Figure 1 Map of the Yellow River Basin drainage area showing the locations of the major reservoirs and of the lower river reaches showing the locations of the major hydrological stations.
Our study reach is from the Huayuankou (HYK) hydrological station in Zhengzhou city to the Gaocun (GC) hydrological station in Heze city (see Figure 2). This reach is a typical braided reach in the LYR, which has the following characteristics (Qian, Zhou, & Hong, 1961; Wu et al., 2005): i) the river is wide and shallow and does not have a stable channel but often consists of two or more channels divided by rapidly migrating bars; ii) the shape of the cross-section changes greatly along the channel, and the mainstream shifts frequently back and forth and continues eroding the floodplains; and iii) the floodplains on both sides of the channel are very wide, and many villages and farmland are located there.
Along the 186.5 km study reach from HYK to GC, seven reaches of equal length are established, namely, Huayuankou - Huanglianji (HYK - HLJ), Huanglianji - Weicheng (HLJ - WC), Weicheng - Wang’an (WC - WA), Wang’an - Jiahetan (WA - JHT), Jiahetan - Youfangzhai (JHE - YFZ), Youfangzhai - Yangxiaoji (YFZ - YXJ), and Yangxiaoji - Gaocun (YXJ -GC), as shown in Figure 2. Each reach consists of the main channel and the floodplain, and the area of each part is calculated (Table 1). The total surface area of the study reach is approximately 1,710 km2, of which approximately 356 km2 marks the main channel, accounting for 21% of the total area, and the remaining 1,353 km2 consists of floodplains, accounting for 79% of the total area.
Table 1 Divisions and areas of the reach between HYK and GC of the lower Yellow River