Look at my pond build. Almost identical aside from the size. Mine is 10x20x6.5.
I build mine as a linear flow. Every thing enters on one end and exits on the other. Bottom drains and skimmers are at one end, tpr's at the other.
Mine is 10' wide and I have two skimmers and two bottom drains. Drains go to two totes for settlement. Skimmers go to pump, then to s/g filters.
The top of the totes need to be at water level, that make your wall between the pond and the pit a "common" wall and will take a little extra reinforcement. That is a lot of water to hold back. I tied the end wall in with the sides with rebar. Each cell has both vertical and horizontal rebar. Holding up like a champ after 3(?) years.
If I had to do it again, I might spend the extra on a preformed liner. The folds on mine were a ***** and I never did get them perfect.
Jerry
Opportunity is missed by most people because it is dressed in overalls and looks like work.
- Thomas A. Edison