If I wanted to keep a record of the clay turbidity of my Yabby dams, how would I measure it?
A simple, but scientific, measurer is called a Secchi disc. Cut out a 30 cm diameter tin disc, mark it out in eight sectors of the circle and paint alternate sectors with flat white and black paint; screw the disc at its centre to one end of a pole, a metre or so long, marked at one centimetre intervals. The Secchi depth, as a measure of turbidity, is the water depth where the disc just disappears from view as you lower it or just reappears as you raise it (take the average of the two readings). Monthly recording is often enough. Very muddy red clay dams may have a Secchi depth of 5 cm (the Department of Fisheries of penetration of most of the sunlight).
