The Issue
Moorland gripping was practised extensively in the Swale catchment during the 1960s and 70s, encouraged by significant grants from the Ministry of Agriculture, Fisheries and Food (MAFF), because it was believed that drier moorland, as a result of the increased drainage would benefit grouse and sheep. The practice of gripping has resulted in the moorland of the upper catchment being criss crossed by a series of drainage channels.


Click on picture above to view the herringbone pattern caused by the effect of moorland gripping.

It is thought that these channels increase the speed water flows across the moorland, because any rainfall reaches the main river quicker, as it does not have to percolate through the peat. Instead it flows along the grips (However the density of grips is a significant factor).



In some areas the grip channels have become severely eroded and deepend. As these enlarged channels are bigger they are even more efficient at transferring the rainfall to the river. Moorland gripping is believed to have contributed to an increase in flashiness of the main river, that is the sudden rise and fall of the water level, which in turn may have increased river bank erosion and contributed to the frequency of flooding of settlements downstream.

The benefits of Grip Blocking to Restore Blanket Bog
In recent years, MAFF and English Nature have recognised the adverse environmental effects of gripping and have begun to provide grant aid to block grips, to restore the important blanket bog habitat in the upper catchment. There are a number of methods by which grips can be blocked, but the most widely used is to scoop an adjacent bit of vegetation and peat, and to place this in the grip channel, this is repeated at regular intervals along the length of the channel. Sedimentation then occurs behind the blockage, and over time the channel fills in and the blanket bog habitat is re-established.

Hydrological Benefits of Grip Blocking
This practice of grip blocking is also believed to reduce the rate of surface water runoff. However, any benefit is seen as secondary as the lack of quantitative data means this cannot be the main justification for the work. It is also likely that grip blocking will only reduce the rate of run-off, up until the point where the blocked grip is full of water. When this point is reached, water will flow along the blocked grip, similar to a reservoir being over topped at the head of a river. This means that until sedimentation of the grip is complete, grip blocking is likely to reduce the rate of river run-off during minor storm events, when the ground is not already saturated, but grip blocking is likely to have minimal impact on run-off during major flood events.

Any grip blocking within the catchment can only be undertaken with the landowners consent, and approximately 150 hectares of moorland (a small proportion of the area gripped) has been grip 'blocked' [see map] to date in the Swale Regeneration Project Area. Further areas are proposed if funding can be found.

The need for more Research
The limited area of grip blocking in the Upper Swale catchment relative to the number of grips, and lack of long-term river flow data means it is difficult to identify the impact of grip blocking on the Swales river levels.
It is important to find out more about the areas in the Dales which have been gripped, and to look at existing run-off and rainfall records to model the effects of grip blocking, and to also identify the impact of climate change on run-off. The Environment Agency (Dales Area) and Leeds University are hoping to carry out research in relation to the River Wharfe catchment, (where there is better data) to see if the anecdotal evidence is backed up by empirical data, and to model the various factors to predict likely effects. It is hoped that these results will be transferable to other catchments and can then be used to help inform and prioritise any future grip blocking proposals within the Swale catchment.