Forthbank Wind Energy Development - Partnerships for Renewables

Forthbank Wind Energy Development
Table 13.10 Greenfield Runoff Rates
Catchment
Infrastructure Landtake
per catchment (ha)
Calculated 2yr Greenfield
Runoff Rate (l/s)
Attenuation Storage Required
(m 3 ) from a 30yr event
River Forth 1.269 7.4 530
Black Devon 0.821 5.1 332
13.4.49 The rates of runoff have been determined using the current ‘industry best practice’ guidelines
as outlined in the Interim Code of Practice for SUDS 4 . The recommended methodology for
sites up to 50 hectares in area is the Institute of Hydrology Report 124 method (IoH124) 5 . The
runoff rates have been calculated using the Micro Drainage WinDes software suite.
13.4.50 The following parameters have been incorporated into the runoff calculations:
• Average Annual Rainfall (SAAR): 853mm/year;
• Soil: 0.40;
• Paved Area: 0% to best represent Greenfield conditions; and
• Region No: 2.
Potential Operational Effects on Soils
Changes to Soil Interflow Patterns
13.4.51 The interception of diffuse overland flow by the tracks and their drainage will disrupt the natural
drainage regime of the site and concentrate flows. This prolonged or permanent alteration to
the drainage and soil interflow patterns may lead to the soils becoming drier, which can
ultimately lead to increased erosion.
13.4.52 These potential impacts on soils during the operational phase are considered to be of minor
magnitude.
13.4.53 Levels of erosion and sedimentation will also be much lower than during construction as there
is unlikely to be excavations or bare exposed ground, following post construction restoration.
Some erosion and sedimentation is still possible on the site tracks, hardstandings and
drainage ditches as a result of scouring during extreme rainfall events.
13.4.54 The magnitude of these impacts is considered to be of a minor magnitude.
Potential Operational Effects on Geology
13.4.55 The turbine foundations and the deep (piled) foundations, if required, could have on-going
adverse effects on the local geological resource, in particular near surface coal seams and two
adits located in the north-western part of the site.
13.4.56 Should piled locations be required in coal seams or near adits in the north-western part of the
site, the stability of the foundations may be impacted during the operation of the wind energy
development.
November 2010 Chapter 13 Page 27
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