Donald Wilson, of Balclutha, asks :-

Can water in a gravity-fed irrigation scheme be made to also go briefly uphill using a reverse syphon?

Pedro Lee, a civil engineer at the University of Canterbury, responded.

Yes most certainly water can be made to move briefly uphill provided the initial energy at the upstream reservoir is sufficient for it to go over the hill. You will find that if the hill is close to the reservoir, you may even get the water to rise a few meters above the water level in the reservoir. (Theoretically a maximum of close to 9 meters though I suspect it could only do 3 m or so at best if the water contains a lot of dissolved air). If the hill is far from the reservoir the water will likely not go over a hill that is higher than the reservoir due to the friction losses between the reservoir and the hill.

In all these cases the pressure at the top of the hill will be negative (below atmospheric). This is basically a syphon.

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