Rewetting moorland

Grip blockingAfter the Second World War, government incentives paid for widespread moorland drainage with the primary aim of improving the land for livestock. This is now thought to have been misguided because the environmental impacts were not appreciated at the time and because this drainage did not achieve its intended purpose. It is often incorrectly stated that moor owners drained the moors for grouse shooting and that this practice continues. In recent years many grouse moor owners have contributed to blocking up these drains, thereby rewetting the landscape.

Q: Why were our moors drained?
A: Although some moorland drainage has been carried out for centuries, often to enable peat cutting for fuel, the extent and intensity of drainage increased from the 1950s to the 80s. During this time, government subsidies were paid to landowners for digging drainage ditches (known in some places as ‘grips’). Drainage was intended to remove surface water and lower the water table on moorland primarily for agricultural purposes – to improve grazing for livestock, as part of the post-war drive for “more food from our own resources”. In the same era, large areas of British moorland were drained for commercial forestry. Woodland planting on the hill and hill edge continues to affect upland landscapes, habitat and water.

Q: Weren’t moors drained to help grouse?
A: At the time it was thought there may be benefits to grouse, from improved food and cover to reduced disease transmission, but this was not the main reason.

Q: Did drainage have a positive effect?
A: Drainage failed to increase the vegetation that sheep prefer. Gripping actually decreased the amount of heather cover and caused the spread of unpalatable grasses. Nor was there any benefit to grouse: drainage did not obviously reduce disease transmission; grips are a danger to young grouse chicks, which can fall into them; and the ditches are obstacles for livestock and people. On lower moors, drainage removes pockets of wet deep peat, which reduces the diversity of invertebrates, especially affecting those insects that emerge in spring and are a major component in the diet of young grouse. As far back as 1970 when government grants for drainage were at their height, the GWCT advised that draining on level waterlogged peat was slow, costly, usually ineffective, and could lead to gully erosion.

Q: What are the effects on peat and carbon storage?
A: Due to its low density, peat is highly vulnerable to erosion, particularly through the action of running water over bare ground. By lowering the water table, drainage can cause the peat layer to shrink – leading to subsidence and increased erosion. This means that drains cut 50cm deep may erode down to several metres. Healthy peat acts as a carbon store, locking in carbon, but drying peat out increases its rate of decomposition with the potential for it to release that carbon. Drainage can also reduce the abundance of peat forming plants such as Sphagnum moss and cotton grass, which prefer wetter conditions.

Q: What effects did moorland drainage have on water?
A: Upland drainage has been associated with several negative impacts on water. These include affecting the flow of water over and through the soil, increases in the rate at which water runs off the moor into rivers during rainstorms, otherwise known as flood peaks, greater sediment flow into river systems and increased colouration of water from the peat. Levels of dissolved organic carbon (DOC) in water running off the moor have shown to be significantly higher on drained slopes. This leads to a significant cost for water companies, which are required to remove it in order to comply with water quality standards.

Q: What is happening with moorland drains now?
A: Many upland landowners, including grouse moor owners, are actively blocking drains to restore moorland, both at their own expense and with support from government agri-environment funding and other grants. The Moorland Association has reported an estimate by Natural England that around 18,000 hectares of moorland habitat on grouse moors has been restored in this way across northern England. Similar schemes and activity are underway in Scotland.

Q: How are moors being ‘rewetted’?
A: Various methods are used on a site-by-site basis. Typically, drains are physically blocked at intervals along their length. Drains can be blocked with peat if they are small and on a flat area. This method is preferred by land managers and is the most cost effective. Larger drains have been blocked with bales made of woody stems of heather, or with wooden or plastic dams. Some drains can also be ‘reprofiled’ where steep edges are flattened out, reducing flow rates and encouraging plant growth.

Q: Will this have a positive effect on flood risk management, sediment and colouration?
A: There is good evidence that drain blocking is an effective way to reduce the amount of sediment reaching the stream and river network. Drains damned at intervals along their length have been shown to have low sediment levels. Blocking has also been shown to reduce colouration by between 60% and 70% compared with a drained site making it a highly successful technique in this regard. Both the National Ecosystem Assessment and Natural England review indicated that the opportunities for rewetting to reduce run-off were few, their effect uncertain, actually increasing the risk of flood in some cases, but that it may be beneficial if done sensitively.

Q: Will this have a positive effect on peat and carbon storage?
A: We know that rewetting can enhance peatland by increasing cover of healthy bog vegetation, in particular peat-forming Sphagnum, but responses are variable and more long term studies are needed. It has also been shown to be highly successful in reducing DOC loss.

Peat erosion can be reduced by grip blocking, and focusing efforts on sloping drains is more efficient as drains on flat ground are much less vulnerable to erosion. These effects are likely to improve peat health, and therefore benefit carbon storage.

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