Quantifying uncertainties in the discharge distribution over the river Rhine branches using expert elicitation

For flood protection it is essential to have accurate estimates of river water levels. In a bifurcating river system, the uncertainty of the discharge distribution over the down­ stream branches has a main impact on the river water level uncertainty. Sources of uncertainty within the discharge distribution are manifold: e.g. wind, river geometry, main channel and floodplain roughness, primary defense and regulation structures. This study aims to quantify these uncertainty in the discharge distribution at the Pannerdense Kop, the major bifurcation of the Dutch Rhine river. Seven experts were interviewed and quantified both the uncertainty in the discharge distribution per individual source of uncertainty as well as the total amount of uncertainty. The experts state that the geometry, main channel and floodplain roughness are the most important sources of uncertainty. The 90% confidence interval of the discharge distribu­ tion was quantified as 571 m3/s, which is around 4% of the upstream discharge.