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旗山溪位于台湾南部,往年每逢大雨,居民便担心河道溢流造成区内外严重淹水,其中高茎作物的种植为争议之一。水利主管部门为考量社会需求及河川管理实务需要,拟适度放宽高茎作物种植申请许可,特制定“河川区域种植规定”。“河川区域种植规定”依据河宽、平均坡降、平均流速及高滩地水深计算值,配合权重计算分数后得到评估等级,并依据桥梁限制等综合评估后进行等级调整。此方法虽可利用评估分数与水位抬升率回归分析值对照表,快速由评估等级推求种植密度,但并非适用于每条河川,故利用HEC-RAS模型仿真种植区域,借由调整模型糙率系数增加值,来评估水位抬升率(水位增加值占出水高1.5 m之百分比),在“河川区域种植规定”中最大水位抬升率不得大于12%规定下,可进一步对照糙率系数增加值与灌木种植密度关系表,得到容许种植密度。结果显示:根据水位抬升率计算的容许种植密度应可高于“河川区域种植规定”之限制,因此目前“河川区域种植规定”中对容许种植密度的要求趋于严格。
Qishan Creek is located in southern Taiwan. In the past year, residents were worried about severe flooding inside and outside the districts due to heavy rains. Among them, the planting of high-stem crops was one of the controversies. In order to consider social needs and practical management of river management, water conservancy authorities intend to moderate the application for permission for planting high stem crops, and formulate “Regulations for the planting of rivers”. “River District Planting Regulations ” Based on the river width, the average gradient, the average flow rate and the calculated height of the highland water depth, the assessment grade is obtained after the score is calculated according to the weight, and the grade is adjusted after the comprehensive assessment according to the bridge restrictions. Although this method can make use of the HEC-RAS model to simulate the planting area, the roughness index of the model can be calculated by using the regression analysis of the evaluation score and the water level rise rate comparison table to rapidly calculate the planting density by the evaluation level, but not for each river. Value added to assess the rate of elevation of the water level (the added value of the water level accounts for a percentage of 1.5 m above the water level). Under the provisions of “Regulations on the planting of rivers”, the maximum water level rise rate shall not be greater than 12% Density relationship table with shrubs, to allow planting density. The results showed that the permissible planting densities calculated according to the rate of water level rise should be higher than the limit of “Regulations for the planting of rivers”. Therefore, the current requirements of planting density in the “River Areas” tend to be strict with the allowable planting densities.