本文選題：三角洲堆積體 + 沖積河槽��； 參考：《武漢大學(xué)》2014年博士論文

【摘要】：天然沖積河流的形成和發(fā)展是一個漫長而復(fù)雜的過程。前人對沖積河流初期階段的形成發(fā)展規(guī)律研究較少,本文從影響河床演變的主要控制因素：來水、來沙和侵蝕基準(zhǔn)面三個方面入手,采用概化水槽試驗手段進行初步研究。試驗水槽長24.6m,寬3m,高0.6m,為方便分析,現(xiàn)規(guī)定：起點距在-150cm至-50cm之間的區(qū)域為左側(cè)區(qū)域,起點距在-50cm至50cm之間的區(qū)域為中間區(qū)域,起點距在50cm至150cm之間的區(qū)域為右側(cè)區(qū)域。試驗中分別用塑料沙和天然沙對水流泥沙從山區(qū)進入開闊水域的三角洲堆積體形成發(fā)展過程和堆積體中河槽形態(tài)演替規(guī)律進行研究,其中塑料沙試驗主要在單一恒定流量下進行,天然沙試驗先在某一恒定流量下進行,后在已形成的河床基礎(chǔ)上改變?yōu)榱硪缓愣髁坷^續(xù)進行,主要研究成果如下： 1三角洲堆積體形成發(fā)展過程 塑料沙：水流泥沙從山區(qū)進入開闊水域后三角洲堆積體的形成發(fā)展過程可分三個階段：第一階段,水流泥沙在初期依次按小沙波體、帶狀沙波體、扇形三角洲堆積體和舌狀三角洲堆積體形態(tài)形成發(fā)展,堆積體表面無明顯主河槽且兩側(cè)區(qū)域無串溝；第二階段,堆積體表面逐漸形成河槽,先在中間偏向左側(cè)區(qū)域(右側(cè)區(qū)域)形成順直微彎河槽,水流泥沙很快在左側(cè)區(qū)域(右側(cè)區(qū)域)向前推進并淤積抬高,引起水流泥沙在左側(cè)區(qū)域(右側(cè)區(qū)域)流動受阻,轉(zhuǎn)而向右側(cè)區(qū)域(左側(cè)區(qū)域)分流分沙并使其向前推進,待右側(cè)區(qū)域(左側(cè)區(qū)域)堆積體淤積成型后,水流泥沙折返,使水流泥沙又從右側(cè)區(qū)域(左側(cè)區(qū)域)轉(zhuǎn)向左側(cè)區(qū)域(右側(cè)區(qū)域)推進,左側(cè)區(qū)域(右側(cè)區(qū)域)堆積體淤積抬高,之后水流泥沙運動周期性重復(fù)上述發(fā)展過程。進入第三階段,堆積體推進長度逐漸變長,河槽形狀呈現(xiàn)彎曲狀。受彎道環(huán)流作用影響,局部彎道河槽出現(xiàn)銳彎現(xiàn)象,在彎道河槽處發(fā)生凹岸撇彎使水流泥沙在堆積體表面沖刷出新的河槽。位于彎道上段的過渡段河槽受水流泥沙的側(cè)蝕作用在凸岸切灘形成較小的分流口,整體仍然呈蜿蜒狀河槽進行分流分沙。 天然沙：水流泥沙從山區(qū)進入開闊水域后三角洲堆積體的形成發(fā)展過程主要包括兩個階段：第一階段,水流泥沙在初期按水下舌狀三角洲堆積體、扇狀三角洲堆積體和樹枝狀三角洲堆積體形態(tài)形成發(fā)展,堆積體表面有明顯的主河槽且兩側(cè)區(qū)域有較多串溝。第二階段,堆積體表面依次形成的順直河槽、分汊河槽和微彎河槽形態(tài),使水流泥沙沿不同河槽的主流方向以不同方式向前推進：形成順直河槽時,水流泥沙在堆積體的中間區(qū)域居中擺動推進；形成分汊河槽時,水流泥沙沿分汊河槽向兩邊壁方向推進,后再沿河床中間區(qū)域推進；形成微彎河槽時,水流泥沙主要以沿邊壁向中間區(qū)域、沿中間區(qū)域向邊壁及沿單側(cè)邊壁三種方式推進。 經(jīng)對比塑料沙和天然沙試驗,在縱向推進速率上,初始?xì)v時下的塑料沙的推進速率要小于天然沙的縱向推進速率,隨歷時增加,塑料沙呈現(xiàn)逐漸增大趨勢,而天然沙逐漸減小,最終兩種試驗沙推進速率基本相同；在垂向變化規(guī)律上,兩種試驗沙在垂向上先迅速淤積抬高,隨后淤積抬高速率逐漸減小,最終以相對穩(wěn)定的速率抬高；在橫向展寬規(guī)律上,初期受河槽底部泥沙淤積抬高的影響,水流泥沙向兩側(cè)區(qū)域漫流,隨堆積體縱向推進長度變長,水流泥沙在河槽主流中出現(xiàn)橫向泥沙輸移現(xiàn)象。2沖積河槽形態(tài)演替規(guī)律 塑料沙：在恒定的來水來沙作用下,沖積河槽形態(tài)的演替規(guī)律與三角洲堆積體形成發(fā)展過程中所呈現(xiàn)的三個階段相對應(yīng),依次為：初始順直河槽、微彎河槽和分漢河槽、蜿蜒狀河槽。堆積體的整體縱向坡降隨歷時增加逐漸變緩,利于河槽的彎曲狀發(fā)展,使河槽最終形成蜿蜒狀形態(tài)。 天然沙：流量變化前,三角洲堆積體表面的沖積河槽形態(tài)演替過程經(jīng)歷了兩個階段：第一階段為初始?xì)v時下的順直狀河槽和分漢狀河槽交替出現(xiàn)階段。第二階段主要為單一微彎河槽階段,隨微彎河槽的凹岸不斷沖刷后退致使其曲折系數(shù)變大,最終呈現(xiàn)蜿蜒型河槽形態(tài)。流量變化后,三角洲堆積體表面的沖積河槽形態(tài)演替過程依次經(jīng)歷了四個階段：順直分汊河槽階段、微彎河槽階段、分漢河槽階段和微彎河槽階段,最終以穩(wěn)定的單一微彎河槽狀存在。 經(jīng)對比塑料沙和天然沙沖積河槽形態(tài),其演替規(guī)律均出現(xiàn)了順直河槽形態(tài)、微彎河槽形態(tài)、分汊河槽形態(tài)及蜿蜒狀(微彎)河槽形態(tài),且最終形成的河槽形態(tài)均具有正弦曲線形態(tài)特征。在堆積體輸沙特性方面,主要對流量變化后的天然沙試驗結(jié)果進行分析,得出堆積體在整個試驗出口段的輸沙量與進口段的來沙量的比值隨著試驗歷時增加逐漸增大,并在1附近基本穩(wěn)定,說明整個堆積體的輸沙變化逐漸趨于平衡狀態(tài)。
[Abstract]:The formation and development of natural alluvial rivers is a long and complicated process. The research on the formation and development of the initial stage of alluvial rivers is less. In this paper, the main control factors that affect the evolution of the river bed are three aspects of water, sediment and erosion datum surface, and the preliminary study of the test water trough is carried out by the method of the experimental trough. Long 24.6m, wide 3M, and high 0.6m for convenient analysis, it is now stipulated that the region between the starting point and the -150cm to -50cm is the left area, the starting distance between -50cm and 50cm is the middle area, the starting distance between 50cm and 150cm is the right area. In the experiment, the sediment and the natural sand are used to enter the open waters of the water and sediment from the mountain area respectively. The formation and development process of the delta accumulation body and the succession law of the channel form in the accumulation body are studied, in which the plastic sand test is mainly carried out under a single constant flow, and the natural sand test is first carried out at a constant flow rate and then on the basis of the formed River bed to another constant constant flow. The main research results are as follows:
The formation and development of the 1 delta accumulation body
Plastic sand: the formation and development process of the delta accumulation after the flow of water and silt from the mountains into open waters can be divided into three stages: in the first stage, the formation and development of the flow and sediment in the early stages are small sand wave body, banded sand wave body, fan-shaped delta deposit and tongue shaped Delta, and there is no obvious main channel and two sides on the surface of the accumulation body. There are no trenches in the region; in the second stage, the surface of the accumulation body forms a river trough gradually, and the straight and straight micro bend channel is formed in the middle to the left area (right area), and the flow and sediment are quickly pushed forward and silted up in the left area (right area), causing the flow of water and sediment to be obstructed in the left area (right area) and turn to the right area (left side). In the region, the sediment is divided and pushed forward. After the accumulation of the right area (the left area), the sediment is deposited and formed, and the flow and sediment are returned to the left area (the left area) to the left area (the right area), and the silt in the left area (the right area) is raised, and then the sediment movement periodically repeats the above development. In the third stage, the propelling length of the accumulation body gradually becomes longer and the shape of the river channel presents a curved shape. Under the influence of the circulation of the bend channel, the sharp bend appears in the local bend channel, and the concave bank skimming at the bend channel causes the flow and sediment to scour out the new river trough on the surface of the accumulation body. The river trough in the upper section of the bend is subject to the sediment. The side erosion formed a smaller diversion port on the shoal bank, and the whole still had a sinuous channel to divide and divide the sand.
Natural sand: the formation and development process of the delta accumulation after the flow of water and silt from the mountainous area into the open waters mainly includes two stages. In the first stage, the flow and sediment are accumulated in the early stage of the underwater tongue Delta, the fan like delta deposits and the dendrite delta deposits form, and the surface of the accumulation body has a clear main channel. And there are more trench in the two sides. In the second stage, the surface of the smooth channel, the branching channel and the micro bend channel form in order form the surface of the accumulation body, so that the flow and sediment move forward in different ways along the main direction of the different river channels: when the River trough is formed, the sediment is swinging in the middle area of the accumulation body, and the branching channel is formed. The flow and sediment propelling along the two side walls along the branching channel and then advancing along the middle area of the river bed, when the micro bend channel is formed, the flow and sediment mainly move along the edge wall to the middle area along the middle wall and the side wall along the unilateral side wall in three ways.
Compared with the test of plastic sand and natural sand, the propelling rate of plastic sand under the initial diachronic speed is less than the longitudinal velocity of natural sand at the initial diachronic speed. With the increase of time, the plastic sand gradually increases, while the natural sand gradually decreases, and the two kinds of experimental sand pushing rate are basically the same, and two kinds of vertical change laws. In the vertical direction, the test sand is rapidly silted up and raised, then the rate of sedimentation is gradually reduced, and the velocity of sediment is gradually raised at a relatively stable rate. Lateral sediment transport phenomenon.2 succession pattern of alluvial channel
Plastic sand: under the action of constant water and sediment, the succession law of alluvial channel form corresponds to the three stages in the process of formation and development of the delta accumulation body, in turn, the initial straight straight river trough, the micro bend channel and the Han River trough, and the meandering river trough. The longitudinal gradient of the whole body of the accumulation body gradually slows down with the increase of the time and is beneficial to the river. The curved development of the trough causes the channel to form a serpentine form eventually.
Natural sand: before the flow change, the formation process of the alluvial channel on the surface of the Delta has undergone two stages: the first stage is the alternate stage of the straight channel and the Han shaped River trough under the initial diachronic period. The second stage is mainly a single micro bend channel stage, and the erosion of the concave bank of the micro bend channel causes its twists and turns. After the flow change, the formation process of the alluvial channel on the surface of the Delta has undergone four stages: the straight branching channel stage, the micro bend channel stage, the stage of the Han River trough and the micro bend channel stage, and the stable single micro bend channel shape.
After comparison of the morphology of plastic sand and natural sand alluvial channel, the succession law of the river trough appears the shape of the straight river trough, the shape of the micro bend channel, the form of the branching channel and the form of the meandering (micro bend) channel, and the form of the river trough which is finally formed has the morphological characteristics of the sinusoidal curve. The results are analyzed, and the ratio of sediment transport to the inlet section of the whole test exit section increases with the increase of the test duration, and it is basically stable near 1, indicating that the sediment transport in the whole accumulation gradually tends to balance.
【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TV147

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