STEM - build a river model - Guidance Document is below the video. Also, there is an extra super-challenge where the children can build a bridge to go over their river. See the extra PP.
NOTE: If you do not have any sand or pebbles, you can substitute these with other materials such as rice, grains, Lego, or blocks. If you use other materials, make sure they are not able to dissolve in water or float on the water surface.