Post on 28-Jul-2020
1
Appendix 5 - Revised Proposed Mitigation for Culverts and River Crossings
The following table lists actions to be taken as part of the Mynydd y Gwynt Wind Farm Project following specific queries raised by NRW with regard to
hydrological mitigation. A photographic record of relevant sites is given in Appendix A of this document and a plan showing the location of all site
specific items in Appendix B.
Item Number
Item
Photo numbers
Notes
Culvert extension/ replacement
Bottomless culvert
Clear Span
Causeway
1 Concrete 18" culvert
1 to 3 Culvert to be extended or replaced. No NRW fish concerns. NRW Geomorphologist prefers clear span or bottomless culvert.
x
2 225mm plastic culvert
4 to 5 Extend on low side to avoid trees. Goes to trickle in dry periods. NRW satisfied with culvert extension.
x
3 225mm plastic culvert
6 to 7 Culvert to be extended or replaced. NRW satisfied with culvert extension.
x
4 225mm plastic culvert
8 Culvert to be extended or replaced. Bottomless culvert preferred by NRW
x
5 225mm plastic culvert
9
Clear span or bottomless culvert preferred by NRW
x
6 Concrete 18" culvert
10 to 11
Fish of little concern. NRW Geomorphologist prefers clear span to replace culvert.
x (possible
merge culverts to single
crossing - subject to final agreed design)
7
Concrete 18" culvert
12 to 13
8 225mm plastic culvert
14
NRW satisfied with culvert extension.
x
9
Not present
n/a
Culvert did not exist. Watercourse heads along trackside ditch to culvert 10.
n/a
n/a
n/a
10 15 to 16 x
2
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
Concrete 18" culvert
Clear span requested. 10a and b were 150mm culverts on side ditch that would not be encroached upon.
11 225mm plastic culvert
17 to 18
Dry channel. NRW satisfied with culvert extension.
x
12 225mm plastic culvert
19 to 20
Bottomless culvert requested by NRW
x
13 225mm plastic culvert
21 to 22
NRW satisfied with culvert extension.
x
14 225mm plastic culvert
23
NRW satisfied with culvert extension.
x
15 225mm plastic culvert
24
NRW satisfied with culvert extension.
x
16
225mm plastic culvert
25 to 26
Extend and move outfall downstream away from dam bank. NRW satisfied with culvert extension. This culvert position is more than a safe distance from the Water Vole burrow(s) identified at the pond to the west of the track to be affected by the Project.
x
17
1m concrete culvert
27
Not affected by project but NRW to consider if culvert removal to allow fish movement would be favourable over any increased risk of removing the sediment pond or harm to water voles. Any culvert removal works may interfere with Water Voles and be need to carried out under NRW licence.
see note
18 300mm plastic culvert
28
Single-wall sewer - extend
x
19
Large dia. corrugated steel culvert
29 to 31
Not in project but if fish important it may be possible to construct a new open spillway (bridged), with invert 150-300mm below current overflow level to provide continuity of a primary flow watercourse channel. But NRW to consider this against possible risk of altering the sediment pond in this way.
see note
3
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
20
12" concrete & 225mm (x2) plastic culverts
32 to 35
NRW request Clear Span. Culverts to be replaced by a single Clear Span, with secondary overflow culvert if required for flow. NRW are not concerned about the removal of the pond that would occur.
x
21
12" concrete & 225mm plastic culverts
32 to 35
22 225mm plastic culvert
36 to 37
NRW satisfied with culvert extension.
x
23
12" concrete primary flow and 300mm overflow culverts
38 to 39
Open Span requested by NRW - unless track widening not needed. NRW are not concerned about the removal of the pond that would occur.
x
24 Peaty gulley crossing
40
Floating track / causeway proposed. x
(floating)
25 225mm plastic culvert
41
NRW satisfied with culvert extension.
x
26 Culvert (dia unknown)
n/a NRW satisfied with culvert extension. x
27 225mm plastic culvert
42 to 47
NRW satisfied with culvert extension.
x
28
225mm plastic culvert (Abandoned and not functional)
42 to 47
NRW request Clear Span. Culverts to be replaced by a single Clear Span. NRW are not concerned about the removal of the pond that would occur.
x (Single Open
Span)
29 450mm plastic culvert
42 to 47
4
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
30 600mm plastic culvert
42 to 47
31 225mm plastic culvert
48 to 50
NRW satisfied with culvert extension downstream side of track.
x (extend on downstream
side)
32
Ford in causeway
51 to 52
High water level upslope of causeway to be maintained and causeway to be widened on low side. Design tbc, with NRW but may have several culverts at same height to distribute across lower wetland.
x see note
33
Turbine 27
53
NRW do not consider a new settlement pond is required. Cross-drains can be installed within the new track to direct runoff to side ditches with check dams to soakaway or be dispersed as overland flow. All parties agreed that the watercourse shown running west to east towards turbine 27 was in fact the vestige of a former grass track and not a watercourse channel. This will be removed from the mapping if possible as it is misleading.
n/a
n/a
n/a
n/a
34
Large car park
54
The large car park is prone to erosion. This car park is to be used for construction site offices. No storage of materials, e.g. excavated soils, peat, etc, will take place within this compound. The area to be used for the project is to be resurfaced with an improved granular material. Surface water within this area is to be intercepted by new swales and directed through a new sediment basin before being disbursed as overland flow at an agreed controlled greenfield runoff rate.
n/a
n/a
n/a
n/a
35 55 n/a n/a n/a n/a
5
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
Existing track erosion downslope of large car park
This area is not affected by the Project.
The shaley banks sloping towards the track at this location are eroding. The banks will be stabilised to reduce the risk of erosion, possibly involving re-grading the slope and/or installing bank protection before applying soil and reseeding. Given the slopes and soil types it is likely that a non biodegradable geotextile membrane will be used to provide long term support on the bank. Final design would be subject to a full level survey but there is no reason why conventional stabilisation methods would not be suitable. The ditch alongside the track will also be fenced off to prevent pedestrians and vehicles from disturbing the verge, banks and bed of the ditch. Check dams will also be installed as extra precaution to aid the settlement of sediment.
36 225mm plastic culvert
56 to 58
NRW satisfied with culvert extension.
x
37 225mm plastic culvert
59 to 61
NRW satisfied with culvert extension.
x
38 225mm plastic culvert
62 to 64
NRW satisfied with culvert extension.
x
39 225mm plastic culvert
65 to 67
NRW satisfied with culvert extension.
x
40 225mm plastic culvert
68 to 70
NRW satisfied with culvert extension.
x
41 225mm plastic culvert
71 to 73
NRW satisfied with culvert extension.
x
42 225mm plastic culvert
74 to 76
NRW satisfied with culvert extension.
x
43 225mm plastic culvert
77 to 79
NRW satisfied with culvert extension.
x
6
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
44 225mm plastic culvert
80 to 82
NRW satisfied with culvert extension.
x
45 225mm plastic culvert
83 to 85
NRW satisfied with culvert extension.
x
46 225mm plastic culvert
86 to 88
NRW satisfied with culvert extension.
x
47 225mm plastic culvert
89 to 91
NRW satisfied with culvert extension.
x
48 150mm plastic culvert
92 to 94
NRW satisfied with culvert extension.
x
49
Tracks construction period
n/a
Track construction will only take place under suitably dry weather conditions to reduce the risk of soil erosion. The construction period is to run over a number of years and therefore there will be plenty of opportunity to manage the construction activities so that they run during suitably dry conditions.
n/a
n/a
n/a
n/a
50
Track construction areas
n/a
Tracks will be constructed progressively along their lengths, so that they strip, form and surface the track progressively in short lengths. Therefore no long continuous slopes will be stripped and left vulnerable to soil erosion. Where necessary, the contractor will arrange the stripped soils in bunds to exclude surface water runoff from the higher land from the construction site and contain any runoff within the site for treatment with control dispersal over the rough grassland or via sediment. Similarly, drainage ditches/swales will be formed at any early stage to manage the water within and around the site.
n/a
n/a
n/a
n/a
51 Online ponds
n/a No on-river settlement ponds will be utilised for the treatment of runoff from the site. Any water treatment will take place off-line. The final detailed surface water management plan will be agreed with NRW.
n/a
n/a
n/a
n/a
52
Peat
n/a
NRW raised concerns about the potential for peat loss as a result of the new infrastructure. GIS shape files for the Worksplan and Peat survey were provide to NRW on 2nd December 2014. This information was used to strategically position the infrastructure away from areas of deep
n/a
n/a
n/a
n/a
7
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
peat. Micrositing will further aid the avoidance of any localised deep peat and there is sufficient space to avoid other issues, such as the distance from watercourses – around which the infrastructure positions has similarly been planned. After track and turbine construction there will be a surplus of peat. This will be placed and graded around areas where peat is degrading following historic cutting for fuel. This will preserve the surplus peat and halt the degrading process of the peat islands.
53
Restoration of temporary construction sites
n/a
NRW raised concerns about the potential for habitat loss as a result of poor reinstatement. The long construction programmes means that earth works can be programmes to take place during the driest periods. This means that soil structural damage will be kept to a minimum so that the restoration of soils and the subsequent habitat will have the greatest chance of success. A Soil Management and Handling Plan will be provided before construction begins.
n/a
n/a
n/a
n/a
54
Groundwater quality
n/a
NRW raised concerns about the potential for contaminated leachate entering the groundwater. This may be based on a misunderstanding of the Hydrology chapter 14 in the ES. There is little risk of groundwater contamination. Surface water is at risk of contamination from eroded material that remains in suspension in surface water runoff and not from dissolvable substances that could contaminate groundwater.
The River Basin Districts Typology, Standards and Groundwater
threshold values (Water Framework Directive) (England and Wales)
Directions 2009’ in which the River Wye is specifically mentioned,
identify a level of 7.2 µg / l as the EQS value. Analysis of the samples
found that metal levels normally associated with lead mining were not
significant and lay in the range <0.1 – 5.2µg/l. The mean value was
1.8µg/l. As both the mean value and highest level in the range are
below the EQS it is concluded that there is no risk to surface waters
from the car park which is proposed to be used as a contractor’s
compound.
n/a
n/a
n/a
n/a
8
Item Number
Item Photo numbers
Notes Culvert
extension/ replacement
Bottomless culvert
Clear Span
Causeway
55
Water quality monitoring
n/a
A water quality monitoring system will be installed on site to measure the quality during construction, operation and decommissioning of the site. This system will be monitored regularly and during specific events, e.g. the Rally, to identify any changes in water quality so that appropriate mitigation can be implemented. The precise mitigation measures employed will depend on the event causing the water quality change.
n/a
n/a
n/a
n/a
56
Land Drainage Act
n/a
Land drainage consent will need to be sought from Powys County Council for all water course crossing installations. All culverts will be designed to cater for an agreed storm return period. All open span structures will be formed so that there is no reduction to existing channel dimensions.
n/a
n/a
n/a
n/a
57
Flood Risk
n/a
The site is not at risk of flooding and no concerns about flood risk were raised during the joint site visit on 25th November. The new tracks will be crushed stone that will create a semi permeable surface. All new hard surfaces of this nature will comprise less than 3% of the total site area and runoff from tracks will be shed sideways into soakaway ditches (to be designed as part of the final surface water management plan). Therefore, there will be negligible increased flood risk to other parties downstream.
n/a
n/a
n/a
n/a
Photographic Record of Site Specific Hydrological Items
Item 1
Photograph 1
Photograph 2
Appendix A
i
ii
Photograph 3
Item 2
Photograph 4
3
Photograph 5
Item 3
Photograph 6
4
Photograph 7
Item 4
Photograph 8
5
Item 5
Photograph 9
Item 6
Photograph 10
6
Photograph 11
Item 7
Photograph 12
vii
Photograph 13
Item 8
Photograph 14
8
Item 9
No Item exists
Item 10
Photograph 15
Photograph 16
9
Item 11
Photograph 17
Photograph 18
10
Item 12
Photograph 19
Photograph 20
11
Item 13
Photograph 21
Photograph 22
xii
Item 14
Photograph 23
Item 15
Photograph 24
13
Item 16
Photograph 25
Photograph 26
14
Item 17
Photograph 27
Item 18
Photograph 28
15
Item 19
Photograph 29
Photograph 30
16
Photograph 31
Items 20 & 21
Photograph 32
xvii
Photograph 33
Photograph 34
18
Photograph 35
Item 22
Photograph 36
19
Photograph 37
Item 23
Photograph 38
20
Photograph 39
Item 24
No culvert present. Localised shallow valley feature to have floating road.
Photograph 40
21
Item 25
Photograph 41
Item 26
No image available
Item 27-30
Photograph 42
xxii
Photograph 43
Photograph 44
23
Photograph 45
Photograph 46
24
Photograph 47
Item 31
Photograph 48
25
Photograph 49
Photograph 50
26
Item 32
Photograph 51
Photograph 52
xxvii
Item 33
Photograph 53
Item 34
Photograph 54
28
Item 35
Photograph 55
Item 36
Photograph 56
29
Photograph 57
Photograph 58
30
Item 37
Photograph 59
Photograph 60
31
Photograph 61
Item 38
Photograph 62
xxxii
Photograph 63
Photograph 64
33
Item 39
Photograph 65
Photograph 66
34
Photograph 67
Item 40
Photograph 68
35
Photograph 69
Photograph 70
36
Item 41
Photograph 71
Photograph 72
xxxvii
Photograph 73
Item 42
Photograph 74
38
Photograph 75
Photograph 76
39
Item 43
Photograph 77
Photograph 78
40
Photograph 79
Item 44
Photograph 80
41
Photograph 81
Photograph 82
xlii
Item 45
Photograph 83
Photograph 84
43
Photograph 85
Item 46
Photograph 86
44
Photograph 87
Photograph 88
45
Item 47
Photograph 89
Photograph 90
46
Photograph 91
Item 48
Photograph 92
xlvii
Photograph 93
Photograph 94
i
Appendix B
Schedule of Site Specific Hydrological Items Plan
0
35
355 0
36
365
0
37
375
380
385
390
39 5
400
410
415
420
430 400
440
435 405
5 44 450
410
455 415
460 420
380
0
37
365
0
36 5
35
340 345
350
355
340
5
34
#
Work No. 2
Temporary Blade Storage Area
Work No. 3
Location of Site Entrance
Work No. 4
Electricity Substation
Work No. 5
Temporary Construction Compound
Work No. 6
Existing Access Track to be Upgraded
Culverts to be constructed
New Access Track to be Constructed
Work No. 7
Underground Cables
Work No. 8
G Meteorological Mast
Work No. 9
Settlement Pond
- 0 100 200 300
Metres
Scale 1:2,500 at A0 size
Yn seiliedig ar fap digidol 1:10000 gyda chaniated yr arolwg ordnans ar ran
Rheolydd Llyrfa ei Mawrhydi. Hawlfraint y Goron.
ADAS trwydded CCC. 100020033
Based on digital 1:10000 map by permission of Ordnance Survey on behalf of the
Controller of Her Majesty's Stationery Office. © Crown copyright. All rights reserved.
ADAS Licence No 100020033 December 2014 For reference purposes only. No further copies may be made
Doc Ref: MYG-ES-FIG6.11 19/11/2014 Mynydd y Gwynt Wind Farm Site Specific Hydrology Items
Sheet 1 of 3
465
440
30
27 28 29
365
285700
285800
285900
286000
286100
286200
286300
286400
286500
286600
286700
410
405
400
395
390
3 3 90 8
5
4 4 40 5 4 0 0 0
4 40
6 5 5
6 0
4
4 5
4 5 41 7
0 415 0
4 7
48 5
5
420
480 42 5
95
450
445
440
435
430
425
420
415
#
37
39
415
Work No. 2
Temporary Blade Storage Area
Work No. 3
Location of Site Entrance
Work No. 4
Electricity Substation
Work No. 5
Temporary Construction Compound
Work No. 6
Existing Access Track to be Upgraded
Culverts to be constructed
New Access Track to be Constructed
Work No. 7
Underground Cables
Work No. 8
G Meteorological Mast
Work No. 9
Settlement Pond
- 395
40
0 100 200 300
Metres
Scale 1:2,500 at A0 size
Yn seiliedig ar fap digidol 1:10000 gyda chaniated yr arolwg ordnans ar ran
Rheolydd Llyrfa ei Mawrhydi. Hawlfraint y Goron.
ADAS trwydded CCC. 100020033
Based on digital 1:10000 map by permission of Ordnance Survey on behalf of the
Controller of Her Majesty's Stationery Office. © Crown copyright. All rights reserved.
ADAS Licence No 100020033 December 2014 For reference purposes only. No further copies may be made
Doc Ref: MYG-ES-FIG6.11 19/11/2014
Mynydd y Gwynt Wind Farm Site Specific Hydrology Items
Sheet 2 of 3
Causeway to be
culverted
510
460
00
284200
284300
284400
284500
284600
284700
284800
284900
285000
285100
285200
5
44 0
5
42
51 4
0 2 4
415
410
405
400
395
390
395
390
5 41 7 0 0 3 37
0 2
5 415
4
2 4
3 390 9 5
4
430 3 5
44 0
445
45
0 4 5
7 6
4 0
4 4 4
5
4 5 5
48
6 0 5
0 5 48
7 4
#
440
45
46
47
Work No. 2
Temporary Blade Storage Area
Work No. 3
Location of Site Entrance
Work No. 4
Electricity Substation
Work No. 5
Temporary Construction Compound
Work No. 6
Existing Access Track to be Upgraded
Culverts to be constructed
New Access Track to be Constructed
Work No. 7
Underground Cables
Work No. 8
G Meteorological Mast
Work No. 9
Settlement Pond
- 0 100 200 300
Metres
48 33
Scale 1:2,500 at A0 size
Yn seiliedig ar fap digidol 1:10000 gyda chaniated yr arolwg ordnans ar ran
Rheolydd Llyrfa ei Mawrhydi. Hawlfraint y Goron.
ADAS trwydded CCC. 100020033
Based on digital 1:10000 map by permission of Ordnance Survey on behalf of the
Controller of Her Majesty's Stationery Office. © Crown copyright. All rights reserved.
ADAS Licence No 100020033 December 2014 For reference purposes only. No further copies may be made
Doc Ref: MYG-ES-FIG6.11 19/11/2014 Mynydd y Gwynt Wind Farm
Site Specific Hydrology Items
Sheet 3 of 3
1
440
430 450
460
470
282800
282900
283000
283100
283200
283300
283400
283500
283600
283700
283800