Peat depth surveys on potential development sites

Peat - an overview

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Peatlands form a unique natural habitat that supports a range of plant and animal species. They are recognised under international and national legislation, act as important stores of carbon, and play an important role in the global hydrological cycle helping maintain both water quantity and quality. In the UK are thought to play an important role in flood prevention.

Damage to peatlands from drainage, burning, agriculture, forestry, development and extraction can result in these stores of carbon being lost to the atmosphere and the positive impact on upland hydrology being reduced.

Peat is very reactive to changes in drainage and will often lose its physical structure and stability when disturbed or excavated. In many cases excavated peat will be regarded as waste in law and regulatory controls will apply to its storage, treatment, recovery and/or disposal.

In all cases, the prevention of damage or excavation of peat is the preferable course of action, through proper survey, planning and design, and where disturbance cannot be avoided, implementation of appropriate mitigation measures.

Issues

The main issues from a design perspective are where to locate infrastructures such as access tracks and the turbine locations. Conducting a peat depth survey will help to identify the areas on a site where peat depth is then shallowest resulting in the reduced amount of peat needed to be extracted for the development.

Where it is not possible to avoid areas of peat, a development will often require a peat management plan to be produced as part of the planning condition discharge process. This document will use the planning specifications to calculate the amount of peat that will need to be excavated, identify mitigation measures to reduce the negative impact on the peat, propose best practice methods for excavation, storage and reinstatement, and identify areas where peat can be reused on site instead or being disposed of as waste. Ideally, all peat will be reused on site, resulting in none being exported off site as waste.

Solutions

There are two phases to a peat depth survey:

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  • Phase 1 – peat depth is measured using a peat probe which is inserted into the ground until it meets resistance. This is carried out on a 100 x 100 m grid across the entire site. This preliminary survey is on a wide scale and used in the early stages of infrastructure design.

  • Phase 2 – Detailed peat depth measurements are taken on a 10 x 10 m grid across all areas targeted for development. In addition, augers are used to collect soil cores and texture, soil moisture, organic matter content, and bulk density are measured either in the field or in the lab. This survey will aid the micro siting of infrastructure.

Benefits

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The peat depth survey is not just for the siting of infrastructure. Where developments occur on peatland, there is often a requirement to offset any potential damage by carrying out enhancement measures in neighbouring areas. This is often in the form of peatland restoration measures, which can include reprofiling of established gullies, blocking of smaller ditches using a combination of peat, plastic, timber and stone, and seeding areas of bare peat to reduce erosion damage.

Implementation of the restoration works will require a specialist groundworks contractor with appropriate equipment, as well as project management and environmental supervision from an experienced Environmental Clerk of Works. Something which Nevis staff have extensive experience with.

To find out more on our pioneering peat bog restoration work, visit our Corriegarth case study: