Charlie, Manuel, and Jamal are brave adventurers. They like to follow rivers through unexplored territories. They travel in a canoe because it is a lot easier than walking through the woods carrying heavy packs of supplies on their backs. Our adventurers know that the water in rivers always flows downhill. This makes canoeing easier if you want to go in the same direction that the water is flowing. It's a bit more work to paddle the other way, against the current, but it is possible. The downhill flow of water is not a problem for boats unless you come to a place where the river drops quickly, like in rapids or over a waterfall, dangers that could spell doom for these three adventurers! Our explorers might have wrecked their canoe if they had gone over this waterfall! If a boat is small, like their canoe, you could empty everything out, carry the boat past the waterfall, put everything back in, and continue your journey. Another choice would be to transfer everything from one boat above the falls to another below (if you had a second boat). You could build a canal around the waterfall but then the river would just race around in the new path. It could still be dangerous. There is a safe solution to this problem. First, dig a canal, but don't connect it to the river at either end just yet. Then build a lock. Start with walls along part of the canal. Build doors called gates at both ends. Add some pipes and valves to let water through. (Roll over this picture with your mouse to see the gates open and close.) Dig out the last dirt to connect with the river at both ends and let the water flow into your canal. Now our explorers have a safe and easy way to get past the waterfall. Charlie and Manuel will climb out of the canoe to operate the lock. They start with the gates closed. The water on the side of the lock where the canoe waits is the same height as the river before it flows over the waterfall. The water inside the lock, between the sets of gates, is the same height as the river after it goes over the waterfall. The water outside the second gate is the same height as the water between the gates. Charlie turns a handle to open a valve and lets water into the lock. The lock fills up to the same level as the water where the canoe is. Charlie and Manuel open the first two gates by pushing on long wooden levers. Jamar paddles the canoe into the lock. Charlie and Manuel close the gates and then Charlie opens a different valve and lets water flow slowly out of the lock. The level of the water in the lock goes down until it matches the water outside the second set of gates. Jamal and the canoe go down, too. Charlie and Manuel open the second set of gates, let the boat out, close the gates again, and walk down to get back into the canoe with Jamal. Finally, our explorers are safely on their way again, without wrecking and without having to unload their boat. They are happy. Locks are a great invention, but the surprising and amazing thing about locks is, you can go through them backwards, from the low side to the high side! If one of our explorers forgot his teddy bear and wanted to go home, they would paddle back to the lock, open the gate, paddle inside, close the gate, open the valve to fill the lock, open the other gate, paddle out (now on the high side), close that gate, and paddle home. Because locks make it possible to go around dangerous obstacles, boats of all sizes can go up and down the river. A lock could be so busy that someone has to be there all the time to help people go through. Questions about rivers and locks: Why does water in rivers flow downhill? Is it easier to paddle a canoe downstream or upstream? Name three ways you could get past a waterfall with your boat and supplies. Which way would be easiest? Why do locks need to have gates and valves? Can you name three parts of a lock? What are they? If you went on a three-day canoe trip, what would you take with you? Back to top of page. © 2014 Jerry Jindrich. All rights reserved. Revised 1/25/2016.