Storage features and infiltration features should be able to half drain within 24 hours for all storms up to and including the 1 in 30-year storm.

When sizing attenuation storage it is necessary to demonstrate that all storage features have capacity for the 1 in 100-year storm event plus climate change. In addition to this it should be shown that there is 50% of the storage available within 24 hours of a 1 in 30-year storm event plus climate change. If it is not possible to have a half drain time of less than 24 hours the LLFA expects that the feature is capable of storing a 1 in 30-year storm event plus climate change and subsequent 1 in 10-year event. This is also the case for all infiltration features. It should be noted that the feature should still have the capacity to attenuate water for the 1 in 100-year storm event plus climate change.