PM Submission - Paul Noonan - MCU25/0118

                     30 October 2025. On that occasion the site received the same quantity (64mm) of rain in
                     merely 25 minutes. At that rate the proposed OSD would overflow in 4 minutes.

                     The town planning report states the OSD design requires 3kL of reuse water capacity per
                     dwelling and 3kL for gardens which comes to (25+1) x 3kL providing 78kL and bringing the
                     total to 108kL (108m3) on site. Relating this to the 3161m2 size of the C2B block we get
                     108m3 / 3161m2 = 0.034m (34mm) of total rain capture. This represents half of the
                     downpour in both recent <1hr storms which partly flooded and temporarily blocked the
                     intersection, so in these and larger storms LMD would flood, potentially quite often, and only
                     after (9/0.5)=18 minutes or (4/0.5)=8 minutes based on the current OSD design.

                     The capacity of the bio-retention basin might help but cannot be relied on to add storage
                     capacity if it contained water before a further downpour.

                     I realise the C2B proposal has a landscaped perimeter. But this will not retain any water if the
                     ground is already saturated. The ground here can be saturated for a month or more after rain.

                     Neither the 30 Oct or 15 Nov rain events were major for total rainfall or duration. They were
                     isolated short heavy events. Some heavy rain events here have lasted over a week and
                     dropped hundreds of mm of rain. Modelling previously shown to residents by Council
                     suggests that LMD would remain passable except under extreme storm events. Still, LMD
                     became impassable during the brief 31 October downpour as seen below.




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Document Set ID: 24329288
Version: 1, Version Date: 24/11/2025