Research types of dams, construction tips, forces that affect dams, problems facing dam engineers and how shape affects the strength of a structure. Check your local library for books on dams and dam construction . PBS' Building Big has a useful resource page on dams as well.
Draw a diagram of a popsicle stick dam that will best withstand the flow of water.
Place the container on a solid surface. Pour the dirt or sand into your container until it is half full. Use the spoon to contour the landscape and cut a path for the river that runs the entire length of the container.
Fill the river bottom with a thin layer of gravel.
Choose a point in the river to place a dam and decide what type of dam would work best at that location. Compare that design with your dam drawing and make modifications to the design, if necessary.
Construct the dam according to your design using popsicle sticks, gravel, dirt or sand, tape, string and glue. Cut the popsicle sticks into any shape or size as needed. Create a sluice gate to start and stop the flow of water as needed. Decorate the landscape, if desired, by placing toy fish, trees, bushes, and animals on the land and in the river.
Close the dam gate to prevent the flow of water through the dam and fill the bucket with water.
Slightly elevate one end and slowly pour the water into the river channel until it flows down to the dam.
Open the gate and watch the water flow through the dam. Continue adding water, opening and closing the sluice gate to test its capacity to control water flow.
If you are not satisfied with the function of your dam, identify the weakness and redesign the dam and sluice gate. Siphon the water from the container with the baster and install the new dam in the river.
Repeat testing steps 1-4, to determine whether you have solved the problem, until you are satisfied with the results.