Abstract: Storm rains and floods are major natural disasters occurring in the middle reaches of the Yellow River and the tributary rivers. They have caused serious soil erosion and economic losses in the drainage basins. Historical and modern flood stage indicators were investigated in the bedrock gorges of the Malianhe River, which is a major tributary of the Jinghe River in the middle reaches of the Yellow River. During our widespread fieldwork, A group of four flood stages was identified by the clay and silt deposit of 1－3 cm in thickness on the cliff bedrock walls of the river channel in the lower reach gorges of the river. Sediment samples of this flood deposit at the SZZ site were taken during fieldwork. And another group of samples was taken from the MJY loesssoil profile in the drainage basin for comparative study. Laboratory analysis of the grainsize distribution indicates that silt content is very high, clay and sand contents are low in these flood sediment. These features are very similar to that of the loess and soil in the MJY profile in the drainage basin. Magnetic susceptibility of the flood deposit is very low and much similar to that in the Malan Loess and modern soil in the MJY profile, but much lower than that in the Holocene soil S0 in the MJY profile in the drainage basin. The grainsize distribution indicates that this flood deposit was sourced mainly from the erosion and transport by storm rain and floods over the loess regions in the drainage basin of the Malianhe River. The low magnetic susceptibility indicates they are fresh deposit without weathering and pedogenic alteration. The peak discharges of the first three flood events were 1 170 m3/s, 4 060 m3/s and 5 690 m3/s, respectively, as reconstructed by using the hydrologic method. These results correspond with the peak discharges of the gauged flood in 1977,2003 and 2005 on the Malianhe River. The peak discharge of the forth flood event was reconstructed 13 980 m3/s. It occurred in 1841 during the Daoguang 21 year in the Qing Dynasty as known by the local villagers. These flood events also well correlated to the flood events recorded on the Jinghe and Weihe Rivers. This research is of great importance for hydraulic engineering constructions, for flood control and for soil and water conservation in the Malian River basin and the middle reaches of the Yellow River.

Key words: Malianhe River, flood stage indicator, flood deposit, flood discharge