科尔沁沙地西部响水河河水与其河岸相互作用的初步研究

Interactions between Xiangshui River and its banks on the western Horqin Sand Land,Northeast China

近年来,半干旱地区的风水相互作用正成为风沙地貌研究的新热点,为探讨科尔沁沙地西部响水河河水与其河岸间的相互作用,通过对科尔沁沙地西部响水河的3个典型河段的6个断面的断面形态、流速进行现场实测,同步采集了31个水样,然后在室内对其泥沙含量进行测试,并推算断面流量。结果表明:由南向北3个河段瞬时流量和泥沙含量呈递增的趋势,集水效应十分明显;该河丰水期水量较为丰沛,河流与河岸间的相互作用明显且活跃,主要存在河水掏蚀河岸陡坡等5种相互作用的方式;当下风向陡岸弯道的法线方向与当地盛行风向一致时,气流发生明显汇聚,侵蚀加强,形成风蚀槽,且当风蚀槽接近谷底时,又为曲流的摆动创造了有利条件;河流受到沙丘前移的压迫与下风向河谷陡坡的阻挡,曲流较为发育但不完美,属于非自由曲流。

The fluvial-aeolian interaction in semiarid areas is becoming a new hot issue of aeolian geomorphology research. In this paper,the field survey and observation were both conducted along the Xiangshui River on the western Horqin Sand Land,Inner Mongolia,China,three typical sections were selected with each having two transects. In each transect,the cross-sectional shape and flow speed were measured;meanwhile,31 water samples were collected in total,and the sediment loads were acquired by desiccation method. The discharges are calculated according to the speed and cross-sectional area. Results show as follows：（1）The instantaneous discharge and sediment load apparently increase from south to north,because the catchment area of mobile dune fields along the river successively augments streamwise and the riverbed is composed of loose sand which is easily eroded and carried by the flowing water.（2）In summer,the discharge is larger,and the interactions between river and its banks are evident and active. The manners of interactions are fundamentally shown as follows：running water eroding upwind riverine dunes and encroaching into the river valley by lateral erosion;upwind marginal dunes burying and pressing riverbed;the running water eroding the steep downwind valley walls composed of Q3 lacustrine sediments;river eroding the river floodplain;river laterally eroding the riverbank dunes;sand dunes in the river valley burying the river way.（3）When the normal direction of downwind steep bend coincides with the local prevailing wind direction,airflow shows an obvious convergence,wind tends to speedup,thereby exerting more intensive erosion by wind and promoting the formation of groove-shaped blowouts. Consequently,this,in turn,facilitate the formation and development of the riverbank dunes,and as the concave bank is seriously eroded,and the load accumulates at the convex bank,then favorable conditions for meandering are created.（4）As the river is not only suppressed by encroaching upwind dunes,but also blocked by downwind valley walls,the development of meandering of Xiangshui River is well-developed,but not perfect without standard loops. Therefore,the river is not a free meandering,but a confined one.