Do not throw away any pieces of pond liner. Bog filtration areas provide growing areas for some of the prettiest flowers found around a pond. It is not necessary to have a hill or berm for a waterfall to get the benefit of a bog filtration area. You will need an space just higher than the surface of your pond. A filtration bog is just a shallow pond 6 to 9 inches deep filled with pea gravel and some larger rocks.
Water is pumped in to the bog at one side and trickles out of the other side.
Water flow through the bog is a gentle flow. The current hardly bends a leaf or moves a pebble. Dish out a spot in the berm or raised area , beside your pond. Lay some of that left over liner into this depression. The overflow of your bog should be the lowest side of your bog leading back to your pond.