In this Master thesis it's investigated how surface runoff from impervious areas impact the drainage system. The surface runoff is calculated under Danish soil conditions, to evaluate the impact on the drainage system in Denmark. The analysis is divided into five steps: input parameters, runoff model, surface runoff, drainage model and impact on drainage system.

The first step is analysis of the input parameters which include both Danish and American soil samples as well as soil samples from a case area located in Lystrup. The case area in Lystrup is included because the surface drainage and soil conditions are registered here. Which make it possible to compare calculated runoff with measured runoff.

Step number two is to set up a dynamic model out of the data from Lystrup. The dynamic model calculates the infiltration rate in the unsaturated zone to investigated the surface runoff.

The runoff model is calibrated against recorded runoff data from Lystrup and used to investigate surface runoff from Danish soil conditions. This is step number three. Step number four in the analysis is to setup the drainage model for the case area in Lystrup. The drainage model is modified so the impervious areas are incorporate in the model. The impervious area is defined from the result of the runoff model.

The influence of the drain system is step five in the analysis. The influence of the impervious areaas on the drainge system is analysis based on changes in the drainage system's functional practice vs. a reference model where the impervious areas doesn't contribute to the drainage system.

The study has been carried out in MIKE URBAN and shows that surface runoff from impervious areas is importance for the drainage system to make sure it is calculated correct.