嫩江上游河型转化控制因素及转化模式

Controlling influences and models of river pattern transformation in the upstream of the Nenjiang River

河型转化是河流演化由量变到质变的综合反映,具有科学研究和服务生产的双重价值。以嫩江干流上游(以下简称嫩江上游)为研究区,利用遥感影像和地貌、气候等资料描绘了1985—2020年嫩江上游的河流形态特征,分析了河流类型、河型转化控制因素及河型转化模式。研究表明:①嫩江上游整体为稳定的河流且稳定性先增后减,顺河流方向发育三种河型——低坡度高弯度稳定的曲流河(河段Ⅰ)、高坡度高弯度稳定的曲流河(河段Ⅱ)、低坡度较稳定的网状河(河段Ⅲ);②构造活动微弱是河流稳定的前提,气温和降水变化量是稳定性变化的控制因素,且气温变化量的贡献率更大;③河段Ⅰ转化为河段Ⅱ的控制因素为断层和冻土,土壤起协同作用,河段Ⅱ转化为河段Ⅲ的控制因素为地形和河流边界岩性,土壤、植被起协同作用;④嫩江上游的河型转化是一种流域尺度内构造运动限制的中纬度半湿润-湿润区山地曲流河向平原网状河转化的模式,这一模式常见于东北亚。

River pattern transformation is a comprehensive reflection of the evolution of rivers and the whole basin from quantitative to qualitative change, and is valuable in terms of both scientific research and production service. Taking the upper reaches of the main stream of the Nenjiang River(hereinafter referred to as the upstream of the Nenjiang River) as the study area,this study depicts the morphological characteristics of the upstream of the Nenjiang River from 1985 to 2020 using remote sensing images, geomorphological data, vegetation coverage data and climate data. Then it analyzes the morphological characteristics of the river, types of rivers,the controlling factors and models of river pattern transformation. The study shows that:(1)The upstream of the Nenjiang River is stable on the whole, and the overall stability first increases and then decreases. It is developed with three river patterns in the river direction: lowslope, high-curvature, stable meandering river(Stream Ⅰ), high-slope high-curvature, stable meandering river(Stream Ⅱ), and low-slope, less stable anastomosing river(Stream Ⅲ).(2)The river width increases in the direction of the river, the slope increases and then decreases,the curvature index is greater in single-channel areas than in multi-channel areas, and the stability of plain rivers is lower than that of mountain rivers.(3) Weak tectonic activity is a prerequisite for river stability, and temperature and precipitation variability are controlling factors of stability change. The contribution of temperature variability is greater.(4) The transformation from Stream Ⅰ to Stream Ⅱ is controlled by faults and permafrost, with soil acting synergistically. By contrast, the transformation from Stream Ⅱ to Stream Ⅲ is controlled by landform and river boundary lithology, with soil and vegetation acting synergistically.(5)The river pattern transformation in the upstream of the Nenjiang River is a pattern under midlatitude semi-humid-humid climate, where meandering river in the mountains changes into anastomosing river in plain constrained by tectonism within the basin scale. It is common in Northeast Asia, especially in areas where permafrost is more developed. Variations in the contribution of three types of controls-tectonic, climatic and river boundary properties,contribute to the spatiotemporal variability and complexity of river pattern transformations.