San Francisco Stormwater Design Guidelines
Case Study: Berlin Treatment Train The design for Potsdamer Platz, one of Berlin’s most important public squares, includes a stormwater treatment train that uses multiple stormwater management strategies (indoor use, storage, biofiltration, and outdoor use) to control both the quality and the volume of stormwater on-site. The roofs of the development, some of which are vegetated roofs and some of which are traditional, harvest rainwater to be used in the buildings for toilet flushing and irrigation. During large storm events, five underground cisterns store rainwater and then release it slowly into a series of pools and planted ‘biotopes’ for filtration. In the summer months, additional filters can be added to remove algae. Treated rainwater then flows through a very popular outdoor waterscape where employees and visitors gather. Like San Francisco, Berlin has an average annual rainfall of 21 inches.
Treatment Train Principles Think of each element in a treatment train as a separate functional unit. Before adding additional elements to a treatment train, analyze their performance relative to previous BMPs in the train. If the expected water quality benefits are limited, the increase in cost may outweigh the benefits. Do not alter or remove design measures used to reduce the size of stormwater treatment measures without a corresponding resizing of associated stormwater treatment BMPs, otherwise the capacity of the BMPs will be exceeded.
The Stormwater Control Plan
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