The relationship between rainstorm , landslide and sediment discharge in Shihmen reservoir
Date Issued
2010
Date
2010
Author(s)
Tsou, Nien-Chiao
Abstract
Rainfall properties had been mentioned as an important factor to trigger landslides of watershed in many literatures. In this study, I try to use the rainfall data of the QPSUMS (Quantitative Precipitation Estimation and Segregation Using Multiple Sensor) from Central Weather Bureau and JWD (Joss-Waldvogel Disdrometer) data to figure out the relationship between rainfall, landslides and sediment discharge during the typhoon Matsa and typhoon Sinlaku. Investigation results indicate that the rainfall kinetic energy is approach to the 29 J/m2-mm when the rainfall intensity exceeds 40 mm/hr. During these events, the highest kinetic energy of accumulated rainfall was reached to 17,000 J/m2 around the Siouluan sub-watershed. The sediment discharge of the Bai-shi sub-watershed was more than 2.6 Mt, and occupied around 45% in total of the study area. The landslide ratio of the study area is 1.03% in Matsa typhoon event and 0.96% in Sinlaku typhoon event by using the Formosa II images judgments. The various formations of Aoti, Kankou and Datunshang have more than 80% landslide distribution in total study areas, and the Datunshang Formation have highest distribution 33%. The results on the above mentioned have links with rock strength 57.1 MPa and volumetric joint 19.5. The new generation ratio 74.7% and reactivated ratio 31.9% in typhoon Matsa are higher than typhoon Sinlaku in 66.1% and 24.6%. It seems to have relative connection with accumulated rainfall 632.5 mm in 44 hours during typhoon Matsa.
Compared with rainfall kinetic energy and sediment discharge in these events, the sediment discharge increased obviously when the accumulated rainfall kinetic energy exceeds 2000 J/m2. This result show that the accumulated rainfall kinetic energy of 2000 J/m2 is seems a thresholds value in triggering landslide. It means the previous landslides were reactive or new landslides occur when the accumulated rainfall kinetic energy exceeds this thresholds value. And these materials were be flush out by the massive runoff. In this study, I also use the Polarmetric Dopplar Radar to estimate the rainfall rate and kinetic energy. Although the results from Polarmetric Dopplar Radar are smaller than QPESUMS couples with JWD estimation, the high resolution in spaces of the rainfall rate and kinetic energy are very helpful to understanding the rainfall distribution affect the landslide and sediment yields.
Subjects
Rainfall kinetic energy
Landslide
Sediment discharge
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