圖書典藏及影音數位平台

高屏溪經歷年整治，現有防洪設施已具規模，各主要地區多半獲得保護。為考量部份河道沖刷現象之影響，實有必要進行完整水砂平衡評估。故有必要針對全流域之產砂、河道輸砂量及河床穩定趨勢，及更深入瞭解河道輸砂特性對於近海岸之影響，作為未來河道治理與管理之參據。

Drastic climate changes in recent years have substantially affected the sediment transport characteristics of estuaries. The coastline near the Kaoping River Estuary has retreated annually. Sediment transport and general erosion data of the Kaoping River Estuary are scarce because of the limited professional personnel involved in relevant research and difficulty of field observation. Thus, this study first collected and summarized sediment transport of the Kaoping River Estuary and relevant data of nearby coastlines to establish sediment transport theory and a numerical model applicable for the Kaoping River Estuary. Subsequently, the effect that sediment transport of the estuary had on nearby coastlines was determined and evaluated before relevant improvement strategies were developed. The results can be used as references for future river management and governance, environmental planning, and management design tasks. The overlay maps of Pingtung coastlines of 1905, 1944, 1985, 1992, 1999, 2008, and 2013 show that the north side of the Kaoping River Estuary has exhibited coastline retreat since 1905. The Pingtung coastline between the south side of the Kaoping River Estuary and Donggang River showed coastline retreat at the embankments of Jialian Village and Nanping Village. According to the measurements of the overlay maps, the maximal retreat distance between 1905 and 2013 was approximately 250–300 m. The Kaohsiung coastline in 1904 was used as the baseline to compare yearly with the coastline. During the 102 years from 1904 to May 2006, the coastline of Linyuan Township from the Zhongmen Embankment to Xishan Embankment retreated approximately 88 m on average. The most notable retreats were 65 m on average between 1904 and 1925 and 72 m on average between 1954 and 1967. The numerical model was used to calculate the coastal characteristics affected by waves during Typhoon Morakot (estuary sediment transport not considered). Wave height at nearshore waters was mostly between 2.0 m and 4.0 m at the sea side of detached breakwaters and was below 2.0 m at the land side of detached breakwaters. Detached breakwaters were not established in only the northern part of Zhongyun Harbor and in partial areas north to the Dapeng Bay. The nearshore wave height in Zhongyun Harbor was between 2.0 m and 4.0 m. High nearshore current speeds (approximately 1.5–1.8 m/s) were observed at the western side of the Kaoping River Estuary (i.e., the offshore open sea south to the Shanwei Harbor). The south sides of Zhongyun Harbor and Donggang Harbor were affected by the wave effects of Typhoon Morakot and exhibited stable nearshore waves at the land side of detached breakwaters, whereas erosion was observed at the sea side of the detached breakwaters. This phenomenon showed that detached breakwaters achieved the effect of attenuating waves. The wave field distribution during the highest wave height during Typhoon Morakot was compared with the wave field distribution when estuary sediment transport was not considered. The comparison result indicated that the wave field distributions were nearly identical. The only difference was present in the Kaoping River Estuary because the flow discharge from Kaoping River reduced the wave height of the estuary. The coastal flow field distribution during the highest wave height during Typhoon Morakot showed that the channel flow rate of Kaoping River was faster than that of the sea area. A comparison between coastal flow field distribution during the highest wave height and the coastal flow field distribution when estuary sediment transport was not considered revealed that the west-side flow fields at the Kaoping River Estuary were nearly identical. The only difference was observed in the east-side flow field. Because the water flows southeastward to the Dapeng Bay after the Kaoping River enters the sea, the vortex that originally existed at the north side of Yanpu Harbor disappeared, forming a flow field flowing southeastward. The bed-level sediment variations after Typhoon Morakot were compared with the bed-level sediment variations when estuary sediment transport was not considered. The results showed that the bed-level sediment variations at the west side of the Kaoping River Estuary were nearly identical. Differences in bed-level sediment variations were observed only at the east side of the Kaoping River Channel and Estuary. After Typhoon Morakot, the large flow rate of Kaoping River resulted in a sediment accumulation at the external side 20 m deep in the water between the Kaoping River Estuary and Donggang Harbor. A numerical simulation analysis of coastal morphological changes that considered sediment transport of a 100-year recurrence interval of the estuary revealed that the sediment transport of a 100-year recurrence interval of Kaoping River and Donggang River caused by a high flow rate caused sediment accumulation at the external side 20 m deep in the water between the Kaoping River Estuary and Donggang Harbor.