How is the wetted perimeter of a river measured with a metal chain?

• A. Measuring river depth at a single point
• B. Using the chain to shape along the bed and banks and then pulling it out to measure length
• C. Measuring river velocity
• D. Measuring air temperature

Answer: (B)

Wetted perimeter is the length of the channel boundary that is in contact with water at a cross-section. To measure it with a metal chain, you lay the chain along the wetted boundary—tracing across the river bed and up the banks where water touches them—so it follows all the curves of the channel. Then you pull the chain out straight and measure its length. This length is the wetted perimeter. This method directly records the edge between water and land, rather than measuring depth at a point, flow speed, or air temperature.