Increased run-off from urban development is often mitigated through flow attenuation systems. These limit the post development discharge to the ‘greenfield’ pre-development flow rate (referred to as ‘hydraulic neutrality’).
Whilst the concept is applied relatively commonly, there are methodological differences in how these systems are designed across New Zealand. With hydraulic modelling, or full hydraulic routing of such systems becoming more and more prevalent, there is more need for the designer to understand the impact of certain design assumptions.
What do these differences mean in terms of effects and which method provides the best outcome in terms of good stormwater management and delivering resilient design? This paper seeks to explore those differences to provide guidance to practitioners and regulators.