"Tim+" wrote in message
...
Why not syphons? I mean, pumps use power, quite a lot of it and are
relatively expensive. For a syphon, you just need a suitably sized bit of
pipe.

I suppose they would still need a pump to "prime" the syphon, and it would
have to remain "in circuit" afterwards, because would be very difficult to
remove safely when there's a lot of water flowing, and an unpowered pump may
significantly reduce the possible flow rate. It also depends on there being
a significant head of water between the inlet point and the point where it
discharges into the spillway after going over the "hump" between reservoir
and spillway.

I wonder whether the power needed to drive the pumps does decrease once
water is flowing and syphon conditions exist, or whether it is substantially
the same no matter if the outlet is at the same level as the input or if the
output is a lot lower than the input.