The goal of the uncertainty analyses within the SBW Wadden Sea project is to find out which accuracy in HBC can be achieved, given the current state of scientific knowledge and technical instruments. Furthermore, we wish to quantify the contribution of the SWAN model and other components to the overall uncertainty in HBC. In order to answer these and related questions we first need to identify and quantify all the possible sources of uncertainty in the HBC calculation. This report gives an overview of the sources of uncertainty that contribute to the overall uncertainty of the HBC in the Wadden Sea. Most of the uncertainties can only be quantified roughly, for example by an estimate of the bandwidth or variance. For the present study this is sufficient. The next step is to analyse how the sources of uncertainty propagate in the resulting HBCs. This report gives a specification of the calculations that are expected to give insight in the error propagation of the relevant sources of uncertainty. The calculations themselves will be done in the second half of 2007 and the results will be reported in a follow-up document.