fig. 6. Each year there have been a few
300mm or more 2-day precipitations recorded, but no event comparable to the heavy rainfall of July 29-30 had occurred in the pre-

CHARACTERISTICS OF THE HEAVY RAINFALL DISASTER IN CENTRAL TAIWAN, JULY 29 TO 30, 2001.

Table 2

3

Human casualties

Fig. 5 Monthly mean precipitation at Alishan and Keelung, 1961 to1990.

est rainfall recorded anywhere in the world. Although while
typhoon No. 0108 was indeed produced heavy rainfall, it is clearthat a typhoon with much higher rainfall rates had been documented several years previously (Table 1).
3. DAMAGE CHARACTERISTICS

Fig. 6 Monthly highest 2-day precipitation at Alishan, Jan. 1997
througho Aug. 2001.
Table 1Comparison of Typhoons No.9608 and 0108

3.1 Damage Outline
The heavy rainfall on 29 to 30 July triggered many flood andsediment disasters throughout Taiwan. The number of dead andmissing persons was more than 210. Table 2 gives the number ofdead and missing persons by prefecture as of 8 August 2001([Taiwan] National Fire Administration, 2001).
Material damage was reported throughout Taiwan (Taipei Times,
2001a) : There were 93 debris flows or landslides. Electricity was
cut off to about 340,000 houses, and the water supply to about
520,000 houses was suspended. Roads were destroyed at 109
points mainly in Nanto and Hualien prefectures. The agriculturaland livestock losses were estimated at NT$ 1.28 billion (as ofAugust 2001, NT$ 1= 3.64 Japanese Yen).
3.2

vious five years.
The heavy rainfall that fell in Taiwan July 30 to August 1,
1996 as a result of typhoon No. 9608 (Herb) is recognized as oneof the heaviest rainfalls in recent history (Hydrotech ResearchInstitute, National Taiwan University, 1997). That heavy rainfall
also was concentrated in the central mountainous area. The highest
accumulated precipitation over 3 days was 1994 mm, and the highest 24-hour precipitation 1748 mm, both recorded at Alishan.
Moreover, a precipitation rate of 80 mm or more per hour continued for 12 hours. The heavy rainfall area was more extensive thanin typhoon No.0108. For that typhoon, the area with accumulated
precipitation of 600 mm or more was about 150 km2, whereas for
typhoon No. 9608, it was about 400 km2. The 24-hour precipitation of 1748 mm recorded at Alishan in 1996 approached the high-Flood Disasters in Nanto Prefecture
The Choshui River, the longest river in Taiwan, rises in theCentral Mountains and the Alishan Mountains and flows westward
debouching in the Taiwan Channel. The design flood discharge at
the river's mouth is 27,000m 3/s (Water Conservancy Bureau,
Taiwan, Republic of China, 1996). This river has many tributaries,
inclouding the Chingshui River. The Tungpurei River, one of its
left-side tributaries upstream of The Chingshui River, overflowed
its banks near the Yenping Bridge in the suburb of Chushan, Nanto
Prefecture (see Fig.7). Near that overflow point, the river bankalso was breached. As a result, Mujiliao Village downstream was
hit by a flood and nine persons were killed or missing. Damage inthe village is shown in Photo 1. This area is very near the seismic
center of the 1999 Chichi earthquake (Iemura, H. et al., 2000). The
river width near the Yenping Bridge is about 100m, and the estimated mean grain size in the river bed more than 50mm (visual
measurement). The averaged bed slope from Yenping Bridge tothe confluence of the Choshui River is 0.01 (Water Conservancy
Bureau, Taiwan, Republic of China, 1996).
The Tungpurei River overflowed its left bank just upstream of
the Yenping Bridge, and flood cascaded down forward Mujiliao

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M. USHIYAMA, K. TODA AND H. NAKAGAWA

Fig.7

Locations surveyed in Nanto Prefecture

Village in the low elevation area. There after, the left river bank
was breached downstream of the bridge, and the flood flow battered the village (Fig.8). That is, flood flows caused by both theoverflow and bank breach struck the village at separate time.
According to members of the Disaster Prevention Research Centerof National Cheng Kung University who accompanied us, themaximum discharge at that time amounted to more than 1,630m3/s
the 50 year return period discharge.
The causes of the overflow and bank breach are not still not
clear, in the central area of Taiwan, there was heavy rainfall caused
by a typhoon. Five years ago, from 30 July to 1 August 1996, at
which time the total rainfall exceeded that the 2001 event. River
bed elevation produced by sediment runoff in the flooding of 1996
may have facilitated the later overflow and bank breach.
In the upstream area of the Tungpurei River, rainfall intensity
increased from dawn 30 July, and the highest river water stage
occurred at about 8:30 on 30 July near the bank breach location.
According to residents of the village, at about 7:30, those who had
been informed of the high river water stage started to evacuate thevillage. As houses were destroyed by the flood flow just after 8:30,
the lives of some of the residents may have been saved by that
evacuation. Many large boulders with a maximum diameter ofmore than 1m were deposited along the trace of the flood flow.
The flood flow carried a great deal of sediment. Moreover, the passthat the water flowed down was very narrow, indication that theflow occurred at high speed without stoppage or diffusion. In thestricken village, there was very little distance between completely
destroyed houses and those that remained intact.
Our survey was made about two weeks after the flood disaster, when such temporary measures as restoration of the river bankand the dredging of sediment were being carried out. At that time,some residents still were taking refuge at the junior high school in
Chushan.
3.3

Fig.8

Inundation at the Yenping Bridge on the Tungpurei River

Photo 1: Flood damage at Mujiliao Village

Sediment Disasters in Nanto Prefecture
Heavy rainfall also occurred from dawn on July 30 along the
Chenyulan River, a tributary of the Choshui River, on the west sideof the Central Mountains and the Yushan Mountains in Nanto
Prefecture. Consequently, many sediment disasters occurred.
Heavy damage was concentrated in the area of Shuili and Hsini
counties. The number of dead or missing persons was 39 in ShuiliCounty and 51 in Hsini County.
Along the national road from Shuili to Hsini, some villages
located on steep slope areas had been destroyed by debris flows.
Heavy damage caused by debris and sediment flows in particularoccurred at Chunkeng in Shuili County, at Hsinhsiang in Hsini
County and elsewhere. Photo 2 shows Chunkeng Village after thedebris flow. This photo clearly indicates the severity of the debris
flow by the trace it left. In this village, the first floor of the social
activities center was demolished by huge boulders. The building
which, if in Japan, would be used as a refuge shelter was badly
damaged by the debris flow. Further upstream, the scale of thedebris and sediment flows damage was even greater, and hugeboulders and large deposits of sediment could be seen in many
places in Hsini County. Moreover, many roads and bridges also
were damaged.
Although the cause of those sediment disasters clearly was theheavy rainfall of more than 400mm that occurred during 24 hours,

CHARACTERISTICS OF THE HEAVY RAINFALL DISASTER IN CENTRAL TAIWAN, JULY 29 TO 30, 2001.

5

The local newspaper reported that another possibility for the huge
sediment yield was that betel palm plantations planted illegally inthe public mountainous area may have made worsened soil conditions (Taipei Times, 2001b).
3.4

Photo 2

Result of the sediment disaster at Chunkeng Village

Sediment Disasters in Hualien Prefecture
Hualien Prefecture was hit by heavy rainfall during theevening of 29 July, and debris flows occurred at eight locations
early in the morning of 30 July. Tashing Village in Kuangfu
County and Shuiyuan in Fenglin suffered particularly heavy damage (Fig.9). Though Hualien Prefecture is famous for the production of marble, but the disasters occurred in a geological andesite
zone.
At Tashing Village, the large scaled debris flow was causedby slope failure. An enormous volume of gravel and sedimentyield flowed down, some of which overflowed the bank and struckhouses and fields. Photo 3 shows part of destruction at Tashing
Village. Forty-one persons died or were missing. About 200 houses were damaged, 16 of which were completely destroyed, andabout 50 hectares of fields were buried under sediment. Maximum
sediment accumulation thickness was 15m, and the total volume of
sediment moved was estimated to be about 1.5 million m3. Public
officials of the Hualien prefectural government said that whenremoval of the sediment and driftwood was finished, they planned
to make residents affected by the debris flow move to a new location.
A debris flow also took place at Shuiyuan in Fenglin. The
total volume of sediment yield was estimated to be about 70 thousand m3. Three houses were buried, one of which housed sevenpersons, five of whom were killed and one missing. The number ofhouses inundated was about 100.
4. CONCLUSION

Fig.9

Photo 3

Locations surveyed in Hualien Prefecture

Debris left by the sediment disaster at Tashing Village

previously this area had frequently experienced heavy rainfall;heavy rainfall greater than that of 2001 event had been recorded
five years before, but no severe sediment damage was reported atthat time. Due to the heavy rainfall, the great volume of unstablesediment left by the Chichi earthquake of September 1999 in themountainous area, may have moved and flowed down abruptly.

(1) A heavy rainfall disaster occurred in the central area of
Taiwan, July 29 to 30 2001, that was caused by typhoon
No.0108 (Toraji).
(2) The highest accumulated precipitation for typhoon No. 0108
was 758 mm (3-day), recorded at Alishan (Nanto Prefecture,alt. 2406 m). In Hualien and Nanto prefectures an hourly precipitation of 100 mm or more continued for about 3 hours.
The highest 1-hour precipitation was 149 mm, and the highest
3-hour precipitation 390 mm. There had not been much precipitation preceding the event.
(3) Nanto Prefecture is a high rainfall area in Taiwan. The highest monthly normal precipitation at Alishan (Nanto P.) is
820mm (Sept.), higher than the accumulated precipitation of
the 2001 event. In contrast, the highest accumulated precipitation for typhoon No. 0108 in Hualien Prefecture was 565
mm, about 1.5 times the region's normal highest monthly precipitation. The rainfall of July 29-30, 2001 may have beenvery high for Hualien Prefecture but not so high for Nanto
Prefecture, even though the accumulated rainfall was higher
for the latter prefecture.
(4) When typhoon No. 9608 (Herb) descended on Taiwan in July
1996, rainfall higher than that for 2001 event was recorded
over a wide area (the highest 3-day precipitation was 1994mm). The damage done by the 2001 event, however, was6M. USHIYAMA, K. TODA AND H. NAKAGAWA

greater than that done by typhoon No. 9608.
(5) The heavy rainfall triggered sediment disasters in many placesin Nanto and Hualien prefectures. Moreover, in Nanto
Prefecture severe inundation flows caused by both overtopping and river bank breaching struck a village downstream,
causing severe damage.
(6) As to the sediment disasters in Nanto Prefecture, there is thepossibility that a great volume of unstable sediment left on themountains by the Chichi earthquake of September 1999 wascaused to flow down violently owing to this heavy rainfall.
ACKNOWLEDGMENTS
Special thanks are due to Professor Dr. Chjeng-Lun Shieh,
Mr. Wen-Chi Lai, and Mr. Morris Lee of the Disaster Prevention
Research Center, Taiwan National Cheng Kung University. This
research was supported by a grant from the Disaster Prevention
Research Institute of Kyoto University.

REFERENCES
Hydrotech Research Institute, National Taiwan University, 1997. Analysis
and examination of Herb typhoon disaster in 1996 (in Chinese).
Iemura, H, 2000. Preliminary Report on the 921 Ji-Ji Earthquake, Taiwan,of 21 September 1999, Journal of Japan Society for Natural Disaster
Science, 18, 425-440 (in Japanese).
National Fire Administration, 2001. http://www. nfa. gov. tw /nfaasp/typhoon toraji 900801 21th.htm.
Taipei Times, 2001a. http://www.taipeitimes.com/news/2001/08/01/story.
Taipei Times, 2001b. http://www.taipeitimes.com/news/2001/08/05/story.
Taiwan Central Weather Bureau, 2001. http://www.cwb.gov.tw/
Water Conservancy Bureau, Taiwan, Republic of China, 1996. FloodControl Report for the Choshui River (Choshui River and its tributary,
the Tungpurei River) (in Chinese).