Crater garden or pond?

Sometimes it’s good that you can’t make a start on things when you first thought of them. I’ve been wanting to put a pond below our barn ever since we bought this property. It hasn’t been a priority however, and will not be a trivial exercise, so I’ve just been plotting and scheming but not actually broken turf yet.
This is the area as it stands at the moment:

View looking South across potential pond area

The area is a little plateau above an escarpmentto the left (East), so I was thinking that, with some excavation, redistribution of rock and soil with a bit of imported bentonite clay, a natural looking pond could be made. I’d like to grow some edible plants, but also I’d like a pond deep enough to swim in, or at least for the dogs, since stripping off weather doesn’t happen that often here.
Then I came across this thread: https://permies.com/t/37563/Crater-Gardens amongst others and started looking at crater gardens and the possibilities suddenly opened up. I’d seen Sagara’s lovely natural swimming pond in his garden in East Devon, but never really considered making something similar here.

Sagara's Natural Swimming Pond

I think I thought the effort involved wouldn’t be worth the results, however now I’m having second thoughts. Some of the advantages of a crater garden I don’t need, or won’t get. We’re not particularly cold in winter for example; a frost of lower than -5C is pretty unusual. Also I’m not short of water for much of the year; rain can fall anytime, although we do get a drier spell in late spring. What I am interested in however, is raising the temperature a few degrees in summer. This might make it more comfortable should I get a pond deep enough to swim in, but also transform the productiveness of one or two plants that survive, but never reach their full potential here, because there just isn’t a high enough temperature in summer. A South facing well drained rocky bank, in a sheltered suntrap, just might make the difference for some of them. Another advantage that a crater might give, is unique to our situation on the side of a U shaped valley. We face our neighbours on the opposite side of the valley. We can see what they are up to, and they can see what we are up to, and it’s amazing how many seem to be glued to their binoculars! If we had a little hidden valley we could have a skinny dip or urinate outdoors without the neighbours being any the wiser!
I schemed up a little picture of how it might be, using a photo taken before the sheep were evicted.

Crater Garden scheming

I had left this area deliberately bare of new trees so that I had space for the pond. With trees planted on the bank on the North side, together with more to the South and South West the shelter of the banks should be increased. The land slopes away to the East, and I currently have two paths which would be either side of the crater going down to the rest of the tree field. The slight ditch in the foreground has already been filled in. I’m not quite sure how to arrange access into the crater and I’m wondering what issues or other considerations I should think about before getting the digger fired up. I’m imagining going quite a bit lower than current land level for the dry bit in the centre of the crater. This may involve digging out rock even for this bit, let alone deeper for a nice pond. I’ve not had experience digging on this scale, I’ve paced out the area as about 16 metres x 14 metres (approximately 52 ft x 45 ft). I’m imagining I’d want the walls of the crater 6 – 8 ft high on the down hill (East) side for shielding, they could be less on the uphill side. I guess I need to measure the slopes out in a little more detail to check it will work, rather than just guessing by eye.

I can’t get the idea of a crater garden out of my head, so have started surveying the site to get an idea for feasibility. I marked out a cross along the North-South and East West axis of the site at 1m intervals using random sticks. I was intending to mark each stick with a level with some masking tape, using a level and some string, but dog help put paid to that and after three broken sticks I called it a day.’
The next day as the light was fading, I put the dogs inside and borrowed my husband’s special laser toy tool which sends out a horizontal line. Using this I noted the depth to the ground at each stick. It turns out that the site is actually much more level than I had thought, being entirely within 2 metres in height. It is also bigger than I guessed: I think I can use an area of about 30m x 20m (98 x 66 feet).

Site Survey

I spent quite a bit of time trying to work out the potential volumes of soil and rock to be removed and stacked up into berms, and with some approximation think it looks feasible from that point of view. The main point of issue is that when I dug a test pit at the centre of my cross I only found 40cm soil depth before I hit rock. Digging out a couple of meters of solid rock is a little daunting….

Test pit at site centre

I don’t know whether there is some good guidelines for crater design? My reading indicates that the wall height should be more than half the width of the hole for a sheltered courtyard, but that windbreaks provide some protection for 8 x their height – so that’s quite a variation in possibilities. Some of the height can come from trees around and on top of the berm, although I’ll have to check that they are not likely to cause too much shade.
I’ve been sketching possible profiles, and making planting lists, and getting far too excited.

Nancy Reading wrote:
It turns out that the site is actually much more level than I had thought, being entirely within 2 metres in height. It is also bigger than I guessed: I think I can use an area of about 30m x 20m (98 x 66 feet). .. The main point of issue is that when I dug a test pit at the centre of my cross I only found 40cm soil depth before I hit rock. Digging out a couple of meters of solid rock is a little daunting….

I don’t know whether there is some good guidelines for crater design?

Ah, some good news but 0.4 m is less than we hoped. Mum was very interested, how many test pits are you planning?

I hope someone who has successfully built a crater garden, will come forward to share their learning & experiences with you.

Ac Baker wrote:[
Ah, some good news but 0.4 m is less than we hoped. Mum was very interested, how many test pits are you planning?

I hope someone who has successfully built a crater garden, will come forward to share their learning & experiences with you.

I've dug a couple of test pits. The deepest one did have a bit more depth before hitting rock at about 60cm! so still pretty shallow. I've decided to put this idea on hold until the spring. The weather will be better then for getting the digger out. Depending on priorities at that time I'll have a go at digging and assess whether to go for the crater, or whether a pond with a smaller berm is going to be more achieveable. My thoughts now are turning to another part of the property and a different water feature. I'll start a new thread about it!