Characteristic Rain Events – A tool to enhance amenity values in SUDS-design

To overcome the challenge of designing good-looking open detention/retention areas in the urban landscape that can manage stormwater runoff from both the large, rare events and the frequent smaller events without looking empty and oversized a new approach referred to as Characteristic Rain Events (CRE) is proposed. The idea of the CRE is to demonstrate the water dynamics of a detention/retention area in a number of characteristic situations, in this way allowing the designer to
work in a more tangible way with the design.Based on historical rain series single events are selected, representing the day-to-day domain, the design domain and the extreme domain as defined in the Three Point Approach (3PA). In this paper the ability of CRE to unfold the water dynamics of a detention/retention area is investigated by applying four CRE to a fictive rain garden including frequent, short event, a frequent long event, a seldom heavy event and a rare extreme event, and comparing resulting numbers for time with standing water, water depth, retention volume, overflow volume etc. The CRE approach is concluded to hold potential for improving the design process and thus the final design of detention-retention areas.