In a situation like that I would probably go with either EPDM or a PPL-24 Liner mainly due to the lack of a true watershed to keep the pond full. Also with your location I fugure you have a high sand content in your soil. My .4 acre pond is natural bottom and my Koi pond is with a liner and veggie filter feeding a water fall section. Also the liner would be easier to keep cleared of leaves and debris I use a 20 gallon shop vac and a long extension for mine. Just my 2 cents worth. PPL-24 is a little cheaper than EPDM. Take a look.

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Bob