Strictly Come Damming!

Blawhorn Moss NNR

After spending a few days this winter conducting peat depth surveys of the newly acquired section of Blawhorn Moss, we learned that this area is far more peat-rich than expected, with up to 4 metres of peat below the surface in places! A promising start to the future restoration of this area, except for the fact the new section is so blooming dry.

Historically the land has, like many bogs, been drained for farming. You can still see the remnants of this in the vegetation, with strips of darker, heather covered ground running parallel to areas of lighter, cotton-grass covered ground – these indicate where the drains used to be and where the water is likely still flowing underground and off the moss.

It is this flow that we must attempt to block, allowing the water to back up through the moss and eventually collect on the surface. But how best to do this? Well, given this is a new area, we aren’t quite sure yet! We needed to run some tests first. And so our volunteer work party last Wednesday was a bit of an experimental one.

The experiment was in the form of two types of dam: hand-dug peat dams and plastic piling. We wanted to try both because, as much as plastic dams are effective, we want to reduce the use of plastic wherever possible since they will remain in the earth potentially indefinitely. If hand-dug dams work just as effectively, we can reduce our plastic footprint on the reserve and also potentially provide opportunities for future volunteers and local community groups to more easily get involved.

So, how do you create a peat dam?

Remove the surface layer of turf and dig down through the drier peat until you reach the sloppy wet stuff and can clearly see a source of water flow. You need to dig this far down or you’ll not actual block anything as the water will just run underneath and away. Once you’ve reached this point, begin re-adding healthy peat back into the hole. Someone will need to jump down into the hole to stomp and squelch all the peat down so that it’s nice and compacted. Avoid falling in or losing wellies.

Chances are that once you’ve compacted all the peat, you won’t have enough from the hole you just dug to fill it, so you’ve got to go and make another, smaller hole from which to take healthier peat – aptly called a borrow pit. But what makes peat healthy, and why can’t you shove any old peat in there? Healthy peat is un-oxidised and wet, with a rich brown colour. Unhealthy peat is oxidised due to air exposure, turning black, dry and cracked. You need the sloppy, healthy stuff to effectively hold the water, whereas dry peat struggles to absorb it and does not easily integrate with the healthy peat when stomping.

Here you can see the colour difference between healthy brown peat (left) and unhealthy black peat (right)

Once you have filled in the hole with healthy peat, top it off with the unhealthy stuff to create a bit of a raised bump, and then put the turf back on top and compact it all down. You don’t want to leave any peat exposed, as this can release harmful emissions and degrade the bog.

Quite the recipe! Plastic damming is much simpler. You cut a line into the ground with a shovel where you want your dam to go, slot the pieces of piling together, and bang them into the ground. Well, simple in theory anyway. The piling is 2 metres tall and fairly easily broken from being bashed with a heavy hammer. Since you can’t leave a dam with any gaps, every time a break occured we needed to saw that section off. Thankfully, we only really had small breakages to deal with – anything particularly large and you could be looking at removing the entire thing! It meant we also had to resort to this rather cartoon-esque rubber mallet at times. And while it makes for a fabulous action shot, it lacks practicality, bouncing rather comically off the plastic with seemingly little effect. There was a lot of huffing, puffing, and taking it in turns to s l o w l y get the piling down to ground level.

Et voilà! Not too shabby for a first attempt if I do say so myself. Now we just need to give them some time (and rain) to see if they work! We will be checking them each time we come to Blawhorn, but I think the big excitement will be to compare them one year on from the day they were created. Hopefully we see a marked difference in the wetness of the ground as well as key changes in vegetation – the more sphagnum moss that grows, the healthier the bog.

Depending on results, this task will influence future peatland restoration work on the new section of Blawhorn Moss, with the more successful damming method being applied to all the core drainage ditches, restoring the area to it’s former boggy glory over time.

One completed plastic piling peat dam. We leave a small section still visible so that a) we know where it is and b) so that if it is a success, there is also a surface barrier to prevent water running off at the surface.

One completed peat damn, nicely camouflaged with the removed turf placed back on top.
The dark peat to each side was placed back in the borrow pit.