圖書典藏及影音數位平台

白河水庫於民國54年6月完工，完工庫容為2,509萬立方公尺，兼具灌溉、防洪、給水及觀光等多目標功能之水庫，由嘉南農田水利會營運管理。近年水庫淤積嚴重，為恢復蓄水庫容、減低缺水風險及提昇防洪功能，落實水庫永續經營，本局近年持續辦理水庫相關更新改善規劃及工程施作，「白河水庫水利設施改善工程計畫」，包括新建庫區防洪防淤隧道、大壩壩體改善、2座出水工改善以及壩前庫區清淤使水庫恢復庫容至1,100萬立方公尺，已納入曾南烏穩定南部地區供水計畫項下辦理；「後續更新改善工程計畫」分兩階段清淤，配合澐水溪越域引水及與烏山頭水庫聯合運用後可增加公共給水每日2.8萬噸，增設繞庫排砂工程，可提高整體水力排砂效率，使水庫永續利用更具有可行性。 其中，更新改善之越域引水工程應實施環境影響評估，且部分工程位於地質法公告之地質敏感區，依「地質敏感區基地地質調查及地質安全評估作業準則」規定，應辦理區域調查及細部調查，並完成「基地地質調查及地質安全評估結果」報告及送審作業，爰辦理本計畫，以利後續推動。

The impact of sediment accumulation now is creating a serious issue at the Baihe Reservoir. The Baihe Reservoir is a reservoir with functions such as water supplements, irrigation and flood controls since 1965. The Taiwan Chia-Nan Irrigation Association is the owner of Baihe Reservoir who manages the operation of the facilities of reservoir. However, because of the serious sediment accumulation problem, the capacity of reservoir is reduced. In order to restore the function of the reservoir, the southern region water resources office, WRA, MOEA started a project named “The updating the Baihe Reservoir” since April 2017, under the forward-looking infrastructure plan-water resources project. The project includes the transbasin diversion and desilting of the sediments with EIA(Environmental Impact Assessment), which involves the geologically sensitive area investigations(this project). The focusing area of geologically sensitive area investigation located in Zhongpu Township, Chiayi County and Tainan in southern Taiwan (R.O.C.). The headrace project begins from the weir situated at the mid-stream of Yunshui River, crossing Luliao River and Touqian River to Baihe reservoir. Accordingly, there are no any complex geological structures, only monocline folding showing in the area. The strata exposed on the ground are Kanchialiao Fm and Erchungchi Fm. The lithological characters show that the mudstone, muddy sandstone and interbedded mud with muddy sandstone are the main geological material. The strike of the strata is N26°~38°E, dipping to west 22°~31°, increasing from north to south. The two joint sets measured from the survey area are N45°E/76°W and N09°W/80°E both with high dipping angle. On the other hand, the landslides geologically sensitive area can be divided into 5 main parts and subparts like A, B(B1~B3), C(C1~C4), D and E(E1 and E2). The vegetation covered well along the project zone, only few steep slopes exposed the bedrock to the ground surface. It is suggested that slopes are relatively stable other than the bedrock exposed slopes. The main geological materials can be classified into few layers. Such as soil layer, gravel layer, weathered bedrock and bedrock according to the drilling results. The thickness of the soil layer is about 0.3~3.2m. The thickness of the gravel layer is about 1.4~3.5m. The thickness of weathered bedrock is about 0.5~4.4m. Adding up the 3 main layers mentioned, it is lower than 5m representing that the layers near the ground surface are thin. The uniaxial compressive strength of the muddy stone bedrock is 2.13kgf/cm2 to 28.05kgf/cm2, which belongs to weak or very weak rock base on ISRM table. The RQD value is 80~100 which is very well, but the bedrock is easily weathered and decreasing the strength of rock because of the high water content in the muddy sandstone. Also, the bedding plane is not clear in the muddy sandstone bedrock either cracks inside. However, the aquifer is hard to find because the characteristics of the muddy sandstone bedrock could form as an aquitard layer. The 5 sites of detailed investigation area (focusing area) of the geologically sensitive area are zone A, B1, C1, D and E1. The slope type among zone B1, C1 and D is dip slope with low geological hazard potential. In the dip slope zone, the lithologic characters could be categorized as a homogeneous layer without clear bedding plane and weathered bedrock. The previous survey results show that there are no and geological hazard records, and the surface runoff is hard to seep into the ground because of the muddy sandstone. The strata dip angle is higher than the dip angle of the slope surface, and without the day line line showing on the slope toe. It is suggested that the slope in the geologically sensitive zone B1, C1 and D is stable. The slope type in zone A and E1 each are anaclinal slope and orthoclinal slope. The main geological hazard are debris flows and rock falling, both hazards located in the subsurface with small scale. The detail description and investigation results for each geologically sensitive zone are written in the following sections. Geologically sensitive area zone A: The slope located at the underdrain section and slope protection section. The slope type belongs to orthoclinal slope. Landslide type is debris flow on the near ground subsurface, obviously. Covered soil layer near surface thickness is 2.2m, and the thickness of the gravel layer is 3.5m. Because of the steep slope, it indicates that the soil is hard to preserve on the ground. The steep slope also caused the debris flow but in the small scale. At the toe of the slope where is the cutbank site of the Yunshui River, the quantity of flow is much higher, so that the erosion potential of the slope toe is higher. In return period flow rate of 25 years with protection on the cutbank, the scouring deep is about 0.53~0.77m. In spite of the results of slope stability is qualified, it is suggested that setting a protection at the toe of the slope could prevent from the cutbank erosion and the slope unstable situation. Geologically sensitive area zone B: The slope is located at the jacking method section. The jacking method section of the pipe line passes through the surface of the slope under 53~77m ground. The type of the slope is dip slope. The condition of the road on the slope is good without ruptures or cracks. The potential of slope slump is low. Coverage of the soil layers combine with weathered bedrock thickness is about 0.6~5.8. It is expected that small scale of the debris flow might happen in part of the area, and the potential of the deep slide in bedrock is low because the day line does not come out. Geologically sensitive area zone C1: The slope is located in the underdrain section of the pipe line project. The underdrain section is at the toe of the slope. The type of the slope is dip slope with well-constructed retaining wall. No cracks which might influence safety the can be found on the retaining wall. Adding the soil layer and the weathered bedrock thickness is about 2.6~4.8m, might only cause a small part of the debris flow area. In the 50 years return period of flow, the erosion deep is about 0.43m. Though the slope stability analysis shows a qualified result of the slope safety, it is suggested that protection on the riverbank. Geologically sensitive area zone D: The slope is located in the jack method section of the pipe line, and situated near the slope toe around 21~25m. The slope type is dip slope. Part of the subsidence road revealing that the slope is partly slumping and subsiding. In addition, the drilling results presents that the quality of bedrock in this area is qualified with less cracks or other discontinuities. The soil layer thickness is around 0.7~2.0m, lower then other area. The pipe line is on the edge of this geologically sensitive area, which won’t cause serious geological hazard. Geologically sensitive area zone E1: The slope is located in the jack method section of the pipe line, and situated near the slope toe around 16~35m. The slope type is anaclinal slope. The soil layer thickness is about 1.25m because of the steep slope and rapid changes of the slope. The outcrop shows that the lithologic characters is mainly muddy sandstone. Large amount of talu can be found at the toe of the slope. Base on the topography and geological material, the only geological hazard is the rock falling. Hence, using the jack method in this area could prevent the damage. However, the geological survey results shows that it is the entrance of the jack method at the toe of the slope. Low potential of the slope has been done by the slope stability analysis. It is suggested that setting a protection from preventing the rock fall is essential.