1. 2011/7 Umyeonsan Mt.
Debris flow problem
Prof. Ko-Fei Liu
National Taiwan University

2. The Interim Report
1. Is a very good report regarding potential
hazard and related assessment. Or the
best I have ever seen.
2. But discussion on individual site can not
only rely on statistic data analysis which is
correct to use for a larger number of sites.
3. Regarding the issues that needs resolved,
this report is not prepared for it.
4. Dispute resolving equals lawsuit and needs
evidence or some kind of proof of the crime.

3. Adequacy of recovery works done for the
slopes failed in 2010
1. Not considering ground water issue, and not
enough protection for rain fall, it is indeed mot
adequacy. I do agree with the report.
2. But a more detailed description for 2010
emergency countermeasure design is necessary.
So that there is enough evidence to identify the
responsibility of design or construction.

4. Effect of landslide and drained
water from Air Force base
Water seeps in
Soil
Military base wall
Concrete and without drainage system

5. Military base wall
Concrete and without drainage system

6. To identify the responsibility of air force base,
we need information on
1. Drainage system design on 2011/7
2. If there is still construction work which
requires vibration or penatration
3. The new drainage system which put water
in downstream channel is a lot safer and a
huge improvement.

8. How much rainfall? The probability of occurrence is too high alone boundary

9. Water level high, Top soil depth is thin
So land slides and debris flow should start
from mid stream

10. Ecological reservoir
To identify the role of ecological reservoir, it is essential
to know what is flow out of the ecological reservoir.
1. If only mud flow flows out of the reservoir, then the
reservoir has succeeded in storing all the sediments
and therefore reduced the disaster. There is no
description of the situation right after the disaster. Is it
a lot of debris hit and deposited in the downstream, or
just mud flow came down and flood most of the people.
This has to be ensured through photos or interviews
with local people.

11. Reservoir 1死

12. There in not much of
big boulders or
debris, so it could be
mud flow. Then
reservoir is good

13. To upstream
原游泳池所在地點 破壞點

14. 典型支流,坡陡料多
典型邊坡,嚴重沖刷,
鬆軟中空,多裂縫, 多波土石流遺跡

15. 斷層,兩側不同組成

16. Natural
dam
Main
source

17. There was a
natural dam as
high as 20m

18. Source is from air force base

19. 1. If it was debris flow came out of the damaged
spillway, then a simulation of debris flows is
necessary. Since the main stream from spillway to
500m upstream, it is very flat with less than 10
degree, so if debris flow came as one single large
wave, this reservoir should play a role of reducing
the disaster. However, if debris flows came as
many small waves, this reservoir may have
collected all the sediment and created a huge
debris flow and make more damage to
downstream.
2. A careful numerical simulation can solve this
question

20. Further improvement
There will be debris flow and landslides
in the future in this watershed.
A regular inspection plan and
mitigation might be needed

21. Blast from tunnels
1. Logically, places near the blast should be influenced more
severely. So if blast indeed has its effect on soil and bedrocks,
then the portion just above the tunnel can be a best proof.
Since there is no evidence of landslides or debris just above the
tunnel or in the surrounding area, this is a proof that blasts had
little or no effect of initiation of land slides or debris flows
2. Does the blasts weaken the soil and bedrocks such that debris
flow came from upstream? There is no trace of erosion near the
blast.
3. Soil actual can absorb energy from blasts, so there should be
no effect from the blasts for 2011/7 debris flow.
4. Will there be any long term effect if bedrocks are cracked,
remains to be seen