The relationship between sediment discharge, river chemistry, and landslide of Linpien River, Pingtung
Date Issued
2014
Date
2014
Author(s)
Chen, Kuan-Hua
Abstract
The weathering of geomaterial can be classified into physical and chemical weathering. The dissolved load and sediment discharge can be considered chemical and physical weathering product in a drainage basin. Therefore, we can understand the weathering in the drainage basin by studying the characteristics of dissolved load and sediment discharge in river water. The typhoon events would cause massive landslides in mountains, which are important sources of sediment discharge in Taiwan. This research utilizes sediment discharge during 1982 to 2013, 5 typhoon events during 2005 to 2012, and river chemistry during March 2013 to April 2014 of Linpien River to study the relationship between river chemistry, sediment discharge and landslide.
The annual sediment discharges ranged from 0.06 Mt to 8.08 Mt, with an average of 1.40 Mt. The sediment discharge yielded during wet seasons (May to October) contributes 97.47 % to the annual sediment discharge. In addition, the average sediment discharge during typhoon events contributed 39.02 % to the annual sediment discharge and the average landslide ratio for five typhoon events during 2005 to 2012 was 4.69 %. It implies that the factor of high rainfall during wet seasons or typhoons controls the variations of sediment discharges in the Linpien River.
The analyses of distributions of landslides caused by typhoon events revealed that the higher sediment discharge of Morakot in 2009, Kalmeigi in 2008 and Haitang in 2005 with higher newborn ratio, which implies that the newborn landslides would contribute abundant sediments to the river, and resulted in the increase of sediment discharge of the typhoon events.
The analyses of major elements in water samples collected in the basin during March 2013 to April 2014 showed the major cation was Ca (52.1 %) and the major anion is HCO3 (66.6 %). The contribution of river chemistry from carbonate was highest (82.33 %), next was silicate (13.82 %), and the last was atmospheric input (3.85 %) in upstream samples. This implies that the trace carbonates in metamorphic rock could influence river chemistry significantly. The high SO4 in river water is contributed from chemical weathering of pyrite, not from anthropogenic pollution. The river chemistry of the downstream samples collected at Hsinpi Station was contributed most from carbonate (62.12 %), next was atmospheric input (14.90 %), then was silicate (14.74 %), and the last was external factor (8.23 %). Although the proportion of external factor is insignificant, the impact on river chemistry is innegligible.
The monthly chemical weathering flux ranged from 125 ton to14,844 ton, with an average of 2,944 ton during March 2013 to April 2014. The chemical weathering flux during wet seasons contributed 88.38 % to annual chemical weathering flux. The chemical weathering rate of Linpien River was 110 t km-2 yr-1, and the silicate chemical weathering rate was 29 t km-2 yr-1. Both were 5 times higher than the world average. During the study period, the physical weathering rate was 4,062 t km-2 yr-1, which was about 40 times higher than the chemical weathering rate. It indicates that the weathering in the drainage of Linpien River is mainly physical weathering. For Linpien River, the high sediment discharge and the massive landslides caused by typhoon events during wet season would transport weathering products continuously. It makes the fresh surfaces of bedrock be exposed to earth surface, and results in the intense chemical weathering. In the conclusion, the physical weathering has significant influence on chemical weathering.
Subjects
林邊溪
崩塌地
輸砂量
化學風化
SDGs
Type
thesis
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