Wow.....i wish i had been here on the start of this thread. I have installed multiple liners into earthen ponds. It is actually pretty simple AFTER you have installed a few. I will try and give my input that i have learned on my own along with advice i have received from the pros. I will also post pics tmrw since i have just now came across this at 12:15 am.
First i will start with drainage.......They actaully make a venting system for this http://stoneycreekequip.com/form/multivent.htm
. This is what i use under all my large ponds. There are multiple ways of using this vent too.
I would highly suggest using this not only for water shed going under liner but if u use the existing soil back in the bottom of the pond(under the liner) u will surely have a gas build up from all the decaying sludge and debris. We actually tore out about a 1/4 acre pond where the last installer didn't drain out all the water, sludge and debris out of the pond (which had a liner) and put a new liner over top of the old liner, sludge and debris....well a few weeks later he had what we call whales(this is where it looks like the back of a whale at the surface of the water). If the liner bubble/whale is flush with the water surface it is usually water under the liner but if the bubble/whale exceeds above the water surface it is usually gases.
Second i would definetly use underlayment. If it is a really large pond (like the 1 acre i did 2 yrs ago) u might be concerned about keeping the underlayment from blowing around. Well theres a trick to that also. We take a small propane torch and heat one edge of the fabric while another person simply layes it back down on the adjoining peice beside it. Instantly bonds together. Then i use biodegradable plastic like stakes to pin it down. I worry if u use metal stakes after time the would rust maybe causing a sharp edge. I am referring not to use the ones used to hold landscape fabric down. Kinda like a u shape.
Third using a liner can cause problems for the owner in certain situations(which can be overcome). For instance if u are installing a pond where deer, cows or large animals will be drinking from it, u want to design a ballast around the edges, in my opinion. As time goes by guess what starts forming on the liner......an ecosystem. I know u already knew that sorry. Well this will cause the liner to be slick, so if a large animal goes for a swim or falls in and tries to get out (of course this does depend on the steepness of the pond walls) they are more likely to be thrashing their feet to gain their footing. Also we have installed a ballast for a cemetary pond due to the fact if a child fell in they would have a way to get out. I have seen some people just put rock around the edge..........nope not for me. Once again depending on steepness of pond wall, the rock will end up in the bottom of the pond. We were taught a simple yet effective way to stop the rock slide. My pics will show this design.
Fourth definetly dig an anchor trench around the pond for the liner. If conditions are good u can use a walk behind/ride on trencher. Make sure to at least get 6"-8" wide. Or to be safe 1'-2' for larger application ponds.
Now as far as liners. There are 3 liners i will use on large ponds. Depending on size this will mean seaming or welding liner panels together. EPDM, Aquaweave and Easyweave are the ones i use.
I have never used a pressure relief valve for water and gas under liner. I have always worried what if a peice of rock or dirt clod caused it to stick open. I might be over thinking it. IDK
Well hopefully this is a start and will help u. STL u can call me anytime with questions. U know typing it and speaking it are two different things....i hate typing!!!!!!!