Increase of urbanization and climate change are one of the factors that have been highlighted to influence hydrography. This is resulting in an increase in peak flow within an urban watershed. Downstream floodingand increased pollution arethe problemsthat arises. To solve this, the sustainable urban drainage system techniques are adopted for reducing peak flow and increase baseflow. This thesis studies the assessment and optimisation of multipurposeconstructed structures usedin drainage systems in the Lussebäcken catchment in Helsingborg to reduce the possibilities of flooding while serving an environmental task.The water is transported from an upstream high plain catchmentwith a good fall height through Ramlösaravineand discharges in the Råå Brook near the sea. Downstream within the low-lying area are residential buildings, industries and roads that are sensitiveto flooding.Using the computer software MIKE URBAN with MOUSE engine, rainfall runoff was simulated and flow in the network system was computed. Three scenarios have been simulated; before 2008, when no additional ponds were added, the current situation with new constructed ponds and wetlands added to the model and a proposed modification to improve the regulation of the already existing infrastructures.The results show an improvement of over 20% of reduction of the peak flow in the mainstreamaround the most critical areafor the current situation over the 2008 situation and 8% more of improvement is obtained by regulating the output of one of the ponds.From the obtained results the main improvement could bemadewhen storing capacity to the network rahter than regulatingthe existing ponds

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