Relationship of high turbidity to landslide debris after heavy rainstorm in Shihmen
Reservoir
Hongey Chen1, Guan-Wei Lin1, Ming-Jame Horng2, Shuei-Ji, Wu3, Bin Chuang4
1
Department of Geosciences, National Taiwan University, No.1, Section 4, Roosevelt Road,
Taipei, Taiwan
2
Water Resource Agency, Ministry of Economic Affairs, No. 41-3, Sec. 3, Hsin-yi Rd., Taipei,
Taiwan
3
Aerial Survey Office, Forestry Bureau, Council of Agriculture Executive Yuan, No. 61-3,
Chao Zhong St., Taipei, Taiwan
4
Forestry Bureau, Council of Agriculture Executive Yuan, No. 2, Hangchou S. Rd., Sec. 1,
Taipei, Taiwan
Email: hchen@ntu.edu.tw
Abstract
Rates of deposit sedimentation and turbidity of reservoir water in mountain catchments are
often considered determined by the landsliding and sediment transfer in upstream area of the
reservoir. To explore this notion, landslides caused by five typhoons have been mapped in the
upstream area of the Shihmen Reservoir in northern Taiwan, where water and sediment
discharge, water turbidity and rock mechanical characteristics are well measured.
Typhoon-triggered landslides delivered huge amounts of sediment to the upstream channel of
Shihmen Reservoir. The nephelometric turbidity in reservoir rapidly increased up to ten-fold
from the river catchment drainage, and landslide volume exceeded sediment discharge by
five-fold. Examining observation data following five major typhoon events from 1985 to
2006, we find that high water discharge transporting hyperpycnal sediments into the reservoir
denudated the bottom-squeezed fine fraction sediment, which then ascended to reservoir
surface water. Our findings demonstrate that increasing water turbidity in Shihmen reservoir
is indirectly related to large landslides occurring in the catchments upstream.
Keywords: landslide, reservoir, turbidity, discharge, hyperpycnal sediments