Technique of the Week: Peat Dams

For the third blog in this series (1, 2), we’re going to look at peat dams.

Much like plastic piling, this technique is used to block artificial drains to keep more water on the bog. A healthy peatland is a wet peatland, after all.

Why restore peatlands?

Micro gullies and haggs - types of micro-erosion that often forms into deeper erosion features downstream.

An unhealthy, degraded peatland can result in downstream flooding, poorer water quality, loss of biodiversity, and a loss of carbon (which means more carbon emissions). Degraded peatlands are often carbon sources, rather than carbon sinks.

You can read more about why peatlands need to be healthy here and here.

An actively eroding drain.

Why are peatland historically drained?

Because peatlands are waterlogged environments, they cannot easily be used for agriculture, building sites, forestry, or other land uses. Peat is also often used in gardening and growing crops, and can be used as a fuel, and the removal of peat will affect the water table as well.

The peat dam

A peat dam.

Drained peatlands will have a network of artificial drains that shed water off the bog. It's important, in peatland restoration, to fix the hydrology of these landscapes, and so drains need to be blocked.

Peat dams are great because they’re using material already on-site. That makes them cheap and fairly easy to create. But a peat dam should only be used when a drain has not been eroded down to the mineral layer, as part of what makes these dams so good is that they can be compacted and knitted into the peat material around the drain.

When making dams, it’s important to reprofile the area around the drain as well. Dams should not just shed water back into the drain, so they have to be angled in certain ways as to ensure this. Over time, a healthy and well-made peat dam will fade into the background, as sphagnum grows over the top and water sits naturally behind.

Over time a good peat dam will blend in to the environment.

A peat dam may seem like an ideal way of blocking drains – much better than the plastic piling we’ve already reviewed – but there are circumstances when they do not work.

When the land is too sloped, the drains too active, or the drain has eroded to the mineral layer, then peat dams will not work. Additionally, high numbers of herbivores may start walking over the dams to cross waterlogged areas and drains – this will weaken and potentially break the dam - so peat dams won't work here either.

On forest to bog sites – that is, peatland sites which were used for plantation forestry and then restored to healthier peatlands – then roots or stumps may make it impossible to collect the peat and compact it into the drain.

As you can see, there’s a lot to consider when a Peatland ACTION project officer plans on how to restore a site. You can read a little more on that from Anna, who wrote about her experiences and the peat canyon here.