This paper is based on a land development in Alstrup, northwest of Holstebro. The paper describes how to drain off rainwater locally and in open channels, where road- and roof water are separated. It is requested by Holstebro municipality to separate road- and roof water due the pollution in road water. Therefore, it is examined how a system that takes both the drainage of roads and drainage of propriety into account can be established. There will, furthermore, be established basins to delay the water before it is discharged to a nearby stream called Ellebæk and other basins for percolation of roof water. The first part of the paper is a terrain analysis which is based on an analysis of the existing conditions in Alstrup. The terrain analysis is used to assess where the water will end up naturally and where it will make sense to place road channels, ditches and basins. To improve the drainage system, there are made a few changes in the land use compared to the municipality’s district plan. The Rational method and Colebrook & White are used for the detailed project engineering of the drainage system. To make sure the depth of the road channels does not become deeper than 50 cm, which is a safety precaution, the depth is fixed in the computations. To make the maintenance of the ditches easier, the bottom width of the ditch must be at least 30 cm. Therefore the bottom width is fixed in these computations. Finally the DHI program, Mike Urban, will be used to verify the designed drainage system. This will be fulfilled by simulating the surface runoff and pipeflow. Three kinds of storm water loads will be used; boxrain with different intensity, CDS rain and historical rain from Holstebro and Herning. Based on the results of these simulations, the system will be regulated until the criterion of the return period has been reached.