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.
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.
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.
Ah I didn’t think of the risk of the orchard trees all being swept up into a missile to hurl at bridges. Maybe the answer isn’t to try to widen the river, but instead split it. Allow it to fork off and have multiple channels. Maybe even breaking off streams upriver to prevent the river rising so much.
Although I guess the point of the article is that we shouldn’t mess with the river so much 😅
Yeah I spent a day helping clear up at an orchard after Gabrielle and there was a whole field where some younger trees were all just gone. I think what had happened in a lot of places was debris from upstream just washed through at velocity and broke everything above ground level away then pushed it down until it hit a barrier it couldn’t get over or around.
And in some places, where that barrier was a bridge the weight of water & debris was enough to wash that away too.