Measuring Head

You will need to measure the vertical drop in feet or meters (referred to as head or fall). 

Altimeter - obtain an altimeter accurate to 10 feet (3m), this is good for measuring falls greater that 70 feet (20m). Take the average of several readings.

Builder’s optical level - measure the fall of the river as you progress along its length. This is good for lower falls and it is very accurate.

Low cost laser level - at dusk or in low light conditions project a horizontal beam and using a long staff measure the vertical drop, as you progress down the stream. You may have to repeat this at a few locations.

Pipe - lay a length of 3/4 inch (20mm) plastic pipe or hose in the riverbed, fix a pressure gauge to the end and measure the pressure of the water with the pipe full, 14.5 psi is 33 feet of fall (100 KPa is 10m of fall). Make sure you clear the line of all air first. This is a very accurate method and easy to do.