网状河流的构型、流量-宽深比关系和能耗率

网状河流作为一类新河型,已经受到研究者的关注,但对其研究还不充分.该研究基于目前已经报道过的资料及新近取得的研究成果,从河流构型、河道过水断面宽深比与流量关系及能耗率等方面对该河型展开论述,期望引起大家对该河型的兴趣.网状河流在许多方面表现出了独有的特色.从平面构型来看,它以相互连通的多河道围绕非常稳定的泛滥盆地为特征,其中泛滥盆地上植被发育、沼泽湖泊可见.从河道纵、横剖面来看,它具有非常小的河道比降和一般小于40的河道宽深比,总体上属于各类河型中最小的.从沉积体系的剖面构型来看,它以多个孤立的河道砂体"漂浮"在细粒泥质沉积物中为特征.在河道过水断面宽深比与流量的半对数图中可见,其宽深比随流量的增大而减小,并且其散点位于各类河流的最下部.由于其河道比降一般很小,多河道体系中的单个河道的流量相对于其决口前的老河道显然较小,从而其能耗率就相对很小.文中所讨论到的长江三口分流网状河道:东松滋河、西松滋河、虎渡河、藕池河、北藕池河和松澧合流,其能耗率分别为3.0 W/m2,5.5 W/m2,2.8 W/m2,6.4 W/m2,3.7 W/m2和2.7 W/m2,显然都小于10 W/m2,这与长江主河道在枝江附近的140 W/m2相比,差两个数量级.所有这些特征都预示着网状河流与以长江中下游为代表的分汊河流之间有着完全不同的特性,与其他河型更是大相径庭.

Architectures, Relationships between Discharges and Width/depth Ratios of Stream Cross Profiles, and Stream Powers of Anastomosing Rrivers

As a new type of rivers, anastomosing river has been concerned by researchers although some questions about it was not clear for understanding it. This paper discusses the river architectures, relationships between width/depth ratios of stream cross sections and discharges, and stream powers of anastomosing rivers according to references and obtained data recently. It is helpful to researchers who is interested in this river pattern to develop the theory for it. Many aspects of anastomosing river appear particular characteristics compared with other river patterns. In the planform architectures, the multiple channels joining each other enclose flood basins on which vegetation, swamps and lakes develop basically. Longitudinal gradients of the channels are very low while the channel width/depth ratios are smaller than 40. In the depositional architectures of cross profiles, some isolated sand bodies of channel deposits are "floating" in the mud bodies of flood basins. In the half logarithm diagram of width/depth ratios of stream cross profiles vs. discharges, the scatters of anastomosing rivers are below compared with that of other river patterns. The stream powers of anastomosing rivers are very low compared with the old trunk channel from which it diverted because the channel gradients and discharges of every anastomosing channel are smaller than that of the old trunk channel. The specific stream power of the anastomosing channels: eastern Songzi River, western Songzi River, Hudu River, Ouchi River, northern Ouchi River and Songliheliu River are 3.0 W/m 2, 5.5 W/m 2, 2.8 W/m 2, 6.4 W/m 2, 3.7 W/m 2 and 2.7 W/m 2, respectively. Obviously, all of them are smaller than 10 W/m 2. But the specific stream power of anabranched Changjiang trunk channel is 140 W/m 2. All of the characteristics of anastomosing rivers indicate that this river pattern is different from the anabranched rivers represented by the lower Changjiang River, especially from other river patterns.