平衡河道之探討

Study on Channel Stabilization

洪炳麟(Pin-lin Hung)

《中華水土保持學報》 4卷2期 (1973/12) Pp. 96-137

https://doi.org/10.29417/JCSWC.197312_4(2).0010

摘要

自然河道之形成，乃因其具有輸送降水曁携帶泥砂能力之所致。河道上游大部坡陡流急產生侵蝕作用，將大量泥砂輸送至下游平緩地區，促成發展爲洪積平原或冲積平原。其肇因諸凡雨水流出特性，泥砂輸出過程，地質地形變化，降水區域與時間之分佈，日照影響，氣候變遷均有密切之關係，導使河道常期不斷變遷。防洪方法，不外乎「蓄」「分」「防」「導」四類。往昔治河方法，由於地廣人疏，或限於經費，或限於局部之開發，大部側重於築堤防洪。築堤防洪，非但易於見効，計劃時僅注意於河道洩洪斷面之股計，然終爲治標方法。臺灣之河流均發源於中央山脈，上游段兩岸爲高山，坡陡流急，斷面狹深，沿岸土質脆弱，時常崩塌，泥砂礫石隨水流下，不但溪水長年渾濁，大量推移質砂石傾注中下游，造成嚴重淤積。例如本省中部主要河川，濁水溪，大甲溪及大安溪等，其中下游河床標高均超于堤內田面一至三公尺。最近二三十年來，水利局曾就實際需要情形，予之加高堤防二至三次，唯徒增堤防高度既非一勞永逸之法且有增大災勢之嫌。因之本省近年來對於河防之觀念，逐漸由建堤防洪階段進入降低河床水位，以「導」爲治理時期。今者世界各國，治河技術日益猛進，「河道平衡」及「泥砂輸送」兩理論，已由經驗與論斷趨勢階段漸次發展至相當把握可推測數量階段。河道平衡坡度硏算，爲治河之基本法則，雖有多種方法在理論上大致可歸納為「靜態平衡」與「動態平衡」兩種，至該兩種計算方法，對各河道之適應度如何？胥視河性及河道工程設計佈置等條件而選定之。倘再進一步將泥砂楡迯過程亦同時考慮在內，推求自然河道之變動，上述兩種平衡理論，仍嫌不足。且上述二已有理論公式內，甚多因素込需依賴實測資料。由於洪水時期觀測困難，所得資料難期十分準確，不無影響推算成果。本文編者就數年來河道規劃所得之經驗，彙集國內外有關穩定河道之理論學說，特將河道平衡坡降計算作簡單之實用介紹，尙請諸先遂多予指正，俾對河道治理規劃設計研究參考或稍有俾益焉。

並列摘要

The heavy load of sediment carried by the rivers in Taiwan is a dominant factor in the present use and future development of the river basin and adjacent areas. According to the records of annual survey, most of the river bed has been raised year by year. This phenomena has greatly increased the damage potential of the rivers during the flood season. Thus, the task of the river regulation and research works of the stable channel design has been more emphasized rescent year. In order to deal intelligently with certain problems of maintenance of channels in erodible materials, it is important to know what shape and dimensions a channel should have in order to avoid changes of cross section due to scour or sediment deposition. A knowledge of stable shapes finds application to the problem of designing canals in earth and to the problems of river regimen. In this paper, the author theoretically analyzed the equibrium bed slope in rivers with sediment transport with gradually varried width and same width of regular cross sections, in consideration of the new developments in the many researches of flowing water and sediment transport in open channels. Besides, a numerical example was added to demonstrate the method of application to a rivers with sediment transport.