Effects of the coarse sediment movement in the flood on Inner Mongolia Reach of Yellow River in 2012

Coarse sediment movement in rivers is one of the key factors in causing changes in channel characteristics. The duration of the 2012 flood in the Inner Mongolia Reach of the Yellow River (IMYR) was the longest and the peak discharge was the biggest since 1989. The aim of this study was to investigate the impact of the movement of coarse sediment during the 2012 flood on the riverbed of IMYR, a coarse sand reach. The wide valley reach of IMYR is bounded by the Bayangaole, Sanhuhekou and Toudaoguai gauging stations from upstream to downstream. The coarse sand in the channel is one of the most important factors impacting riverbed erosion and deposition. Using real observational data, we analyzed the water and sediment characteristics of IMYR during the 2012 flood. By calculating sediment discharge of the bed load and comparing the river bottom of the fixed sections during the flood, this paper assesses the effect of the movement of coarse sediment on the river bottom adjustment. The results show that, ① the coarse sediment was scoured in the upstream part of the IMYR and deposited downstream during the flood in 2012; ② the open area beneath the fixed low water level followed the rule of scouring during the flood rising period and deposition during the flood falling period; ③ the open area under the low water at Bayangaole and Sanhuhekou gauging station expanded by 19 m² and 29 m² respectively, while the same at Toudaoguai gauging station decreased by approximately 100 m². Owing to the imbalance of coarse sediment ejection after the flood, the actual elevation of the riverbed bottom did not get lower, and the flood risk remains at a similar level.