Triangle Shaped Bends Associated with Peat in the Zoige Basin, Northeast Qinghai – Tibet Plateau, China

Abstract:

The bends of alluvial meanders show repeating planforms, among which the sine-generated curve and Kinoshita curve have been proposed as good descriptions. Indeed, the dynamics of meander bend initiation and evolution have been extensively studied. Modelling research coupling flow and sediment dynamics has shown that a meandering channel with a homogenous floodplain generates bends with the classical Kinoshita form (panel a of Figure). Other forms are thought to be brought out by floodplain erosional heterogeneity, which could be pre-existing or self-formed. An extreme case of meander planform influenced by erosional heterogeneity is when the channel hits the valley wall, namely, confined meanders (panel b of Figure). Confined meanders generate acute turns the points contacting the valley wall, thus forming different planforms from their freely meandering counterparts. Nicoll and Hickin (2010) suggested that they should be regarded as part of a continuum of meandering river pattern. Here we consider another kind of river planform with acute turns, that is, sinuous rivers in peatland (panel c of Figure). As is shown in panel c, the planform of the downstream Heihe River in the Zoige Basin, Northeast Qinghai – Tibet Plateau, China, shows sharp turns alternating with straight reaches upstream and downstream of the bend apex. Rather than Kinoshita or sine-generated curves, the bends of Heihe River are more suitably described as triangle-shaped. To look into this planform, we first did a statistical comparison between planforms of common alluvial meanders and those of peatland meanders. We find the distribution of dimensionless curvature can help distinguish them. Some river reaches show both alluvial smooth features and peatland angular features. Since there is a continuum of types, we speculate that peatland meanders could also be regarded as part of a continuum of meandering river pattern. We question whether this angular planform is caused by erosional heterogeneity of peatland. We measured peat depth distribution along rivers in the Zoige Basin, Northeast Qinghai – Tibet Plateau, China. We also collected bank samples. We find that while heterogeneity does exist, it is not directly related to peat depth. A more thoroughly study is needed to unveil the dynamics of sinuous channels in peatland.