Harryburn Wind Farm - Innogy · 1 Harryburn Wind Farm ... Review of British Geological Survey (BGS)...

Harryburn Wind Farm

Technical Appendix 13.1

GWDTE Assessment

SLR Ref: 405.06525.00001 Version No: Final

April 2017

Harryburn Wind Farm Limited i 405.06525.00001 Technical Appendix 13.1: GWDTE Assessment April 2017

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CONTENTS INTRODUCTION .................................................................................................................... 1 SITE HYDROLOGY, GEOLOGY AND HYDROGEOLOGY ................................................... 2 NVC MAPPING ....................................................................................................................... 4 TRIAL PITTING ...................................................................................................................... 5 CONCEPTUAL HYDROLOGICAL SITE MODEL .................................................................. 6 POTENTIAL OCCURRENCE OF GWDTE AT SITE .............................................................. 7 CONCLUSION AND RECOMMENDATIONS......................................................................... 8 PHOTOGRAPHS .................................................................................................................... 9 FIGURES .............................................................................................................................. 11

Harryburn Wind Farm Limited 1 405.06525.00001 Technical Appendix 13.1: GWDTE Assessment April 2017

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INTRODUCTION

The scope of this report has been informed by investigations completed at site, including National Vegetation Classification (NVC) surveys1 and site walkovers to inspect potential areas of GWDTE. Reporting also makes reference to guidance contained within Scottish Environment Protection Agency (SEPA) Guidance Note 312.

1 Harryburn Wind Farm – Phase 1 Habitat and National Vegetation Classification Survey Report. SLR Consulting Limited, January 2016. 2 Land Use Planning System – SEPA Guidance Note 31: Guidance on Assessing the Impacts of

Development Proposals on Groundwater Abstractions and Groundwater Dependent Terrestrial Ecosystems. Version 1, Published 6th October 2014.


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SITE HYDROLOGY, GEOLOGY AND HYDROGEOLOGY A detailed description of the site hydrology, geology and hydrogeology is presented in Chapter 13 (Hydrogeology and Hydrology) of the Environmental Impact Assessment. Summary details are given below in order to provide context for the GWDTE assessment. The site comprises an area of elevated terrain and numerous hill summits. The hills from distinct features and are typified by steep sides and relatively flat summits and short ridges (see Figure 13.1). The site and surrounding area receives a relatively high annual rainfall; the average annual rainfall (1981 – 2010) at Camps Reservoir located c. 5km north-east of the site recorded by the Met Office is 1310.9mm. The site is divided between the catchment areas of the Glengonnar Water (to the north), the Elvan Water (to the south). Both of these watercourses are tributaries of the River Clyde, which flows in a generally northerly direction, to the east of the site boundary.

Review of British Geological Survey (BGS) geological mapping indicates that the bedrock geology, at surface and beneath the superficial deposits across the Site, comprises Lower Palaeozoic (Ordovician) sedimentary rocks from the Leadhills Supergroup and predominantly the Portpatrick Formation which is part of the Scaur Group. These rocks are described in the BGS Memoir for the area as greywackes, i.e. poorly sorted turbidite sandstones with a mud matrix, which are interbedded with siltstones and sandstones. See Cheater 11 (Geology and Peat for further details).

The majority of the site is shown by BGS mapping to be free of superficial deposits, with bedrock found at or close to the surface. Isolated peat deposits are identified around the summits of Harryburn Brae and Peat Hill. Glacial Till deposits are recorded at lower elevations surrounding the surface watercourses draining the site, with significant alluvium deposits of gravel, sand and silt recorded adjacent to the larger watercourses, including Elvan Water, Glengonnar Water and the River Clyde.

Extracts of the published geological mapping are shown in Chapter 11 (Geology and Peat).

The published superficial and solid geology have been confirmed by the site walkover and by an extensive programme of peat probing undertaken at site. In summary, the site works have proven:

• shallow isolated deposits of peat, or absence of peat, on the hill tops and on the

connecting ridges; • an absence of peat on the steep sides to the hills; and • a thin covering of Glacial Till below deposits of peat;

BGS Hydrogeology mapping classifies the bedrock beneath the site as a ‘low productivity aquifer’, with small amounts of groundwater in the near surface weathered zone and secondary fractures. Sand and occasional gravel horizons within the Glacial Till have the potential to store groundwater but the predominance of clay and silt within this unit will prevent significant groundwater storage or movement. In contrast, the Alluvium, where present, adjacent to the larger watercourses would be expected to contain groundwater which is likely to be in hydraulic continuity with the surface water locally.

Numerous disused mine shafts are located in the west of the site. Review of the BGS Mining Plans Portal (BGS, 2014) indicates that these shafts are associated with historical lead


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mining operations between 1851 and 1959. Further details, including a mining risk assessment, are given in Chapter 11 (Geology and Peat).


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NVC MAPPING Figure GWDTE1 shows the NVC classifications recorded at site and characterises these into areas that may be potentially moderately or highly groundwater dependent with reference to SEPA screening guidance. Review of GWDTE1 shows: • potentially large areas of the site might be classified as sustaining habitat which is

moderately groundwater dependent; • areas of the site, typically at lower elevations and close to watercourses, are classified

as sustaining habitat which might be classified as highly groundwater dependent; and • areas of potentially highly groundwater dependent habitat are shown on the east of the

site to the east of Harryburn Brae where surface gradients are shallower and where many buried services are known to cross the site.


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TRIAL PITTING In addition to the NVC mapping 8 hand dug trial pits have been advanced to access the nature of the soils at site – trial pit locations are shown on Figure GWDTE1 and the trial pits on Figure GWDTE2. The site investigations confirmed the published geological and hydrogeological mapping and in particular: • the site is used for grazing and shooting, and a number of man-made drains have been

constructed to improve the drainage; • the majority of the trial pits were recorded as dry and where water was recorded it was

recorded as a slight seepage below the soils (e.g. trial pit 2 and 8); • much of the site was recorded as dry underfoot; • the soils were proven to be shallow.

The site investigations have confirmed that: • much of the site is heavily managed heather moorland with evidence of frequent artificial

drainage and muir burning; • much of the potentially moderate GWDTE is located on the steep sided hillsides and on

the ridge lines which join the hilltops; • virtually all of the moderate GWDTE was recorded as dry underfoot and to lie above thin

soils and bedrock; • open drains have been constructed on parts of the site to improve drainage (and it is

improved habitat for grouse); • some of the moderate GWDTE is recorded in these waterlogged channels (see

Photograph 2); and • some of the potentially high GWDTE is associated with disturbed ground (e.g. the High

Pressure Gas (HPG) pipeline) to the north of the Elvan Water (see Photograph 3).


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CONCEPTUAL HYDROLOGICAL SITE MODEL

Following review of the site setting and the results of site investigations the following conceptual model has been developed:

• the site is located in an area that receives frequent rainfall and a high annual rainfall total;

• where there are no drift deposits present (e.g. on the hill tops), there is limited potential for some shallow groundwater to be present in the upper weathered surface of the bedrock. This is however generally on elevated sloping ground where rainfall would preferentially form surface runoff;

• any groundwater flow in the upper weathered surface of the bedrock will readily flow within the weathered upper surface of the bedrock and follow topography to the valleys between the hills (e.g. groundwater and surface water catchments are likely to be similar);

• in other areas (e.g. on the lower flanks of the hills and across the valley bases) any potential for rainwater recharge to groundwater within the bedrock will be limited by clays associated with the Glacial Till and which was witnessed over the lower lying areas of site and in the base of the valleys between the hills. Again, rainfall is likely to preferentially form surface runoff or shallow interflow within the thin soil horizons on top of the clays of the Glacial Till;

• groundwater is likely to be present in the alluvial deposits that bound the larger watercourses in the valley bottoms. This groundwater is likely to be perched locally above the clays of the Glacial Till and be in hydraulic continuity with surface water;

• NVC mapping confirms that potential high GWDTE habitat is largely limited to watercourse corridors and areas of shallow relief on site (e.g. east of Harryburn Brae); and

• some of the recorded potential GWDTE habitat is noted to be relatively species-poor community of limited floristic diversity. This is characteristic of flushing by base-poor water (e.g. rainfall runoff).


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POTENTIAL OCCURRENCE OF GWDTE AT SITE Based on the site observations and our understanding of the site geology and hydrology it is considered: • There is little potential for groundwater to sustain habitats on the hill tops or the ridges

that connect the hill tops at site – any incident rainfall will preferentially from surface water runoff or shallow groundwater flow to the valleys bottoms at site. This was confirmed by site observations during the site surveys that generally proved dry conditions underfoot, in trial pits and in soil probe holes. Any local waterlogging of soils occurred in small and discrete depressions on the hill tops and ridges and it is thought that the water at these locations represents local surface water runoff and ponding on low permeability soils (peat and thin Glacial Till) as a result of frequent rainfall e.g. the waterlogging is not sustained by a contribution from groundwater.

• Whilst there is potential at lower elevations at site for groundwater to sustain habitats this is considered unlikely. The shallow topographical gradients in the valleys, the high rainfall and rapid runoff from the steep sided hills will result in much water being shed to and water logging of the soils in the valleys. The low permeability drift geology and high rainfall will sustain the water logging of the surface soils from surface water runoff.

• Where alluvium is recorded adjacent to the larger watercourses (e.g. the Elvan Water) it is likely that there will be shallow groundwater and thus a much greater propensity for GWDTE.


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CONCLUSION AND RECOMMENDATIONS It is concluded, that potential areas of GWDTE should not pose a significant development constraint as it considered that the habitats are not sustained by groundwater but rather are sustained by rainfall and surface water runoff. Given this conclusion, the buffers to GWDTE stated in the SEPAs guidance3 need not apply.

Subject to adoption of best practice construction techniques the surface water contribution to the areas of potential GWDTE can be maintained and the existing habitats maintained.

It is recommended that the following standard best practice construction techniques are specified in a site specific Construction and Environmental Management Plan (CEMP):

• installation of cross drains beneath access tracks to ensure current surface water flow

paths are maintained; • any temporary (and limited) dewatering from the proposed turbines should be discharged

locally to ground and within the same surface water catchments as it is abstracted; • during construction and during operation an Ecological Clerk of Works (ECoW) should

be deployed to assess the efficacy of the drainage measures; and • a toolbox of drainage and water monitoring protocols should be specified in the site

CEMP that will allow the contractor and ECoW to maintain drainage paths and water quality.

3 Land Use Planning System – SEPA Guidance Note 31 which states a 100m buffer to site infrastructure with an excavation of up to 1m (e.g. tracks / compounds) , and a 250m buffer for exactions of more than 1m (e.g. turbines and borrow pits).


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PHOTOGRAPHS

Photograph 1 – Shallow Peat on Thin Glacial Till between T2 and T3 (note local waterlogging)

Photograph 2 – Example of Artificial Drain and Local Ponding of Water (near T2)


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Photograph 3 – Example of Waterlogged Soils on Shallow Relief Land North of Proposed Substation / Elvan Water

Photograph 4 – Alluvium Adjacent to Elvan Water


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FIGURES

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!(

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!(

!(

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TP1

TP2TP3TP4

TP5TP6

TP7

TP8

T3

T2

T1

T4

T5

T6

T7

T17

T16

T8

T9

T15

T14

T13

T12

T11

T10

H12

H12

H12

H12

H12

H12

H12

H12

H12

H12

H12/M15/M25

H12/U5

H12/U5

H18

H18

H18

H18

H18

M15

M15

M15

M15

M15

M15

M15

M15

M15

M15

M15

M15

M15

M15/M25

M17

M17

M17

M17

M17

M17

M17

M19

M19

M19

M19

M19

M19

M19

M19M19

M19

M19

M19

M19/M20

M20

M20

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23

M23/M25

M23/M25

M23/U20

M23/U4

M23/U4/U5

M25M25

M25

M25

M25

M25

M25M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25

M25/M17

M25/M23

M25/M23

M25/U5

M25/U5

M25/U5

M25/U5/U4

M25/U6

M6/M25

MG10

MG10

MG10MG10

MG10

MG10

MG10 MG6MG6MG6MG6

MG6

MG6

MG6

MG6

MG6

MG6MG6

MG6/MG10

U2

U2

U2

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20

U20U20/M23U20/M23

U4

U4

U4

U4

U4

U4

U4

U4/H12

U4/M25

U4/U20

U4/U20

U4/U20

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5

U4/U5/M23

U4/U5/U6

U4/U5/U6

U5

U5

U5

U5

U5

U5

U5

U5

U5

U5

U5/H12

U5/U20

U5/U20

U5/U6

U5/U6

U5/U6/M25

U5/U6/U20

U5b

U6U6

U6

U6

U6

U6

U6

U6

U6/M15

U6/M15

U6/MG6

288000 290000 292000 294000 29600061

4000

6160

0061

8000

6200

00LEGEND

SITE BOUNDARY

!(PROPOSED TURBINELOCATIONS

>PROPOSED PERMANENT METMAST LOCATION

TRIAL PIT (SEE GWDTE 2)

PROPOSED ACCESS TRACK

PROPOSED CRANEHARDSTANDING

PROPOSED SUBSTATION

PROPOSED CONSTRUCTIONCOMPOUND

EXTENT OF NVC MAPPING

LIKELY GROUNDWATERDEPENDENCY

MODERATE

HIGH

250m BUFFER FROM HIGHGWDTE

¯

© This drawing and its content are the copyright of SLR Consulting Ltd and may not be reproduced or amended except by prior written permission. SLR Consulting Ltd accepts no liability for any amendments made by other persons.

0227

3.00

053.

18.G

WD

TE1

Pot

entia

l GW

DTE

© Crown copyright [and database rights] (2017) 0100031673. Expires 06/04/2017.

DateScale@ A31:30,000

4/5 LOCHSIDE VIEWEDINBURGH PARK

EDINBURGHEH12 9DH

T: +44 (0)131 335 6830www.slrconsulting.com

HARRYBURN WIND FARM

GWDTE1AREAS OF POTENTIAL GWDTE

0 0.4 0.8 1.2 1.6 2

Kilometres APRIL 2017

TECHNICAL APPENDIX 13.1

TRIAL PIT 1

TRIAL PIT 2

TRAIL PIT 3

GROUND CONDITIONS

GROUND CONDITIONS

GROUND CONDITIONS

TRIAL PIT

TRIAL PIT

TRIAL PIT CO-ORDINATE294948, 617700

DIMENSIONS: 0.4m x 0.3m

0 - 0.3m BROWN DRY FIBROUS PEAT (SOIL)

>0.3m BROKEN GREY ROCK IN CLAY MATRIX

NO WATER INGRESS

DRY UNDERFOOT



0 - 0.4m BROWN DAMP FIBROUS PEAT (SOIL)


VERY SLIGHT WATER SEEPAGE AT BASE

DRY UNDERFOOT



0 - 0.4m DRY BROWN MINERAL SOIL

>0.4m BROKEN GREY ROCK

NO WATER INGRESS

DRY UNDERFOOT

TRIAL PIT

0227

3.00

053.

18.G

WD

TE2

Tria

l Pits

1-3


1. REFER TO FIGURE GWDTE1 FOR TRIAL PITLOCATIONS.

NOTES

GWDTE2Date

TRIAL PITS 1 - 3


EDINBURGHEH12 9DH


HARRYBURN WIND FARM

APRIL 2017


TRIAL PIT 4

TRIAL PIT 5

TRAIL PIT 6

GROUND CONDITIONS

GROUND CONDITIONS

GROUND CONDITIONS

TRIAL PIT

TRIAL PIT



0 - 0.1m DAMP BROWN PEATY SOIL


NO WATER INGRESS

DRY UNDERFOOT



0 - 0.5m DAMP DARK BROWN FIBROUS PEAT

>0.5m GREY ROCK

NO WATER INGRESS

DRY UNDERFOOT

LOCATED ADJACENT TO SMALLWATERCOURSE CHANNEL



0 - 0.45m DAMP DARK BROWN FIBROUS PEAT

>0.45m GREY ROCK IN CLAY MATRIX

NO WATER INGRESS

DRY UNDERFOOT

TRIAL PIT

0227

3.00

053.

18.G

WD

TE2

Tria

l Pits

4-6



NOTES

GWDTE2Date

TRIAL PITS 4 - 6


EDINBURGHEH12 9DH


HARRYBURN WIND FARM

APRIL 2017


TRIAL PIT 7

TRIAL PIT 8GROUND CONDITIONS

GROUND CONDITIONS

TRIAL PIT

TRIAL PIT



0 - 0.3m SLIGHTLY DAMP DARK BROWN/BLACKPEATY SOIL


PIT DRY

DRY UNDERFOOT



0 - 0.4m DAMP DARK BROWN FIBROUSPEATY SOIL


DRY UNDERFOOT

SLIGHT SEEPAGE AT BASE OF PEAT

LOCATED ADJACENT TO SMALLWATERCOURSE CHANNEL

0227

3.00

053.

18.G

WD

TE2

Tria

l Pits

7-8



NOTES

GWDTE2APRIL 2017

Date

TRIAL PITS 7 - 8


EDINBURGHEH12 9DH


HARRYBURN WIND FARM


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Harryburn Wind Farm - Innogy · 1 Harryburn Wind Farm ... Review of British Geological Survey (BGS)...

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Transcript of Harryburn Wind Farm - Innogy · 1 Harryburn Wind Farm ... Review of British Geological Survey (BGS)...