There are many different walls that you can build to support the soil of the waterfall. The cheapest and easiest wall will be the “Dry Stacked Rock Wall”. These walls have been built as far back as the roman times, and still stand today. These walls consist of natural rock that are set in the soil, and built up on top of each stone. It is important to utilize a rock that is more squared or angular, than a smooth rock, for they will stack easier. The bottom rock is your foundation rock, and should be the biggest, as well as the most leveled rock. From there each rock should be tamped into place with a rubber mallet until each rock is set. Then back fill with soil as you go, until you reach the top.
This type of rock wall will be totally stable up to 3′ tall, after that height the constitution of the wall is weaker. These rock walls are successful due to the natural drainage it provides. Each rock space will drain the water from the ground above. Most walls fail due to build up of water behind the wall, which in turn blows the wall out.