Carving soil and rocks out for the foundation. Concrete poles with 12 mm rebar is used. They are the building blocks; piled up horizontally with muck. Low quality concrete is made from the gravel from the creek with lime to reduce the acidity and then with cement. Rebar is used horizontally, perhaps it lacks vertically. Loose gravel is placed at the draining holes and concrete poles inside to prevent tipping over.
Hopefully the soil that must be added will be done by the heavy rains, when the water flows through and the soil and gravel will be left behind the wall. Or will it collapse? Let me know in the comments what you think and I will update the result in a new video.