Simulation of Different Section Type Dredging affect on theRiver Hydraulic -Section 2-1 to 20 of Chen-Yu-Lan-Chi Creek as an Example

Abstract

The mountain area of Taiwan is precipitous and geology is broken, The hillside fields are often utilized improperly. After 921 earth quack and typhoon attack , that threatened resident's life and property of hillside fields. It cause dike burst and flood downstream. To eliminate calamity occur, the governments often used dredge way in mudflows heap section. This research use HEC-RAS software, collect section data and dredging of method of the 90th and 93th year, is it dig volume regular and in different to dredge Chen-Yu-Lan-Chi under the behavior with simulation. The condition has flowed in a piece of 2-1 rivers and creeks to section 20, and according to the regulation of the management method of rivers and creeks, is it have Chen-Yu-Lan-Chi ideal way of dredging. The dredge ways divide into 4 kinds. A：Dredge in the left side of river ; B：Dredge in the right side of river ; C：Dredge wide and shallow of river ; D：Dredge narrow and deep of river. Finally analysis Labrize dredge groove problem. The dredge models of the 200 years returned period. That dredge in accordance with water level energy and water level line, propose this section to adopt 「narrow and deep dredge way」; If dredge in accordance with average water speed propose this section to adopt 「wide and shallow dredge way」, is the least 0.11m/s. In Labrize dredge groove problem, the average safe coefficient of left dredge way is 23.480％ that’s the best；The average safe coefficient of right dredge way is 19.695％ that’s the second；The average safe coefficient of narrow and deep dredge way is 19.695％ that’s the third；The average safe coefficient of wide and shallow dredge way is 19.695％ that’s the forth. So the left dredge way is the best way of this channel.

臺灣山區地勢陡峭、地質破碎，加上坡地常被不當利用，尤其1999年台灣發生百年頻率之九二一大地震時，大量山區岩層多被震鬆後每遇豪雨或颱風來襲，即發生土石災害且有逐年加重之趨勢，嚴重地威脅坡地居民生命及財產之安全。在中、下游處則造成潰堤及淹水，為消滅災害之發生，政府對土石流堆積河段多採疏浚方式處理。 本研究利用HEC-RAS軟體，蒐集曾發生嚴重土石流堆積災害之陳有蘭溪於民國90與93年之大斷面資料及現行之疏浚方法，並利用挖槽體積固定以模擬在不同疏浚行為下，陳有蘭溪中自斷面2-1至20之河川流況，再依據河川管理辦法之規定，建立陳有蘭溪理想之疏浚模式，其結果可供日後相關機關在實施疏浚計畫時參考之依據。 陳有蘭溪河床疏浚行為之模式模擬可分為4種：A.河道左側疏浚；B.河道右側疏浚；C.河道寬淺開挖方式疏浚；D.河道窄深開挖方式疏浚，最後分析其流況，並以列普尼茲挖槽回淤量問題評估。 依本研究所模擬之疏浚模式，於200年重現期洪峰流量之驗證下，若依水位能量線以及水位線做為疏浚之考量，建議本河段採用「窄深開挖疏浚模擬」，做為疏浚之方法；若以挖槽內平均流速做為疏浚前後所考慮的重點下，則建議採用「寬淺開挖疏浚模擬」，其所造成之疏浚後挖槽內平均流速增加最少為0.11m/s。 在列普尼茲挖槽回淤量問題評估中，河道左側疏浚中所得出之列普尼茲挖槽回淤量係數合格率平均值為最高23.480％，即最好；河道右側開挖疏浚合格率為19.695％次之；第三為窄深開挖疏浚合格率為17.420％；寬淺開挖模擬疏浚中所得之平均合格率為最低15.907％，亦即效果最差，故左側開挖疏浚應為此河段較佳之疏浚模式。