I've been reading a bit of the forums to try and figure out the steepest reasonable slope I can get for a small pond, but most the of the replies seem to be basing the slope on ease of maintaining the side and/or being able to easily get out of the water. I'm looking for info about the safety of the dam itself - not wanting to have any instance where it might collapse.
I'm looking to build a small (around ~150 cubic metre / 5000 cubic feet) pond/swimming hole on our semi-rural property. We have a small valley (no stream in it) around 4 metres wide with an average slope of 1:4 that I want to dig out and dam at one end. Local regulations are that the maximum height from dam crest to base of dam is 4 metres.
The soil is mostly rock/clay. The plan is to line the dam to prevent leakage, and I'll have to aerate/treat it to keep it clear. This question is mainly about dam construction as opposed to keeping the water clear.
If I go 1:3 slope on the front and back of the dam, it leaves very little area for the pond, and very little depth (only around 1m, whereas ideally, I'd be getting around 3m depth). I'm not concerned about the steepness of the slope for maintenance as the dam is only a few metres wide, and I'm too concerned about ease of getting in and out as I will be building an overhanging structure to get in and out easily.
So to the question - how steep can I go, and how narrow can the crest of the dam be before it's becoming a risk? I'm also not opposed to driving some piles in and retaining the middle of the dam if that helps. The attached diagram is a side on view of the slope the dam will be on. The valley walls rise about 2-3m on either side of this slope the whole way down. The numbers on the bottom represent the width of the valley at each measurement point.
Thanks heaps for any advice, happy to answer any questions.
