Spillways. I'm not too sure you have any idea about what you are talking about. Anyway, water at scale is a scary thing. A cubic meter of water is a tonne -

Spillways. I'm not too sure you have any idea about what you are talking about. Anyway, water at scale is a scary thing. A cubic meter of water is a tonne - 1000 Kg. Look at any river or even a stream and try and mentally construct a cross-section. Say 30m wide and say 3m deep, and assume a 75% section - that's 30x3 = 90x0.75 = 67.5m^2. Let's call it 70m^2. If the flow in this river is 1 ms-1 then 70 tonnes of water flows per second. That's roughly one and a bit main battle tanks per second! 1 m/s = 2.2 mi/h Let's set walking speed at 3 mph and a river in spate at say 15mph (6.7m/s). Far worse has been seen. Now you have 70m^2 x 6.7ms-1 = 469 tonnes of water per second. Let's call it 500 tonnes per second.