10th Asian Regional Conference of IAEG (2015)

Potential Slope-Failure Hazards of the Batongguan Historical Trail in the Yushan
National Park, Taiwan
Keng-Hao Kang (1*), Ming-Wan Huang (2), Chu-Chun Lo (2), Shun-Hsing Yang(3),Yii-Wen Pan (1) and Jyh-Jong Liao (1)(1) Department of Civil Engineering, National Chiao Tung University, Taiwan(2) Disaster Prevention & Water Environment Research Center, Taiwan, National Chiao Tung University, Taiwan(3) Yushan National Park Headquarters, Taiwan(*)E-mail: kangkanghk@gmail.com
Abstract
The Batongguan Historical Trail is an east-west traversing trail in the Yushan
National Park built in 1921. This trail, with a gentle slope, was built to transport heavy
military supplies in the Japanese Colonial Era. Since 60’s, it has become a popularmountain hiking trail. After the 1999 Chi-Chi earthquake and several typhoons with heavy
rainfall, a couple of sections within the trail were detoured to steep by-pass routes due toslope failures. The worst section is the one connecting Guangao and Batongguan, wherewas severely damaged by the typhoon Morakot in 2009. Multi-staged stereoscopic pairs ofaerial photographs from 1980 to 2010 were used to identify the potential hazards caused by
the slope failures. Afterwards, field investigation was conducted to investigate the slope
failure features along the section connecting Guangao and Batongguan of the Batongguan
Historical Trail. The results show that most the slope failures in the detoured trail between
Guangao and Batongguan were caused by headwater erosion.
Keywords: Yushan National Park, Historical Trail, Potential hazards, Slope failure
1.

Introduction

distance, and takes threefold time to pass this detour
area (Fig.1, Fig.2). In this work, we used multi-staged
stereoscopic pairs of aerial photographs from 1980 to2010 to identify the potential hazards caused by theslope failures, and field investigation to explore theslope failure features in the section between Guangaoand Batongguan of the historic trail.

The Batongguan Historical Trail begins Dongpu,Nantou in the west, ending at Yuli, Hualien in theeast with a total distance of about 116km. This
pathway has a width within 1.2 and 1.8 meters and analtitude from 140 to 3280 meters. It was opened inJanuary, 1921. This trail was regarded as an
East-West traffic renovation by the Office of theGovernor – the general during the Japanese ColonialPeriod.
Since 60’s, the Batongguan Historical Trail has
become a popular mountain hiking trail. The 1999
Chi-Chi earthquake hit central Taiwan with its
epicenter in Chi-Chi, Nantou.
The earthquake
triggered lots of landslides (Liao, 2000). As a result,the Batongguan trail was closed because of safety
reason for two years. In 2009, the typhoon Morakot
brought 1623mm of rainfall within 24 hours in thearea (Jou et al., 2010). This event resulted in manyslope failures along the Batongguan Historical Trail;
the trail had to detour in many places, especially from
Guanggao to Batongguan. The detour path has tohike 300 meters of elevation, 1 more kilometer of2.

Site backgrounds

2.1 Topography
The Batongguan Historical Trail in Nantou wasbuilt along the right bank of the Chenyoulan River,along north-west direction (Fig.1). From Dongpu toBatongguan, the altitude rises from 1156 to 2824
meters. Except the detour section, the trail was ingeneral built along the mountainside. In the detoursection, the trail reaches the ridgeline 600 meters
away from the north of Guangao. After passing thedetour section, the trail returns to the mountainsideleading to Batongguan.
Most part of the trail is parallel to the ChenyoulanRiver; the trail turns to the North-East direction when
it reaches the head of the Chenyoulan River where1

10th Asian Regional Conference of IAEG (2015)

Fig. 1 The geological map of the Batongguan Historical Trail western section.
The strata between Guangao and Batongguan
belong to the the Tayuling Formation.

3200
3100

Elevation(m)

3000

3.

2900
2800Interpretation of aerial photographs

2700

To understand how serious the Batongguan
Historical Trail was damaged, we used multi-staged
stereoscopic pairs of aerial photographs to identify
the potential slope failure area, the aerial photographs
were taken in year 1980, 1988, 1996, 2000, 2007, and2010. We compared and interpret the aerial
photographs taken in different years; the attempt was
to identify the failure mechanism in the detoured trailarea.
At the detoured area, the trail and the topography
in the aerial photographs are very similar up to 2000,which was one year after the Chi-Chi earthquake.
Since 2000, the headwater erosion of an unnamed
stream in the detoured trail area became more andmore serious (Fig. 3). Before 2000, the unnamed
stream was joined by 3 tributaries. Most of thelandslides distributed in tributary II, rest of thelandslide distributed in the left bank of tributary I.
The Batongguan Historical Trail was then covered byplants, hard to be identified from the aerial
photographs.
In 2007, the headwater erosion developed further,
especially along tributaries I and III.
Morelandslides took place, especially the landslides
distributed along tributary I. The landslide D
expanded because two landslides had joined together.
The landslide E was also formed, the ridgeline wastoward south. There were also landslide F and G
formed along the tributary II and the unnamed stream.
The pre-exist landslides along the tributary II, thelandslide B were expanded, but landslide A and C
were not.
In 2010 (one year after typhoon Morakot), a new

Batongguan Historical Trail

2600

Detoured trail
2500
0200400600

80010001200

1400

1600

Distance to Guangao(m)Fig. 2 Elevation difference between the old trail
and the detoured trail.
the detoured section of the trail is located.
2.2 Stratigraphy
According to the report of Taiwan Central
Geological Survey (Central Geological Survey, 2008),
the strata in the region covering the trail can bedivided into five formations based on rock typeclassification (Fig.1).
(1) The Tayuling Formation (Ty) is mainlycomposed of slate with occasional thin layersof meta-sandstone.
(2) The Chiayang Formation (Cy) is mainlycomposed of slate with occasional thin layersof meta-sandstone.
(3) The Yushanchushan Formation (Ya) is mainlycomposed of interlayers of meta-sandstone andslate, slate with thin-bedded sandstone, andsome thick layers of meta-sandstone.
(4) The Tachien sandstone (Tc) is mainlycomposed of meta-sandstone with thin layersof slate occasionally. The mineral grain sizeof the meta-sandstone is medium to coarse.
(5) The Shihpachunghsi Formation (Sp) is
composed of slate with thin layers (a fewcentimeters to tens of centimeters) of graymeta-sandstone,
interbedded
slate andmeta-sandstone.

210th Asian Regional Conference of IAEG (2015)

TheFig. 3 Identify result of stereoscopic pairs of aerial photographs between year 2000 to 2010, it shows thetributaries start to show up and the landslide area are getting bigger.
tributary was formed and almost all the landslides
distributed along tributary I had joined together.
Because of the headwater erosion, the ridgeline
moved further south. The landslides along tributary II,landslide A, B, C expanded; a new landslide I wasformed. On tributary III, there were at least threelandslides formed after typhoon Morakot. The
landslide F distributing along the right bank of theunnamed stream also expanded into a large landslide.
Based on the identified results of stereoscopic
pairs of aerial photographs from 2000 to 2010, it
appears the tributaries started to show up and thelandslide area expanded. The ridgeline in the northof Batongguan moved further south. It appears themajor cause for the development of the slope failures
should be attributed to headwater erosion.
4.

over there is lightly weathered slate, with high angle
cleavage and at least two sets of joint in obliqueangles that cause rock block failure.
The trail slight cut through landslide C, which
expand very fast since year 2000.

Results of field investigation
Fig. 4 Picture of the destroyed trail caused by thelandslide H.

To examine the slope failure modes of thedetoured area, we conducted field investigation along
the Batongguan Historical trail in April, 2015. The
slope along the Batongguan Historical Trail is still
unstable. Debris from upper slope covers half of thetrail, the thickness of debris is about 10 to 30
centimeters. The detoured trail between Guangao andBatongguan, is very seriously damaged.
In the landslide H influenced by the major
headwater erosion, the colluvial deposit in thetributary III has almost been washed out by runoff.
The trail has disappeared; passing the area becamevery difficult and dangerous (Fig. 4).
The landslide A is similar to the landslide H.
The situation in landslide A is the worst part of thistrail. The whole trail has disappeared. With barely
spot to step on, there was no time and no room formeasuring joints over there (Fig. 5). Most of the soil
and weathered bedrock do not exist in the gullies;
they were all scoured by runoff. The rock outcrop

Fig. 5 Picture of the destroyed trail caused by thelandslide A.
5.

Results of topographical analysis

We used the Digital Surface Model (DSM)
produced from stereoscopic pairs of aerial310th Asian Regional Conference of IAEG (2015)

Fig. 6 Elevation difference between year 2007 and 2010 compare with identify result ofstereoscopic pairs of aerial photographs.
photographs to calculate and compare the elevation
between 2007 and 2010 (Fig. 6). Comparing thesurface elevations in 2010 and 2007, it was found thesurface elevation in the tributaries significantlydecreased. It implies the right bank of tributary I wassubjected to severe erosion. As a result, morelandslides occurred from 2007 to 2010. The upperstream side of the trail passes through tributary III;the landslide H was formed over there, and thesurface elevations decreased a lot. The area is where
the original trail disappears.

block the trail as well.
The tributaries between Guangao and Batongguan
area expanded quickly in width and slope angle andso that the upper slopes were difficult to maintainstability. Many parts of Batongguan Historical Trailfrom Guangao to Batongguan are no longer existing;thus, it is extremely dangerous for hikers to passthrough. The landslide area is still expanding so far.
For safety concerns, steep by-pass routes passing near
the ridgeline are recommended at present.
Acknowledgements

6.

Conclusions
This research was supported by the Yushan
National Park Headquarters, Taiwan.

The Batongguan Historical Trail in the Yushan
National Park was serious damaged by large-scalelandslides after the 1999 Chi-Chi earthquake and the2009 typhoon Morakot in 2009. The trail has todetour in several sections seriously damaged bylarge-scale landslides. In this work, site investigation
for the large-scale landslides along the Batongguan
Historical Trail was conducted.
The site
investigation made use of stereoscopic pairs of aerial
photographs to interpret the distribution and the causeof the landslides. Field investigation was followed
to confirm the interpretation by remote sensing.
Most the slope failures in the detoured trail area in thewestern section of Batongguan Historical Trail werecaused by headwater erosion. The damage of trail
was especially serious when the trail went across astream. Once the debris or deposit materials were
washed away by runoff during a heavy rainfall, thetrail would be destroyed. In some cases, the trail
may be covered by large amount of debris so thatReferences
Central Geological Survey (2008) Geological
Investigation and Database Construction for The
Upstream Watershed of Flood-Prone Area. (Firstphase)- Geological Investigation, Landslide-DebrisFlow Investigation and Their Susceptibility
Evaluation in the Watershed Area (1/3).
Ben Jong-Dao Jou, Yi-Chiang Yu, Feng Lei,Yung-Ming Chen, Cheng-Sheng Lee, Ming-Dean
Cheng (2010) Synoptic Environment and Rainfall
Characteristics of Typhoon Morakot (0908),
Atmospheric Sciences , Vol. 38, No. 1, pp. 21-38.
Hsuan Wu Liao (2000) Landslides Triggered byChi-Chi Earthquake. Institute of Geophysics,
National Central University, Taiwan.

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