Water clarity (transparency) measurements are taken with a transparency tube; a clear, narrow (4.5 cm), graduated, plastic tube (60 cm long) with a black and white image and drain tube at the bottom.
A water sample collected from the lock wall upstream of the dam is poured into the transparency tube and then drained off until the black and white image at the bottom of the tube just becomes visible.
The level of the water is then read to the nearest centimeter (cm) from the scale on the side of the transparency tube.
The maximum value is 60 cm and the minimum value is 1 cm. Higher readings represent clearer water.