Effects of Operation of the Xiaolangdi Reservoir on Sedimentation of the Lower Yellow River

The Xiaolangdi Reservoir is the another large project 130 km below the famous Sanmenxia Reservoir. It has a dam with the maximum height of 170m and a reservoir volume of 126.5×10⁸m³, and has the comprehensive tasks for flood prevention, irrigation and power generation, etc. The reservoir was impounded in Oct., 1999. Then, it was managed in such a mode that in non-flood season. The reservoir stored the incoming runoff at a rather high water level, and in flood season, the water level was obviously dropped down to release the flood water. Thus the incoming sediment was also regulated by the reservoir. From Oct., 1999 to Oct., 2016, the reservoir volume was lost by 32.62х10⁸ m³.

The Lower Yellow River is notorious for its abundance of sediment and enormous deposition. Especially in 1985~1999, a special dry hydrological series came the river, the incoming runoff was decreased by 35% as compared with that in 1950~1999. About 31% of the incoming sediment load settled down in the Lower Yellow River, and 72% of the deposition was in the main channel. As a result, the flood conveying capacity of the Yellow River was drastically dropped by 30~50% as compared with those in 1950s. The Lower Yellow River was developing into a withered river, and seriously threatened the safety of flood prevention.

Since the impoundment of the Xiaolangdi Reservoir, the conditions of incoming runoff and sediment of the Lower Yellow River have been changed. The sediment released out of the reservoir accounts for 21.1% of that of the inflow in flood season, and in non-flood season, the fresh water (sediment free) is sluiced. Thus, the river channel of the Lower Yellow River has been transformed from aggradation into degradation. The total erosion amounted to 27.56х10⁸t from 1999 to 2016. Therefore, the flood-conveying capacity (bankfull discharge) was increased by 50%~200% and the water level of 3000 m³/s has dropped 1.2~2.2 m, as compared with those in 1999, the beginning of the impounding, because the cross-sections were enlarged. The channel erosion is still going on till several years later, the fact proves that the shrunk Lower Yellow River could be resuscitated its vigor though reasonable operation of water and sediment regulation by the Xiaolangdi Reservoir.