glyn rhonwy pumped storage development …...hlca name distance from development* 2 fachwen woods...

Glyn Rhonwy Pumped Storage Development Consent Order

Appendix 6.1 ASIDOHL

Glyn Rhonwy Environmental Statement

Appendix 6.1 ASIDOHL for the Dinorwig

Historic Landscape

Page 1 of 26

Introduction

SPH is proposing to develop a Pumped Storage scheme in the disused slate quarries at Glyn

Rhonwy, near Llanberis in Gwynedd (hereafter referred to as the ‘Development’). This document

assesses the potential impact of this development upon the Dinorwig historic landscape.

This is the second iteration of this ASIDOHL, the first having been included in the 2012

Environmental Statement (AECOM 2012).

Consultation

Consultation with the Gwynedd Archaeological Planning Service (GAPS) has established that the

Development was of sufficient scale for Assessment of the Significance of the Impact of

Development on Historic Landscapes (ASIDOHL) to be required.

The scope of assessment was determined through consultation with GAPS. This consultation

identified the need for assessment of the effects of the Development on Dinorwig historic

landscape, in which it lies and where visual change will be most significant.

Whilst the Development can theoretically be seen from the eastern fringe of the Ogwen

Valley/Dyffryn Ogwen historic landscape, the extent of change to existing views is negligible.

Ogwen Valley has therefore been scoped out of this assessment. Consultation determined that no

historic landscape other than Dinorwig needed to be considered.

The original version of the ASIDOHL was reviewed by GAPS subsequent to the publication of the

2012 Environmental Statement. The comments made by GAPS have been addressed within the

current version of the ASIDOHL.

Consultation undertaken on archaeological matters for the 2015 ES is detailed In Chapter 11,

Section 11.4.

Assessment Standards

The assessment has been undertaken according to the ASIDOHL Version 2 methodology (CCW,

Cadw and WAG 2007).

Stage 1: Contextual Information

Description of development

The Development comprises pumped storage in the disused slate quarries at Glyn Rhonwy, near

Llanberis in Gwynedd. A description of the development is provided in Chapter 4 Project

Description. The principal components of the Development to be assessed are as follows.

Permanent features:

Upper dam on Chwarel Fawr (Q1) (maximum elevation up to 395m AOD) with reservoir, relief

valve and access shaft with relief spillway at Q1 to Nant Y Betws

Lower dam on Glyn Rhonwy (Q6) (maximum elevation up to 154m AOD) with reservoir, scour

value and access shaft and spillway with inlet and outlet from Q6 to Llyn Padarn

4.5m underground penstock connecting Q1 to Q6 through a bifurcation chamber and the

turbine hall


Volume 3, Appendix 6.1 – ASIDOHL for Dinorwig Historic Landscape

Page 2 of 26

Turbine house (maximum elevation of 15m to apex) located on existing development platform

adjacent to Q6

4.5m tailrace tunnel connecting Turbine House to Q6

Pumping station, above ground kiosk and pipe inlet / outlet at Llyn Padarn

Access to Q1 via a minor road (known locally as Green Lane) from Waunfawr

Access to Q6 from the A4086 and through existing industrial estate internal roads

Spoil heaps to the south-west of Q1, to accommodate approximately 930,000m3

Temporary features during construction:

Site offices

Construction compound (upper)

Construction compound (lower)

Temporary access shaft and tunnel from Q6 to penstock

Assessment context

This ASIDOHL has been undertaken as an integral part of the Environmental Impact Assessment

(EIA) for the Development. This ASIDOHL forms an appendix to the Environmental Statement (ES).

Other chapters and appendices of the ES contain information which informs this assessment,

principally the following:

Chapter 4 includes a scheme description, and supporting information for this chapter is

contained in Volume 4 Figures

Chapter 6 presents the Landscape and Visual Impact assessment (LVIA). Supporting

information, including photomontages, can be found in Volume 4 Figures

Chapter 11 presents the assessment of impacts on Cultural Heritage, and also discusses the

policies relevant to heritage

Policy Context

The planning policy background is discussed in Chapter 5 of the Environmental Statement. Key

legislation and guidance relating to archaeology and cultural heritage comprises the following.

National policy

Ancient Monuments and Archaeological Areas Act 1979

Planning (Listed Buildings and Conservation Areas) Act 1990

National Policy Statement (Energy) EN-1, Section 5.8

Planning Policy Wales Edition 7 (July 2014)

Welsh Office Circular 60/96: Planning and the Historic Environment: Archaeology

Welsh Office Circular 61/96: Planning and the Historic Environment: Historic Buildings and

Conservation Areas

Welsh Office Circular 1/98: Planning and the historic environment: directions by the Secretary

of State for Wales



Page 3 of 26

Gwynedd Unitary Development Plan 2001-2016

Built and Historic Environment - Strategic Policy 3: relates to the protection of the area’s built

and historic environment and design standards for new development which will maintain or

improve their special character

Policy B3 – Development Affecting the Setting of Listed Buildings: relates to proposals on sites

affecting the setting of Listed Buildings, including the protection of important views to and from

the building

Policy B4 – Developments in or Affecting the Setting of Conservation Areas: relates to the

preservation and enhancement of conservation areas and their setting, including the protection

of important views across, into or out of the conservation area

Policy B7 – Sites of Archaeological Importance: relates to the protection of archaeological

remains, whether designated or not, and includes the criteria under which development

affecting remains would be permitted. This includes the requirement for archaeological

assessment and/or evaluation, and for designs which allow preservation in situ of nationally

important remains

Policy B12 – Protecting Historic Landscapes, Parks and Gardens: relates to proposals which

may cause significant harm to the character, appearance or setting of registered sites

Policy C6 – Glyn Rhonwy Redevelopment Site: proposals must not, inter alia, adversely affect

the outstanding visual and natural environment that it is set within. Any new buildings or

associated development will have to integrate effectively with the topography, character and

setting of the site.

Eryri Local Development Plan 2007 – 2022

Strategic Policy Ff: Historic Environment – Development will not be permitted that will adversely

affect Heritage Assets, or their settings and significant views. This includes Conservation Areas,

Scheduled Monuments, Historic landscapes, parks and gardens and Listed Buildings.

Confidence levels

The Development is fully described and illustrated by the ES. The physical form and appearance of

the development is fully understood. Photographs and photomontages have been prepared which

illustrate the appearance and scale of the scheme from a number of locations, including from

positions within the Dinorwig historic landscape. The Dinorwig historic landscape is outlined in the

Register of Landscapes of Outstanding Historic Interest in Wales (Cadw, CCW & ICOMOS UK

1998). It has been subject to a detailed characterisation exercise undertaken by Gwynedd

Archaeological Trust (GAT).

The Zone of Theoretical Visibility (ZTV) for the development has been established by the LVIA

(Chapter 6; Figure 6.3) and has been refined in the field by both the landscape architect and the

archaeologist undertaking the ASIDOHL. The field visits enabled the true situation on the ground to

be appreciated, particularly in terms of the role of tree cover and other vertical landscape elements

which dictate the availability of long-distance views.

Confidence levels for this ASIDOHL are therefore high in most respects. However, effects on

access and amenity (i.e. indirect physical impacts), which may be either positive or negative, cannot

be quantified. Although the project has aspirations for enhanced public access and amenity within



Page 4 of 26

the Order Limits, no measures to achieve this have been defined. An element of uncertainty

therefore remains within the Stage 3 calculations.

Qualifications and experience

This ASIDOHL has been undertaken by Andrew Pearson MA PhD MIfA FSA. Dr Pearson has

worked as an archaeologist in Wales for 15 years and during this time has undertaken a significant

number of ASIDOHL studies. He has also carried out critical review of ASIDOHL and other

landscape studies on behalf of CCW.

Process description

This assessment has been undertaken to ASIDOHL Version 2 standards. All five stages have been

undertaken.

Historic landscapes under consideration

The proposed project lies within the Dinorwig historic landscape, as described in the Register of

Landscapes of Outstanding Historic Interest in Wales (Cadw, CCW and ICOMOS UK 1998).

This document is complemented by the characterization exercise for Ardal Arfon. This area

incorporates the historic landscapes of Dinorwig, Ogwen Valley and some of North Arllechwedd (the

rest of the latter being included in a separate study). The characterization exercise is available at:

http://www.heneb.co.uk/arfonintro/arfonlandscapemap.html

Identification of key historic landscape characteristics and determination of study area

The Dinorwig historic landscape preserves evidence of land use and settlement from the prehistoric

period onwards, superimposed by recent extensive and outstanding remains of the 19th and 20th

century slate industry.

The key characteristics of the Dinorwig historic landscape are listed in Table 1. Each historic

landscape character area (hereafter abbreviated to HLCA) within the historic landscape has

individual key characteristics: these are outlined in Tables 3 to 13. The Dinorwig historic landscape

is shown in Figure 1.

Table 1. Summary of key characteristics of the Dinorwig Historic Landscape as a whole

Key Characteristic

Iron Age hillforts, settlements and fields

Dolbadarn Castle

Medieval settlements

19th and 20th-century quarries, waste tips, settlements, transport systems and port

Vaynol Hall and Park

Dinorwig underground hydro-electric pumped storage scheme

Historic literary and artistic associations (late 18th and early 19th century)

The HLCAs defined within the Arfon historic landscape do not conform to the boundaries of the

historic landscapes of Dinorwig, Ogwen Valley and North Arllechwedd as defined in the 1998

Register. A number fall within both Dinorwig and Ogwen Valley, whilst HLCA 36 (Unenclosed

Mountain, North Carneddau) is a very extensive area that extends across all three historic

landscapes.

http://www.heneb.co.uk/arfonintro/arfonlandscapemap.html



Page 5 of 26

There are 38 HLCAs that are within (or partly within) the boundary of the Dinorwig historic

landscape – though some of these only intersect to a very slight degree.

It is clearly neither necessary nor practical to evaluate all HLCAs within the historic landscape. Only

four lie within the Order Limits (i.e. the ‘red line boundary’ for the project); these are assessed in

Stage 2. An additional seven HLCAs that fall within the Development’s ZTV are assessed in Stage

3. The HLCAs assessed by the ASIDOHL are listed in Table 2.

Table 2. HLCAs within the Dinorwig historic landscape considered by the ASIDOHL

HLCA Name Distance from development*

2 Fachwen Woods 0.25 km

4 Llanberis 0.15 km

5 Dolbadarn and Pentre Castell 0.8 km

6 Glynrhonwy Quarry Within Order Limits

7 Gallt Celyn Within Order Limits

11 Dinorwic, Marchlyn, Gallt-y-llan slate quarries and Llanberis copper mine

2.5km

21 Padarn and Peris Lakes Within Order Limits

36 Unenclosed Mountain (North Carneddau) Abuts Order Limits

42 Gwaen Gynfi enclosed area 0.6km

44 River Valleys above Llanberis 0.4km

45 Cefn Du and Garreg Lefain Within Order Limits

* ‘Distance from development’ refers to the shortest distance between the HLCA and the Order

Limits

Table 3. Key Characteristics of Historic Character Area 02 (Fachwen Woods)

Key Characteristic

19th-century plantation with some elements of more ancient woodland

Quarries and associated structural remains, 18th and 19

th century

Industrial infrastructure: road, narrow gauge railways, possible quay

Table 4. Key Characteristics of Historic Character Area 04 (Llanberis)

Key Characteristic

Victorian domestic, hotel and commercial architecture

19th-century quarry workers’ terraced housing

Focus of historic (Victorian) and modern tourism

Table 5. Key Characteristics of Historic Character Area 05 (Dolbadarn and Pentre Castell)

Key Characteristic

Dolbadarn medieval castle

19th-century tourist infrastructure, including the Royal Victoria Hotel and the Snowdon Mountain Railway

lower terminus. Utilization of natural and designed landscape

Late 18th and 19

th-century literary and artistic cultural associations

Table 6. Key Characteristics of Historic Character Area 06 (Glynrhonwy Quarry)

Key Characteristic

Open slate quarries extending from Llyn Padarn to Cefn Du: 18th, 19

th to mid-20

th century date

Extensive spoil tips

Quarry infrastructure: inclines, stone embankments for ropeway systems into individual pits

World War Two bomb-storage facilities (Lower Glynrhonwy pit)



Page 6 of 26

Table 7. Key Characteristics of Historic Character Area 07 (Gallt Celyn)

Key Characteristic

Prehistoric occupation: stone-built hut circles and enclosures

Post-medieval settlement and agricultural sites

Cultural associations: meeting place of North Wales Quarrymen’s Union (1874)

Table 8. Key Characteristics of Historic Character Area 11 (Dinorwic, Marchlyn, Gallt-y-llan slate quarries and Llanberis copper mine)

Key Characteristic

Late 18th to later 20

th century slate quarries

Dinorwic: visually-spectacular galleried open slate quarries; associated infrastructure and machinery

Llanberis: 18th and 19

th century copper mine with possible Bronze Age origins

Table 9. Key Characteristics of Historic Character Area 21 (Padarn and Peris Lakes)

Key Characteristic

Natural glacial lakes

Transport artery from medieval to modern times

Table 10. Key Characteristics of Historic Character Area 36 (Unenclosed Mountain – North Carneddau)

Key Characteristic

Vast area of unenclosed mountainside with few modern intrusions

Prehistoric settlement and agricultural sites – very fine examples

Deserted medieval rural settlements, many associated with seasonal exploitation of summer upland pasture

Table 11. Key Characteristics of Historic Character Area 42 (Gwaen Gynfi enclosed area)

Key Characteristic

18th century squatter settlements

19th century smallholder enclosures

Relict industrial-era roads and railway

Table 12. Key Characteristics of Historic Character Area 44 (River Valleys above Llanberis)

Key Characteristic

Area of upland farming settlement

Substantial farmhouses, now falling into ruin

Table 13. Key Characteristics of Historic Character Area 45 (Cefn Du and Garreg Lefain)

Key Characteristic

Largely unenclosed upland area

Historic pastoral use: regularly laid-out sheepfolds

Cart road to Cefn Du quarry, early 19th century

Stage 2: Assessment of Direct Effects

Basis of assessment

The Order Limits encompass 91 ha, though only a part of this ground will be subject to disturbance

or alteration. 7.2 ha lies outside the historic landscape boundary. The impacts of the Development

upon cultural heritage sites within that boundary are assessed in Chapter 11 (see in particular

Tables 11-6 and 11-7). Stage 2 of this ASIDOHL draws directly upon these findings.



Page 7 of 26

The Development falls within four HLCAs. By far the greatest part lies within HLCA 06 (Glynrhonwy

Quarry), with only very small parts extending into HLCAs 07 (Gallt Celyn), 21 (Padarn and Peris

Lakes) and 45 (Cefn Du/Garreg Lefain). The impact on HLCAs 06, 07 and 45 are summarized in

Tables 14 to 16.

For HLCA 21, due to the negligible area loss (0.07 ha out of a total of 144 ha) and the absence of

specific impacts upon sites, the physical effect is considered to be neutral. No tabulated

assessment is given for this character area.

In terms of impacts upon individual sites, the archaeological and cultural heritage assessment

(Chapter 11) has had to contend with a number of uncertainties within the design. It therefore tends

towards a ‘worst case’ scenario. It also discusses the sites in terms of a ‘Certain’, ‘Likely’ and

‘Unlikely’ impact. This ASIDOHL includes all sites for which a Certain or Likely impact is predicted,

but excludes those where impact is considered unlikely. Impacts are based on the predicted scores

prior to mitigation (Chapter 11, Table 11-6), as opposed to residual impacts after mitigation (Chapter

11, Table 11-7). This is because the mitigation takes the form of preservation by record: this does

not compensate for physical losses to the historic landscape.

Impact (in absolute terms)

31.2% of HLCA 06 (79.11 ha) will be permanently lost or removed by development

(Considerable)

1.7% of HLCA 07 (2.84 ha) will be permanently lost or removed by development (Very Slight)

0.5% of HLCA 45 (1.57 ha) will be permanently lost or removed by development (Very Slight)

There will be no loss of land within HLCA 21 (the Order Limits extending into Llyn Padarn but

not requiring ‘land-take’ or drainage)

Impact (in relative terms)

In HLCA 06 ten elements, comprised of 73 individual archaeological sites (45% of all present),

will be lost or removed by development. Impact: Considerable

In HLCA 07 one element, comprised of 6 individual archaeological sites (37% of all present),

will be lost or removed by development. Impact: Considerable

In HLCA 21 no known archaeological sites will be lost or removed by development

In HLCA 45 one element, comprised of 4 archaeological sites (<5% of all present), will be lost

or removed by development. Impact: Very Slight

Note: Chwarel Cefn Dû, slate quarry II lies in both HLCAs 06 and 07. It is therefore double-counted

in the statements above, and in Tables 14 and 15 below.

Impact (in landscape terms)

In HLCA 06 there will be a moderate loss of archaeological sites that contribute to the value of

the character area

In HLCA 07 there will be a slight loss of archaeological sites that contribute to the value of the

character area

In HLCA 21 there will be no loss of archaeological sites that contribute to the value of the

character area



Page 8 of 26

In HLCA 45 there will be a slight loss of archaeological sites that contribute to the value of the

character area

Table 14. Assessment of direct, physical impacts on HLCA 06 (Glynrhonwy Quarry)

Absolute Impact (Loss of Area) 79.11 ha, 31.2% of area Total area HLCA = 253 ha

Magnitude and Score Considerable – 4

Relative and landscape impacts (loss of known elements or characteristics) and scores Element / % loss

Category Magnitude Landscape value Landscape value effect

Slate quarry I, Bryn-Mawr (comprising 2 individual sites) 20% loss

B – 3 Moderate – 3 Considerable – 4 Moderately reduced – 3

Bryn-Mawr, slate quarry, quarry buildings, including Building VI (comprising 5 individual sites) 90% loss

B – 3 Very Severe – 6 Medium – 3 Moderately reduced – 3

Bryn-Mawr Trial Mine I and II (comprising 5 individual sites) 20% loss

B – 3 Considerable – 4 Considerable – 4 Moderately reduced – 3

Chwarel Cefn Dû, slate quarry II (comprising 6 individual sites) (part also in HLCA 07) 30% loss

A – 4 Considerable – 4 High – 5 Moderately reduced – 3

Chwarel Fawr Quarry and associated features (comprises 48 individual sites) 85% loss

B – 3 Very Severe – 6 Considerable – 4 Considerably reduced – 4

Railway over reclaimed land in Llyn Padarn (comprises 2 individual sites) 10 % loss

C – 2 Slight – 2 Medium – 3 Very slightly reduced – 1

RAF Llanberis (comprises 1 site) 10% loss

C – 2 Slight – 2 Low – 2 Very slightly reduced – 1

Sheepfold (Site No. 156) (comprises 1 site) 10% loss

C – 2 Slight – 2 Low – 2 Very slightly reduced – 1

Sheepfold (Site No. 201) (comprises 1 site) 100% loss

C – 2 Very Severe – 6 Low – 2 Very slightly reduced – 1

Agricultural remains (comprises 2 individual sites) 45% loss

C – 2 Severe – 5 Considerable – 4 Moderately reduced – 3

Average score for each element = 12.2 (rounded to 12)

Magnitude of absolute impact = 4

Grade of direct physical impact: 12 + 4 = 16 = Considerable



Page 9 of 26

Table 15. Assessment of direct, physical impacts on HLCA 07 (Gallt Celyn)

Absolute Impact (Loss of Area)

2.84 ha, 1.7% of area Total area HLCA = 168 ha

Magnitude and Score

Very Slight – 1

Relative and landscape impacts (loss of known elements or characteristics) and scores Element / % loss Category Magnitude Landscape value Landscape value effect

Chwarel Cefn Dû, slate quarry II (comprising 6 individual sites) (part also in HLCA 06) 30% loss

A – 4 Considerable – 4 Low – 2 Moderately reduced – 3

Average score for each element = 13



Table 16. Assessment of direct, physical impacts on HLCA 45 (Cefn Du/Garreg Lefain)

Absolute Impact (Loss of Area)

1.57 ha, 0.5% of area Total area HLCA = 342 ha

Magnitude and Score

Very Slight – 1

Relative and landscape impacts (loss of known elements or characteristics) and scores Element / % loss Category Magnitude Landscape value Landscape value effect

Glyn Rhonwy Quarry (Lower) (Q6) and associated features (comprises 4 individual sites) 100% loss

B – 3 Very Severe – 6 Low – 2 Slightly Reduced – 2

Average score for each element = 13



Stage 3: Assessment of Indirect Impacts

Indirect physical impacts

There will be no permanent indirect physical effects arising from the Development.

The tunnel connecting the upper and lower parts of the scheme will be bored. This technique avoids

impact upon a heritage resource that essentially exists at and above ground level (i.e. upstanding

buildings and other features), with little or nothing by way of sub-surface remains.

The function and articulation of the historic features within the landscape of the Development area

(i.e. HLCA 06) will remain legible. Public access will be temporarily restricted during construction,

but is anticipated to be unchanged from the present situation once the scheme is in operation.

Amenity (with the caveats expressed above in the section for Confidence Levels) is predicted to be

unaffected or enhanced.



Page 10 of 26

Indirect visual impacts

The ZTV developed for the Landscape and Visual Assessment establishes that the Development

will be visible from various places within the Dinorwig historic landscape. A zone of theoretical

visibility (ZTV) map has been produced to illustrate the potential visibility of the proposals and is

illustrated on Figure 6.3 of the ES.

The baseline landscape and its broad visual context are given by ES Chapter 6 under Section 6.6.

The visual context of the site is described in Section 6.7.2 and can be summarised as follows:

Distant views from the north are generally well screened by intervening topography and

woodland vegetation within the study area

The site is most visible from the north-east and east, from the opposite side of the Dinorwig

valley

The elevated nature of the landscape to the south and south-east of the site, within Snowdonia

National Park, allows distant views into the site, with the stepped profile of the quarries being a

feature in views along the Dinorwig valley

Views from the west are generally well screened by the topography of the study area, although

there are views into the upper quarries within the site from Cefn-du, a mountain immediately to

the west of the site

Despite being in close proximity to the settlement of Llanberis, woodland to the north and west

of the town screens the majority of views towards the site.

This situation has dictated the evaluation of Stage 3 for this ASIDOHL. The viewpoints on which the

analysis is based are listed in Table 17 and shown in Figure 1. Where possible the viewpoints

generated for the LVIA have been used, though an additional viewpoint was added for HLCA 11

(Figure 2 of this ASIDOHL).

The indirect visual impacts of the Development for each of the assessed HLCAs are given in Tables

18 to 28. Each table is followed by a brief comment on the character of the visual effects.



Page 11 of 26

Table 17. Viewpoint information

HLCA no. and name LVIA Viewpoint No. or Figure No.

Grid Reference Viewpoint direction

Distance to Development

02 Fachwen Woods, 21 Padarn and Peris Lakes VP4 (Llanberis Lake Railway)

257403

361402

SE

0.6km

04 Llanberis VP5 (Llanberis)

257403

361402

E

1.3km

05 Dolbadarn and Pentre Castell VP9 (Dolbadarn Castle)

258620

359831

E

1.9km

06 Glynrhonwy Quarry See Photographs 11.1 – 11.10 for representative views of the HLCA

Various locations – VP3, VP4, VP5, VP6, VP8, VP9, VP10, VP11, VP12

Within Order Limits

07 Gallt Celyn VP6 (Pen-y-llyn)

256011

362401

S

1.4km

11 Dinorwic, Marchlyn, Gallt-y-llan, Llanberis Figure 2 (public viewpoint above Dolbadarn)

259090

360390

E

2.1km

36 Unenclosed Mountain (North Carneddau) VP1 (Snowdon) VP2 (Moel Eilio) VP11 (Elidir Fach)

260943 255588 260390

354371 357748 361338

NE N E

7.6km 2.2km 3.4km

42 Gwaen Gynfi enclosed area VP8 (Dinorwig)

258102

361967

W

1.1km

44 River Valleys above Llanberis VP12 (Hebron Station)

258330

358458

NE

2.7km

45 Cefn Du and Garreg Lefain VP7 (Cefn Du)

254832

360370

S/SW

0.2km

Table 18. Indirect visual effects: HLCA 02 (Fachwen Woods)

Characteristic / element Status & Score

Impacts Magnitude & Score

19th century plantation; ancient woodland C – 2 Development form

and appearance Very Slight – 1

Quarries and associated remains B – 3

Industrial infrastructure B – 3

Score (average element status + impact magnitude) = 2.6 + 1 = 3.6 (out of a possible maximum score of 10)

Overall magnitude of impact score = 3.6 x (28 ÷ 10) = 10.08 = Moderate

Fachwen Woods: There will only be views of the Development from the south-eastern fringe of the

HLCA. Within the woodland that prevails in the HLCA there are no long-distance views. The

Development will only occupy a small part of existing views and will blend into the current

landscape. No historic settings or sightlines will be altered. The value of the HLCA will not be

diminished.



Page 12 of 26

Table 19. Indirect visual effects: HLCA 04 (Llanberis)



Victorian domestic, hotel, commercial architecture

B – 3 Development form and appearance

Very Slight – 1

Quarry workers terraced housing B – 3

Focus of Victorian and modern tourism B – 3

Score (average element status + impact magnitude) = 3 + 1 = 4 (out of a possible maximum score of 10)

Overall magnitude of impact score = 4 x (28 ÷ 10) = 11.2 = Moderate

Llanberis: From most locations the Development will be screened by intervening topography and

vegetation, although glimpsed views may be possible from a few locations in the more northerly

parts of the HLCA. No historic settings or sightlines will be altered. The value of the HLCA will not

be diminished.

Table 20. Indirect visual effects: HLCA 05 (Dolbadarn and Pentre Castell)



Dolbadarn medieval castle A – 4 Development form and appearance

Very Slight – 1

19th century tourist infrastructure B – 3

Literary and artistic cultural associations B – 3



Dolbadarn and Pentre Castell: There will be glimpsed views of the lower dam and turbine house,

but the change to existing views from and within the HLCA will be negligible. The settings of the key

sites of the castle and Royal Victoria Hotel will not be altered. No historic settings or sightlines will

be altered. The value of the HLCA will not be diminished.

Table 21. Indirect visual effects: HLCA 06 (Glynrhonwy Quarry)



Open slate quarries B – 3 Development form and appearance

N and S of site: Severe – 5 Centre of site: Slight – 2

Extensive spoil tips C – 2

Quarry infrastructure B – 3

World War Two bomb-storage facilities C – 2

Score (average element status + average impact magnitude) = 2.5 + 3.5 = 6 (out of a possible maximum score of 10)

Overall magnitude of impact score = 6 x (28 ÷ 10) = 16.8 = Considerable

Glynrhonwy Quarry: The Development will introduce significant visual changes to this character

area. These will mainly occur in the north and south of the HLCA, where the two dams are to be

built: whilst industrial in nature, their character is distinct from the existing extractive industrial

remains that prevail in the HLCA. The spoil tips generated by the project will add to those which

already exist: these will be a far less significant change. The centre of the HLCA – and the sites it

contains – will be largely unaffected, as the penstock tunnel will not be visible. The overall score of



Page 13 of 26

Considerable therefore comprises an average that takes in very severe visual changes to historic

character in the north and south of the HLCA, and slight changes in its central part.

Table 22. Indirect visual effects: HLCA 07 (Gallt Celyn)



Prehistoric occupation sites B – 3 Development form and appearance

Very Slight – 1

Post-medieval settlement and agriculture B – 3

Cultural associations with North Wales Quarrymen’s Union (1874)

B – 3



Gallt Celyn: Whilst there will be views of the lower dam and reservoir from the extreme south-

western fringe of this HLCA, the majority of the HLCA will have no views of the Development due to

the intervening (rising) topography. The HLCA will also not be seen in combination with the

Development, for example from viewpoints on the opposite side of Llyn Padarn. No historic settings

or sightlines will be altered. The value of the HLCA will not be diminished.

Table 23. Indirect visual effects: HLCA 11 (Dinorwic, Marchlyn, Gallt-y-llan slate quarries and Llanberis copper mine)



Late 18th to later 20

th century slate quarries A – 4 Development form

and appearance Very Slight – 1

Galleried open slate quarries A – 4

Copper mine B – 3



Dinorwic, Marchlyn, Gallt-y-llan slate quarries and Llanberis copper mine: The Development will be

a slight and distant addition to existing views from much of this HLCA. It will occupy only a small

proportion of existing views. No historic settings or sightlines will be altered. The value of the HLCA

will not be diminished.

Table 24. Indirect visual effects: HLCA 21 (Padarn and Peris Lakes)



Natural glacial lakes B – 3 Development form and appearance

Very Slight – 1

Medieval and post-medieval transport artery B – 3



Padarn and Peris Lakes: There will be views of the Development from much of the HLCA, as it

comprises open water. The potential development will only occupy a small part of existing views to

the east and south-east, and will blend into the current landscape. No historic settings or sightlines

will be altered. The value of the HLCA will not be diminished.



Page 14 of 26

Table 25. Indirect visual effects: HLCA 36 (Unenclosed Mountain – North Carneddau)



Unenclosed mountainside C – 2 Development form and appearance

Very Slight – 1

Prehistoric settlement and agricultural sites A – 4

Deserted medieval rural settlements B – 3



Unenclosed Mountain – North Carneddau: Much of this very large HLCA will have no views of the

Development. Where it is visible it will be a very minor addition to existing views and the extent of

change will be negligible. No historic settings or sightlines will be altered. The value of the HLCA will

not be diminished.

Table 26. Indirect visual effects: HLCA 42 (Gwaen Gynfi enclosed area)



18th century squatter settlements B – 3 Development form

and appearance Slight – 2

19th century smallholder enclosures B – 3

Relict industrial-era roads and railway B – 3


Overall magnitude of impact score = 5 x (28 ÷ 10) = 14 = Considerable

Gwaen Gynfi: Much of the eastern part of this extensive HLCA will have no views of the

Development. From the western parts some elements of the Development will be visible across the

Dinorwig valley, most notably the lower dam and reservoir and the turbine house. The upper dam

and reservoir will be screened by the topography of the site. The Development will occupy only a

small proportion of wider views across the Dinorwig Valley and mitigation measures will ensure the

elements of the development are in keeping with the character of the existing Glyn Rhonwy site. No

historic settings or sightlines will be altered. The value of the HLCA will not be diminished.

Table 27. Indirect visual effects: HLCA 44 (River Valleys above Llanberis)



Area of upland farming settlement C – 2 Development form and appearance

Very Slight – 1

Substantial, ruined, farmhouses C – 2


Overall magnitude of impact score = 3 x (28 ÷ 10) = 8.4 = Slight

River Valleys above Llanberis: Much of this HLCA will have no views of the Development. Where it

is visible it will be a very minor addition to existing views and the extent of change will be negligible.

No historic settings or sightlines will be altered. The value of the HLCA will not be diminished.



Page 15 of 26

Table 28. Indirect visual effects: HLCA 45 (Cefn Du and Garreg Lefain)



Largely unenclosed upland area C – 2 Development form and appearance

Slight – 2

Historic pastoral use: sheepfolds C – 2

Cart road to Cefn Du quarry C – 2



Cefn Du and Garreg Lefain: Parts of the HLCA will have views of the Development – mainly from

the summit of Cefn Du. The northern and western parts of the HLCA will have no views in this

direction. From Cefn Du the upper dam and reservoir will be a prominent new addition to existing

views, which currently take in the landscape of quarries and spoil tips. However, views of and within

HLCA 45 are essentially unaffected: its character as unenclosed upland remains legible. No historic

settings or sightlines will be altered. The value of the HLCA will not be diminished.

Stage 4: Evaluation of Relative Importance

The following tables comprise the evaluation of relative importance of the character areas assessed

within this study. This takes three parts:

Development in relation to the whole of HLCA 06, in which the vast majority of the Development

would be located (Table 29)

HLCAs in relation to the whole of Dinorwig historic landscape (Tables 30 to 40)

HLCAS in relation to the national context (Table 41)

No tables are provided for assessment of relative importance of those parts of HLCAs 07, 21 and 45

that fall within the Order Limits. As discussed in relation to Stage 2, in both cases these parts

represent only a negligible proportion of the whole HLCA (<2%).



Page 16 of 26

Relative importance: a) in relation to the whole of the HLCAs directly affected

Table 29. Evaluation of relative importance: Development area in relation to the whole of HLCA 06 (Glynrhonwy Quarry)

Criterion

Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med

3

Low

2

Very Low/ Poor

1

Rarity X

Representativeness X

Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 32 out of possible maximum of 55: 32÷55*100 = 58.1 Grade of overall value = 58 = Considerable

Comment: The area of Development takes in a part of HLCA 06 which is completely representative

of the whole character area. Extending from an area close to the lake shore, all landscape zones

are represented, as are all types of archaeological site present within the HLCA as a whole.

Relative importance: b) in relation to the whole of the Dinorwig historic landscape

Table 30. Evaluation of relative importance: HLCA 02 (Fachwen Woods) in relation to the whole historic landscape

Criterion

Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med

3

Low

2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: This HLCA comprises a range of interconnected and associated industrial features, now

mostly within plantation. These features are moderately well documented and have some research

potential, but relatively little potential as an amenity or educational resource.



Page 17 of 26

Table 31. Evaluation of relative importance: HLCA 04 (Llanberis) in relation to the whole historic landscape

Criterion

Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med

3

Low

2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: A settlement in which historic structures exist amongst modern buildings, infrastructure

and open space. Its history and evolution is well-understood but it has little by way of amenity,

research or educational potential.

Table 32. Evaluation of relative importance: HLCA 05 (Dolbadarn and Pentre Castell) in relation to the whole historic landscape

Criterion

Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med

3

Low

2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 41 out of possible maximum of 55: 41÷55*100 = 74.5 Grade of overall value = 75 = High

Comment: Period-diverse character area in which well-preserved medieval and post-medieval

remains are blended. These represent a highly legible resource with significant amenity value, not

least because of the literary and artistic figures with which they are associated.



Page 18 of 26

Table 33. Evaluation of relative importance: HLCA 06 (Glynrhonwy Quarry) in relation to the whole historic landscape

Criterion

Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med

3

Low

2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: Well-articulated industrial (extractive) landscape. The sites present are moderately well-

preserved and documented but have relatively little potential as an amenity or educational resource

– particularly when compared to the nearby quarries at Dinorwig. Gwynedd Archaeological Trust

has undertaken a review of all quarry sites in an attempt to assess the condition of slate mining

sites and aid their preservation: the quarries at Glynrhonwy are considered to be of national (Welsh)

or regional (Gwynedd) significance (GAT 1994).

Table 34. Evaluation of relative importance: HLCA 07 (Gallt Celyn) in relation to the whole historic landscape

Criterion Value / Score

V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 25 out of possible maximum of 55: 25 ÷55*100 = 45.4 Grade of overall value = 45 = Considerable

Comment: Upland character area which is distinct to those neighbouring it, for example HLCA 45.

The sites present are reasonably well-preserved and sit within a landscape in which their settlement

and pastoral function remains legible. The HLCA has little by way of amenity, research or

educational potential.



Page 19 of 26

Table 35. Evaluation of relative importance: HLCA 11 (Dinorwig, Marchlyn, Llanberis) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: Visually-spectacular landscape in which features relate to quarrying and mining, though

not to associated settlement. These remains are extremely well-preserved and articulated. They are

easily understood and have high potential for research, and as an educational amenity.

Table 36. Evaluation of relative importance: HLCA 21 (Peris and Padarn Lakes) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 25 out of possible maximum of 55: 25 ÷55*100 = 45.4 Grade of overall value = 45 = Considerable

Comment: Many Stage 4 scoring criteria are difficult to apply to this HLCA, which comprises a

natural body of water. The sites with which it is associated (i.e. upon its shore) lie within the

adjacent character areas. The lakes represent a rare element of the historic landscape and have

had usage in the past as a transport artery. That function is probably not obvious to visitors.



Page 20 of 26

Table 37. Evaluation of relative importance: HLCA 36 (Unenclosed Mountain – North Carneddau) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: Very large character area which is atypical of much of the Dinorwig historic landscape, in

that it preserves features of prehistoric and medieval date but has little post-medieval or industrial

imprint. The early domestic and pastoral sites are well-preserved for their type and are nationally

important. They have high research potential (for generating archaeological rather than historical

data), whilst the only limitation on their amenity and educational value is their comparative

inaccessibility.

Table 38. Evaluation of relative importance: HLCA 42 (Gwaen Gynfi enclosed area) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X


Comment: Large character area which contains an interesting landscape of small settlement

enclosures. The land-pattern is well-preserved and legible. The HLCA is representative of the

settlement aspect of the historic landscape as a whole, but lacks substantial quarrying remains. It

has relatively little potential for research or as an amenity.



Page 21 of 26

Table 39. Evaluation of relative importance: HLCA 44 (River valleys above Llanberis) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 20 out of possible maximum of 55: 20÷55*100 = 36.3 Grade of overall value = 36 = Moderate

Comment: Upland area in which sparsely-distributed ruinous farms are the main historic element.

These are of little historical or archaeological interest. This HLCA is not representative of the core

(industrial) character of the historic landscape, whilst also lacking the archaeological value of other

upland areas – notably HLCA 36.

Table 40. Evaluation of relative importance: HLCA 45 (Cefn Du and Garreg Lefain) in relation to the whole historic landscape


V. High /V. Good

5

High / Good

4

Mod/ Med 3

Low 2

Very Low/ Poor

1

Rarity X


Documentation X

Group Value X

Survival X

Condition X

Coherence X

Integrity X

Potential X

Amenity X

Associations X

Score = 19 out of possible maximum of 55: 19÷55*100 = 34.5 Grade of overall value = 34 = Moderate

Comment: Upland area that is largely unenclosed. Some prehistoric features exist on the HLCA’s

northern fringe, but otherwise archaeological features are very sparse and of low value. As with

HLCA 44, this character area does not reflect the core characteristics of the historic landscape and

is archaeologically less valuable than HLCA 36.

Relative importance: c) in relation to the national context

Of the 58 registered historic landscapes in Wales, many contain relict remains of mineral or stone

extraction. These include: HLW C 2 Holywell Common and Halkyn Mountain (lead mining); HLW D

1 Black Mountain and Mynydd Myddfai (stone quarrying for lime); HLW G 9 Nantlle Valley (slate



Page 22 of 26

quarries, copper mines); HLW C 6 Vale of Llangollen (stone quarrying). However, there are several

registered landscapes whose overarching characteristic is of post-medieval industrial remains.

These are: HLW G 3 Blaenau Ffestiniog (slate mining); HLW Gt 4 Clydach Gorge (ironworking,

limestone quarries, lime-working); Merthyr Tydfil HLW MGl 2 (iron, coal and stone); The Rhondda

HLW MGl 5 (coal mining); and Blaenavon HLW Gt 1 (iron).

Dinorwig is most comparable with Blaenau Ffestiniog. In part this is due to the obvious focus on

slate mining, but their geographical proximity also places them in broadly similar landscape,

historical and social contexts. The industrial landscapes of South East Wales, though contemporary,

belong to a somewhat different set of contexts. Moreover, in the main, stone extraction in South

Wales was largely a corollary of the exploitation of iron and coal, rather than being the prime

economic product.

ASIDOHL guidance states that decreasing rarity (i.e. the existence of similar land parcels in other

historic landscapes) is not a reason to downgrade the value of a character area within the national

context. It is therefore considered that the assessments given in Tables 30 to 40 also accurately

reflect the character areas’ value in national terms, as summarised below in Table 41.

Table 41. Character area value in relation to the national context

Character Area Value

02 Fachwen Woods Considerable

04 Llanberis Considerable

05 Dolbadarn and Pentre Castell High

06 Glynrhonwy Quarry Considerable

07 Gallt Celyn Considerable

11 Dinorwic, Marchlyn, Gallt-y-llan slate quarries and Llanberis copper mine High

21 Padarn and Peris Lakes Considerable

36 Unenclosed Mountain (North Carneddau) High

42 Gwaen Gynfi Moderate

44 River Valleys above Llanberis Moderate

45 Cefn Du and Garreg Lefain Moderate

Stage 5: Assessment of Overall Significance of Impact

Table 42 presents a summary of the ASIDOHL findings in relation to each HLCA. The overall

(averaged) impact of the proposed project is shown in Table 43.

Table 42. Summary of ASIDOHL Findings by HLCA

HLCA

02 04 05 06 07 11 21 36 42 44 45

Value (Stage 4)

Med 5

Med 5

High 8

Med 6

Med 4

High 8

Med 4

High 7

Med 6

Low 2

Low 2

Direct Physical Impact (Stage 2)

None 0

None 0

None 0

Med 5

Med 5

None 0

None 0

None 0

None 0

None 0

Med 5

Indirect Impact (Stage 3)

V.Low 1

V.Low 1

V.Low 1

High 7

V. Low 1

V.Low 1

V.Low 1

V.Low 1

Low 2

V.Low 1

V.Low 1

Reduction in Value of HLCA

V.Low 1

V.Low 1

V.Low 1

High 7

Low 2

V.Low 1

V.Low 1

V.Low 1

V.Low 1

V.Low 1

V.Low 1

Total Score 7 7 10 25 12 10 6 9 9 4 9

Grading Slight Slight Mod’t Severe Mod’t Mod’t Slight Slight Slight Slight Slight



Page 23 of 26

Table 43. Summary of overall significance of impact (averages for all HLCAs assessed)

Criteria Notes

Value of HLCAs

5 = Medium (range: Low to High; average value 5.2)

Impact caused by development

Direct Physical: Medium – 5 (HLCAs 06, 07 and 45 only) Indirect Physical: None – 0 Indirect Visual: Low – 2 Average impact score = 5 + 0 + 2 / 3 = 2.3 = Low

Reduction in value of historic landscape

Low – 2 (range: High to Very Low; average score 1.6)

Overall significance of impact = Slight

Total Score = HLCA value + Impact + Reduction in value = 5 + 2.3 + 2 = 9.3 (rounded down to 9)

Summary and Conclusions

This ASIDOHL reaches three principal conclusions.

1) In relation to HLCA 06 (Glynrhonwy Quarry) it finds that there will be a moderate to high

significance of impact, in terms of direct physical and indirect visual impacts respectively.

2) In relation to HLCAs 07 (Gallt Celyn) and 45 (Cefn Du/Garreg Lefain) it finds that there will be a

moderate significance of impact. However, their Stage 2 scores of Considerable both seem

overstated, given the very small percentage of land within each that falls inside the Order Limits

(<2%), and the minimal number of elements actually affected by development. Their Stage 2 scores

derive from the fact that a single high-value element within each is impacted; had numerous lesser-

value sites also been damaged or destroyed, the Stage 2 score would actually have been lower. It

should also be noted that Chwarel Cefn Dû, slate quarry II, which essentially underpins the

Considerable Stage 2 score for HLCA 07, lies mainly within HLCA 06 and is also included in the

assessment of the latter character area.

3) For all other HLCAs it finds that there will be no physical impact, and that the changes to existing

views will be slight or very slight. Most of the scoring in Stage 3 produced grades of Moderate, but it

is important to note that this was derived almost completely from the value of the character area, as

opposed to the magnitude of change.

Potential mitigation, compensation and enhancement measures for the Development are discussed

in Chapter 11 (section 11.8). These mitigation measures primarily deal with the amelioration of

impacts during construction – primarily through archaeological works or building recording.

However, further measures that address the operational period of the Development may be

formulated post-consent. These could concern amenity, for example the maintenance or

improvement of public access and improved interpretation (i.e. through signage). Under EIA, these

measures could be considered to offset, or compensate for, any residual impacts of construction.

ASIDOHL methodology, however, does not allow any such positive aspects of design to be taken

into account, nor for the offsetting of impact against benefit.



Page 24 of 26

The final grade calculated in Table 43 lies on the interface between a Slight and Moderate impact. It

reflects a Development which will have a localized impact that is largely confined to a single HLCA,

and which in some places is severe. Beyond the boundaries of this HLCA the wider Dinorwig

historic landscape will be essentially unaltered.

This conclusion is comparable to the original ASIDOHL undertaken for this project as part of the

2012 Environmental Impact Assessment.

References

AECOM, 2012, Glyn Rhonwy Environmental Statement.

Cadw CCW and ICOMOS UK, 1998, The Register of Landscapes, Parks and Gardens of Special

Historic Interest in Wales. Part 2.1: Register of Landscapes of Outstanding Historic Interest in

Wales, Cardiff

CCW, Cadw and WAG, 2007, Technical Annex: A Staged process for the Assessment of the

Significance of Impact of Development on the Historic Landscape Areas on the Register of

Landscapes of Historic Interest in Wales (ASIDOHL), in Guide to good practice on using the

Register of Landscapes of Historic Interest in Wales in the Planning and Development Processes,

Cardiff accessed at -

http://cadw.gov.wales/docs/cadw/publications/LandscapesRegisterGoodPractice_EN.pdf: accessed

02/10/2015

Gwynedd Archaeological Trust, 1994, Gwynedd Quarrying Landscapes: Slate Quarries, Report 129,

Unpublished Report

Gwynedd Archaeological Trust, 1999, Glynrhonwy Slate Quarry, Llanberis: Archaeological

Assessment, Report 338, Unpublished Report

Gwynedd Archaeological Trust, 2000a, Historic Landscape Characterisation: Ardal Arfon, Report

351, Unpublished Report

http://cadw.gov/



Historic Landscape

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Figure 1



Historic Landscape

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Figure 2

glyn rhonwy pumped storage development …...hlca name distance from development* 2 fachwen woods...

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