Water Level Uncertainties Due to Uncertain Bedform Dynamics in the Dutch Rhine System

Quantitative estimations of water level uncertainties are essential for the design and assessment of flood protection systems. This work aims to quantify the water level uncertainties in the bifurcating Dutch river Rhine system as a result of main channel roughness uncertainty. An one-dimensional hydraulic model of the Rhine branches is used to estimate the water levels in the system for several roughness scenarios. Model results show that the roughness effect has a large influence on the modelled water levels. However, for the larger Waal branch, the changing discharge distribution counteracts the roughness effect, thereby decreasing the range of possible water levels. For the smaller Nederrijn and IJssel branch it is possible that the discharge in the respective branch increases even though the branch has a high roughness. Thereby, for these branches the discharge distribution effect increases the range in modelled water levels. The large and varying effects on water levels by roughness uncertainty and changing discharge distributions in a bifurcating river system indicate the importance to consider the system as a whole instead of as separate branches in the design and assessment of river engineering works

Modelling effects of an asphalt road at a dike crest on dike cover erosion onset during wave overtopping

Structures integrated in a grass-covered dike may increase erosion development. Currently, safety assessment methods for flood defences are only applicable for a conventional grass-covered dike and the effects of structures on dike cover erosion are poorly understood. Since many dikes have a road on top, it is important to study the effect of such a road structure on erosion onset during wave overtopping. To investigate this effect, a coupled hydrodynamic–eroison model was developed. The erosion onset caused by overtopping waves was predicted by combining the time-varying bed shear stresses from the hydrodynamic model with a depth-dependent erosion model. The results show that roads on top of a dike increase the erosion of the neighbouring grass cover. This increase in erosion may have a negative impact on dike stability. Therefore, we recommend considering effects of constructions on top of dike profiles during safety assessments. Explicitly, consideration of the roughness transitions in the safety assessments of dikes is recommended.The article was published Open Access under the Dutch Compact Agreement; however, due to an internal system error, previous HTML rendering of the article did not reflect this.Water Resource

Uncertainty in high and low flows due to model structure and parameter errors

This paper aims to investigate the uncertainty in simulated extreme low and high flows originating from hydrological model structure and parameters. To this end, three different rainfall-runoff models, namely GR4J, HBV and Xinanjiang, are applied to two subbasins of Qiantang River basin, eastern China. The Generalised Likelihood Uncertainty Estimation approach is used for estimating the uncertainty of the three models due to parameter values, henceforth referred as parameter uncertainty. Uncertainty in simulated extreme flows is evaluated by means of the annual maximum discharge and mean annual 7-day minimum discharge. The results show that although the models have good performance for the daily flows, the uncertainty in the extreme flows could not be neglected. The uncertainty originating from parameters is larger than uncertainty due to model structure. The parameter uncertainty of the extreme flows increases with the observed discharge. The parameter uncertainty in both the extreme high flows and the extreme low flows is the largest for the HBV model and the smallest for the Xinanjiang model. It is noted that the extreme low flows are mostly underestimated by all models with optimum parameter sets for both subbasins. The largest underestimation is from Xinanjiang model. Therefore it is not reliable enough to use only one set of the parameters to make the prediction and carrying out the uncertainty study in the extreme discharge simulation could give an overall picture for the planners