Best material to fix a wall?

Hello all!

I have two ponds.
The larger one is fed by the run off from the land, 25yrds across.
The smaller one is fed by a drainage pipe, and the old well. It is dug out, but one the one side it has a concrete retaining wall. It also has a concrete channel, to allow for water to exit into the ditch behind it, which in turn feeds big pond. The channel also controls the water level.
Unfortunately the previous owners did not take care of it, and it is leaking well below the channel. The level of the pond is well below what it should be.

Does anyone have suggestions of how to repair the wall?

I have considered using earth, rock, mix of the two, but I think I would like to use concrete. Thought I would post it here before I proceed.

If I could, I might be able to use the channel to make a micro-hydro unit!

Thank you in advance!

Brian Mallak :Those big ugly Outdoor signs are made of a very heavy vinyl material, if you are willing to wait for low water this fall you can pump out, and/or divert
the water away from the base of the dam and spread out the old sign* as a watertight membrane, you may want to spread a layer of clay before to protect against
punctures and afterwards to hold the plastic to the ponds bottom and to protect it against the sun !

This is just my personal opinion, but I would call this up-cycleing ! Good luck ! Big AL

* these are replaced when the advertisement contract is dumped, long before the sign is showing wear, check the bottom of an Outdoor sign for a company name !

Some folks use pigs. Might find some ideas in this thread.

https://permies.com/t/196/ponds/fix-leaking-pond