While no climate change analysis was carried out on the open storm water system, it was designed to accommodate a 15 year rainfall event as the baseline. The project involved retrofitting SUDS within existing development and infrastructure, and with residents in situ.
The completed stormwater management system includes a total of 6km of canals and water channels and ten retention ponds. Rainfall is collected in natural ditches and reservoirs before directing it into a conventional sewer system. The rainwater from roofs, roads and car parks is channelled through visible trenches, ditches, ponds and wetlands. These landscape features are integrated into the townscape within 30 courtyard areas, which also provide recreational green spaces for the area’s residents. Whilst green spaces were increased in size and number, the specific style of the 1950’s was maintained so as not to compromise the aesthetics of the area. Some of the green spaces can be temporarily flooded, which helps to manage water by slowing its entry into the conventional storm water system.
In addition, green roofs have been installed on all developments built post 1998. Some buildings existing prior to 1998, such as garages that have been reused as offices, have also been fitted with green roofs. Altogether, there are 30 green roofs in the neighbourhood and 2,100 square meters of green roofs are provided on houses. In addition, a Botanical Roof Garden, which covers 9,500 square meters of an old industrial roof, was developed between 1999 and 2001, and remains the largest green roof in Scandinavia.
As a result of the implementation of the initiative, there have not been any floods in the area since the open stormwater system was installed. Moreover, a 50 year rainfall event was experienced in the summer of 2007, which cut most of Malmö off from rest of Sweden. Augustenborg was not affected by this event, suggesting the design of the storm water system is performing better than conventional design standards and that Augustenborg is well prepared for more intense rainfall events in the future.
It is estimated that 90% of the stormwater from roofs and other impervious surfaces is led into the open storm-water system. In addition, the total annual runoff volume is reduced by about 20% compared to the conventional system. This is due to evapotranspiration from channels and retention ponds between the rain events. Also, the runoff peak flows are delayed and attenuated.
The implementation of an open stormwater system at Augustenborg has improved not only stormwater management in the area, but also the performance of the combined sewer system that serves the surrounding area. The volume of stormwater draining into the combined system is now negligible, and this system now drains almost only wastewater.
The alternative option of reducing flooding via a conventional separated stormwater system for Augustenborg would have meant major earthworks. This approach could also have caused problems further along the stormwater drainage network, such as bottlenecks where the system joins with older pipes. Moreover, the receiving areas could have suffered increased flood risk, erosion or water quality degradation. Therefore, the implementation of the open stormwater system described above was considered to be the most sustainable option aligning with the vision of the regeneration initiative Ekostaden Augustenborg.