The River Watch Activity Pack

Measuring the width and the depth of the river

Key Objective:

To determine the cross sectional area of the river

Equipment needed

• Tape measure
• Meter rule
• String/ rope
• Weight

Photograph provided by Horton Kirby Educational Centre

This should be a problem solving exercise for the children to solve. The simplest way is to use the tape measure to measure from one bank to the other and record that width. Then you need to record the depth at three places across the river, do this quarter of the way, half way and three quarters of the way across the river. Record the depth. Back in the classroom draw a scale graph on graph paper to determine the cross sectional area in square metres (a simple way is to count the squares on the paper)

Problems

This is very simple if the river is less than 30 cm deep and the velocity is less than walking speed. If the river is deeper or faster than that you must not go in the river. Hence the children need to solve the problems of how to measure this. You can measure depth and width using bridges. The depth can be determined from the bridge by using a piece of string with a weight on it. Use a lesson before hand to solve these problems.

Why are you doing this?

As we move down the river from source to mouth then we expect the cross sectional area of the river to get bigger. We also use the cross section area to work out the discharge.