Disposal of Stormwater Flows Generated by Climate Change-Induced Heavy Rainfall Events

Stormwater pipes are a very important part of urban infrastructure. The designs are usually carried out to accommodate a stormwater flow due to 10-year ARI rainfalls. In such designs, historic long-term local climate/rainfall data were used to estimate stormwater volumes. Due to recent climate change, the rainfall events have increased in intensity, resulting in exceeding the capacity of stormwater pipe network. This is a new challenge for engineers sizing stormwater management devices for a design life of 100 years. This paper looks at the new design value amplifiers introduced in New Zealand to accommodate various future climate change scenarios. As a case study, a small (26 ha) new housing development in Auckland (New Zealand) is looked at, to ascertain the effect of having individual or common rainwater storage tanks, in reducing the flood peaks. It is shown that rather than increasing the stormwater sewer pipe sizes at a higher cost, providing the rainwater tanks on a cost recovery basis is an option the city council can investigate.