Definition and use of term ‘Hydrologically Restored Area’ by the
Dartmoor Mires Project
Hydrologically Restored Area, is a term adopted by the Dartmoor Mires Project for the area
considered to be benefited by implementation of restoration. This has been adopted by project
partners as the relevant area contributing towards targets for extent of area restored.
Background
The main features targeted for restoration are gullies and peat pans which have developed
through natural processes in response to damage to the surface of the bog. These are irregular
and generally combine into a dendritic pattern. They function to form channels for water flow, and
exhibit the characteristics familiar in river development.
The Dartmoor Mires Project prioritises activity to areas of deep peat, and where intact,
characteristic blanket bog vegetation communities are threatened by encroaching or increasing
gullies. Once they begin to form natural processes act to continue and accelerate their
development in extent and size across the whole bog. Where they occur, the water table is
lowered and they are associated with drying areas and ‘hags’ characterised by modified
vegetation in which bog species are absent or scarce. Gullies are most frequent on the edges of
intact bog although patches may occur within intact areas.
Hydrological contributing area
Blanket bogs are entirely rain-fed systems, and in good condition are essentially saturated almost
constantly, with a watertable within 5cm of the surface. Rain is dispersed over the surface by the
vegetation provided the vegetation remains intact. Once channels start to form water processes
cause them to migrate upstream so rain falling on higher adjacent areas will contribute to erosion.
On this basis, reducing or halting the erosion in eroded areas also halts the migration of channels,
protecting the uphill areas. Therefore these areas (which contribute rain which falls on them) are
potentially threatened by unaddressed erosion, and benefit from the restoration and are
considered to be hydrologically restored.
Method
Procedure for calculating the Hydrologically Restored Area for each site
1. The eroded areas are mapped on a Geographic Information System (GIS) – on Dartmoor, a
combination of remote sensing and on-the ground mapping using a differential
Geographical Positioning System (GPS) is used.
2. An analysis of the LiDAR data for the area is performed using ARC GIS Hydrology tools, in
order to show pathways of flow across the site to outlets along the perimeter of the eroded
area.
3. This area is mapped on the GIS which calculates the area in hectares. Output maps are
produced to show the area, concerned. A real example is shown at Figure 1.
Figure 1: Showing the relationship between eroded (blocked) areas and the hydrological
restoration area which contributes flow via shown pathways.
NB: Figure one is an actual example, however, the area blocked (purple) is subject to revision,
following post restoration survey.
FC November 2012