Robyn:

Making a soil filled bog garden:

can i use two separate pieces of liner

(Above ground)

1.....................................2 (ground level)
1.....................................2
1.....................................2
1.....................................2
1.....................................2
1111111111111111111 2
....................22222222222


(underneath both over laping liners)

key:
1=liner sheet number 1 in the form of an "L"
2=liner sheet number 2 in the form of a backwards "L"
the dots [.....]=soil contained within the lined escavation and bellow it

1. will the there be a considerable amount of water loss (moisture loss) from the moisture escaping by leaking in between the over lapping liners?

2. eventually, will soil get inbetween the two dove-tailing, overlaping liners, building up and maybe even causing liner number 1 to invert or flap backwards or crease so much as to allow much more moisture out?

I think even with the overlap, there would be water loss there. Now, if you want a bog that's not really full of water but just damp, that might be fine. If you really want it to retain water or live in a drought-prone area, it would make sense to use a single piece of seal the two pieces together. Bogs can be made with a single piece of liner with tiny holes in it if you want the kind that's just damp so if that's what you want, the overlapping liners as you have them, might be fine. If there comes a time that you need to dig the soil out of the pond to change it, it would be easier if the liner was a single piece. Dirt could certainly get into the creases. To slow that progression, you could put an inch of pea gravel in the bottom or a piece of cloth or something. The dirt will eventually work its way down to the bottom though.