Comment 32532

By drhydro (anonymous) | Posted July 30, 2009 at 14:15:25

I think there is a general misunderstanding of the design assumptions and intended performance of most of the storm/wastewater infrastructure here and in any modern city. With the amount of pre-wetting in the Red Hill catchment and the magnitude and intensity of Sunday's event, even normally pervious surfaces (grass, riparian areas, forests, etc.) behaved like impervious surfaces (E.G concrete). Nearly 100 % of the rain that fell would runoff as surface flow (or if you want to get scientific about it, "Hortonian overland flow") and runoff rapidly reaching pipes and creeks nearly instantaneously. Any city's infrastructure would have been stressed and overwhelmed and engineers/planners are always juggling design with cost...and the decreasing rate of return (or safety) with increasing cost.

This was a unique event, although these unique events appear to be occuring with increasing frequency with climate change likely exerting an influence. Granted, there are still many areas of the city that are in need of infrastructure upgrades. Pipes and pump stations are not sexy and typically are not seen as vote getters. Maybe it's time that we hold our politicians to task to ensure that a proper level of resources is dedicated to upgrading, maintaining and sustaining this oft forgotten "out of sight and out of mind" but oh so important infrastructure.

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