Excavators and other large machines are not just used by developers and drainage engineers, but are now widely used for the management of waterways and wetlands for the benefit of environmental interests. They not only allow periodic dredging and other maintenance work to be done, but are also essential for large-scale schemes such as the restoration of reedbeds, tidal marshes and wet grasslands. Work may include digging dykes, constructing banks or bunds, digging scrapes, or in the case of reedbeds, an overall lowering of the ground level over several hectares or more. This type of habitat creation or restoration work is only possible through the use of heavy machinery.
Details and case studies are given in the The New Rivers and Wildlife Handbook (RSPB, NRA and RSNC, 1994); Reedbed Management (RSPB, 1996); Wetlands, Industry and Wildlife (The Wildfowl and Wetlands Trust, 1994); and Enact (Vol. 3, No 1, 1995).
In choosing machinery, the following factors need to be taken into account:
- Access must be suitable, with sufficient clearance height and width, and suitable ground conditions. Machines can work on mats of expanded metal mesh, to prevent them sinking in soft conditions. Access routes should avoid vulnerable habitats. For river and stream management, some smaller machines can track along the bed of shallow, firm-bedded rivers, up to about 300mm water depth. This reduces disturbance to riverside habitats.
- Dredgers and other machinery can work from floating platforms in still water or slow flowing rivers.
- The reach of the excavator arm must be sufficient for excavating and disposing of the spoil. Usually bigger machines with a longer reach are more efficient, as they are capable of doing more work without moving position, compared with a smaller machine.
- The experience and skills of the machinery operator are vital for the success of the scheme. In most cases, land managing authorities use local contractors who become experienced with particular sites and conditions.
