Duncan Dey, Main Arm
Flood modelling takes rainfall as its input, runs it through a catchment to model flood behaviour, and ends, in our case, at the ocean. The flood we focus on is the 1-in-100-year flood, because it is deemed ‘big’ and because our state government says that land-use above that is ‘safe’.
Science best anticipates that flood rain inputs in our area could grow by about 20 per cent in future centuries. Today’s 100-year floods are thus not too bad a match for future century’s floods.
But science also tells us that this century will see one or two metres of rise in sea level. Hence Mullumbimby at about 4m above sea level is deemed ‘safe’ this century. But sea level rise is compounding – next century’s rise could be 3m, and in the century after it could be 6m. The numbers aren’t known but the exponential trend is.
There is no doubt that Mullumbimby will be flooded by the ocean before the cadastral boundaries of its land tenure are superseded. As an
example, allotments subdivided in Australia last century are still around (as are those of the century before). Land boundaries and ownership will likely survive until the next round of colonisation, by China or by whatever other aggressive aliens.
Sadly, the archaic planning regime under which we prepare Floodplain Management Plans ignores sea level rise beyond the year 2100. This Flood Plan is no different. It dooms the Shire to failure next century, and the then townsfolk to a life-style not unlike that of Venice.
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