Comparison of Infiltration Basin Performance for Design and Historical Rainfall Events

Infiltration basins are one of the key elements from a suite of Low Impact Urban Design Devices which treat and dispose of urban stormwater runoff. The design runoff volume that is disposed of by infiltration varies from the minimum First Flush (FF) or Water Quality (WQ) Volume through to the total runoff volume from the design event. In this paper, recorded rainfall data are used to quantify the relationship between infiltration basin volume and the performance of the infiltration basin in terms of, volume of runoff treated, time spent by stormwater in the infiltration basin and the statistical significance of overflow events. The volume of the infiltration basin was varied to match the numerous volumes required for various design events.

The difference in basin performance in response to historical as opposed to design rainfall events is assessed and discussed. Statistical analyses performed on historical rainfall records were used to identify the Average Recurrence Interval (ARI) of events that were equivalent to their design ARI event counterpart. Both equivalent rainfall events were run through a purpose-built model to highlight differences in infiltration basin performance.