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Based on research undertaken by Dr Vincent Cooper, in his report entitled Flood Reduction on the Saint Augustine Campus UWI, it was suggested that a return period of 25 years would help to eliminate flooding. This was further supported by the Vulnerability and Capacity
Assessment Report (VCA) for Trinidad and Tobago which stated that was an increase in rainfall during the period 2006 -2011 would need to be accounted for in a larger return period due to climate change and urbanization. However for this initial design for the detention basin, a period of 10 years was used instead, as there is a lack of available space for the 25 year storm design, and hence inflow and volume will be directly affected resulting in the design process becoming more difficult.
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The duration of the design storm was estimated to be 20 minutes, due to the fact that the mean rainfall intensity over short durations will be higher than long durations, indicating that a smaller return period, will allow the critical storm duration to lead to maximum effect and can hence be designed for. In addition, in this design, the time of concentration is given as 20 minutes which indicates the time, it takes for rainfall from the most remote point in the catchment to reach the outlet of the catchment, and hence is the minimum duration that can be designed for in order to determine the peak flowrate for the detention basin.