Many locals don't believe Council's flood extents for our catchment. For one thing, they are much bigger than an extremely rare flood event that happened here in 1976. An eye-witness tells us Council's flood map goes about 70m beyond the point on his property where the 1976 flood came up to. He's shocked, because there were significant drainage improvements done after the 1976 flood (news article attached - "Silverstream, Whitemans Road, flood alleviation scheme"). All eye-witness accounts tell a similar story.
Are you struggling to understand our story? Don't worry, you're in good company. A woman with a PhD emailed us recently saying, "Please don't be offended, but I struggle to follow this ... I have a PhD in geophysics specialising in fluid flow modelling ... I am really confused by your 100 v 500 v 3000 v 10,000 year events thing and what it pertains to. I hope you don't mind me saying this, but I figured if I am confused others probably will be too...".
If this intelligent woman, kind enough to give us some honest feedback, is confused then we're not surprised if others are too. We're doing our best to be clear, but obviously we need to do better. We want you to be able to see what we can now see.
We're working on some future posts that we hope will make things clearer, but just for now we'll have a go at clarifying the "100 v 500 v 3000 v 10,000 year events thing."
Council keeps referring the public back to a large flood that happened in Pinehaven and Silverstream in December 1976, saying it was about a 1-in-100 year flood event, and that Council's 1-in-100 year flood maps roughly match flood extents in the 1976 flood, therefore Council is confident that their Pinehaven/Silverstream flood maps are reliable. They're not!
The truth is that the 1976 flood was much bigger than a 1-in-100 year event. How much bigger? Statistically speaking, a flood event the size of the 1976 flood hasn't occurred before in Pinehaven and Silverstream since at least the end of the Middle Ages (about 500 years ago) and at most since the invention of writing (Egyptian hieroglyphics about 3,000 years ago)! Let's pick somewhere in the middle and say that, on average, the last time a flood event like 1976 occurred in Pinehaven was at about the time of the birth of Christ. It truly was an epic, rarely seen flood event.
The storm that caused the 1976 flood event was recorded at the nearby Department of Scientific and Industrial Research (DSIR) weather station (in Taita, now closed) as being a 1-in-10,000 year rainstorm, one of the biggest in New Zealand's recorded history.
So let's be clear. Council's 100-year flood map for Pinehaven is INFLATED TO BEYOND EPIC FLOOD EXTENTS!!!
Why is this a problem? It's not just a problem; it's extremely dangerous for Pinehaven community. We'll explain on another day why Council's grossly inflated flood model poses a clear and imminent danger for Pinehaven. Our safety depends on Council fixing their flood model, so please support our petition for proper flood protection for Pinehaven!