from either the banks or from flume pipes laid in the river to maintain flow and provide an equipment crossover from one bank to the other. After excavation of the trench, a section of ducting is placed into the trench.
386. For both techniques, timing of the works is important. Periods of low flow would be chosen wherever practicable.
387. The banks of the watercourse would be reformed and profiled in accordance with the project Reinstatement Plan. The banks would be reinstated to maintain the pre- construction channel width/ hydraulic capacity
388. Erosion control measures (e.g. silt fencing) would be installed and maintained until the area stabilised and vegetation became sufficiently re-established. Where there is a risk of sediment run-off, sediment interception techniques would be used.
5.6.4.8.2 Rivers 389. Where the onshore cable route is required to cross main drains and rivers HDD methods would be used to install ducts under these watercourses before cables are pulled through the ducts. The HDD entry and exit points for these works are likely to be from 10 to 20m away from the banks of the watercourse and the depth to the lowest point of the duct would be at least 1m below the bed level of the watercourse to ensure that drilling mud has no risk of escape to the watercourse.
390. The exit pit locations would be within the onshore cable route at the other side of the watercourse where sufficient space would be required to assemble and pull in the length of HDPE duct required for the crossing.
391. Consent is required from the relevant authorities (Environment Agency and internal drainage board) for crossing main drains and rivers prior to commencement of the works and the detailed working methods would be agreed as part of that consent.
5.6.4.8.3 Railways 392. Railways can be crossed with HDPE ducts pre-installed under the track by HDD. Network Rail guidance requires a minimum depth of 4.3m, where practical, therefore it would be necessary to increase the spacing between circuits up to about 10m to achieve the necessary thermal independence between circuits. The detailed installation method for each railway crossing would be agreed with Network Rail for each case.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 83
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