Dam Building, Pond Creation and Rabbit Impact
This now defunct 1.5m deep channel offers an interesting pond-building opportunity
9th April 2024 Dam and Pond Building
Last week I had a go at addressing my inner navvy - working on the Wilderness Wood equivalent of the Three Gorges Dam. In reality I hope not, since the Three Gorges dam is infamous for drowning a vast area of China, displacing massive numbers of people and having a major impact upon the local environment.
On the other hand our dam is a much more sustainable approach towards managing nature. Several hundred years ago a penstock pond was created by damming the Wilderness Stream. The water from this pond would have been used further downstream to generate water power for iron smelting and forging. It has long since silted up and been abandoned.
Eighteen months ago we dredged silt from the old pond to create 3 smaller ones. We also bypassed these ponds by taking the Wilderness Stream back along its original, natural course and braiding it through the wet woodland below.
The former (man-made) channel has since been blocked off and is largely dry. It does however take some leaking water from upstream and from the adjacent hill slopes when it rains. The 'gorge' made by the stream over the centuries is 1.5m deep and could be a danger to anyone going 'off-piste' in the woods. So the idea is to put a series of earth dams across the old stream course, enabling us to have a line of cascading ponds (see diagram below).
The three scrapes, the former course of the stream and the wet woodland are closely linked
After an hour or two of digging (following a similar activity a few weeks ago) a big pile of orange and grey clay had grown across the bottom of the 'gorge', blocking-off the water which now trickles down the channel to form the new in-line pond.
I put an old white drain pipe into the upper part of the earth dam in the hope that once the water reaches this level it will overflow through the pipe and not wash my dam away. We'll see. If I am lucky, we may have a permanent body of water, surviving the whole of the summer drought period. Seasonal ponds are great for some creatures, but others prefer longer lived water.
The ponds will also exchange water with the adjacent wet woodland that I am attempting to convert into Alder Carr. At present naturally forming pipes in the clay subsoil carry trickles of water into my new pond. These are probably where former, long-dead, tree roots have decomposed, or possibly mammal burrows.
Water drips from natural pipe-ways - blue circles - (decayed tree roots) in the clay subsoil. This significant flow of water happens along the whole length of the stream channel
Currently the saturated soil under the wet woodland looks set to feed water into our dammed-up channel, at least until the water behind the dam is level with the water table under the wood. It could well be that in the summer, when the Wilderness Stream always dries up and our new 'gorge' ponds are full of water, the flow will be in the reverse direction keeping the woodland soil moist.
The finished dam doesn't look much but it should be a good test of the principle, acting as a working model. If this one works then we can dig more clay from the river banks and create still more of them in the summer months.
Defunct stream channel has potential for further dams and new ponds like this one, in the wood
16th April 2024 Bat Park Rabbit Update
Today I spent a further 2 hours creating the rabbit-proof ring of chicken wire around this area of the wood. It is nothing like as much fun as dam building, but should make a big impact upon the vegetation within Bat Park.
Currently our rabbit population grazes unimpeded on the Bat Park turf. Jake thinks the numbers are well down, but fresh rabbit droppings and tufts of munched Soft Rush indicate that the bunnies are about still.
Freshly grazed Soft Rush reveals the presence of rabbits at Bat Park
We have about 115 metres of fencing to add before we will know if the rabbit deterrent works.
There are various examples of how rabbit grazing affects the grassland here.
The steeper slopes have become clothed in a low-growing moss (Polytrichum), probably because the rabbits graze any competing taller plant species to the benefit of the mosses.
Polytrichum moss is too short to suffer from Rabbit grazing so thrives in places
Areas of heavily grazed Sort Rush stand next to large areas of seemingly untouched rush at the Nina Arena end of Bat Park. This causes me to scratch my head as to why they favour the one area over the other. I suspect they avoid the Nina Arena because it is ringed by tall bramble growth. A rabbit likes open spaces where it can see threats coming. This doesn't apply to Jake and his air-rifle. Apparently they are aware of him leaning on the gate, but don't see him as a threat – until it is too late!
Flowering tufts of sweet vernal grass push their flower brushes skyward amongst the Soft Rush at Nina Arena. It is the first time I have seen this species in flower at Bat Park and is yet another milestone in the vegetations development. Sweet Vernal Grass is one of the more typical acid lowland grassland species we are trying to attract.
Paintbrush flower heads of Sweet Vernal Grass
The exclosures created to keep rabbits out of our permanent quadrats indicate what the vegetation is likely to be once the rabbits are excluded from the whole of Bat Park. In one of them the flowering heads of a sedge would stand no chance in the rabbit grazed areas.
Just inside the rabbit exclosure a sedge bursts into flower - much to the irritation of local rabbits
One major success at Bat Park continues to be the amazing growth of formerly sad little hawthorn saplings. Here the erecting of the deer fence has finally allowed them to grow properly. The contrast between before and after indicates what the overpopulation by deer is doing to our woodland. There is little point in planting lots of young trees to address the climate and biodiversity emergencies when most of them are at risk of being destroyed by browsing deer.
Lush new hawthorn growth since deer were excluded from Bat Park. Rabbits next!
David Horne
My blog posts for the last 12 months have now been published as an illustrated book through Kindle Direct Publishing - A Year in the Wilderness: Wildlife Conservation 2023-2024, David Horne. This is available from Amazon or you can buy copies from The Hatch at Wilderness Wood.