Estimation of River Bend Migration Rate for a Meandering River by Using Tree Ring Analysis

A meandering river has dynamic geomorphological evolution characteristics of creeping movement, and studies on evolution process of the meandering river have both scientific significance and engineering practice value. The source region of the Yellow River is located in the northeastern part of the Qinghai-Tibet Plateau, where meandering rivers are extensively developed. Due to the source region is inaccessible and lacking of long-term river monitoring data, studies on river evolution process in this region are difficult. Combined with the field investigation and sampling in the source region of the Yellow River in 2016 and 2017, total 9 river bends of the Baihe River, a typical meandering river, are selected as an example to analyze the evolution process of the river with help of tree ring analyses in this paper. The vegetation distribution in the convex bank of the river bends was analyzed, and the tree ages were obtained by tree ring analysis. The method of estimating the migration rate of a river bend using the tree rings analysis was proposed base on the relationship between convex bank growth with sediment deposition and the vegetation succession. It was a beneficial attempt to study the river evolution process by applying the tree ring analysis for rivers lacking long-term measuring data. It shows that under the influence of meandering river evolution and vegetation succession, belts of cobble and gravel, sparse herbaceous vegetation, dense herbaceous vegetation and trees of Salix atopantha were distributed in sequence from the bank in the convex bank of the river bends. The trees were also distributed in belts that the trees were short in the belt near the bank and tall in the belt farther away from the bank. Samples of the tree cores or discs collected in the convex bank of the river bends were studied by tree ring analysis to obtain the tree ages, and the migration rates of the river bends were estimated based on the relationship of tree positions and tree ages. The values of migration rate of the river bends of the Baihe River range (0.38-6.10) m/yr. The scales of the migration rate of the river bends were estimated by using remote sensing images, and it was found by comparison that the scales were basically consistent to the values estimated by the tree ring analysis. The comparison results indicated that the migration rates of the river bends estimated by the tree ring analysis were acceptable.