Large debris can damage the generator blades so it should be filtered, and cleaned regularly. 
One primary goal is to create as much head (pressure) as possible in the piping so that when it comes out of the nozzles it is at high velocity. Different pipes, angled at different gradients, will have different pressure characteristics. Loss of pressure can occur due to friction, bends in the pipe, or lack of input and output. The steeper the flume the more pressure you can achieve under the force of gravity.
Simple idea... 4 tight nozzles pointed at a spinning generator. The water hits the blades and causes it to rotate, just like the old waterwheels that ground flour, except now were utilizing the rotation to generate an electrical current and not a direct physical act. 
The little blue prop to the top right struck me with amazement. You just drop it into any moving waterbody and can get 100W of energy. Need to charge your Satellite phone while kayaking at Big Bay? Drop the blue gadget into the water (blades protecting by some shield), plug it in, and gather the energy while you troll for dolly vardens and salmon. Now if wind and solar were this simple, life would be really easy in the backcountry. Personal free energy systems for the backcountry? Scientists do it here, but it's bulky, heavy, and costly. Smaller the better. 
We talked about hydroelectric rig jobs. Folks were saying that you could reverse the gears in certain motors and play with alternators to get a generator. One guy hooked up an exercise bike to an alternator and found a way to power his TV. If his Boy wants to watch television, he has to peddle. Lots of mechanical mumbo jumbo I need to learn. How about we do this with the 10 exercise bikes in the gym? This could light up the room or radio or TV. Why not at the bigger gyms in the U.S.? Those machines you bike on are great sources of energy. 
