Rain gardens and sustainable urban drainage systems in Bergen, Norway

Bryggen, the old wharf of Bergen, is a reminder of the town’s importance as part of the Hanseatic League’s trading empire from the 14th to the mid-16th century and is on UNESCO's list of the world's cultural heritage. For about 30 years large amounts of groundwater have leaked, threatening the survival of the ancient site. Sustainable water treatment and climate adaptation measures (involving the largest rain garden of Norway, swales etc.) at Bryggen have proven to have many advantages, and with an interdisciplinary approach, the water balance at Bryggen now have been restored. (Ref. 1) Develop measurements that stabilize the groundwater, improve the preservation opportunities of the cultural heritage and reduce the uneven subsidence under the buildings (Ref. 2). • Raising of the water table in the most badly affected areas to levels as close as possible to those existing prior to the hotel’s construction (ideally, up to 1 m below the surface) • Reducing groundwater flow to a minimum • Reducing the diffusion of oxygen into the ground • Reducing the rate of subsidence to 1 mm per year or less • Reducing the average annual temperature in the deposits to 9 degrees C or less • Ensuring a minimum of intervention in intact archaeological deposits • To ensure that the weight loss of solids does not exceed 0.001% per year as a result of decomposition and leaching • Securing, and if possible increasing, the supply of groundwater upstream (Ref. 1)