圖書典藏及影音數位平台

本計畫將在現有供水方式前提下分析集集攔河堰完工後之供水效益及設施功能評估，並探討濁水溪下游河道變遷、集集攔河堰操作對改善濁水溪河口揚塵對策研議及對地層下陷改善成效評估，期能兼顧穩定供水與環境復育之發展目標，達成水環境資源永續經營，而本計畫同時製作3D電腦動畫，使關心本計畫議題之民間團體及民眾能充分瞭解計畫內容。

The groundwater extraction in Changhua and Yunlin, central south Taiwan has caused land subsidence in decades. In order to reduce the land subsidence and enhance the water supply from Zhuo-Shui River, the Chi-Chi common diversion project was approved by the Executive Yuan, R.O.C., Taiwan on November 1989. It was noticed that the project supports the treatment of irrigation and industrial water. In 2002, the project was finished, and the facilities were completed together with operation, simultaneously. However, the change of geography and hydrology around the Zhuo-Shui River has been revealed. It is related to (1) the climate change and (2) the 1999 Chi-Chi earthquake, according to previous research. (1) The climate change has caused the stream flow increasing a little in long-term. But during the dry spell and high flow period may face the water intake problem because of the stream flow changes suddenly. (2) The base-level of erosion has been changed since the 1999 Chi-Chi earthquake, the sediment transport among the Zhuo-Shui River has increased, influencing the water turbidity for water intake. In this project, we will focus on the sustainable development of water resource issue at Zhuo-Shui River. We provide the analysis of Downstream Channel Morphology Transition, fugitive dust at estuary, land subsidence and different operating way model of Chi-Chi weir, in respond of such climate change issue mentioned above. The computer animation in 3D that showing the complements in this project might give a fine understanding to the people who focus on the sustainable and development of water resource of Zhuo-Shui River. 1.Water resource effectiveness of each target (1)Public use water a. Current water supply In 2015, the intake water reached 41,450,000 m3 per year, which is higher than the target 30,000,000 m3 per year of Chi-Chi common diversion project in 2019. b. Water invocation Department of irrigation and engineering supports the public use water while the supply is insufficient. The amount of diversion is around 32,600-19,230,000 m3, totally 9~44% of the public use water. c. Water supply effectiveness analysis The water supply of the surface flow from the Chi-Chi weir since 1996 the facilities completed had increased from 10% to 51%. In 2016, the amount of diversion of surface flow had adjusted to 36-37% because the Hu-Shan Reservoir provided part of the public use supply. The usage of underground water of public use had decreased since 2005. It decreased from 100% to 27%. The average usage per year of underground water had reduced about 39,000,000 m3. Accordingly, the amount of water usage of each person is higher, comparing the data of 2006 and 2017. The amount of water usage for each person has raised from 5 L/day to 365~387 L/day. (2)Industrial use water a. Current water supply The yearly average of industrial use water is about 104,100,000 m3, lower than the value 254,000,000 m3 of Chi-Chi common diversion project in 2019. In addition, the daily usage is about 345,495 ton/day reported by the Environmental Protection Administration in 1997. b. Water invocation Department of irrigation and engineering supports the public use water while the supply is insufficient. The amount of diversion is around 31-91% per year, which is enough for industrial use. c. Water supply effectiveness analysis The increasing of the industrial use water value was adequate during 2002 to 2007 base on the Chi-Chi common diversion project in 1993. In 2008, the construction of Yunlin industrial park was suspended, so that the diversion of the water in the project had changed. Furthermore, the Mai-Liao seawater desalting plant construction program shown that it could provide the fresh water 80,000 to 105,000 m3 per day while the industrial water is insufficient. (3)Agricultural use water a. Current water supply The yearly water usage of agriculture is around 1,263,490,000-2,272,340,000 m3. The average of each year is about 1,794,000,000 m3, which is higher than 1,769,780,000, the value of the Chi-Chi common diversion project in 2019. b. Water supply index The usage percentage of agriculture of water is 65.66%. The usage in the high water period, the typhoon might influence the usage, which is around 54.16-72.83%. During the dry season, Chi-Chi weir provides the water for agriculture use, and the usage percentage is around 66.62-82.14%. The water supply rate could reach 109-149%, and for each year is about 120% which are better than our expect. The water supply rate of the program for each year is about 71.4-128.4% and average is 101.4%. Those data show that the water supply rate could be highly influenced by the dry and high water season. c. Water supply effectiveness analysis The channel connected from the north-south Chi-Chi weir enhance the availability of water resource in Changhua and Yunlin area. The expected supply value of water has a positive ratio to the real supply value since the Chi-Chi weir operated. There are more urbanized area in Changhua and Yunlin area. The area for the agriculture is getting less than before, which is related to the expected usage value of water in the project. The real water supply value is related to the dry and high water season. Base on the research, Chi-Chi weir provides more water to Changhua area than Yunlin area so that the water supply of Yunlin are mostly from the underground water resource. (4)Climate change influences the water supply effectiveness Base on the method (data AR4) showing in the project ”Assessing the Impact of Climate Change on Hydrological Risk”, the stability water supply of the Chi-Chi weir is analyzed under the consideration of the climate change happens or not. The results provide that if the Chi-Chi weir supply the water stably or intake the water without the Chi-Chi weir, the ratio could be around 33-26%. The climate change influence ratio is about 4-8%. The amount of water supply would decrease about 20% during the dry season, which impacts the first crop. On the other hand, the Chi-Chi weir may influence the second crop during the high water period, the water supply value difference could be reach to 50%. 2.Evaluation of existing facility functions The Chi-Chi weir has been used 18 years. In order to make sure the facilities are functional and correspond to the stander of the project of Chi-Chi weir basic design report of the weir engineering, we focus on the functions of facilities that are intake facility, headrace channel, desilting basins, connecting channel and fishway. (1)Functions of existing facility a. North intake facility, headrace channel, desilting basins and connecting channel: The intact value of the north intake facility and headrace channel is designed as the water supply value 77 CMS, including 7 CMS for Slag Removal. According to the 2002-2017 annual report, the intake facilities took about 66.88 CMS for the maximum intake value, which is match to the standard of original design. North desilting basin could desilt the sand with 0.2 mm particle size in original design. In recent in situ test with the desilt basin, it matches the original design standard. The connecting channel with the surrounding facilities are all functional, that could reach the target value for each year. b. South intake facility, headrace channel, desilting basins and connecting channel: The intact value of the south intake facility and headrace channel is designed as the water supply value 108 CMS. According to the 2002-2017 annual report, the intake facilities took about 84.99 CMS for the maximum intake value, which is match to the standard of original design. South desilting basin could desilt the sand with 0.2 mm particle size in original design. In recent in situ test with the desilt basin, it matches the original design standard. In recent in situ test with the desilt basin, it matches the original design standard. The connecting channel with the surrounding facilities are all functional, that could reach the target value for each year. c. Spillway, scouring sluice, clean pool and fishway: The flow of the spillway is design as 18,914 CMS. In the frequency flood of Q200 situation, the elevation of the water level is about 218.26 m, which is enough for flood discharge. The scouring sluice is functional, according to the maintenance report of each year. The abrasion damage of the clean pool in recent year is still in control, which is still functional. Most of the fish kind could not climb along the fishway to the upper stream instead of the fish with the climbing ability at the entrance of the fishway. (2)Fishway improvement In this project, we plan to extent the fishway to the energy dissipation. However, there is an elevation difference between the fishway and energy dissipation. We re-design a box culvert part for migratory fish kind, stairs section and nature section for fish kinds to take a rest. (3)Silting reduce in weir storage area analysis The driving depth might be not enough if we reconstruct the spillway to scouring sluice. However, we could reconstruct from the middle of the weir, making three of the spillways into one scouring sluice and two smaller spillways. Recently, the silting of the Chi-Chi weir does not influence the main function of raising the water level. In 2016, it can find some stones with large particle size in the clean pool, showing that the bed sediments could travel through the Chi-Chi weir. This shows that the reducing the silting of weir is not in urgent. Also after the typhoon Toraji, it made the silting of the weir in balance. 3.Transition analysis of downstream channel (1)Zhuo-Shui River’s flow path transition and graded stream over the years According to elevation of main channel, storage area of Chi-Chi weir has reach the spillway, hence bed load above the elevation could be transmit to downstream by flood event. Due to ground uplifting caused by 921 earthquake, headwater erosion result in rejuvenation and construction of Chi-Chi weir. The study compare to Da-An river, Da-Jia river and Wu river, which undergo 921 earthquake as well. Even without hydraulic construction across the channel, Da-An river generate canyon topography because of headwater erosion and deeper channel caused by ground uplifting. Headwater erosion isn’t occur to Da-Jia river untill 921 earthquake. While A-Zhao-Wu canal ground sill act as controll section upstream, Wu river effectively shorten the distance of headwater erosion. As for flow path change, extention of Fu-Zhou dike contribute to concentration of flow path during Chi-Chi weir’s construction period. Increasing scouring energy transform the flow path from braided morphology to single channel. For segment from Ershui railway bridge to estuary, streamway regulation and constucted dike such as Xiao-Shui-Pu, Er-Shui, Lin-Nei, Hsin-Hu-Wai at 1917, centralized the seperated flow path to main stream nowaday. Constructed dike along the segment from Chung-sha bridge to estuary also reduce length of alluvial fan and flood plain to 2~4 kilometer, which are originally 30 kilometer. Based on information of bed material distribution for past years, bed material of Zhuo-Shui section 85~130 before and after operation is gravel and sandy gravel respectively. Soft rock downstream are fine mud and sand remaining. D50 from Ershui railway bridge to estuary get finner since 921 earthquake and operation. In recent years, D50 from Zhuo-Shui section130 to estuary show similar outcome to measure result before operation. (2)Continuity of river According to “Chi-Chi Weir Monitoring and Security Checks in Environmental and Ecology Monitoring Report(2017)”, Chi-Chi weir downstream’s suspended solid(SS) and turbidity are at high side. Ming-Zhu bridge, Zhang-yun bridge observe high value on BOD, ammonia nitrogen and total phosphorus, which because of wastewater from domestic, husbandry and irrigation drainage. On the upstream of Chi-Chi weir, pisces population has no obvious variation and show smooth succession trendency. Besides, Holland’s carp have been found in succession since 2004 around the region. Because of silting caused by climatic variation and scouring, biological volume do not increase evidently. (3)Numerical Simulation of scouring and silting toward Chi-Chi weir’s stream channel This study adopt DEM data from 2017 measured section to created numerical Geometry. Focus on current condition and NGO group’s recommendation , this study review the influence of scouring and silting under different condition, such as lower spillway or without Chi-chi weir. In the event of lowering spillway W2 and W20, main scouring area is headwater erosion source. Upstream of W2 and W20 have scouring distribution, which is approximately 10m wide and 15m long, while scouring deep about 5~6m is near drop elevation of spillway. Under condition as stated above, deposit volume within storage area decreased 1800 m3. Compared to current deposition, which about 5 million m3, only 0.36% improvement is expected. Without Chi-Chi weir, obvious erosion occur at dowmstream of apron, south bank scouring sluice, and upstream of original site. Previous deposit elevation is at spillway elevation, thus scouring depth could reach 10m and also develop upstream, while headwater erosion downstream has 4m scouring depth. The result shows that without Chi-chi weir, headwater erosion toward downstream make no influence in short-term, but increase at original apron. In long-term, headwater erosion should be monitored. (4)Relevance analysis between construction of Chi-Chi weir and coast line On the basis of hydrological annual report, this study collect suspended load sediment discharge of Zhan-yun bridge, Xi-Zhou bridge and Zi-Chiang bridge, reviewing sediment discharge’s variation after construction of Chi-Chi weir. The results shows that sediment discharge increase significantly since 1999. Refer to Fourth River Management Office “Geomorphic Changes in the Zhuo-shui River Estuary: Effect on Downstream Anti-flooding Structures and Assessment of Proposed Countermeasures(2013)”. Aggradation after 1999 is more than one during 1985~1999. Estuary area shows scouring trend in 2000, and continually deposit after then. Considered remote scouring distance, conclusion could made that there’s no association between coast line and construction of Chi-Chi weir. This study extract Fifth River Management Office “The effects on the protection works at Chia-Yi coast by the changes of Wai-San-Ding sandbar(2013)”, reviewing relavence between operation of Chi-Chi weir and dissipation of Wai-San-Ding sandbar. According to sediment discharge and extract content, there is no positive correlation between Zhuo-Shui river’s sediment discharge and area of Wai-San-Ding sandbar. 4.Strategy proposal for Chi-Chi weir’s manipulation against fugitive dust (1)Dust emission’s source and cause According to physicochemical analysis of exposed land in central region, Ca2+ andSO42- have higher proportion, lead to the summary that the major source of Zhuo-Shui river’s fugitive dust is river bed and exposed land. Research on Zhuo-Shui river’s dust emission has conducted for several years. Fugitive dust’s cause is mainly affect by rainfall, wind velocity and relative humidity. Moreover, Zhuo-Shui river’s fugitive dust has been problem since japanese occupation. It could be evident that construction of Chi-Chi weir has no direct impact on fugitive dust. (2)Fugitive dust’s influence area analysis for Zhuo-Shui river estuary During prevailing northeast monsoon, both middle and lower reaches of Zhuo-Shui river are influenced by dust emission. Hot spot for fugitive dust is located in the range from Zi-Chiang bridge to estuary, especially for south bank downstream, which cover distance range up to 7 kilometer. (3)Effectiveness assessment for Chi-Chi weir’s manipulation against fugitive dust Refer to Environmental Protection Agency’s forecast, discharge accommodation will be implemented based on water Information, once PM10 of Lun-bei station or Mai-Liao station reach alert standard (exceed 255 μg/m3). This study adopt HEC-RAS, which is one-dimension hydrography analysis software, to simulate difference of Zhuo-Shui river’s cover area against discharge increment of 100 thousands tf/day. The result shows that exposed area decreased by 0.27~0.57%, which have baraly influence on hot spot of dust emission. Thus, as mitigation project, suggestion is made that the amount of discharge could be substituted by spraying system or storage pond. 5.Effectiveness assessment for Chi-Chi weir’s manipulation against land subsidence (1)Cause and trend of region land subsidence Because of economic development, demand on water resource for western plain sharply increase. With accessibility to underground water, overexploitation lead to land subsidence. Changhua and Yunlin is the most severe region, major subsidence area has move from coast to inland. In Changhua, Xi-Zhou’s total subsidence is 80cm, maximum subsidence rate is 3.5 cm/year which is the only area exceed 3 cm/year. In Yunlin, Hu-Wei, Tur-Ku, Yuan-Chang, Bao-Zhong are the major subsidence region in recent years. Maximum subsidence rate is 6.4 cm/year which currently slow down. (2) Preliminary assessment for Chi-Chi weir’s manipulation against land subsidence a.Hill area Hill area isn’t part of overexploitation area, nor obvious subsidence area based on settlement monitoring recent years. Most of the gaging well are stable on water level. Thus, operation of Chi-Chi weir have no impact on ground water table of hill area. b.Plain area More surface water is provided to Changhua and Yunlin for agricultural use after operation of Chi-Chi weir. Depends on substantial drop in plain area’s ground water usage for agriculture in recent years, ground water table retrieve the level at the moment Chi-chi weir was built. The area show mitigation trend on substantial rate, conclusion could be made that operation of Chi-Chi weir contribute to recovery of water table and land subsidence improvement. c. Coastal area In the past, aquaculture raise great demand on water usage, leading to land subsidence caused by excessive and concentrated overexploitation. However, positive factor like conservative action, industry guidance and circulating-water cultivation achieve significant effectiveness. Cultivation area and ground water usage present the trend of decreasing. Currently, ground water level gradually recover and land subsidence improved in coastal area.