When preparing to build water clean outs or water ways for rain, you will have to make special forms for the concrete. This would involve the standard process of forming up the sides of your path, and then going over its surface secondarily with a precast mold to form the concrete into a trough for the water to run along. You can make this mold out of plywood, and you can use it over and over again until the edges become worn and unworkable. Using this method, you can form a water path from a driveway or downspout and redirect it to any other place you want, providing it is on a downward decline.
Step 1 - Form the Side Walls of the Waterway
Just as any other forms for concrete, you will want to use your hammer, nails and timber to form up the sides of the waterway, using standard techniques to make flat outer edges. In most cases, you are going to want to dig into the bank and set your sides down into it, as once finished, it should shore up evenly with the sides of the trough. This way when it rains, the majority of the water is going to wash off of the embankment and down into your cement waterway and off to wherever you're sending it.
Step 2 - Make a Curve Pattern with the Plywood
Once you have the side forms for the concrete waterway in place, you will want to calculate how deep or shallow you want it to be. This will be the distance from the top edge to the bottom of your trough or water's path. Once you have this measurement, calculate if you are going to want a lip on its outer edges as well to prevent back flow of water. Generally, a waterway will have a curved 2 to 3 inch lip running along the sides to prevent water from dropping out of the waterway and pooling next to it. Once you have the measurements, go ahead and cut the very curvy capital M shape out of the plywood and place it in your form to check for corrections. The outer edges of the tool you just made should fall exactly just inside your forms and pitch downward into the trough for the distance that you desire.
Step 3 - Pour your Concrete Mix
You are now ready to pour the concrete into the form, and when doing so, be sure to leave 1 to 2 inches from the top of your side forms clear of cement to allow you movement with your tool. There are several ways to construct the side forms for concrete, and any will suffice. The important part is the actual tool you made to pull cement down the shoot as you go, forming the trough and rounded edges as you go along. You may want to overfill at the top of your form and then slowly move downhill as you go, repacking cement into areas and reforming as you shape the materials toward its final destination.