This study evaluated multiple aspects of flood risks and effects on the Cinan Feizuo flood protection area in the Huaihe River basin. Flooding remains a leading problem for infrastructure, especially in urban, residential areas of the region. Effective flood modeling for urbanized floodplains is challenging, but MIKE (ID-2D) is paramount for analyzing and quantifying the risk in the vulnerable region. The Saint-Venant equation and a one-dimensional (1D) MIKE 11 model were used to understand the flood dynamics in the Huaihe River, and a two-dimensional (2D) MIKE 21 model was applied to assess the risk in the Cinan Feizuo flood protection area. The finite volume method (FVM) was used for discrete grid problems, and the models were coupled through the weir equation to find the flow volume from the 1D domain to the 2D domain to investigate water level changes. Flood inundation maps were generated for the flood protection area. The maximum discharge, velocity, and submerged depth for 50- and 100-year flood events were assessed with flood risk. Chenbei indicated a high flood risk level in 50 to 100 years in which the water level exceeds a high level and inundates the maximum area with minimum time. Conversely, the 100-year flood inundation in the flood protection area was comparatively higher than the 50-year flood, with a lower time step. The risk analysis identified significant damage caused by the flood over the target regions. The findings of this study provide technical support for flood risk analysis and loss assessment within the flood protection area and have important reference values for regional flood control, disaster reduction decision making, and constructive planning.

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.

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.