Shiyan Zhang

Simulation of Unsteady Flow and Soil Erosion in Irrigation Furrows

AbstractThis study developed a one-dimensional numerical model for the simulation of unsteady flow and the resultant soil erosion in irrigation furrows. The model solves a modified version of the Saint-Venant equations that consider the loss of mass and momentum attributable to infiltration and sediment transport. The transport rate of fine sediment was predicted with a modified Laursen formula that treats the tractive shear stress as a function of both Reynolds number and the particle size. The modified Laursen formula was verified by using the erosion data measured in the field and in a laboratory flume. The model accurately predicted flow advance times and outflow hydrographs in comparison with data measured in irrigation furrows at Kimberly, Idaho. Sediment discharge predictions were less accurate.

Evaluation of flow and sediment models for the Rillito river

Hydrodynamic and sediment transport models are useful engineering tools for predicting flood flow. Many models such as HEC-RAS, HEC-6, IALLUVIAL, SRH-1D were developed for perennial rivers, and may not be suitable to ephemeral rivers in arid and semi-arid regions. This paper outlines a comparison study that examined the water surface and bed elevations of a flood event exceeding 100-year flood in the Rillito River at Tucson, Arizona. The result of IALLUVIAL2, HEC-RAS and GSTAR1D models were compared with field survey data. Results showed that IALLUVIAL2, which cannot compute bridge effects, predicted a flood similar to that of the more commonly used HEC-RAS model, which take bridges into account. Both models underestimated the flooding by about 2 to 4 feet, but accurately predicted the progression of each flood flow. This study also found the most appropriate sediment transport and roughness equations for this particular river are Laursen sediment equation and Mannings relation. The results indicated the need of an appropriate model for predicting flood flows in ephemeral streams for water resource managers, engineers, and urban planners.

Evaluating spatial variation of suspended sediment rating curves in the middle Yellow River basin, China

The suspended sediment load in the middle Yellow River basin (YRB) cannot be well predicted by capacity‐based transport formulas because a large fraction of suspended sediment load is composed of wash load. This study evaluated the spatial variations of sediment rating curves (SRCs) in the middle YRB. Both power and linear SRCs were used to fit daily flow and suspended sediment concentration (SSC) historical data at 49 gauging stations throughout the middle YRB. The spatial variation in regression coefficients was investigated, and the relationship between regression coefficients and the physical characteristics of watersheds was discussed. The results indicate that SRC regression coefficients vary with drainage area and basin slope, but their responses to these parameters are remarkably different in watersheds with different underlying surfaces, which indicates the significance of sediment availability, erodibility, and grain size distribution. For power SRCs representing sediment transport in unsaturated flows, the regression coefficients are more closely correlated with the drainage area in loess regions and with the basin slope in rock mountain regions. For linear SRCs representing sediment transport in saturated flows, saturated SSCs vary with coarse (particle size > 0.05 mm) and fine (particle size < 0.01 mm) fractions in suspended sediment. The maximum saturated SSC among the different gauging stations is associated with the optimal grain size composition of suspended sediment, which has been proposed for loess regions in previous studies. This study provides theoretical support for estimating the regression parameters for sediment transport modelling, especially in ungauged basins.