IMMORALITY IN CICERO. I. Hammar Making Enemies. The Logic of Immorality in Ciceronian Oratory. Pp. 381. Lund: Lund University, 2013. Paper. ISBN: 978-91-7473-613-7.

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Irregularity of bedform dimensions

Measured bed elevation profiles show that bedforms are far from regular. Even under controlled steady flow conditions in laboratory flumes bedforms are irregular in size, shape and spacing. Here we present a new Bedform Tracking Tool to determine the (stochastics of) bedform characteristics in an objective manner. This tool helps us in developing a model for variability in bedform dimensions. Form drag, i.e. the flow resistance that is attributed to the presence of bedforms, depends on bedform dimensions. We expect that by taking into account the variability in bedform dimensions the prediction of form drag will be improved. Present research focuses on the effects of variability in bedform dimensions upon form drag

Variations in roughness predictions (flume experiments)

Data of flume experiments with bed forms are used to analyze and compare different roughness predictors. In this study, the hydraulic roughness consists of grain roughness and form roughness. We predict the grain roughness by means of the size of the sediment. The form roughness is predicted by three approaches: Van Rijn (1984), Vanoni & Hwang (1967) and Engelund (1966). The total roughness values (friction factors) are compared with the roughness values according to the DarcyWeisbach equation. Results show that the different methods predict different friction factors. In future research uncertainties in the hydraulic roughness will be taken into account to determine their influence on the computed water levels

Stochastics of bedform dimensions

Often river dunes are considered as regular bed patterns, with a mean dune height and a mean dune length. In reality however, river dunes are threedimensional and irregular features that cannot be fully described by their mean values. In fact, dune dimensions can be considered as stochastic variables. Their probability distribution can be characterized by a mean value and variance. The stochastic properties of dune dimensions are relevant for (see e.g. Van der Mark et al., 2005):\ud • Shipping - highest crests\ud • Pipelines & cables - deepest troughs\ud • Modelling cross-strata sets - troughs, dune heights\ud • Modelling vertical sorting - troughs\ud • Modelling bed roughness - dune heights\ud In the present research the stochastics of crest elevation, trough elevation and dune height are investigated by analysing three sets of flume experiments

On modeling the variability of bedform dimensions

ABSTRACT: Bedforms are irregular features that cannot easily be described by mean values. The variations in the geometric dimensions affect the bed roughness, and they are important in the modeling of vertical sorting and in modeling the thickness of cross-strata sets. The authors analyze the variability of bedform dimensions for three sets of flume experiments, considering PDFs of bedform height, trough elevation and crest elevation divided by its mean value. It appears that the dimensionless standard deviation of the bedform height is within a narrow range for nearly all experiments. This appears to be valid for the trough elevation and crest elevation, as well. For some modeling purposes, it seems sufficient to assume that the standard deviation is a constant, so that the variation in bedform dimension can be modeled by only predicting the mean bedform dimension.