My main concern with digging the pond would not be the proximity of the Willow roots (it looks quite a young/small tree) but the build up of willow leaves at the bottom of pond once it has been insitu for a few years.
Yes, Willow trees are naturally found on the banks of rivers and lakes etc. but these are naturally balanced environments.
I hand dug a biggish garden pond under the canopy of a Weeping Willow (bigger than the one in the photo). It looked great for a few years and I had fish in it. Then one day all the fish died and when we investigated it we discovered the toxic soup of decomposing willow leaves in the bottom that stunk to high heaven. Before this we did our best to keep the leaves out of the pond but it was an up-hill battle and this was compounded by 'shard' like pieces of branch that fell off every time the wind blew.
My advice - locate the pond away from the Willow.
Nice site by the way!
I have a suspician that willow leaves can be toxic so I'd avoid siting the pond under the tree for that reason alone (I may be wrong there - but worth checking!) Also large amounts of leaf and twig debris will build up in the pond and lower the oxygen levels as they rot down. That's bad news for the general health of the pond.
Puddling isn't difficult. Just remember to gently slope the sides so that the machine you're using to track the clay in can actually press down on the clay. If the sides are too steep the weight of the machine will be on the back and not under the tracks where you need it. this is often the reason why puddled clay pools leak along the sides. Otherwise, for a wildlife garden, I think a clay-lined pool would be much better then a liner.
As the others say, leaves and ponds don't go well together. As they decompose they can cause oxygen levels to drop and they release nutrient into the water.
As Spring comes this nutrient causes blanket weed to run away and form a floating mass on the surface......eutrophication.
Don't make the pond too shallow because otherwise the temperature fluctuations will make it hard for the system to stabilise.
weird just done the same style pond but bigger 14x9m.
there are products such as root barriers that will deflect the roots away from the pond.
Flexible lining products are a good help.
a safe distance of 6m away from the pond is okay with out any roots but also if your planning on lining the pond the underlay fabric will be okay as a barrier.
I would dig it out and replant it
puddling is an artform your better off lining. is it to be a filtered pond? there will be a million and 1 leaves in it every year from the willow, even with a net on it they will get in with them being pinate they go straight through
As well as the leaves I wouldn't situate the pond under the willow as the roots will more than likely penetrate the liner, willows roots always find the water.
As a clay lined pond it wouldn't be as bad but still not good.
How did this end up Angela?