Amphidromic points are places where the tidal range (difference in height between high and low tide) is zero compared with other areas in the basin.

Materials

• Table 6.1
• Ruler
• Wood skewer or other long probe
• Cylindrical container
• Water
• Permanent marker
• Food coloring
• Towels

Procedure

1. Using the ruler and a marker, mark the wood skewer every 1 cm.

2. Use a marker to place an “X” in the center of the container, at the edge of the container, and then halfway between these points (Fig. 6.13.1).
    
3. Fill the container approximately half way with water. Add a few drops of food coloring to the water.

4. In your model, you will gently swirl the water around in the container. Consider what will happen to the water level in the container as you swirl the container. Make predictions about what you expect the water level will be in the container above the ‘X’s drawn in Step 2 as the container is swirled.
   
   1. Fill in the ‘Prediction’ column of Table 6.1.
   2. Make a prediction about which of the ‘X’s would be closest to the amphidromic point.
       
5. While one group member gently swirls the container in a clockwise or counterclockwise motion, take water depth readings using your wooden skewer at each of the ‘X’ positions in the container.
   
   1. Fill in the “Trial 1” column of Table 6.1.
   2. Repeat twice more filling in the next two columns of your chart
   3. Calculate the average depth