Below are a series of photographs to take us through the simple procedures that will give you a home made secchi disc. A secchi disc is used to measure light penetration in water. To make a measurement of turbidity just lower the disc into the water until it is no longer visible. This depth is measured and called the secchi depth.

Materials

Obtain some materials from the hardware and plastic supply shop. A 20cm square piece of white acrylic 6mm thick. A threaded loop with nuts and washers to fit. Two 100mm squares of black polyethylene sheet. Lead sheet. Large square washers, 10 meters of blind chord. Contact cement.

Tools

Scissors, a pencil, a compass to draw a circle, a jigsaw, a ruler, tin snips, belt sander and drill. A sharp knife. Two spanners.

Draw a line from corner to corner to find centre. Make a 200mm circle on your white plastic, use the compass. Cut out the disc with the jig saw or coping saw.

Follow the instructions on the contact glue packet and glue the two squares of black plastic onto the disc as shown in the photo. After the glue has set use a sharp knife to trim the plastic to size.

Drill an appropriate sized hole in the disc to install lead weights and the ring that allows the attachment of the chord. Cut some lead sheet with tin snips to add weight to the disc to allow it to sink more quickly.

The underside of the disc where the weights are attached.

The finished secchi disc after the nuts have been tightened. Now go out to the hardware shop and buy 10 meters of blind chord. You are ready to go to any puddle and check the secchi depth (Turbidity).

More info and infinite detail about its scientific use as well as the different types of charts for water colour comparisons can be found on the web pages listed. Or just put "secchi" in your favourite internet search engine.

Try these URL's to start.

Http://www.mlswa.org/secchi.htm
Http://www.pca.state.mn.us/water/secchi.html
Http://sebagolakeassc.org/secchi.htm