山区河流河床基岩暴露与沙卵石覆盖反常关系研究——以陇西河为例

发布时间：2018-03-25 05:07

  本文选题：基岩暴露　切入点：沙卵石覆盖　出处：《工程科学与技术》2017年S1期

【摘要】：山区河流不同河段的河床形态常处于基岩暴露与沙卵石覆盖的相间变化中。野外调查发现,至少在青藏高原与四川盆地过渡带,不少河流出现坡度大而沙卵石覆盖多,坡度小而基岩暴露多的现象。为了研究该反常规律,以岷江二级支流陇西河为例,进行多次野外观测与数据采集,通过提取流域地形数据,得到并分析其干流沿程剖面,并结合已有的室内水槽试验研究结果,进一步说明床面沙卵石的运动情况与分布特性,得到以下结论:陇西河流域岩性以砂岩为主,干流从上游向下游依次出现陡、缓、陡、缓交替的4段,平均坡度依次为8.1%、0.2%、6.2%和1.2%;较陡的两段全部沙卵石覆盖,较缓的两段全部基岩暴露。产生这种现象的原因:一是较陡段泥沙颗粒通过两侧山体崩塌滑坡侧向补给,床面大尺寸漂石与周围的较细颗粒会逐渐形成相对稳定且水流阻力大的自锁结构,且床面粗糙,有助于提高床面抗冲刷性,抑制基岩的暴露,因此导致输送到下游较缓段的输沙率很低;二是砂岩颗粒岩性较软,少量被输移到下游的颗粒容易破碎成更小的颗粒,更容易被输移,使得较缓段基岩暴露现象突出。较陡段被沙卵石覆盖,将有效抑制窄深处基岩河床的侵蚀下切速率,从而进一步影响相关流域地貌的演化,如增加河流袭夺的机率。
[Abstract]:The river bed morphology of different reaches of mountain rivers is often in the interphase change of bedrock exposure and sand pebble coverage. Field investigation shows that at least in the transitional zone between the Qinghai-Tibet Plateau and Sichuan Basin, many rivers have a large slope and more sand and pebble cover. In order to study this anomalous law, taking Longxi River, a secondary tributary of Minjiang River, as an example, many field observations and data collection were carried out, and the main stream profile along the river was obtained and analyzed by extracting the topographic data of the basin. Combined with the experimental results of indoor flume, the movement and distribution characteristics of bed sand pebbles are further explained, and the following conclusions are obtained: the lithology of Longxi River basin is dominated by sandstone, and the main stream is followed by steep, gentle and steep from upstream to downstream. The average slope of the four sections alternated slowly is 8.2% and 1.2% respectively; the two steeper sections are covered with all sand and pebbles, and all the bedrock in the slower two sections are exposed. The causes of this phenomenon are as follows: first, the sediment particles in the steeper section are recharged laterally through the two sides of the landslide, The self-locking structure with relatively stable flow resistance and rough bed surface will be gradually formed between the large-size drift stone and the surrounding fine particles, which will help to improve the scour resistance of bed surface and restrain the exposure of bedrock. As a result, the transport rate of sand to the slower section of the lower reaches is very low. Second, the sandstone grain lithology is softer, and a small number of particles transported downstream are easily broken into smaller particles and transported more easily. The relatively steep section is covered with sandy pebbles, which will effectively restrain the erosion rate of the bedrock bed in the narrow depth, thus further affect the geomorphological evolution of the relevant watershed, such as increasing the probability of river capture.
【作者单位】： 四川大学水力学与山区河流开发保护国家重点实验室水利水电学院;
【基金】：国家自然科学基金资助项目(51509172;51539007;51609160) 国家重点研发计划资助项目(2016YFC0402302) 国家“十二五”科技计划资助项目(2012BAB05B02) 四川大学青年启动基金资助项目(2015SCU11046)
【分类号】：TV143
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本文编号：1661658