LiDAR Peat Analysis Case Study

Terrain data captured to slow peat erosion on two National Trust sites

Over the last 12 months Haycock have been carrying out detailed analysis of 0.5 metre resolution LiDAR data provided by us. Two large upland areas of Britain were covered in new LiDAR flights by Infoterra’s team, commissioned by Haycock.
The brief was to capture as much terrain detail as possible of the National Trust’s High Peak Estate in Derbyshire, and their Ysbyty Estate in Snowdonia, North Wales.

Peat LiDAR image

LiDAR peat analysis

Both sites are extremely important due to their coverage of peat bogs. Although the areas of peat are extensive, they have experienced dramatic loss of coverage due to the drying out of the landscape and the associated erosion. Large expanses of the moorlands have been historically drained to allow for improved conditions for agriculture. The process of “gripping” is the method by which this is commonly done, where ditches, or “grips” are cut into the peat at regular intervals to increase the drainage.

In recent years the objective of peat management has changed and it is now widely agreed that we must stop the drainage and rapid loss of peat; carbon storage and landscape preservation are just some of the motivations behind this. The most effective way to preserve the intact areas of peat is to prevent the loss of water from the peat system, maintaining the waterlogged conditions by blocking gullies and grips that are known to exacerbate the problem. Grip blocking is an expensive and time consuming operation and therefore it is important that science is used to target the most effective use of resources. This is where Haycock’s role comes in, supported by our remote sensing data.

Digital Terrain Models (DTMs)

High resolution LiDAR data has been used to gain accurate DTM’s (Digital Terrain Models) of the sites. Combining
this data with sophisticated hydraulic modelling and GIS software Haycock have been able to carry out analysis
that would otherwise have taken potentially dozens of people several years to achieve on the ground. There are
two key elements of information that the LiDAR DTM provides when used in the correct software and system of
analysis. The first is information relating to slope and slope diversity. The second relates to the routes of surface
water movement, generating a complete picture of the entire drainage network of a river catchment or subcatchment.
To determine slope variability of these landscapes the gradient of each pixel of the DTM was calculated, averaged
and grouped into gradient classes. The slope diversity was generated for the landscape within a 10 by 10 metre
grid. If there was little change in the average land gradient the diversity of that section of landscape would be low,
however if there were many changes in slope the diversity would be high. The areas of low slope diversity
generated represent areas that have both a low slope and low slope diversity, so are intact, uneroded areas of
land; and therefore potentially peat worth preserving. Those low-slope low-diversity areas went through a process
of “clump” analysis, allowing the identification of blocks of land above 1.5 hectares in area that are worth further
investigation for targeted restoration.

Using specialised software, each pixel of the DTM (in predetermined catchments) was analysed for its
hydrological connectivity. A pixel’s elevation in relation to its neighbours determines the likely flow route of water,
with the potential for water to enter the pixel and then exit in any one of 8 possible directions. This means that
due to the accuracy of the LiDAR the precise flow path of water across the landscape can be essentially mapped
from “source to sea”, even before it enters any mapped watercourse. Entire drainage networks for the project
sites were evaluated, generating detailed drainage networks for river catchments and sub-catchments.

Through further analysis of the DTM and newly mapped drainage networks the depths of the watercourses can
be calculated. Grips and gullies above certain depth thresholds are of interest to the National Trust teams hoping
to block them. If a gully is of a significant size then it has the potential to be of threat to the preservation of the
peat and therefore should potentially be blocked. However, it maybe too deep for blocking to be effective and
therefore this analysis will save time and money on potentially wasted efforts.

Through the use of detail LiDAR DTMs and the appropriate analysis Haycock have been able to increase the
efficiency of the National Trust’s efforts to protect these important upland landscapes. Identifying target areas for
restoration by combing slope and hydrology information derived from LiDAR reduces time and money spent on
the ground, and increases the chance of success.

 

Peat Analysis case study