Nant y Mwyn 25-26 Scour Protection Works

The purpose of these works is to prevent the Nant y Bai watercourse from continuing to scour (causing active erosion of) spoil heaps that make up its banks and causing mobilisation of metal-rich spoil into the watercourse. It is proposed to install a mixture of scour protection interventions including rock filled rolls and bags, geotextile matting and wooden stakes at a number of discrete areas along the bank to stabilise the spoil and prevent ongoing erosion by the Nant y Bai. We would welcome input from the Contractor regarding current design methodology based on previous experiences.

The Works comprise the following

• Install scour protection measures in accordance with the drawings;
• Install slope stabilisation measures in accordance with the drawings;
• Supply and install 150No. rock filled bags as specified on the drawings and as directed on site to provide scour protection in Areas 3, 5 and 6;
• Translocate Purple Moor grass into the working area in accordance with the drawings. The source of Purple Moor grass to be agreed with the ecological supervisor but shall be within the Site;
• Install silt traps in accordance with the drawings;
• Install an overland pipe with associated capture structure and outfall structure in accordance with the drawings;
• Deliver plant and materials along designated routes to limit impact on the protected ecology and provide any equipment necessary to minimize the impact on the designated routes. This may include helicopters to aid in load lifting and placement of rock roll bags; and
• Plan and execute temporary flow diversion measures to enable the Works in the river bed to be completed.

The Works must be carried out, including transportation of plant and materials, in a way that:

• Does not cause undue harm to the local ecology, including plants, trees and particularly the protected Calaminarian habitats (comprising metallophyte flowering and non-flowering plant species);
• Does not damage local heritage features, including historic mining structures and artefacts;
• Does not cause undue disruption to the local community;
• Does not cause damage to existing services;
• Does not cause damage to the forest track road,
• Is in accordance with the relevant Environmental Action Plan (EAP) as prepared by the Mining Remediation Authority and agreed with NRW.