USING A SECCHI DISK

KEY CONCEPTS

  1. The clarity of water depends on how much particulate matter is suspended in it.
  2. Water clarity can be measured with the use of a secchi disk.
 

MATERIALS

  • a pre-constructed secchi disk (click here to see an example of one in use)
  • OR you can construct a classroom secchi disk from wood or plastic. It should be painted white and have weights attached (so it will not float)
  • a rope with graduated depth markings (or knots)
 
 

PROCEDURE

 
 
 

Activity

  1. If possible, take the students out in a boat or along a pier to test the disk. A pool can also be used.
  2. Lower the secchi disk into the water. Note the depth -- in other words, count the marks or knots on the rope -- when the disk is no longer visible.
 
 

Assessment Ideas

  • Students can test different areas of an inland lake or pond, noting differences in clarity. The water body can then be mapped and data entered into a journal or portfolio.
  • Have students design and carry out an experiment that shows what different factors influence water clarity.
 
 
 

CROSS-CURRICULAR IDEAS

  • History/ Social Studies: Where does the term sweet water come from? How did the settlers of the American frontier choose drinking water?
  • Media Arts: Take a trip to the local water purification plant and record your trip on a video camera. Construct a presentation on modern purification techniques
 
 

VOCABULARY

  • particulate matter: it is composed of separate individual particles. In reference to water, the amount of separate individual particles suspended in the water.
  • secchi disk: A device used to determine water clarity
  • water clarity: A term used to describe the distance one can see through water. Clarity is dependent on suspended particulate matter in the water.
 
 

SOURCE

  • Adapted from "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory
 

A secchi disk is a device used to determine water clarity. A weighted, white colored disk is attached to a rope. In this case, the disk is lowered over the side of the boat. The rope itself has markings (or knots) that are used to determine the depth where the disk is no longer visible.