Forthbank Wind Energy Development - Partnerships for Renewables

Forthbank Wind Energy Development
Surface Water Hydrology
13.3.15 Hydrologically, the proposed site lies within the watershed of the Black Devon and the River
Forth. The River Forth discharges into the Firth of Forth at Edinburgh, and then flows into the
North Sea (Figure 13.1).
13.3.16 The River Forth drains the northern and western parts of the proposed wind energy
development site both indirectly through drainage channels and directly through surface and
groundwater flows and can be classed as a large sized, tidal dominated, lowland watercourse
with a channel approximately 600m wide, in the vicinity of the site. The catchment has its
headwaters some 30km to the west of the site boundary, in the Loch Lomond & Trossachs
National Park in the vicinity of Aberfoyle and Loch Ard.
13.3.17 The eastern and southern parts of the site drain directly into the Black Devon before
discharging to the River Forth at the site’s southern tip. The Black Devon is also tidally
influenced in the vicinity of the site, and can be classed as a moderate sized, siliceous, lowland
watercourse. The Black Devon’s headwaters are located approximately 24km to the north east
in the vicinity of Park Hill and Knock Hill to the south west of Loch Glow. West of Forest Mill,
its water is diverted into the Gartmorn Dam Reservoir. The topography of the area in the
vicinity of the site can be seen in Figure 13.2.
Hydrological Regime
13.3.18 The site lies within the catchments of the Black Devon and the River Forth. Peak flows have
been estimated for these watercourses using the Flood Estimation Handbook (FEH) Rainfall -
Runoff Method for a range of return periods, with the results presented in Table 13.6.
Catchment descriptors derived from the FEH CD-ROM and FEH Handbook are inserted into
the ISIS program which calculates the peak flow for the specified return period.
13.3.19 As both watercourses are tidally dominated, flows could not be calculated directly in the vicinity
of the site. The River Forth flows were calculated as far downstream as the confluence of the
River Forth and the River Teith to the north west of Stirling while the Black Devon’s flows were
calculated for a point located approximately 0.8km upstream from the site′s northern boundary.
In reality the area draining to the River Forth to the site boundary is approximately 1519.89km 2 ,
based on its sub catchment areas on the FEH CD-ROM.
Table 13.6 Estimated Q95 and peak flows for site catchments
Catchment Area Q95 (1) Estimated Peak Runoff (m 3 /s) for each Return Period (years)
(km 2 )
2.33 (QMED) (2) 10 30 50 100 200
River Forth 443.43 2.87 152.023 249.03 313.75 348.20 390.34 441.5
Black Devon 59.94 0.066 17.28 27.477 35.32 39.497 44.851 51.11
(1)Flow (m 3 /s) that is exceeded 95% of the time, (2)(Robson and Reed, 1999)
13.3.20 River flow information for the Forth River was also available from an NRFA gauging station
located at Craigforth (NS 7750 9550), as shown below.
November 2010 Chapter 13 Page 10
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