Characteristics of sediment transportation in a river with overloading and underloading conditions

The geology of Taiwan is fragile .Lots of landslides occurred and a amount of sediment was aggradated at the upstream leading to overloading of the creek. Besides,building sediment control structure like Sabo dam to block sediment will be unable to feed enough sediment to the downstream of river and become underloading.Both of above the conditions will cause river regime unbalanced,hence understanding the variation will be helpful to improve the effect on river control. The research on the different discharge(Q = 0.0026 ~ 0.0063 cms)and the slopes(S = 1% ~ 3%),and uniform grain size of sediment(D50 = 1.7 mm) 18 sets of overloading and underloading flume experients were obtained to analysis. All the experiments carried on Wu-Feng fluid laboratory of National ChungHsing University. The experimental results are shown,at high discharge and steep channel,the amount of the sediment scouring and deposition in overloading experiments is less than underloading experiments.Weather in overloading or underloading conditions or not,the value between final sediment transportation rate and initial sediment transportation rate is larger when the slope is steeper.If the discharge is larger,the ratio of sediment transportation rate (qs) to flow discharge (q) qs/q is larger.And if the slope is steeper,the vaule qs/q shows power increase.Finally,making use experiment data to regression analysis,estimating the experience formula in overloading and underloading conditions to provide.台灣地質脆弱，山坡地集水區上游常發生崩塌而造成大量土石落淤河中，使得供砂量大增，供砂量大於水流挾砂能力，而形成超載(overloading)之現象。而防砂壩等防砂構造物的設置在攔阻上游之來砂後，則可能使防砂壩下游面之河道無法獲得足夠之砂石，而形成減載(underloading)之現象。此兩種情形都將使得河道之平衡受到破壞，因此對於其變化情形之瞭解，將有助於對溪流整治效果之提高。 為此本研究以不同流量(Q＝0.0026~0.0063 cms)與不同坡度(S＝1~3%)為變因，採用均勻粒徑砂石(D50＝1.7 mm)進行超載與減載共18組之渠槽試驗，以探討超載與減載之特性。 研究結果顯示，於陡坡高流量下，超載試驗之沖淤量變化幅度隨時間變化幅度較減載試驗小。無論超載或減載之狀況下，最終輸砂量(Qsf)與起始輸砂量(Qsi)之差值隨溪床坡度之增大而變大。而隨流量增大，超載與減載試驗之輸砂量(qs)對流量(q)之比中文摘要……………………………………………………………….Ⅰ 英文摘要……………………………………………………………….Ⅱ 目錄…………………………………………………………………….Ⅲ 表次…………………………………………………………………….Ⅴ 圖次…………………………………………………………………….Ⅵ 符號說明……………………………………………………………… Ⅷ 壹、 前言……………………………………………………………......1 貳、 前人研究…………………………………………………………..4 2-1 平衡輸砂……………………………………..……..……………5 2-2 非平衡輸砂……………………………………………………...12 參、理論分析………………………………………………………....15 3-1 基本方程式………………………………………………….......15 3-2 維度分析…………………………………………………….......16 3-3 河道超載輸砂歷線………………………………………….......17 3-4 超載與減載情況下之泥砂運移…………………………….......19 肆、 研究方法………………………………………………………....20 4-1 試驗設備…………………………………………………….......20 4-2 試驗砂石粒徑分析………………………………………….......22 4-3 上游供砂量……………………………………………………...23 4-4 試驗條件 …………………………………….............................23 4-5 實驗步驟 …………………………………………………….....24 伍、 結果與討論 ……………………………………………………..26 5-1 床面型態之變化…………………………………………….......26 5-2 超載與減載試驗輸砂量隨時間之變化與差異………………...29 5-3 坡度對於輸砂量之影響.………………………………….........34 5-4 床面沖淤變化.………………………………….........................43 5-5 泥砂輸移率隨時間之變化…………….......................................49 5-6 河道沈滓超載與減載之輸砂模式推導………………………...53 陸、 結論.……………………………………………………………..57 柒、 參考文獻.………………………………………………………..58 附表……………………………………………………………………..61 附圖……………………………………………………………………..68 表次 表2.1 各家輸砂公式………………………………….............................4 表4.1 五釐石粒徑分布基本資料……………………………………...22 表4.2 各公式於平衡輸砂試驗時之試驗條件………………………...23 表5.1 超載與減載試驗水理分析數據………………………………...29 表5.2 不同坡度流量下之最終輸砂量與起始輸砂量………………...38 表5.3 超載試驗與減載試驗平均單寬輸砂量………………………...40 附表1 不同流量下超載與減載試驗沖淤量觀測(S＝1%)……………62 附表2 不同流量下超載與減載試驗沖淤量觀測(S＝2%)……………64 附表3 不同流量下超載與減載試驗沖淤量觀測(S＝3%)....................66 圖次 圖1.1 研究流程圖………………………………………………….........3 圖2.1 Shields曲線圖……………………………….................................6 圖3.1 河道輸砂演算原理示圖………………………………………...18 圖3.2 輸砂歷線示意圖…………………………………………….......18 圖3.3河道超載底床變化示意圖...........................................................20 圖4.1 渠槽試驗配置圖…………………………………………...........20 圖4.2 五釐石粒徑分布曲線……………………………………….......22 圖4.3 試驗流程圖………………………………………………….......25 圖5.1 床面型態變化示意圖...................................................................28 圖5.2 S=1%時超載試驗輸砂量隨時間之變化………………………..33 圖5.3 S=1%時減載試驗輸砂量隨時間之變化………………………..33 圖5.4 S=2%時超載試驗輸砂量隨時間之變化………………………..34 圖5.5 S=2%時減載試驗輸砂量隨時間之變化………………………..34 圖5.6 S=3%時超載試驗輸砂量隨時間之變化………………………..35 圖5.7 S=3%時減載試驗輸砂量隨時間之變化………………………..35 圖5.8 Q=0.0026 cms時超載試驗輸砂量隨時間之變化……………....37 圖5.9 Q=0.0026 cms時減載試驗輸砂量隨時間之變化……………....37 圖5.10 Q=0.0035 cms時超載試驗輸砂量隨時間之變化……………..38 圖5.11 Q=0.0035 cms時減載試驗輸砂量隨時間之變化……………38 圖5.12 Q=0.0063 cms時超載試驗輸砂量隨時間之變化……………..39 圖5.13 Q=0.0063 cms時減載試驗輸砂量隨時間之變化…………......39 圖5.14 超載試驗輸砂量對流量之比值隨坡度之變化……………….44 圖5.1