Go to http:website.lineone.netloc-quybarge.htm and make a barge out of paper. Look on the internet for a Roman ship and make a replica out of balsa wood.
Make the hull of a small boat out of vacuum-formed plastic, and an elasticated propeller to make it go forward. If you have access to a small pool or tank of water, race the boats and then discuss how the aqua-dynamics can be improved to increase the speed. You could also stick tissue or paper to the hull to show where the water would flow, and how easily it would flow over the hull. Use a hair-dryer to create the wind.
What energy can be gained from so much water passing up and down the Thames each day and how can it be harnessed?
Design a bridge for the year 3000. Could it go through the Thames, instead of under or above it? Could it float on the surface? What would it look like? How would you separate or move it to allow boats to pass?