水流泥沙造床过程的初步试验研究

发布时间：2018-05-31 19:13

本文选题：三角洲堆积体 + 冲积河槽　；参考：《武汉大学》2014年博士论文

【摘要】：天然冲积河流的形成和发展是一个漫长而复杂的过程。前人对冲积河流初期阶段的形成发展规律研究较少,本文从影响河床演变的主要控制因素：来水、来沙和侵蚀基准面三个方面入手,采用概化水槽试验手段进行初步研究。试验水槽长24.6m,宽3m,高0.6m,为方便分析,现规定：起点距在-150cm至-50cm之间的区域为左侧区域,起点距在-50cm至50cm之间的区域为中间区域,起点距在50cm至150cm之间的区域为右侧区域。试验中分别用塑料沙和天然沙对水流泥沙从山区进入开阔水域的三角洲堆积体形成发展过程和堆积体中河槽形态演替规律进行研究,其中塑料沙试验主要在单一恒定流量下进行,天然沙试验先在某一恒定流量下进行,后在已形成的河床基础上改变为另一恒定流量继续进行,主要研究成果如下： 1三角洲堆积体形成发展过程塑料沙：水流泥沙从山区进入开阔水域后三角洲堆积体的形成发展过程可分三个阶段：第一阶段,水流泥沙在初期依次按小沙波体、带状沙波体、扇形三角洲堆积体和舌状三角洲堆积体形态形成发展,堆积体表面无明显主河槽且两侧区域无串沟；第二阶段,堆积体表面逐渐形成河槽,先在中间偏向左侧区域(右侧区域)形成顺直微弯河槽,水流泥沙很快在左侧区域(右侧区域)向前推进并淤积抬高,引起水流泥沙在左侧区域(右侧区域)流动受阻,转而向右侧区域(左侧区域)分流分沙并使其向前推进,待右侧区域(左侧区域)堆积体淤积成型后,水流泥沙折返,使水流泥沙又从右侧区域(左侧区域)转向左侧区域(右侧区域)推进,左侧区域(右侧区域)堆积体淤积抬高,之后水流泥沙运动周期性重复上述发展过程。进入第三阶段,堆积体推进长度逐渐变长,河槽形状呈现弯曲状。受弯道环流作用影响,局部弯道河槽出现锐弯现象,在弯道河槽处发生凹岸撇弯使水流泥沙在堆积体表面冲刷出新的河槽。位于弯道上段的过渡段河槽受水流泥沙的侧蚀作用在凸岸切滩形成较小的分流口,整体仍然呈蜿蜒状河槽进行分流分沙。天然沙：水流泥沙从山区进入开阔水域后三角洲堆积体的形成发展过程主要包括两个阶段：第一阶段,水流泥沙在初期按水下舌状三角洲堆积体、扇状三角洲堆积体和树枝状三角洲堆积体形态形成发展,堆积体表面有明显的主河槽且两侧区域有较多串沟。第二阶段,堆积体表面依次形成的顺直河槽、分汊河槽和微弯河槽形态,使水流泥沙沿不同河槽的主流方向以不同方式向前推进：形成顺直河槽时,水流泥沙在堆积体的中间区域居中摆动推进；形成分汊河槽时,水流泥沙沿分汊河槽向两边壁方向推进,后再沿河床中间区域推进；形成微弯河槽时,水流泥沙主要以沿边壁向中间区域、沿中间区域向边壁及沿单侧边壁三种方式推进。经对比塑料沙和天然沙试验,在纵向推进速率上,初始历时下的塑料沙的推进速率要小于天然沙的纵向推进速率,随历时增加,塑料沙呈现逐渐增大趋势,而天然沙逐渐减小,最终两种试验沙推进速率基本相同；在垂向变化规律上,两种试验沙在垂向上先迅速淤积抬高,随后淤积抬高速率逐渐减小,最终以相对稳定的速率抬高；在横向展宽规律上,初期受河槽底部泥沙淤积抬高的影响,水流泥沙向两侧区域漫流,随堆积体纵向推进长度变长,水流泥沙在河槽主流中出现横向泥沙输移现象。2冲积河槽形态演替规律塑料沙：在恒定的来水来沙作用下,冲积河槽形态的演替规律与三角洲堆积体形成发展过程中所呈现的三个阶段相对应,依次为：初始顺直河槽、微弯河槽和分汉河槽、蜿蜒状河槽。堆积体的整体纵向坡降随历时增加逐渐变缓,利于河槽的弯曲状发展,使河槽最终形成蜿蜒状形态。天然沙：流量变化前,三角洲堆积体表面的冲积河槽形态演替过程经历了两个阶段：第一阶段为初始历时下的顺直状河槽和分汉状河槽交替出现阶段。第二阶段主要为单一微弯河槽阶段,随微弯河槽的凹岸不断冲刷后退致使其曲折系数变大,最终呈现蜿蜒型河槽形态。流量变化后,三角洲堆积体表面的冲积河槽形态演替过程依次经历了四个阶段：顺直分汊河槽阶段、微弯河槽阶段、分汉河槽阶段和微弯河槽阶段,最终以稳定的单一微弯河槽状存在。经对比塑料沙和天然沙冲积河槽形态,其演替规律均出现了顺直河槽形态、微弯河槽形态、分汊河槽形态及蜿蜒状(微弯)河槽形态,且最终形成的河槽形态均具有正弦曲线形态特征。在堆积体输沙特性方面,主要对流量变化后的天然沙试验结果进行分析,得出堆积体在整个试验出口段的输沙量与进口段的来沙量的比值随着试验历时增加逐渐增大,并在1附近基本稳定,说明整个堆积体的输沙变化逐渐趋于平衡状态。
[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.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TV147

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