Pond side caved in

How to fix my pond side as it has caved in?

on one side the soil has come down and pushed pond liner so now got a massive bulge on one side

• Here's what I do.
• Buy 26 gauge roofing flashing, 15 pound roofing felt and some 1/2" PVC pipe. 
• Pump out the pond,remove the liner, then make the sides of the pond straight up and down. Run the flashing all the way around, stake it with the pipe, cut to 2' or whatever you need. Bend the top edge of the flashing over toward the outside so it does not penetrate the liner. Cover the entire inside of the pond with 15 pound roofing felt. Now back fill where there is space behind the flashing. Do this carefully so you do not force the flashing to bend in toward the pond. Put the liner back, refill the pond and put the plants and fish back in.
• You can see photos on my website at http://www.pondlady.com under 'how to build a pond.'
• Good luck.