The Mystery of The Penstock Pond,

The lower of the 3 new ponds (they are actually restored, rather than new)

6th February 2024

We are back looking at our new ponds today. I'm sorry, but I just can't help myself!

When I first considered the idea of ponds at Wilderness Wood I was thinking in terms of several small ones, for visiting students to study freshwater invertebrates. I decided that these would need to be close to the Central Hub to avoid long walks with nets and trays. They would also need to be fitted with a plastic liner. It never happened and since then my focus has been on habitat improvement rather than education.

I envisaged ponds similar to these installed at Wat Tyler Country Park, Basildon (Note the decking for children to pond dip and tables for sorting)

So it was that 3 or 4 years ago I dug a small pond at Bat Park. It wasn't much of a pond, just a scrape in the ground. It dried out each summer, but whilst it lasted it was a magnet for a range of mammals, birds and insects looking for water, or to prey on smaller beasts further down the food chain which were in need of it. The classic waterhole situation played out in Africa by elephants, wilderbeast, zebra, lions and hyenas.

The muddy fringes of the small pond at Bat Park attracts mud collecting bees and feeding birds

However, it soon became obvious that the best place for ponds would be in the lower part of the wood where water gathers and lingers longer (if only as damp soil in the summer).

About 5 or 6 years ago Dan and Jake cleared a bunch of trees close to points N, O and P on the A-Z Trail and it was only after their removal that I realised the area must at one time have been a pond.

It was evident that I had stumbled upon a piece of woodland archaeology. Across the bottom end of this dip was an embankment, known locally as a pond bay. Pond bays would have been built across a water course to create a ‘hammer pond’. The main purpose for these ponds in the High Weald would have been to store water to be used to drive a water wheel, which in turn would have worked a forging hammer, or the bellows for a blast furnace. That was when The High Weald was ‘iron central’ for the UK. Local iron ore deposits, extensive forest for charcoal and water for power, made it the perfect location for this industry. That is until the 18th Century when coal became king and iron and steel subsequently moved to new industrial towns like Sheffield and my home town of Rotherham.

Reading the landscape and it's archaeology is both challenging and fascinating in equal measure. My first thought was that this was too small to be an abandoned hammer pond. Then whilst reading Oliver Rackham's The History of the Countryside I was convinced it was actually an old fishpond, especially after seeing his sketch map of one from Upminster, Essex.

Upminster Fishpond - the original stream (red) bypassed the pond, but the embankment breach (A) stole its course - as for our new ponds. We have since returned the stream to its course

But a few weeks later I had changed my tune yet again. I now think it was a penstock pond. If you look at OS maps of the High Weald you will find large ponds created by ironmasters, big enough to store sufficient water to drive a water wheel. During the winter months there was enough rainfall to refill these ponds and literally keep the wheels of industry turning. This would have come to an end as summer approached. Therefore, in order to buy a bit more production time, many smaller ponds were created upstream from the main pond, to act as header ponds, or penstock ponds, to top up the larger 'hammer pond'.

Tickerage Stream catchment - big hammer pond lower left (now 3 ponds) fed by numerous penstock ponds (Wilderness Stream and new ponds in red)

Returning to our pond, it was possible to see that the Wilderness Stream's natural course took it along the west side of the valley, following the lowest ground and then through the wet woodland downstream of it. Putting an embankment (pond bay) across the stream held back the water until it was required (as for the Upminster Fish Ponds). At this point a sluice or a breach was opened in the embankment and the water would have rushed downstream to the main 'hammer pond'.

The pond's outlet can still be seen today to the east of the valley, forming a straight, deep gulley before rejoining the Wilderness Stream channel further down. The pond would have become redundant by the 19th century and filled with silt, brambles and trees. However, for the last two years it has been directed back to its original western channel where it supplies water to the wet woodland (alder carr) being restored downstream.

The architecture of the ponds actually works very well, in that during times of flood, the stream fully charged with silt, bypasses the bottom ponds. This means most of the silt is carried away downstream to be added to the wet woodland below. This actually reduces silting of the lower ponds, whilst this is currently not the case for the upper pond, which already shows signs of silting up.

Pond and stream arrangement - lower 2 ponds are not in-line so less silting

Since the pond became redundant (and possibly before) I can imagine the one time owners of Wilderness Wood might have used it to rear fish, providing protein for the table, especially in winter. It might also have been a decoy pond for shooting wildfowl, used for watering livestock and even been used by someone as a vegetable patch when it's fertile alluvial soil would have been suitably damp during the dry summer months.

This is largely conjecture, but it does highlight the likelihood that water in the High Weald would have served many purposes. Conservation is a relatively new one and we now have 3 nice new shallow ponds for wildlife. Further, the Wilderness Stream also waters the alder carr downstream of them. We are considering damming the former deep sluice channel to give additional ponds to provide water for the wet woodland and wildlife in general during the summer months.

David Horne