Numerical modelling of floodplain hydraulics and suspended sediment transport and deposition

Abstract

Abstract:A numerical model is presented for the prediction of¯oodplain inundation extents,¯ow depths and velocities, and patterns of suspended sediment dispersion and deposition. The model employs a simpli®ed and novel treatment of¯uid¯ow and a conventional convection±diusion mass balance relationship for suspended sediment transport and deposition. These relationships are solved over a ®nite dierence grid with a relatively ®ne nodal spacing, which enables a detailed representation of complex¯oodplain topography. The model is applied to a 600 m reach of the River Culm, Devon, UK. Continuous records of river stage and suspended sediment concentration monitored at the upstream boundary of the study reach provide the data needed to operate the model. These data are supplemented by measurements of the in situ settling characteristics of the suspended sediment load. Model predictions of overbank¯ow depths and velocities and patterns of suspended sediment concentrations and deposition amounts are presented. Predicted patterns of overbank deposition are described and compared with ®eld measurements obtained with the aid of astroturf sedimentation traps. Grain size distributions obtained for samples of deposited sediment retrieved from the sedimentation traps are also examined and compared with model predictions. The results of both the ®eld measurement programme and modelling work are shown to have signi®cant implications for the representation of¯oodplain topography and suspended sediment particle size and settling properties in numerical simulations of overbank processes.

Improvement of flood frequency analysis with historical information in different types of catchments and data series within the Ebro River basin (NE Iberian Peninsula)

“…These results seem to agree with Horritt and Bates (2001), who find that, when modelling a flood of the River Severn with the 1D model LISFLOOD-FP and its NCFS version, a resolution of 500x500 m is adequate enough and resolutions finer than 100x100 m do not further improve the results. However, our results are in contradiction with various studies, which have shown that small errors in the topography can have significant effects on model results (Bates et al, 1997;Nicholas and Walling, 1998;Wilson, 2004) and with other studies that even conclude that the representation of the channel geometry seems to be the most influencing aspect of hydraulic modelling (Aronica et al 1998;Merwade et al, 2008;Pappenberger et al 2005). Similarly, Casas et al (2004) conclude that a HEC-RAS model run on coarse-resolution DEM produces lower peak flows than when run on finer DEM, and that this difference is greater for low flows than for high flows.…”

Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models

“…This trend has been previously observed in other studies dealing with contemporary sedimentation rates (Middlekoop and Van der Perk, 1998;Nicholas and Walling, 1998;Thonon et al, 2007). River-floodplain connectivity governs hydraulic patterns of overbank flows, and thus sedimentation patterns.…”

Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models

“…At the reach scale, channel-floodplain geomorphology promoted heterogeneity on the amount and composition of sediment retained during the examined flood (Table 2). This trend has been previously observed in other studies dealing with contemporary sedimentation rates (Middlekoop and Van der Perk, 1998;Nicholas and Walling, 1998;Thonon et al, 2007). River-floodplain connectivity governs hydraulic patterns of overbank flows, and thus sedimentation patterns.…”