Drain of Terror

On hills and other sloping roads, rainwater can get up to a good speed as it flows along the gutter at the side of the road, before pouring into the drain. (I estimated it at several litres per second for the gentle hill and heavy shower when this idea came to me.)

Putting a small water wheel inside the drain would allow us to capture some of this energy and put it to good use.

Okay, there's probably not enough energy to make it worthwhile feeding it into the grid, given all the wiring and suchlike that would be required (and the safety issues; water and electricity are not good friends). But we could use it to power something by or in the drain itself...

Now, you may perhaps think of other ways to put this energy to use. What I thought is that the water wheel could wind up a clockwork-powered device that, at night, makes strange and scary noises to make people think there's a monster living in the drain.

(What kind of noises? Gutteral moans.)