pond being destroyed by frost and dry winters

Hello, Permies!

I posted a message a while back about a small pond we built over 4 years ago  https://permies.com/t/64853/beginner-pond

It was dug into pure clay and compacted with a road roller (see process described in the post above).

The pond acts mainly as a sink for all the water that reaches the bottom end of the property.  It collects water from the French drain around the house, as well as water that leaves the overflow of an underground rainwater cistern.

For the first 2 years, the pond worked well.  The third year, it was okay, but it wasn't holding water as well as before.  This year - especially in recent weeks - it's no longer working as a pond should.

What happened was that, over the years, heavy frosts caused heaving of the clay of the banks above the water line. Due to very dry autumn weather - no or very little rain for months - when the hard frosts of winter arrived, the water level in the pond was already quite low (30 cm below the max level), so the heaving of the clay affected the bank well below the high water mark.  When it thaws, the surface of the clay banks becomes sponge-like and crumbly, and it no longer holds water as it should.  With this phenomenon repeated over the last couple of years, the sides of the pond have become very porous.

Because the sides are steep, I cannot re-compact them with a roller, and I don't have any other idea of how else to achieve compaction.  I've read that ducks can do a great compacting job, but would that work with steep banks? And how many ducks would I need to employ?

I would be okay if the pond acted as a seasonal water feature - filling up during rainy periods, and slowly drying up during droughts - but it just looks very ugly now with the bare, sloping banks.

To improve the aesthetics, I thought of planting willows along the banks, well below the high water mark, so as to mask the bare banks during dry spells, as well as to stabilise the soil, and keep it from crumbling when it heaves because of frost.

Other than that, I'm not sure what to do.  

I'll be grateful for any advice or suggestion !

to my understanding, the ‘gleying’ that ducks or pigs do isn’t compaction, it’s encouraging a certain bacterial/algal population that seals the pond with a kind of bio-film...so it should still work to some degree on steeper sides.

greg mosser wrote:to my understanding, the ‘gleying’ that ducks or pigs do isn’t compaction, it’s encouraging a certain bacterial/algal population that seals the pond with a kind of bio-film...so it should still work to some degree on steeper sides.

I'm wondering how well the technique could work in my situation - where I have cycles of freezing & heaving followed by thawing & crumbling of the clay.

yeah, me too. it seems like for it to work best it should happen while the water level is high so it can reach the ‘top’ edge.