河床質調查位置與數量的合理性探討

Abstract

水利工程進行河川整治，探討水理以及輸砂問題時，河床質的組成是重要影響因子之一。河床質因受多項變異性的影響，調查需依據河相、地質、地形等將河川加以分類，並考慮河川的縱向、橫向以及垂直向之變異性，挑選出具有代表性的取樣位置。 本論文採用傅志偉(2005)提出的河床質調查位置評選方法，以頭前溪為例，為取得合理且具代表性的河床質，進行河床質的調查。主要研究目的在於，觀察河床粒徑於縱斷面、橫斷面的變化情形，提出頭前溪河床質調查的合理調查位置與數量的建議。並探討網格法於台灣河床質調查的適用性及提出網格法細粒料的修正方法，以提升網格法河床質調查的合理性。 研究成果顯示，當調查目的僅需要表層河床質資料時，網格法比起體積法，可經濟且有效率的獲得河床質縱向以及橫向的變化關係。網格法細粒料修正方法，適用於無細料覆蓋之邊灘與無植生沙洲，並可取代體積法表層資料，當施做區域無表面粗粒化現象時，可取代體積法表、底層資料。網格法交織河相與蜿蜒河相的連接槽河段，粒徑於橫向的變化趨勢明顯，亦即粒徑隨著深槽距的增加而減少。河床質中值粒徑縱向變化呈現隨河口距增加而變小，然而受人工構造物影響嚴重。交織河相與蜿蜒河相，建議取樣位置為連接槽邊灘，縱向距離每500公尺佈下1~2組試驗點。辮狀河相，建議調查位置為寬帶沙洲，每一沙洲均佈下取樣點，單一沙洲設置2~3組網格法。若遇到人工構造物，需於構造物上下游增加施作點。

Bed material is one of important influence factors when concerning about the flow resistance, particle initial movement and sediment transport. In general, grid sampling is more economy and efficient than volumetric sampling. Due to the grain size distribution of bed material is strongly affected by river morphology, riverbed material, and river geology, it is necessary to divide a river into several sub-streams by a river classification system before deciding sampling sites. The river classification system proposed by C.W. Fu (2005) was adopted in the thesis. The study aims to study the feasibility of sampling locations and sampling numbers and to present adjusted methods of Grain size distribution curve obtained from grid sampling. The Toucian River was selected as an example. Based on the classification system, the river is divided into 6 sub-streams and 24 sets of volumetric sampling and 66 sets of grid sampling were conducted. Based on the sampling results, the facts reflect that the grain size distribution curve obtained from grid sampling adjusted by the armor fines methods are smooth and reasonable and the method is suitable for the site with non-covered riffle and no plant bar. For the sampling locations and numbers, the results show that in Meandering and Anastomosed river, bed material is finer as the distance between main streamway shorter, 1~2 sampling sites on the riffle of crossing were recommended; in Braided river, 2~3 sampling sites on each bar were suggesred.