The topography, morphology and sedimentation patterns in Sun Moon Lake
Date Issued
2015
Date
2015
Author(s)
Leung, Chung-ning
Abstract
Sun Moon Lake is a famous attraction and an important electricity generation facility in Taiwan. But the underground tunnel’s outlets in the east side of the lake which bring water to the lake will bring water mixed with a large number of muds continuously and accumulate near tunnel outlets, resulting in an alluvial delta in the reservoir. The accumulation will not only reduce the water capacity but also make serious ecological impact to the lake. In addition, the Lake is a basin which changed its appearance to reservoir 70 years ago due to conducting pumping storage project. The development of the project caused the village of Ita Thao near the lake been submerged in the water In this study, we use multi-beam echo sounders, side scan sonar and sub-bottom profiler to collect bathymetric data to observe the underwater terrain and topography of this area, in order to discuss the archeology features under the water and descript the growth of the alluvial over the past decade. We expect to predict the changes of accumulation within the reservoir, perhaps it can provide an important reference for reservoir maintenance. The results show that the west side of Sun Moon Lake has almost no deposit over the years, the Lalu Island which is in the middle of the lake appears almost the same underwater topography like 117 years ago ; But the west side of the lake is controlled by the sand and mud brought from the tunnel outlet.Bathymetry data shows the topographic elevation change is been dividing into three parts, the part which has the the maximum slope (728m ~ 739m) is the main area that the alluvial grew the most since 2006. The new Wu Jie tunnel was enabled to use after 2006, we can clearly see two deposition centers between 2006 to 2012 in deviation topographic map, showing that new Wu Jie tunnel sent the silt out in a different direction from old Wu Jie tunnel. Also, the new Wu Jie sent more silt than the old one, and there is a tendency that the alluvial extends west, and has the tendency to invade toward Ida village; Compared the side scan sonar image to the maps which was 117 years ago, we can find the corresponding structure features underwater such as terraces, roads, rivers and other ancient building remains, indicating that the underwater appearance has very little changed in this 117 years. We also found ancient buildings which the shapes are very similar to the ones on ancient map, but it needs to be confirm via underwater cameras, and that’s our next step. Chirp sonar data indicates the phenomenon of compaction can be found between the stratum layers, and the east side is more notable than the west side. This phenomenon is continuous, and the sediment in the stratum layer will generate gas. We can also see the ancient base plate sunk, perhaps this phenomenon was related to geological structure, not entirely caused by the compaction phenomenon.
Subjects
reservoir
siltation
multi beam
side scan sonar
chirp sonar
archeology
topography
geomorphology
Type
thesis
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