黄河玛曲砾质网状河段河间湿地形态特征及发育程度

河间湿地是网状河流体系中与多河道系统同等重要的地貌单元,其特征和发育程度与河道系统共同决定着网状河流的特性。本文以黄河玛曲网状河段作为研究对象,利用高分辨率Google Earth影像对研究河段河道与河间湿地等微地貌单元进行提取,利用湿地面积与湿地数对河间湿地的组成进行了分析,利用河间湿地面积占比、岸线密度、分汊点密度3个地貌参数,对河间湿地群体（河间湿地与分支河道特定组合体）的平面形态及多河道发育程度进行了研究。结果表明,河间湿地个体以中小型的为主,河间湿地群体则以大型和巨型的为主。河间湿地群体的发育程度与河间湿地群体面积（S_u）明显相关,河间湿地面积占比（P）随S_u的增大而增大,P值70%是河间湿地发育成熟的指标,而P值80%基本是河间湿地发育的上限值,此时河间湿地与分支河道基本达到动态平衡态。岸线密度、分汊点密度随S_u的增加呈减小趋势,这种变化主要是由于不同大小河间湿地群体中河道发育过程差异导致。黄河玛曲段河间湿地群体的形成在于弯曲主河道的主导作用、地形限制因素削弱导致的河道带的发育,以及植被维护的河岸使得河间湿地群体得以较长时间保存。

Planform characteristics and developing level of interchannel wetlands in a gravel-bed anastomosing river,Maqu Reach of the Upper Yellow River

Interchannel wetlands as well as multiple channels are crucial geomorphologic units in an anastomosing river system. Planform characteristics and developing level of interchannel wetlands and multiple channels have effect on anastomosing rivers. To understand the role that interchannel wetlands play in the development of the anastomosing river, a study was carried out at the Maqu reach of the Yellow River, a gravel-bed anastomosing river characterized by highly developed interchannel wetlands and anabranches. Geomorphologic units in the study reach were extracted from high resolution satellite imagery in Google Earth, size distribution of interchannel wetlands and interchannel wetland clusters (special combination of interchannel wetlands and anabranches) were investigated, and geomorphologic parameters including ratio of interchannel wetland area to interchannel wetland cluster area (P), shoreline density (D_l) and node density (D_n) were used to examine planform characteristics of interchannel wetland clusters and the development level of multiple channels in the study reach. The results suggest that interchannel wetlands with small or medium size and interchannel wetland clusters with large or mega size are more common in the study reach. The area of interchannel wetland cluster (S_u) is highly related to other geomorphologic parameters, P increases with the increase of S_u, with 80% of P value being basically the upper limit, indicating that the development of interchannel wetlands and anabranches in an interchannel wetland cluster has entered a equilibrium stage. In contrast, D_l and D_n show a tendency to decrease with the increase of S_u due to evolution processes diversity in interchannel wetland clusters with different sizes. There are three main reasons for the formation of interchannel wetland clusters: stream power diversity caused by the meadering principal channel; development of river corridor due to the weakening of geologic structure control; and high stability of interchannel wetlands due to conservation by shoreline vegetation.