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In this study, the riverbank inundation caused by moderate frequent flooding events (with recurrence periods of less than 20 years), along with the increasingly serious hazards of backward flows in dike-through drainage ditches in the Ningxia Reach of the upper Yellow River (NRYR), were investigated. Then, a comprehensive method for hazard assessment of the floodplains and backward flows in the NRYR was proposed, which fully integrated geographical information systems (GISs), remote sensing (RS), and a digital elevation model (DEM), as well as river dynamics theory. This study first established a one-dimensional unsteady hydrodynamic model for the NRYR. The historical flood hydrology observation from 2012, along with the aerial image measurement data of the study area, were used to calibrate and verify the accuracy of the model. The hazards of riverbank inundation and damages to water affected engineering facilities, as well as the backward flows of dike-through drainage ditches caused by the moderate frequent flooding events, were comprehensively analyzed. Also, this study configured the hazard map and proposed revisions to the flood hazard ranking regime definitions, and discussed the impacts and prevention and control measures of moderate frequent flood damages. The proposed method could effectively meet the hazard analysis demands of the moderate frequent flooding events in the NRYR. are widely used in the field of flood hazard analysis due to the rigorous approach. These abilities mainly include the applications of one-dimensional hydrodynamic models of river channels [4-8]; two-dimensional hydrodynamic models [2,[9][10][11][12][13][14][15]; one-and two-dimensional coupling models [16][17][18][19][20][21][22]; and three-dimensional hydrodynamic models [23][24][25][26][27][28]. In a previous related study, Anees et al. discussed the applicability and limitations of one-, two-, and three-dimensional numerical modeling techniques for flood analyses in river channels and floodplains [29]. With the rapid development of spatial information technology, such as geographic information systems (GISs), remote sensing (RS), and global positioning systems (GPSs), a large number of research studies have been recently carried out regarding the application of "3S" technology in flood inundation hazard assessments in river-floodplain areas. These have included flood inundation connectivity and evolution simulations of floodplains or surface flooding based on GIS and digital elevation model (DEM) technology [30][31][32][33][34][35][36][37][38]; flood hazard analyses and hazard graph mapping based on GIS and hydrodynamic numerical models [39][40][41][42][43][44][45][46][47][48]; and flood impact and loss evaluations based on 3S and DEM technology [49][50][51][52][53]. Meanwhile, some researchers have attempted to predict flood inundation hazards in large range or even global scales with low-resolution DEM data and hydrologic and hydrodynamic models [54][55][56][57][58].In recent years, the research team of the State Key Labora...

Recently, construction of many large-scale water conservancy projects, as well as the vegetation protection and restoration projects in the upper reaches of the Yellow River, have led to serious changes in water inflow processes, sediment inflow processes, and scour and silting situation in the Ningxia section of the Yellow River (NSYR). This study explored the relationship between the sediment scouring and the silting law of the sediment-laden rivers and the equilibrium fluvial facies in the NSYR. The double cumulative curves of the annual silting amounts and annual incoming sediment amounts in the Qingtongxia-Shizuishan section were then established. It has been previously proven the fluvial facies coefficient increases year by year with the increase in the silting amounts in the watercourse, which lead to the evolution of the watercourse toward the wandering reach. The fluvial facies relationships of their cross-sections under an equilibrium state in the NSYR were established using a Yalin fluvial facies method. The Fr values under an equilibrium state and the actual state were analyzed. The results showed the Xiaheyan section was in an equilibrium state, and the Qingtongxia and Shizuishan cross-section were in a scouring state. This conclusion was confirmed by the actual measured results for numerous years.

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