PowerSwitch

Here's a neat idea
http://organicconnectmag.com/wp/micro-h ... vmN3NRIFJJ

Very good.

Wouldn't it get in the way of canal users?

Wont be viable in most circumstances, though perhaps useful in a few cases.

Most UK canals have almost no flow, they are designed to keep the water in, not to let it rush out !
At times of excess flow, then the water overflows via weirs near locks, power could be generated thus, but not much due to the limited head, and only at times of surplus flow.

Cooling water discharges and irrigation channels are designed for minimum loss of head, there is very little energy available.

Flood relief channels and the like are dry for much of the time and could generate power only in flood conditions.

Not at all good due to physical limitations.

Unless there's a sizeable water flow, low head turbines don't produce a great deal of power. It isn't the power that's the issue, so much as the energy return on the level of engineering required to create that power. So a small low head turbines installed with spades and picks isn't so bad; a large industrial gadget installed with cranes and excavators is somewhat different.

Just because the economics of "renewable" power sales make something a worthwhile prospect doesn't mean its a realistic one due to the physical impacts/limitations (e.g. tar sands, fracking, etc.).