Room for the river: The future of Hawke's Bay's Ngaruroro River
Room for the river: The future of Hawke's Bay's Ngaruroro River
www.rnz.co.nz
Room for the river: Is it time to re-think how we manage floods?
This is pretty interesting! I like the bits where they show the 1950s aerial view vs the present ones to show how the river changed.
A lot of the land lost since the 1950s upstream of Fernhill isn't exactly top quality stuff, but allowing the rivers to meander downstream from there will likely mean some folks have to give up some pretty valuable & fertile land. Better that than continuing to get flooded out given repeat Gabrielle's are more likely.
The land is likely fertile because of the flooding. I wonder if there are opportunities to split the difference and farm the land (say, with fruit trees) while having the flood banks built much further from the river, just accepting the land will be flooded from time to time.
From what I understood of the article one of the issues is that the vegetation - particularly willow - causes sediment buildup and soil comes in over top of the gravel bed. That suggests to me that the soil isn't particularly deep and in a Gabrielle level flood could see anything planted in that deliberate flood zone ripped out and shifted down to the next bridge.
In most of those "reclaimed" areas especially upstream of Fernhill the land is pretty scrubby and I would guess not especially good horticultural land. But downstream from there where the stopbanks have protected it for so long I think there's a much deeper bed of soil - probably by that point the rivers would ordinarily have been going much slower so less often gouging out the dirt.
It obviously adds up in cost because of the overall land area, but my dumbies math does sort of suggest the benefit in retreating stopbanks 15-20m either side would mean being able to contain that much greater volume of water during floods, reducing risk of overtopping.