Let’s stop putting stormwater detention in stupid places

Topic: Let’s stop putting stormwater detention in stupid places

Presenters: Dr Rodney Ronalds – Friends Civil Engineering

Date:  Thursday 29 October 2020

Time:  1pm – 1:45pm

Description: Stormwater detention is commonly mandated by local Council’s for all new development sites, regardless of their location in the regional catchment. It is also common for engineers to specify stormwater detention using an isolated assessment of peak runoff at the lawful point of discharge of a site only, without considering the surrounding catchments and watercourses.

The first part of this webinar will cover recent research that conclusively shows that detention in the lower parts of regional catchments (where all of our cities are) can cause increased regional runoff and flood probability. Equations will be presented that can be used to calculate the increase/decrease in regional peak runoff that results from urbanisation with/without OSD at varying locations in the regional catchment. The equations are simple and easy to use, with basic inputs requiring a few measurements of catchment areas and stream lengths.

The second part of this presentation will look at some significant rainfall events that occurred early in this year and exceeded the infamous 1% AEP. The actual recorded rainfall patterns over the regional catchments have been modelled to test the equations response to real rainfall.

The third part of this presentation will respond to some of the feedback that the original study has received from industry experts. One of the main topics from reviewers has been the spatial variance of rainfall (what happens if it only rains in part of the regional catchment or the rainfall is not equal over the catchment). A method for randomly distributing rainfall over the catchment as part of a monte-carlo simulation technique in a hydrologic model will be described to address these reviewers’ concerns.

Lastly, a discussion from the audience will be encouraged. Stories involving projects with stormwater detention at inappropriate locations, and any strategies for driving policy change will be greatly welcomed.

Registration:  This webinar is FREE of charge to all.