This work package deals with improvement on the description of hydrological processes in hillslope regions, where the floods in the main Dutch rivers Rhine and Meuse are generated, and their model representation.
Appropriate decisions to act on consequences from floods can only be based on predictions from models. This comprises both predictions on short time basis and long term forecasting for strategic planning. Inaccurate predictions on short time basis could result in false alarms or failure to alarm. Inaccurate forecasting on the long term results in wrong planning and investment. Hence, discharge forecasting is essential in relation to the societal impact of floods. Unfortunately the technical conclusions on predictions are often indecisive as a result of shortcomings to give the correct hydrological process description, to obtain the model parameterisation and to define the error margins of the results. A better understanding of hydrological processes and their model representation would result at the same time in better predictions to harness against consequences of droughts.

This work package wishes to place hydrological processes in a proper perspective and investigate the improvement in hydrological modelling by introducing new process concepts that can explain the fast subsurface drainage system that is non-linear and highly heterogeneous. Flood generating processes in headwaters of the Rhine catchment are poorly understood.
The need for a new process concept stems from the fact that commonly assumed process concepts can not fully explain the observed runoff processes in the field. For instance, we know that about all floodwater passes the subsurface and that floodwater is a mixture of pre-event and event water. Hence, the flood genesis process is not Hortonian overland flow nor saturation overland flow.
Observations from hillslope regions in the headwaters of the Alzette river in Luxembourg will be used.
The project entails verification of the hypothesized new processes by field verification and modelling. Field verification can be done in established experimental catchments, where measuring campaigns will have to be conducted and additional measuring devices will be installed. In addition to measurements of climate, river discharge, soil properties, geology, soil moisture and groundwater, isotope and tracing techniques will be applied, as these techniques provide the opportunity to verify the residence time and the origin of the water.
Concepts will be modelled, tested and incorporated into existing hydrological models like HBV, or REW on various catchment scales. As such the project aims at improving flood forecasting for the Rhine and Meuse by reducing uncertainty from modelling.
Genesis of floods is identified by the NCR (Netherlands Centre for Riverstudies, a collaboration of major developers and users of expertise in the Netherlands in the area of rivers) as a key theme for further research.

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