EXETER TONEWTON ABBOT GEO - ENVIRONMENTAL RESILIENCE STUDY
Dawlish-Teignmouth Cliffs Unmanned Aerial Vehicle (UAV) Survey Interpretation Report
Prepared for Network Rail
October 2016
Halcrow Group Ltd. Burderop Park Wroughton SN4 0QD
Exeter to Newton Abbot Geo-Environmental
Resilience Study
Dawlish-Teignmouth Cliffs Unmanned Aerial Vehicle (UAV) Survey Interpretation Report
October 2016
Notice This document and its contents have been prepared and are intended solely for Network Rail’s information and use in relation to the Exeter to Newton Abbot Geo-Environmental Resilience Study. CH2M assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents.
Document History
Version Date Description Created by Verified by Approved by
1 Oct 2016 Draft Oliver Dabson Roger Moore Peter Barter
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Contents
Section Page Contents ...... i Acronyms and abbreviations ...... ii 1. Introduction ...... 1 1.1 Summary ...... 1 1.2 Data processing and quality control ...... 2 1.3 Visualisation software and interpretation approach ...... 4 2. Interpretation of UAV dataset ...... 5 2.1 CBU 06 ...... 5 2.2 CBU 07 ...... 7 2.3 CBU 08 ...... 8 2.4 CBU 09 ...... 9 2.5 CBU 10 ...... 10 2.6 CBU 11 ...... 11 2.7 CBU 12 ...... 12 2.8 CBU 14 ...... 14 2.9 CBU 15 ...... 15 2.10 CBU 16 (part)...... 17 2.11 CBU 17 ...... 18 2.12 CBU 18 ...... 20 2.13 CBU 19 ...... 22 2.14 CBU 20 ...... 23 2.15 CBU 21 ...... 25 2.16 CBU 22 ...... 28 2.17 CBU 23 ...... 31 2.18 CBU 28 ...... 34 2.19 CBU 29 ...... 36 2.20 CBU 30 ...... 38 3. Summary and Recommendations ...... 39 Appendix A: Location of CBUs ...... 41 Appendix B: Baseline Report CBU Proformas ...... 45 Appendix C: UAV data capture areas ...... 66 Appendix D: UAV Survey Scope ...... 70 Appendix E: Specification of UAV Survey ...... 74
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Acronyms and abbreviations
BGS British Geological Survey CBU Cliff Behaviour Unit DEM Digital Elevation Model DPC Dense Point Cloud GCP Ground Control Point GPS Global Positioning System LiDAR Light Detection and Ranging NR Network Rail OS Ordnance Survey SSSI Site of Special Scientific Interest TGP Tony Gee and Partners UAV Unmanned Aerial Vehicle UTX Under-Track Crossing
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT II
1. Introduction 1.1 Summary This report provides an overview and the results of a survey by Unmanned Aerial Vehicle (UAV) of the coastal cliffs at Dawlish, which overlook or are adjacent to Network Rail (NR) infrastructure and operations. This builds on the assessment of these cliffs undertaken by CH2M in March 2015, which provided a systematic assessment of the geotechnical asset defects or “hazards” over the same area for the first time using archive aerial photography and LiDAR data. In the context of the assessment, the geotechnical assets of interest include both natural and engineered slopes that form the high cliffs alongside the up main line and above the tunnel portals between Dawlish Warren and Teignmouth stations (denoted Sections 2 to 4 in preceding CH2M reports, see Figure 1-1). The geotechnical asset outside of this prioritised section, including the coastal defence structures adjacent to the down main line, were specifically excluded from this assessment but were covered in other CH2M studies through 2015 and 2016.
Figure 1-1: Extent of study area. UAV survey extent between Dawlish Warren and Teignmouth Stations
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The 2015 baseline report was a high-level report informed by a comprehensive review of available NR reports and datasets supplemented by published data available through regional and national archives, and along with CH2M’s own records, the reports and data have been collated into a fully georeferenced ArcGIS database. These data were supplemented by site observations and records obtained by CH2M geotechnical experts over the period January to March 2015 to characterise the geotechnical asset into discrete units based on cliff morphology and geology – known as Cliff Behaviour Units (CBUs). Following the mapping of the CBUs, a hazard rating for each was determined by an expert panel comprising NR and CH2M geotechnical and geomorphological experts. This classified each CBU into one of three hazard classes: 1. High (red), where the line may be affected for >48 hours or where there is a potential loss of life; 2. Medium (yellow) where the line is affected for <48 hours; or 3. Low (green) which has negligible impact to the line. Locations of each CBU are presented as Appendix A. Detailed proformas of each were documented to compile the hazard ranking, morphology characteristics, historical events, and other key attributes of each CBU, presented in Appendix B. The observations from this baseline report were made using limited data, particularly in Section 3 (Kennaway Tunnel to Parsons Tunnel) where there is no public access alongside the track and a track possession is required to view the cliffs. A UAV survey was proposed as a feasible method of remotely viewing the site at higher resolution and in more detail, to characterise the cliff morphology, geology, vegetation cover and condition, and provide further insight into the cliff instability processes which have occurred in the recent past and could occur in the future. In August 2015, CH2M prepared a Specification and Scope of Works for the UAV survey which detailed capture areas and target resolutions for the UAV imagery. The intention was to capture each CBU as a capture area, and also to capture the intervening headlands where marine erosion may impact the stability or integrity of tunnelled sections of the track; these areas can be viewed in Appendix C. However, a number of issues (which are explained further in Section 1.2 below) including unfavourable weather, technical issues with the aerial equipment, and lack of viewable control points affected the quality of the imagery captured. Data processing effort and interpretation was focused upon CBUs 16 to 23 inclusive where the quality of captured imagery was best, and where access by foot is difficult or impossible. Other priority areas, namely CBUs with a designated High hazard ranking, are also considered although the image capture quality is less than optimum which rather limits the interpretation. 1.2 Data processing and quality control The UAV photograph dataset was collected by Resource Group, a specialist UAS operator contracted by NR following a competitive tender process. A Sony A7R camera was flown on an Ascending Technologies Falcon 8 Trinity rotary aircraft to capture the images, and were supplied to CH2M for processing. Cliff geometry has been generated using photogrammetric principles. A schematic overview of how object geometry can be estimated from overlapping photographs to represent the 3D scene is in Figure 1-2.
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Figure 1-2: Estimating 3D structure from motion using photogrammetric principles
The images and GCPs (Ground Control Points) were processed using Agisoft PhotoScan Professional 2.1.4 software. Images first need to be aligned, thereby producing a basic surface model. This is checked for anomalies such as excessively high or low points; these can be caused by excessively bright or dark areas or objects in images, or water on the site. Anomalies are then removed. The purpose of the GCPs is to fix the 3D model derived from images to real world coordinates. At this stage in the methodology the GCPs are set to their markings within each image, which ties the basic surface model to the coordinates and heights of the GCPs. This produces a high-resolution surface model, which is then triangulated to create a 3D surface model (a mesh) for the site. The GCPs are also used in quality control. A GCP within the site boundaries must be recognisable within the images themselves. When the GPS (Global Positioning System) control point elevations are checked against the final 3D model, the Root Mean Square Error is checked; if they are within the required tolerance for the project (defined in the Scope of Works), a model is exported as a DEM into Esri ArcGIS 10.3. A number of other outputs can be created, such as an orthophoto or a coloured Dense Point Cloud (DPC) dataset. Throughout processing and quality control, a number of data control issues were identified. These primarily related to GCPs, the main issues being: Photos of GCPs were taken too close to the actual marker/location. Therefore, it was difficult using the aerial images to locate where the GCP was positioned without being able to see the general surrounding area; Many higher area GCPs (primarily on cliff tops) could not be seen in aerial images; Most of the higher area GCPs could not be used in oblique images as they were out of line of sight or were not visible; Many low area GCPs were placed on the seawall with very few other locations, resulting in lack of coverage and highly dispersed control. Combined with the visibility problems in higher area GCPs, this resulted in inadequate control in a number of areas. Other issues included: Images were out of focus and unclear when zoomed in. This makes it difficult to fix GCPs accurately to the model; Delays to the specified survey date meant that photographs were taken during the early summer months. Consequently, leaf cover was greater than expected. This obscured many areas of cliff, making morphology and geology detail difficult to observe and interpret. Consequently, the creation of 3D datasets for much of the survey area was not possible. Some were created but do not meet the specification accuracy in elevation, but were nevertheless thought to be useful given access constraints to much of the site. Because the quality of the images themselves were
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poor, tying the ground control and images together was time-consuming and sometimes had to be redone to tighten the accuracy as much as possible. 1.3 Visualisation software and interpretation approach Autodesk ReCap 360 was used to visualise the DCP dataset in three dimensions where 3D datasets could be produced. The software renders the individual data points which have been coloured using the RGB values from the UAV photography. The density of the points produces what appears to be a solid surface which can be manipulated and interrogated. In addition, some basic measurements can be taken from the dataset. ArcGIS is also used to examine fixed-perspective orthophotos, and also to interrogate the digital elevation model (DEM) to determine morphological parameters such as slope and aspect. The vertical aerial photography from this investigation has also been used to update CH2M’s existing photographic record. The interpretation is based on a standard qualitative approach. Linework is added to the 3- dimensional rendering to denote morphological boundaries, which are then interpreted using geomorphological principles to infer cliff failure mechanisms and process dynamics of the landform/landscape. This interpretation is also informed by the other data sources available to CH2M, such as 1:10,000 geological mapping (BGS), bare-earth LiDAR procured for NR in 2014 and mapping supplied by Ordnance Survey (OS).
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2. Interpretation of UAV dataset
The location of each CBU is presented as Appendix A. Proformas documenting the specific characteristics and technical details of CBUs were prepared for the baseline report, and are re- produced in Appendix B. 2.1 CBU 06 Start: 208m 12.5ch (E295070 N73933) BASELINE REPORT CBU 06: Pine Close End: 208m 07.0ch (E295128 N74026) HAZARD CLASS: HIGH
CBU 06 is a regraded rock headland between two large washout embayments, CBU 05 (Cliff Road) and CBU 07 (Footpath Hollow), which both have defined water pathways through their respective units. CBU 06 contains a relatively large exposure of the undifferentiated Alphington & Heavitree Breccias, which is mostly unvegetated and partly netted. This reveals much of the geological structure in the UAV dataset. It must be noted, however, that the UAV ground control is poor in this unit, resulting in erroneous positioning of certain features, such as the railway line. This means that any observations from the UAV dataset must be verified in the field. A prominent feature of CBU 06 is the large high-angle break which bisects the unit (see Figure 2-1). Historical photography indicates that this feature is partly visible during the original cliff scaling works for the railway, but appears to have grown more pronounced since then. It is likely that this relates to jointing, and hence is a structurally controlled element of the landscape. However, it may also be a pathway for surface water flow, as features related to debris washout can be identified: an embayed source area, incised runout channel and an accumulation of debris at the base. Given the poor control, it is difficult to assess the degree of setback between the base of the debris cone and the track.
Figure 2-1: An interpretation of CBU 06 indicating possible runout channel morphology The exposed section in CBU 06 also shows evidence of small to medium-scale rockfall events which may have the potential to impact the line. For the majority of the unit, which has been covered with passive netting, larger rockfall events will be caught. However, the northern portion of the unit is not
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currently netted and contains one notable example of an overhang, presumably where material has been lost as a result of joint-/bedding-controlled rockfall (see Figure 2-2). Due to the poor control, it is not possible to assess the setback or height of this feature from the track from the UAV dataset alone.
Figure 2-2: The large overhang in the unnetted section of the cliff, which may present a serious hazard to the line
The apparent proximity of the CBU to the line, and the indication that the cliff may still be actively shedding large volumes of material in the unnetted portion of the unit, indicates that a High hazard rating is still appropriate. In addition, the possibility that washout of cliff material may be a hazard not yet previously considered in remediation might also present additional hazard to the line.
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2.2 CBU 07 Start: 208m 07.0ch (E295128 N74026) BASELINE REPORT CBU 07: Footpath Hollow End: 208m 02.0ch (E295182 N74117) HAZARD CLASS: LOW
CBU 07 is a densely vegetated washout embayment, comprising two coalescing surface water channels (revealed in CH2M archive mapping). The density of the vegetation means that it is nearly impossible to make any new observations or interpretation, other than to confirm the embayment morphology in a broad sense (see Figure 2-3). However, the continuous coverage of mature vegetation is an indication of longer-term relative stability; consequently the baseline report hazard classification of Low is justifiable.
Figure 2-3: The dense vegetation hinders interpretation in CBU 07
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2.3 CBU 08 Start: 208m 02.0ch (E295182 N74117) BASELINE REPORT CBU 08: Bungalow Headland End: 207m 78.5ch (E295218 N74176) HAZARD CLASS: HIGH
CBU 08 is a regraded rock headland section, situated between two washout features: CBU 07 (Pine Close), a large embayment, and CBU 09 (Bungalow Ravine), a deeply-incised washout gully. Like CBU 07, much of the unit is vegetated and as such the morphology is difficult to assess. However, there is an unvegetated section to the north of the site which exposes the undifferentiated Alphington & Heavitree Breccias. The baseline report describes this unit as being prone to small, joint-controlled rockfalls. Evidence of this is visible in the UAV datasets, but there appears also to be evidence of shallow sliding in addition to this. A headscarp feature is visible at the crest of the slope, which is approximately 4.5m in height (shown in Figure 2-4). In addition, there is little visible bedding structure in the exposed breccia, suggesting that the material there might not be in situ and instead is draped over the existing ground surface. This material has been eroded by surface water, evidenced by rilled features in the lower portion of the slope. However, the quality of the imagery is not good here, and observations must be confirmed in the field.
Figure 2-4: Evidence that CBU 08 may be prone to shallow sliding Based on the slope gradient, the lack of existing slope stabilisation measures and the situation of the unit: a steep headland between two washout features (similar to the Woodland Avenue site), the baseline report classified this area as a High hazard. This classification is supported by new evidence from the UAV survey.
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2.4 CBU 09 Start: 207m 78.5ch (E295218 N74176) BASELINE REPORT CBU 09: Bungalow Ravine End: 207m 76.5ch (E295237 N74204) HAZARD CLASS: HIGH
CBU 09 is a deeply-incised gully on the flank of the Woodland Avenue failure site. According to site investigation reports, the upper section consists of a concrete channel, whereas the lower section is unconstrained by engineering. Because of the vegetation coverage of the adjacent CBU, only a portion of the gully feature is visible; this forms the lower section of the unit. There is evidence of active lateral incision of the Bungalow Ravine stream into the Woodland Avenue failure complex (see Figure 2-5). Water flows down a stream jump/waterfall and through a section of embryonic meanders before reaching the base of the slope. The outer bend of each meander has evidence of lateral erosion, particularly in the vicinity of the waterfall. Water input to this stream system seems to be predominantly from the upslope portion of CBU 09, not visible in imagery. However, there are also clear water pathways from CBU 08 into the stream, evidenced by rill features on the gully sidewall. The system is also clearly transporting sediment: a deposition area is clear at the toe of the slope containing some coarser clasts.
Figure 2-5: Visualisation and interpretation of the Bungalow Ravine gully system It would appear that the principal hazard for this unit is related to erosion caused by the stream; consequently at peak rainfall there is larger potential for a hazard given the increased erosive power of the stream. However, the majority of the erosion will take place at the boundaries between CBU 09 and its adjacent CBUs, and the principal areas where this occurs are have been identified in Figure 2- 5. Failures are likely to be discreet blocks of material rather than whole-slope movements and are likely to fail into the gully system itself rather than directly onto the track. Even though there is little to no visible remediation on the gully slopes, the unit is extensively monitored by NR. The level of hazard to the track itself does not seem as high as was considered for the baseline report, and consequently it can be reduced to Medium.
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2.5 CBU 10 Start: 207m 76.5ch (E295237 N74204) BASELINE REPORT CBU 10: Woodland Avenue End: 207m 72.5ch (E295286 N74274) HAZARD CLASS: HIGH
CBU 10 lies between the gully systems of CBU 09 (Bungalow Ravine) and CBU 11 (Windjammer). It was the site of a complex slope failure in the Spring of 2014, and as such has been subject to a number of detailed site and ground investigations in the following years. The unit is netted and nailed over much of its surface and has been monitored with inclinometers and piezometers since the failure. The present-day morphology is a function of the instability event and the subsequent rescaling/ remediation works on the unit. It consists of a steeper scarp slope to the top of the unit, a lower-angle bench at the centre which falls to the north, and a second steeper-angled section to the base of the unit. Rill features are evident on the upper slope, indicating that surface flow is present in the unit, although this is likely to drain into of the adjacent units (see Figure 2-6).
Figure 2-6: Visualisation and interpretation of the Bungalow Ravine gully system Given the amount of work undertaken at the Woodland Avenue site, the UAV survey does not reveal anything new which may be of concern. The baseline report classified CBU 10 as a High hazard. This is in part due to the potential for lateral erosion of the site by water from the adjacent gully systems which may undermine the stability of the unit. Even though the site has been heavily managed, and readings from the instrumentation show little of concern, it would be prudent to keep the classification as High. This is primarily because the mechanism of the failure itself remains unclear. Given the scale of disruption from the March 2014 event, it is recommended this site remians a priority for monitoring and further inspection.
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2.6 CBU 11
Start: 207m 72.5ch (E295286 N74274) BASELINE REPORT CBU 11: Windjammer HAZARD CLASS: End: 207m 70.5ch (E295308 N74301) MEDIUM
CBU 11 is a deeply-incised gully sustem to the immediate north of the Woodland Avenue site. It consists of a well-defined embayment source, narrow transport route and broad debris fan at the base of the unit. The unit is a zone of extensive remediation and management, includng active netting and soil nailing, drainage measures and a catch fence at the base of the unit. Again, because of the management of the unit the UAV investigation can yield little additional insight into the dynamics of the system. Material deposited on top of the netting indicates ongoing sediment transport processes, most likely to be caused by sediment entrainment through the movement of surface water (see Figure 2-7). This may indicate the potential for further debris washout in the future.
Figure 2-7: Indications of sediment entrainment in CBU 11 In a similar fashion to Woodland Avenue, the scale of investigation of this area following two slope instability events in the early 2010s means that the UAV investigation yields very little new information on the CBU. The hazard classification in the baseline report was Medium, in order to acknowledge the potential scale of the hazard but also the works which had gone into the CBU, and there is little evidence to suggest that this should be changed in the light of the new UAV data.
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2.7 CBU 12 Start: 207m 70.5ch (E295308 N74301) BASELINE REPORT CBU 12: Windjammer Track End: 207m 66.0ch (E295382 N74392) HAZARD CLASS: HIGH
CBU 12 can be subdivided into three morphological sub-units that comprise the system: 1. South-western section with a planar regraded cliff 2. Vegetated central section 3. North-eastern section containing a small washout embayment and debris fan The south-western section was classified as having small joint-controlled rockfalls in the baseline report but the UAV dataset also appears to show evidence of slope instability associated with water, and possibly also shallow sliding. The unvegetated parts of this unit indicate relatively deep lineaments caused by surface water flow, and what appears to be a runout track from the southern edge of CBU 12 into the adjacent CBU 11 (Figure 2-8). In addition, where this section of the unit is fringed with vegetation, there are a number of visible fallen trees which may indicate shallow en masse slope failure.
Figure 2-8: Possible evidence of water-related slope instability in the SW portion of CBU 12 The north-eastern side of the unit contains an incised washout gully which is partially remediated with netting and drainage systems (Figure 2-9). The gully system contains an embayed source area, a narrow washout channel and a debris fan at the base of the system. To the north of this, there is a steep-sided sidewall; this has been partly netted but there is much evidence of rilling and small-scale rockfalls both in and outside this netting.
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Figure 2-9: The washout system to the north-east of CBU 12 The hazard rating of CBU 12 in the baseline report was High; the concern here was the markedly similar form of this system to the pre-failure Woodland Avenue. The UAV dataset does not show anything which would reduce this hazard rating, and given the lack of complete understanding of the Woodland Avenue failure, it is recommended that this section is monitored for any further signs of instability at the site.
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2.8 CBU 14 Start: 207m 46.5ch (E295678 N74655) BASELINE REPORT CBU 14: Smugglers’ Lane Compound End: 207m 43.0ch (E295713 N74670) HAZARD CLASS: HIGH
CBU 14 is a section of the cliff set back from the railway, where the cliffs have possibly not been regraded or reprofiled. These are subvertical and show evidence of minor bedding-controlled rockfalls and surface spalling. The NR Smugglers’ Lane engineers’ compound is located within this unit, which was considered in the baseline report due to the possible impact a geohazard may have on human life. Because the compound is so close to the cliffs, it is unlikely that the UAV interpretation will produce anything which cannot be observed at ground level. In addition, poor control over this unit has meant that the 3D rendering of the cliff in this location is not accurate and hence may be misleading. One feature of note is the presence of a large overhang close to ground level, indicating possible risk of rockfall, highlighted in Figure 2-10.
Figure 2-10: Overhanging sections close to the engineers’ compound The High hazard rating of the baseline report was in part due to the positioning of the engineers’ compound at the base of the exposed cliffs, meaning that it is permanently exposed to rockfall hazard. The difficulty in interpreting this area due to poor control has meant that there is no new information which can be used to modify this hazard rating without investigation at ground level. Consequently, it is recommended that the location remains High hazard.
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2.9 CBU 15 CBU 15: Parsons Tunnel Southwest Start: 207m 43.0ch (E295713 N74670) BASELINE REPORT Portal End: 207m 42.0ch (E295794 N74615) HAZARD CLASS: HIGH
CBU 15 comprises the cut cliffs overlying the southwest portal of Parsons Tunnel, to the south of the Parson and Clerk rocks headland. Much of the CBU is subvertical and unvegetated, and there is no visible remediation or cliff stabilisation aside from a small area of dentition directly above the portal masonry. Interpretation from the UAV dataset has been difficult due to poor control, especially in the upper cliff. The apparent lack of engineering to the cliff is the primary reason for the High hazard rating of the baseline report. The rock wall directly over the tunnel portal has no catch fence or area to catch rockfall debris, meaning that any cliff fall would directly impact the line (Figure 2-11). Using evidence of rockfall further along the coast on the same headland as a proxy, volumes of material may be large to very large. Consequently, it is believe that this section represents significant hazard to the railway.
Figure 2-11: Rockfall hazard overlying the track near Parsons Tunnel The cliff face to the side of the tunnel portal displays some localised setback when compared to the rest of the site. This appears to be related to the movement of water through the area, and could be a feature signifying washout. Morphological boundaries denoting the source area, runout track and debris cone can be drawn onto the cliff face, as shown in Figure 2-12. It is recommended that the interpretation of this feature is verified in the field.
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Figure 2-12: Feature possibly relating to washout on the CBU 15 cliffs Given the minimal setback of the cliffs to the line, and the lack of visible engineering works to the cliff, this location remains High hazard.
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2.10 CBU 16 (part) Start: 207m 28.0ch (E296096 N74717) BASELINE REPORT CBU 16: Parson’s Tunnel Rockfall Shelter End: 207m 18.5ch (E296049 N75024) HAZARD CLASS: LOW
CBU 16 is a near-vertical regraded cliff located directly above Parson’s Tunnel rockfall shelter. Aside from the rockfall shelter itself, there is no evidence that the line has been protected from slope failure; there is no observable remediation in place on the cliff face. As such, there is reasonably good exposure of the stratigraphy of the cliff face, indicating the dip of the sediments is of approximately 16°. A number of morphological zones can be identified from the imagery, based on how competent they appear to be. Some zones are vegetated and at these locations rockfall is thought to be less likely. However, in other areas where the structure and/or bedding is more exposed, the face is exposed to subaerial weathering and erosion. There is evidence of this in localised overhangs (see insert box, Figure 2-13) where blocks of material have been lost along joints and bedding planes in the rock face.
Figure 2-13: Morphological linework and interpretation of CBU 16 Given the size of the failures that can be seen in the imagery, it is likely that only small fragments of material will be mobilised in a rockfall event in this unit. This will fall onto the Parson’s Tunnel rockfall shelter and hence pose a negligible degree of hazard to the line. The evidence provided by the AUV survey and interpretation confirms this location is Low hazard primarily due to the protection afforded by the rockfall shelter.
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2.11 CBU 17 Start: 207m 18.5 (E296049 N75024) BASELINE REPORT CBU 17: Rockfall Shelter Portal End: 207m 14.5ch (E296068 N75097) HAZARD CLASS: HIGH
CBU 17 contains near-vertical regraded cliff. The CBU is noticeably set back from the adjacent units when viewed in plan, and it would appear that a large triangular wedge shape has been lost from the cliffs at some point (see Figure 2-14). Even though a large-scale rockfall was recorded at this location in 1852, other records, such as a contemporaneous painting, indicated that the rescaling of the cliffs produced this feature. This also indicates that the source area for the historic 1852 failure is likely to be within this setback volume and the combination of this event and smaller, more recent failures will have expanded the plan morphology of this unit.
Figure 2-14: Illustration of the setback of the CBU 17 cliffs Examination of the UAV imagery indicates that the rear-scarp of this system is likely to be a cliff face which is still currently active. This extends from the northern extent of the CBU through the unit to the site of the active/historical rockfall source within the set-back area (see Figure 2-15). There is mature vegetation at the base of this scarp, which is most probably masking rockfall debris from past and recent failures. This debris is likely to be marginally stable at best and prone to reactivation. The suggestion that this entire unit may be an active scarp/debris system is particularly concerning. TGP have previously reported the presence of a large “flake” of material which was thought to have been moving away from the cliff1. It now appears that this flake is part of a much larger pre-existing system which was not apparent during the initial assessment for the baseline report, shown in Figure 17.
1 TGP report C102114-801 Rev C, 11 June 2004
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Figure 2-15: Conceptualisation of the CBU 17 failure system Evidence shows that there are active falls from the rear scarp and debris accumulating on the slope. The hazard posed includes fresh failures of the rear scarp with rockfall and debris runout impacting the line. Cumulative loading of the rockslide could trigger larger debris slides or entire failure of the landslide system at some time in the future. Consequently, it can be concluded that the High hazard rating applied in the baseline report is well-justified and that this should be made a priority unit for in situ monitoring, site investigation and remediation.
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2.12 CBU 18
Start: 207m 14.5ch (E296068 N75097) BASELINE REPORT CBU 18: East Down Cliff HAZARD CLASS: End: 207m 04.5ch (E296052 N75290) MEDIUM
CBU 18 comprises near-vertical intact cliffs, approximately 40m high. These are partially vegetated and there is evidence of remediation in the form of passive meshing and pinning in the upper cliff only. On sections of the cliff where vegetation is not present, there is evidence of subaerial weathering and erosion processes. The bedding is visible with a dip of approximately 10° to the north and some small overhangs resulting from joint-controlled rockfalls can be seen in the lower part of the cliff (Figures 2- 16 and 2-17). Here there is little setback from the line, meaning that failed material is likely to directly impact the line. However, the height of these exposed sections and the probable size of the debris indicates that this is unlikely to cause significant impact. There is also evidence of water seepage in a number of locations toward the centre of the CBU. This indicates that there may be groundwater outfall in this CBU, but there is no evidence that this has resulted in large-scale washout events, only smaller joint-controlled rockfalls.
Figure 2-16: Morphological linework and interpretation of the southern portion of CBU 18
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Figure 2-17: Morphological linework and interpretation of the northern part of CBU 18 The baseline report indicates that the suggested hazard level for this is Medium. Even though there is little evidence of large scale slope failures from the UAV, the fact that these are tall cliffs which directly abut the railway suggests that any rockfall debris would be deposited directly onto the line. This is more likely to require closure of the line to clear, and therefore presents a Medium hazard.
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2.13 CBU 19 Start: 207m 04.5ch (E296052 N75290) BASELINE REPORT CBU 19: Smugglers’ Inn Stream End: 206m 79.0ch (E296024 N75400) HAZARD CLASS: LOW
CBU 19 comprises a cut slope, which is intersected by the Smugglers’ Inn Stream approximately halfway down the unit. The morphology of the cut slope contains a series of low-angle benches and a small, near-vertical cut slopes which have a maximum height of approximately 4m. The vertical sections are vegetated with grasses and shrubs, and are netted. The uppermost bench is vegetated primarily with trees; consequently it is difficult to interpret the morphology of this section from the UAV data. The primary feature of interest in this section is the Smugglers’ Inn Stream. The feature is situated in a small, reasonably deep manmade gully, which itself is in a small valley-type feature in the CBU (see Figure 2-18). This drains underneath the track through a UTX pipe.
Figure 2-18: Morphological linework and interpretation of CBU 19 Given the setback of the cliffs to the track, and the morphology and height of the cliffs, this CBU is confirmed as Low hazard.
22 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
2.14 CBU 20 Start: 206m 79.0ch (E296024 N75400) BASELINE REPORT CBU 20: Clerk’s Tunnel South Portal End: 206m 73.0ch (E296032 N75509) HAZARD CLASS: HIGH
CBU 20 comprises steep cliffs adjacent to and above the southern portal to Clerk’s Tunnel. The unit is predominantly composed of steep (>45°) cut cliffs, which are almost fully vegetated with grasses and small shrubs. Despite this, it is possible to make out the bedding along this section at a number of locations, which dips approximately 11° to the north. There appears to be no netting or meshing to the face of the cliffs. The section of the CBU that runs parallel to the track contains a number of small breaks in vegetation indicating fresh rockfall. These lie approximately 20m up the face of the cliff. Since the cliff is near- vertical and there is no visible stabilisation, any debris is highly likely to fall directly onto the line (Figure 2-19). The dimensions of the rockfall scars can be up to approximately 1m by 4m which suggests that a reasonably substantial volume of material is mobilised, assuming that each scar was formed by a single failure event. This may cause a considerable hazard to the railway and rolling stock if present. In this section, there is also a linear depression feature in the upper cliff, which is thought to be a gully formed by surface water flow and possible washout. The surface water is thought to come from properties close to the cliff crest. Given that the feature is vegetated and relatively shallow, it is judged that runout is not a credible hazard to the line in this section of the track.
Figure 2-19: Morphological linework and interpretation of CBU 20 (track-parallel section) The UAV data for the section of cliffs directly overlying the tunnel portal is somewhat patchy, but shows that the face above the tunnel portal is steep and planar. This appears to have been netted and sparsely vegetated, but at some locations the breccia has been exposed. There appears to have been some minor rockfall events onto the top of the portal, as the upper surface of the portal has staining of a similar colour to the geology. These events appear to have been reasonably minor, as the structure of the portal masonry can still be made out. However, the fact that this section also lies directly over the track means that any failed material is likely to fall directly onto the line if not obstructed by the portal.
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 23
A small portion of the Clerk’s Tunnel headland is contained within this CBU. This contains exposed sections which have clearly been subject to subaerial weathering and erosion processes, evidenced by the honeycomb weathering on much of the face. Here, the angle of dip of the bedding (approximately 11° to the north) is also evident (see Figure 2-20).
Figure 2-20: Morphological linework and interpretation of CBU 20 (tunnel portal and headland) In both aforementioned sections of this CBU, there is clear evidence that rockfall is an ongoing hazard. Given the limited setback and the height and angle of the cliffs it is very likely that failed cliff/rockfall debris will land directly on the line. The lack of visible cliff face stabilisation on the track-parallel section may mean that larger blocks of material can be removed from the cliff and may result in a greater than 48-hour disruption to the line and, as a worst-case scenario, fatality. Consequently, the High hazard rating of the baseline report is justified for this CBU.
24 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
2.15 CBU 21 CBU 21: Clerk’s Tunnel to Phillot South Start: 206m 73.0ch (E296032 N75509) BASELINE REPORT Portal End: 206m 68.5ch (E296007 N75612) HAZARD CLASS: HIGH
CBU 21 is a section of regraded steep cliffs located between two spurs containing Clerk’s and Phillot Tunnels to the south and north respectively. The morphology of the section is difficult to assess due to a combination of the state of the vegetation and the management of the slope, which has been cut and netted. The cliff profile for the entire unit is near-vertical. The headland between the tunnels contains good geological exposure due to the general lack of vegetation. A number of beds can be identified which show the dip angle of the geology, which is approximately 7° to the north (Figure 2-21). There is much evidence of volume loss from the cliff face; there is a large overhanging section to the centre of the headland with a darker, stained, indented section beneath. This indicates structure-controlled failure of the cliff face, where the darker staining is possibly related to seepage of groundwater. There is no evidence of debris at the base of the cliff, as this will have been removed by marine processes. Marine processes seem to have directly impacted the face at some locations; there is some evidence of notching and small-scale caving at the base of the cliff past the limit of the seawall. The scale of this is such that it seems unlikely to have an impact on the tunnel infrastructure, but this may be worth future investigation.
Figure 2-21: Morphological linework and interpretation of the CBU 21 headland Above the tunnel portal, the cliff is slightly more set back than on the opposite side of the headland (in CBU 20) and there is evidence of vegetation, such as small bushes and trees, in the space between the cliff and the portal masonry (Figure 2-22). This is possibly masking talus from rockfall above the portal, but this cannot be confirmed from the imagery alone.
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 25
Figure 2-22: UAV visualisation of the Phillot Tunnel portal in CBU 21
The cliff in the central section of the CBU, i.e. between the two tunnel portals, consists largely of cut slope which has been stabilised with passive netting. There are two morphological features of note close to the Clerks Tunnel portal: an overhanging area in the lower part of the cliff and a bench feature toward the mid-height of the cliff (Figure 2-23). The overhanging section is set back slightly further from the rail than the rest of the cliff. This feature may be interpreted as a structure-controlled rockfall but there is no evidence of talus build-up at the base of the slope. This is most likely because it has been cleared given the proximity of the cliff toe to the rail line. The bench feature above this is a protrusion out of the general line of the cut cliff. It is likely that this represents a path of more mature vegetation which has grown outside of the netting and produced a lump on the orthophoto, but this is unclear in the current imagery.
Figure 2-23: UAV visualisation of central section of CBU 21
26 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Almost equidistant between the two portals, there appears to be a small embayment and gully feature in the upper portion of the cliff (Figure 2-24). The exact morphology of this is unclear as it appears to have been filled with gorse, bushes and shrubs, but seems to be concave in plan, embayed in the upper cliff and forming a runout track in the lower half. This is likely to be related to surface water flow from the properties along the crest line of the CBU. Consequently, this feature is likely to be related to washout. To the north of this embayment feature there is a cone of material at the toe of the slope. This looks similar in form to a debris cone from washout, but does not appear to have a source area. Given the netting and the state of the vegetation, a more likely explanation for this feature is that it is ‘false topography’ resulting from thick vegetation, which has grown through the netting. This can be confirmed using photography of the site from a previous lineside inspection. Photographs of this section show that much of the vegetation is reasonably mature and as such it is difficult to resolve whether this topographic feature is a result of slope failure or vegetation growth.
Figure 2-24: UAV visualisation of central section of CBU 21 The potential for hazard was rated High in the baseline report, which also cites rockfall as the primary hazard for the unit. The UAV survey has shown numerous water-related features in the cliff directly overlying the track, which mainly have been formed as a result of drainage of surface water from cliff- top properties. However, these do not appear to be actively transporting material near or onto the line and there is little evidence that this is a credible hazard to the railway. There is very little setback from the toe of the cliffs to the line, which results in a higher degree of hazard. However, there is netting at all locations in this CBU, and very little evidence that recent rockfalls have occurred or are in danger of breaching the existing cliff remediation. Consequently, the hazard rating is reduced to Medium for this section.
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 27
2.16 CBU 22 BASELINE REPORT CBU 22: Shell Cove (includes Phillot Start: 206m 68.5ch (E296007 N75612) HAZARD CLASS: Tunnel) End: 206m 63.5ch (E296060 N75667) MEDIUM
The cliff in CBU 22 is near-vertical and set back from the railway, which runs along a low embankment. At the base of the cliffs there is a developed talus slope which is present through the majority of the unit. The CBU is also characterised by dense mature vegetation, which makes interpretation over much of the site difficult.
The Phillot Tunnel south portal is a sub-vertical cut slope, which is netted directly over the tunnel portal with minimal setback from the line. The cliff is unnetted where not directly over the line of the track or where the cliff stands over an exposed section of the tunnel shaft which protects the line from spalling events. At the latter, there is a large unvegetated exposure approximately 9m in width, which shows the alignment of the beds in the breccias (Figure 2-25). It is possible that this area was exposed following a minor rockfall event, as the area is slightly set back from the rest of the cliff and there appears to be a deposition area either directly below the exposure or on the roof of the tunnel shaft.
Behind this exposure, there is a large fissure trending roughly E-W. Material from this feature has been washed out to form a depositional lobe on the beach rock armour at the base of the cliff. This feature is related to washout; the Shell Cove inspection report indicates that this feature has resulted from drainage of surface water from cliff-top properties. The line is also coincident with a marked fault in Laming’s 1954 section2, indicating that this surface water has travelled along a plane of weakness in the geology.
Figure 2-25: UAV visualisation of southern portal of Phillot Tunnel
The section immediately overlying the north portal of Parson’s Tunnel is very thickly vegetated with large bushes and trees in the upper portion of the cliff (Figure 2-26). As such, there is very limited data
2 Fig 32, “Cliff Section from Teignmouth to Langstone Rock”, from Laming D J C (1954) Sedimentary Processes in the Formation of the New Red Sandstone of South Devonshire, PhD thesis, University of London
28 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
capture here, and no comments can be made on the underlying morphology or structure of the unit. However, close to the tunnel portal, a near-vertical cut slope overlying the portal can be made out. The stepped structure of the tunnel portal roof is clearly visible, which suggests that there is no talus slope on the portal roof and consequently that there have been no significant slope failures over the tunnel portal in the recent past. A feature parallel to the track appears to be a small debris lobe at the base of a thickly vegetated cut slope near the tunnel portal, but may also be a thicker patch of vegetation at the toe of the slope. The presence of a 3-tier gabion basket wall indicates that there may be a risk of some form of cliff failure, but indicators of this are not evident in the imagery.
Figure 2-26: UAV visualisation of northern portal of Phillot Tunnel
CBU 22 also contains a large geological exposure in the upper part of the cliff. This is composed of undifferentiated Alphington & Heavitree breccia which has been extensively affected by honeycomb weathering (Figure 2-27). It is also clear that blocks of material have been removed from the cliff as a result of subaerial weathering and erosion, evidenced by the irregular rock face. There appears to be a large talus slope underneath this exposure, but the exact form of this cannot be resolved from the imagery. The boundary of the CBU 22 geological exposure is a sharp, angular protrusion from the cliff. This is thought to be a surface manifestation of a fault plane, marked in the BGS 1:10,000 geological mapping and Laming’s section in the same location (Figure 2-28).
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 29
Figure 2-27: The geological exposure at CBU 22
Figure 2-28: The mapped fault feature in CBU 22
For the majority of the unit, the degree of setback between the toe and the cliffs means that cliff or rockfall debris is unlikely to reach the track, and will land on the talus slope at the base of the cliff. In the densely vegetated section of the track where washout is more likely to be a hazard, there is still sufficient setback to prevent failed material impacting the line itself. Above and next to the tunnel portal the cliff is netted, and there are protection measures in place to prevent slope instability events from impacting the line. However, there are a number of features to note, including near-vertical cliffs near the line at the tunnel portal, the potential of washout of the talus slope close to the line and rockfall from the angled fault protrusion which is less set back from the line. Consequently, there is still potential for hazards to impact the line and cause delay to operations and the Medium hazard baseline report rating is justified after examination of the UAV dataset.
30 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
2.17 CBU 23
Start: 206m 63.5ch (E296060 N75667) BASELINE REPORT CBU 23: Coryton Tunnel South Portal HAZARD CLASS: End: 206m 60.5ch (E296078 N75751) MEDIUM
CBU 23 is mainly composed of sub-vertical cliffs set back a reasonable distance from the railway. A mixture of vegetation covers the site, including several tall trees; as such, in places it is difficult to assess the underlying morphology. Most of the unit lies directly above the south portal of Coryton Tunnel (Figure 2-29).
Figure 2-29: An illustration of the location of CBU 23
In the vicinity of the portal, the slopes are cut and netted. At the base, there is a rockfall catch fence which runs parallel to the track. Some shrubs and small bushes are growing through the netting and there is little evidence of recent failure of this section of the cliff face. Over the tunnel portal, the slope is again vegetated with a relatively thick covering of vegetation. Multiple rows of catch fences/debris barriers are visible overlying the area above the tunnel portal, which indicates that rockfall hazard has historically been a significant issue for the CBU (Figure 2-30).
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Figure 2-30: Coryton south portal and the nearby cliffs There are two exposed faces on the CBU 23 headwall which appear to be active (Figure 2-31). These will be exposed to subaerial weathering, erosion and gullying as a result of surface water drainage from adjacent property, which will result in cliff spalling and rockfall events over the tunnel portal. In addition, there are several large trees located very close to the edge of the cliff. In windy conditions, there is a danger that these may be blown over and fall directly onto the track, which may cause significant repercussions.
Figure 2-31: Active instability upslope of the catch fences
The headland contained within CBU 23 contains a very good geological exposure, which reveals the angle of bedding (approximately 15°). The area has been extensively affected by honeycomb weathering, and it is clear that the exposure is subject to joint-controlled rockfall. The angled
32 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
protrusion in the headland is evidence of a fault which is marked in the BGS and Laming’s maps; this plane is further evidenced by the alignment of the linear sea stacks. The area has clearly been affected by marine erosion and there are a number of reasonably well-developed caves (Figure 2-32). Continued erosion of these caves may impact on the tunnelled infrastructure through the headland, but it is not possible to assess this through this dataset.
Figure 2-32: Caving at the headland contained within CBU 23
The presence of multiple rows of catch fencing suggests that rockfall hazard is an ongoing problem for the unit. Should these be breached, it is highly likely that material would fall directly onto the track and cause significant delay. Similarly, by the side of the track there is little setback between the cliffs and the track and should an event occur, it is likely that this too will be deposited onto the track. However, there is remediation in place in both locations, which reduces the likelihood of these events reaching the line. Therefore, the Medium hazard rating baseline report is justified in this location.
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2.18 CBU 28
Start: 205m 52.5ch (E296930 N77240) BASELINE REPORT CBU 28: Riviera Terrace HAZARD CLASS: End: 205m 47.5ch (E297004 N77309) MEDIUM
CBU 28 is an embayed section of the coastline with local overhangs and small cavities at the base of the cliff. A vegetated talus slope lies at the foot of the cliffs, considered to be composed of rockfall debris from small joint-controlled failures in the Dawlish sandstone (Figure 2-33). The exposure of the sandstone is designated as a SSSI (Site of Special Scientific Interest).
Figure 2-33: The sandstone exposure in CBU 28
A spur at the south-west forms the boundary between CBU 27 and 28 (Figure 2-34). This is considerably closer to the track than previous CBUs; however, the friable nature of the sandstones means that any rockfall from this area is likely to disaggregate on impact. Due to poor ground control at this location, image quality and interpretation is limited due to the relative inaccuracy of the 3D model. Consequently, it is not possible to provide new insight in this location, therefore the hazard rating remains Medium.
34 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Figure 2-34: The boundary spur between CBUs 27 and 28
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2.19 CBU 29
Start: 205m 47.5ch (E297004 N77309) BASELINE REPORT CBU 29: Rockstone Cliff HAZARD CLASS: End: 205m 44.5ch (E297047 N77349) MEDIUM
CBU 29 is a near-vertical regraded sandstone cliff fronting the town of Dawlish (Figure 2-35). There is little to no vegetation, which exposes much of the geology. Preferential weathering of certain sandstone beds has resulted in small, localised overhangs and cavities, and there is evidence of small bedding-/joint-controlled rockfalls. There is no talus slope and minimal setback from the line, so failed material will impact the track directly. This is likely to be weak friable sandstone, which will disaggregate on impact with the ground.
Unfortunately, due to poor imagery and ground control at this location interpretation is limited due to inaccuracy of the 3D model. The condition of the cliffs can be observed from the coastal path adjacent to the railway.
Figure 2-35: A visualisation of the cliff in CBU 29
An examination of the dentition towards the centre of the unit reveals a number of indicators of instability of the overlying sandstone (Figure 2-36). The left portion of the wall is stained, indicating some movement of the sandstone cliff above. In addition, there are a number of scarp features above this staining indicating that some volume has been lost from the cliff. There is indication that the wall itself has previously failed in addition to the overlying cliff. Some of the wall appears to have been lost to the left of the masonry, as well as at the top in the vicinity of the scarp features. There is also evidence of repairs made to the wall in the bottom right.
36 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Figure 2-36: A visualisation of the dentition in CBU 29 The presence and condition of the masonry dentition in this unit results in a somewhat anomalous circumstance. The baseline hazard assessment solely considered natural geohazards. Given that it is difficult to provide new insight to this area due to the quality of the UAV dataset and consequently it is recommended that the hazard level stays at Medium. It is clear that the dentition may also be vulnerable and has potential to fail, which would also present considerable hazard to the line. Consequently, it is suggested that the dentition is monitored and inspected to assess its condition and stability.
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2.20 CBU 30
Start: 205m 44.5ch (E297047 N77349) BASELINE REPORT CBU 30: Rockstone Footbridge HAZARD CLASS: End: 205m 40.5ch (E297114 N77406) MEDIUM
CBU 30 is an embayed section of the coastal cliffs, with vertical sandstone cliffs and a vegetated talus slope at the base. The unit is bisected by the Rockstone Footbridge. The footbridge separates two distinct halves of the unit. The western side of the bridge contains an unvegetated near-vertical cliff of exposed sandstone. Similar to CBU 29, preferential weathering of certain sandstone beds has resulted in localised overhangs and cavities, which is possible evidence of small structure-controlled rockfalls (Figure 2-36). However, the talus slope at the base sets the cliff back from the track and creates a buffer zone between the cliff and the catch face alongside the track. Conversely, the eastern section is vegetated and more difficult to interpret.
Due to poor ground control at this location imagery and interpretation is limited due to inaccuracy of the 3D model. Consequently, it is difficult to provide new insight at this location and the hazard rating remains Medium. The condition of the cliffs is visible from the coastal path adjacent to the railway.
Figure 2-37: A visualisation of the cliff in CBU 30
38 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
3. Summary and Recommendations
The UAV survey and interpretation provides new data to assess the morphology and hazard status of the cliffs, particularly Section 4 (Kennaway Tunnel to Parson’s Tunnel) where access by foot is difficult. This new assessment and report has considered the location, nature and scale of geomorphological hazards to the line and re-appraises the hazard ratings presented in the baseline report. In most cases, the hazard is reasonably well-defined, but for some locations the nature of the hazard is complex and/or uncertain, and there are grounds for further site investigation and these have been indicated. Perhaps the most significant finding concerns CBU 17, in particular the scale of potential cliff failure that may affect the unit. CBU 17 was previously seen as a series of unconnected steep slopes prone to rockfall, with a large discreet ‘flake’ of material posing a potential High hazard to the line. With the new perspective provided by the UAV survey, it is clear that the flake is part of a much larger system which has unconsolidated failed material resting on the slope. The pre-existing landslide system has and will continue to be loaded by fresh cliff falls from the rear-scarp, which could trigger a large scale landslide that would have significant impact on the line. Although it is understood the flake is being monitored, remediation in this unit appears relatively local and therefore it is recommended that this be considered a priority CBU for stabilisation and/or protection. Further to the UAV and interpretation presented herein, there are not too many instances where the hazard rating for CBUs has changed. The UAV survey has provided valuable imagery and data to support interpretation of cliff mechanisms and potential rockfall at a level of detail not previously possible. The added resolution and detail has in the main highlighted features within CBUs that pose local hazards. As a result of this work, two CBUs hazard ratings have been reduced from high to medium, and one CBU is highlighted for priority action (see Table 3-1). The findings of this assessment should inform subsequent direction of future roped-access surveys and tactile site investigation to ground truth issues highlighted in this report. Where visualisation of the landscape is limited or unclear due to vegetation or UAV data quality, it is recommended that ground truthing is carried out where possible through site inspection of the cliff. Specific sites highlighted for further site inspection including roped-access surveys are listed below: CBU 06: Investigation whether unnetted section is likely to be actively spalling material CBU 08: Investigation whether there is potential for shallow failure of the unit CBU 12: Monitoring for signs of incipient/ongoing instability CBU 14: Further investigation of bare cliff faces close to engineers’ compound CBU 15: Investigation of apparent washout morphology adjacent to track CBU 17: Monitoring of entire system and investigation of vegetated areas to assess stability of debris slope CBU 20: Investigation of the competency of the slope given the lack of observed remediation; investigation of whether vegetation above Phillot Tunnel portal is masking talus CBU 29: Inspection of masonry dentition to assess stability
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 39
CBU Hazard rating (baseline report) Hazard rating (UAV survey) 6 High High 7 Low Low 8 High High 9 High Medium 10 High High 11 Medium Medium 12 High High 14 High High 15 High High 16 Low Low 17 High High – HIGH PRIORITY 18 Medium Medium 19 Low Low 20 High High 21 High Medium 22 Medium Medium 23 Medium Medium 28 Medium Medium 29 Medium Medium – inspect masonry dentition 30 Medium Medium
Table 3-1: Updated CBU hazard ratings
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Appendix A: Location of CBUs
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Parsons Tunnel
Sprey Point
42 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Kennaway Tunnel
Coryton Tunnel
Phillot Tunnel
Clerks Tunnel
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Appendix B: Baseline Report CBU Proformas
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Network Rail Chainage and National Grid Reference Hazard Rating
CBU 6 Pine Close Start: 208m 12.5ch (E295070 N73933) MEDIUM End: 208m 03.5ch (E295128 N74026) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall Geology (Bedrock and Superficial) Undifferentiated Alphington & Heavitree Breccia 80 Formations - breccia. Sub-vertical joints and faults T21 observed in field and recorded on geological maps 70 T22 60
50
40
30 Elevation(mOD) 20
10
Cliff Morphology, Mechanics and Dominant Processes 0 0 50 100 150 CBU is a regraded rock headland between two washout embayments. The lower cliff is sub-vertical, entirely netted, generally free of vegetation and marked by steeply-angled bench formed by jointing. The upper cliff Distance (m) is thickly vegetated, un-netted and has been regraded to c. 45°. Small joint-controlled rockfalls are seen in in the lower cliff Historical Events (Date and Description) Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) No records found
External Linkages (Surface Water, Groundwater and Beach) The position of this CBU means any surface water drainage at the cliff top will be captured by the two adjacent washout embayments (CBUs 5 and 7). The beach is sandy Existing Stabilisation Measures and Hazard Mitigation Measures Passive netting covering lower slope from 12.5ch through CBU boundary (ends 07.5ch) 4.5m mesh fence with 1.5m debris barrier (10ch-7ch) Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records None
Geotechnical Data None
raf_58_2549_psfo_p2_0325 source: English Heritage
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Network Rail Chainage and National Grid Reference Hazard Rating
CBU 7 Footpath Hollow Start: 208m 03.5ch (E295128 N74026) LOW End: 208m 02.0ch (E295182 N74117) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (Lidar 2014) Washout
Geology (Bedrock and Superficial) 70 Undifferentiated Alphington & Heavitree Breccia T23 Formations - breccia 60 T24
50
40
30
Elevation(mOD) 20
10
Cliff Morphology, Mechanics and Dominant Processes 0 The CBU comprises two coalescing washout embayments with headscarps that are set back by up to 130m 0 50 100 150 from the railway line. The northeastern embayment closely follows the alignment of a fault. The lower Distance (m) slopes are relatively shallow (<30°) and mantled with debris that has been subject to small debris slides. The upper slopes are steeper at around 40° and exposed faces are subject to surficial rilling from surface water flows. Seepage was observed along joints Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
Historical Events (Date and Description) None
External Linkages (Surface Water, Groundwater and Beach) Surface water flows are towards the cliff top. The cliff top is well-developed with housing. The beach is of sand Existing Stabilisation Measures and Hazard Mitigation Measures None Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records None
Geotechnical Data None
raf_58_2549_psfo_p2_0326 source: English Heritage
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 47
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 8 Bungalow Headland Start: 208m 02.0ch (E295182 N74117) HIGH End: 207m 78.5ch (E295218 N74176) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 70 Geology (Bedrock and Superficial) Undifferentiated Alphington & Heavitree Breccia 60 Formations - breccia. Sub-vertical joints observed in field 50
40
30
Elevation(mOD) 20
10
Cliff Morphology, Mechanics and Dominant Processes 0 CBU is a regraded rock headland between two washout embayments. Sub-vertical lower cliff with lower -10 10 30 50 70 90 110 130 150 angle, regraded upper cliff. Small joint-controlled rockfalls in the lower sandstone cliff and small falls from the overlying terrace gravels Distance (m) Historical Events (Date and Description)
No records identified Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
External Linkages (Surface Water, Groundwater and Beach) No streams on the upper cliffs. Surface water is directed towards the cliff top in this location, but position of the cliff between two washout embayments means water will be captured by adjacent cliffs. Seepage from the lower cliffs often at the upper contact with beds of breccia. The beach is of sand Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) 3.5m mesh catch fence with 1.5m debris barrier through CBU Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records None
Geotechnical Data
None
raf_58_2549_psfo_p2_0327 source: English Heritage
48 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 9 Bungalow Ravine Start: 207m 78.5ch (E295218 N74176) HIGH End: 207m 76.5ch (E295237 N74204) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Washout, debris flows (high sediment load) 60 Geology (Bedrock and Superficial) Undifferentiated Alphington & Heavitree Breccia 50 Formations - breccia. Fault dissects this CBU
40
30
Elevation(mOD) 20
10 Cliff Morphology, Mechanics and Dominant Processes CBU is a deeply incised gully at the margin on the Woodland Avenue landslide (CBU 10). The upper part of 0 the gully is a concrete channel, but drainage in the lower section is unconstrained by engineering. Washout / 0 50 100 150 debris flows occur as a result of high discharges entraining weathered breccia debris in the gully Distance (m) Historical Events (Date and Description) Slope failures recorded in 2004, 2012 and 2014 Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
External Linkages (Surface Water, Groundwater and Beach) No streams on the upper cliffs. Seepage from the lower cliffs often at the upper contact with beds of breccia. The beach is uniform and of sand Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) 3.5m mesh catch fence with 1.5m wooden debris barrier through CBU Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records Abseiled inspection to inspect the full height of the site (TGP Woodlands Phase 2 Options Report, 2015)
Geotechnical Data None
raf_58_2549_psfo_p2_0327 source: English Heritage
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 49
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 10 Woodland Avenue Start: 207m 76.5ch (E295237 N74204) HIGH End: 207m 72.5ch (E295286 N74274) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Deep-seated failure (upper cliff)
70 Geology (Bedrock and Superficial) T27 Undifferentiated Alphington & Heavitree Breccia 60 Formations - breccia. Upper cliff formed in deeply- weathered breccia T28 50
40
30
Elevation(mOD) 20
10
Cliff Morphology, Mechanics and Dominant Processes 0 The present cliff morphology is largely a result of slope regarding following the March 2014 landslide; however, two general 0 50 100 150 morphological units can be observed. The upper and lower cliffs are separated by a shallow angle bench that slopes at c. 20° towards the northeast (broadly coincident with the geological dip). Below this bench, the lower cliff has been regraded to a uniform c. 40 degree Distance (m) slope, but the cliff toe is mantled by a series of small debris lobes. The upper cliff is a marginally shallower angle uniformly regraded slope. The BGS map shows the CBU is bisected by a fault that is normal to the coastline, but this is not evident in the field. The cliff has been interpreted as a composite landslide, with a bedding-controlled translational failure in the upper part and rockmass failure / rockfall in the lower part. The associations of the two systems are unclear. A high level of antecedent rainfall is thought to have Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) triggered the failure Historical Events (Date and Description) 1920 rockfall Deep-seated failure in March 2014 External Linkages (Surface Water, Groundwater and Beach) Seepage evident from cliff, which may relate to water jetting undertaken to remove landslide debris during stabilisation. Surface water drainage is towards the cliff top in this region. The hinterland is characterised by a shallow embayment that will act to direct surface water towards the cliff top. The beach is of sand Existing Stabilisation Measures and Hazard Mitigation Measures Active netting across CBU 3.5m mesh catch fence with 2m wooden debris barrier across CBU Cliff Monitoring Historical Photo (August 1958) 6 inclinometers (non-operational; mentioned - TGP Note on Woodlands Avenue Slope Failure, 2014) 10 inclinometers; 20 piezometers (TGP Weekly Inspection Reports 2014- 2015; Woodlands Phase 2 Options Report, 2015) Cliff Inspection Records Daily site walkovers for c. 15 weeks to note indicators of ongoing instability following stabilisation works (TGP Woodlands Phase 2 Options Report 2015) TGP Weekly Inspection Reports (2014-2015)
Geotechnical Data 2 rotary cored boreholes (mentioned - TGP Note on Woodlands Avenue Slope Failure, 2014) 4 dynamic probes (WYGE Phase 2 Factual Report, 2003) raf_58_2549_psfo_p2_0327 source: English Heritage SPT testing; packer tests (mentioned - TGP Woodlands Phase 2 Options Report, 2015)
50 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 11 Windjammer Start: 207m 72.5ch (E295286 N74274) MEDIUM End: 207m 70.5ch (E295308 N74301) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation moldel (LiDAR 2014) Washout (high sediment load) No transects for this CBU
Geology (Bedrock and Superficial)
Undifferentiated Alphington & Heavitree Breccia
Formations - breccia. BGS mapping shows a fault
obliquely dissects the CBU
Cliff Morphology, Mechanics and Dominant Processes Deep incised washout gully / mudslide system with well-defined embayed sediment source, narrow transport route and broad debris fan. Ongoing seepage at the top of the cliff, despite drainage measures. Potential for further debris washouts Historical Events (Date and Description) Detached boulder 2004 Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) Cliff slip in 2010 Cliff slip in 2012 External Linkages (Surface Water, Groundwater and Beach) Seepage from the lower cliffs often at the sedimentary contacts. Hinterland topography directly surface water drainage towards the cliff edge. The beach is sand Existing Stabilisation Measures and Hazard Mitigation Measures Active netting and soil nails and french drain along cliff top 3m high mesh catch fence with 1.5m debris pipe across CBU Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records Abseiled drops to inspect the full height of the site (TGP Woodlands Phase 2 Options Report, 2015)
Geotechnical Data 3 dynamic probes (WYGE Phase 2 Factual Report, 2003) raf_58_2549_psfo_p2_0328 source: English Heritage
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 51
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 12 Windjammer Track Start: 207m 70.5ch (E295308 N74301) HIGH End 207m 65.0ch (E295382 N74392) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Deep slide, washout
Geology (Bedrock and Superficial) 60 Undifferentiated Alphington & Heavitree Breccia T29 Formations - breccia 50 T30
T31 40
30
Elevation(mOD) 20
10 Cliff Morphology, Mechanics and Dominant Processes The cliff can be subdivided into a south-western section with a steep, regraded cliff subject to small joint- 0 controlled rockfalls, and a north-eastern section with a small washout embayment and with debris fan that 0 20 40 60 80 100 120 is subject to periodic washouts/debris flows Distance (m)
Historical Events (Date and Description) Cliff falls in 1920s and 1930s Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
‘Small slip’ in 2000 Debris washout in 2013
External Linkages (Surface Water, Groundwater and Beach) Seepage along the section at sedimentary contacts. Debris fan is marshy in places. The beach is sand Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) French drain along part of the cliff top. 3.0m mesh catch fence with 1.5m wooden debris barrier across CBU Localised passive netting over a previous failure site (66ch-65ch) Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records None
Geotechnical Data 3 rotary openhole face probes (WYGE Phase 3
Ground Investigation Factual Report, 2003)
3 dynamic probes (WYGE Phase 2 Factual Report, raf_58_2549_psfo_p2_0329 source: English Heritage 2003)
52 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 14 Smugglers’ Lane Start: 207m 46.5ch (E295678 N74655) HIGH End: 207m 43.0ch (E295713 N74670) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Compound for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall
40 Geology (Bedrock and Superficial) Undifferentiated Alphington & Heavitree Breccia 35 Formations - breccia. Overlain by slope wash (“head”) and alluvium in the valley of the Holcome 30 Stream that flows down Smugglers’ Lane 25
20
15 Elevation(mOD) 10
5
Cliff Morphology, Mechanics and Dominant Processes 0 The cliff is set back from the railway and has probably not been cut back or regraded. It is sub-vertical, with 0 50 100 150 200 weathered beds and thick vegetation. Small joint-controlled rockfalls occur that place the engineers’ Distance (m) compound at risk. Surface spalling evident, and small falls from the overlying terrace gravels
Historical Events (Date and Description) None identified Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
External Linkages (Surface Water, Groundwater and Beach) This cliff is cut through a river valley and surface water will be directed through the cliff towards the Smugglers’ Lane stream. The beach is sandy with a gravel storm beach above High Water Mark Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) Rockfall ditch and bund Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records None
Geotechnical Data 2 dynamic probe tests (CASE Consultants Phase 2 raf_58_2549_psfo_p2_0331 source: English Heritage Rock Trap Fencing Tests, 2003)
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 53
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 15 Parson’s Tunnel Start: 207m 43.0ch (E295713 N74670) HIGH End: 207m 42.0ch (E295794 N74615) (Low = negligible impact. Medium = line affected for <48 hours. High = line Southwest Portal affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 60 Geology (Bedrock and Superficial) T40 Undifferentiated Alphington & Heavitree Breccia 50 Formations - breccia. Slope wash (“head”) mantles T41 the cliff top 40
30
20 Elevation(mOD)
10 Cliff Morphology, Mechanics and Dominant Processes Cliff face formed by northwest-southeast trending joint and forms the side of Hole Head. Other joints form rockfalls. Superficial sediments are prone to spalling. The upper cliff includes several large, shallow-rooted 0 trees -25 25 75 125 175 Historical Events (Date and Description) Distance (m) 1855 slope failure
External Linkages (Surface Water, Groundwater and Beach) Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) The cliff forms the side of a headland and surface water drainage is directed towards the cliff top. Seepage was seen at the sedimentary contacts between beds of breccia and thin sandstone. Predominately sandy beach with gravel storm beach above High Water Mark Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) Dentition on cliff face above tunnel portal Cliff Monitoring Historical Photo (September 1986) None
Cliff Inspection Records May 2015 walkthrough
Geotechnical Data os_86217_v_114 source: English Heritage None
54 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 16 Parson’s Tunnel Start: 207m 28.0ch (E296096 N74717) LOW End: 207m 18.5ch (E296049 N75024) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Rockfall Shelter for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation model (LiDAr 2014) Rockfall (shelter)
Geology (Bedrock and Superficial) 80 Undifferentiated Alphington & Heavitree Breccia Formations - breccia 70 T47
60 T48
50 T49
40 T50
30 Elevation(mOD) 20 Cliff Morphology, Mechanics and Dominant Processes Steep (c. 40°), reprofiled cliff. Evidence of spalling and shallow failures above shelter, rockfall debris 10 reported to be present on shelter roof 0 0 50 100 150 Historical Events (Date and Description) Distance (m) Rockfalls common prior to construction of rockfall shelter in 1920s
External Linkages (Surface Water, Groundwater and Beach) Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) The cliff cuts into a small hill and consequently a small amount of surface water drainage will be directed towards the cliff face. There is a small cobble and boulder beach
Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) The Parson’s Tunnel rockfall shelter protects all but a small northeastern part of the CBU 5m mesh fence with 0.25m wooden debris barrier protects the section not protected by the rockfall shelter
Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records May 2015 walkthrough
Geotechnical Data -+ None
raf_58_2549_psfo_p2_0334 source: English Heritage
55 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 17 Rockfall Shelter Start: 207m 18.5ch (E296049 N75024) HIGH End: 207m 14.5ch (E296068 N75097) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Portal for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation moldel (LiDAR 2014) Rockfall
80 Geology (Bedrock and Superficial) T51 Undifferentiated Alphington & Heavitree Breccia 70 T52 Formations - breccia 60 T53 50
40
30
Elevation(mOD) 20
Cliff Morphology, Mechanics and Dominant Processes 10 Steep rock faces with overhangs. Rockfalls and spalling dominate 0 0 20 40 60 80 100 120 -10 Distance (m) Historical Events (Date and Description) 1852 rockfall
External Linkages (Surface Water, Groundwater and Beach) Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) Cliff cut in small hill with small amount of surface water directed towards the cliff top. Rocky foreshore
Existing Stabilisation Measures and Hazard Mitigation Measures Passive netting from 16ch through CBU boundary (ends 06ch) 5m mesh catch fence with 0.25m wooden debris barrier from previous CBU to 18ch (starts 18.5ch) Fence tied back to slope Cliff Monitoring Historical Photo 1 standpipe piezometer (WYGE Phase 2 Factual Report, 2003) Not available 2 tiltmeters (TGP Phase 4 Rock-Fall Shelters Feasibility Study, 2004) 6 survey targets (TGP Phase 4 Rock-Fall Shelters Feasibility Study, 2004) Cliff Inspection Records Visual inspection, including abseil drops and a topological survey (TGP Phase 4 Factual and Interpretative Report, 2007) Walkthrough May 2015
Geotechnical Data 1 rotary cored borehole; 1 hand dug trial pit; 1 SPT (WYGE Phase 2 Factual Report, 2003) 1 rotary cored borehole; and 1 shearbox test (Emerson Moore Factual Report, 2007) GPR survey (Dawlish Sea Cliffs soils investigation reports, 2003)
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 56
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 18 East Down Cliff Start: 207m 14.5ch (E296068 N75097) MEDIUM End: 207m 04.5ch (E296052 N75290) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 70 Geology (Bedrock and Superficial) T54 Undifferentiated Alphington & Heavitree Breccia 60 Formations - breccia T55 50 T56
40 T57
30 Elevation(mOD) 20
Cliff Morphology, Mechanics and Dominant Processes Near-vertical cliffs cut when railway line was constructed. Spalling and jointing evident within rockface. 10 Joint-controlled rockfalls 0 Historical Events (Date and Description) 0 20 40 60 80 100 120 None recorded Distance (m)
External Linkages (Surface Water, Groundwater and Beach) Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) Cliff on flanks of East Down with most surface water directed parallel to cliff face towards the Smugglers’ Inn stream Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) Passive netting from previous CBU to 06ch (starts 18.5ch) Cliff Monitoring Historical Photo (August 1958) 2 standpipe piezometers (WYGE Phase 2 Factual Report, 2003) Cliff Inspection Records Visual inspection, including abseil drops and a topological survey (TGP Phase 4 Factual and Interpretative Report, 2007) May 2015 walkthrough
Geotechnical Data raf_58_2549_psfo_p2_0337 source: English Heritage 2 rotary cored boreholes; 2 hand dug trial pits; and 2 SPTs (WYGE Phase 2 Factual Report, 2003)
1 rotary cored borehole; and 3 shearbox tests (Emerson Moore Factual Report, 2007)
GPR survey (Dawlish Sea Cliffs soils investigation reports, 2003)
57 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 19 Smugglers’ Inn Start: 207m 04.5ch (E296052 N75290) LOW End: 206m 79.0ch (E296024 N75400) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Stream for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 50 T67 Geology (Bedrock and Superficial) 45 Alphington and Heavitree Breccia Formation – T68 40 breccia. Superficial alluvium from the Smuggler’s Inn stream 35 30
25
20
Elevation(mOD) 15
10 Cliff Morphology, Mechanics and Dominant Processes Steep rock face with overhangs and benches that is bisected by the Smugglers’ Inn stream 5 Historical Events (Date and Description) 0 Slope failures recorded in 1865 and 1906 0 20 40 60 80 100 120 Distance (m) External Linkages (Surface Water, Groundwater and Beach) CBU bisected by the Smugglers’ Inn stream. Surface water directed parallel to cliff face towards valley bottom. Rock foreshore platform with no beach Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
Existing Stabilisation Measures and Hazard Mitigation Measures None Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records Visual inspection, including abseil drops and a topological survey (TGP Phase 4 Factual and Interpretative Report, 2007) May 2015 walkthrough
Geotechnical Data raf_58_2549_psfo_p2_0337 GPR survey (Dawlish Sea Cliffs soils investigation source: English Heritage reports, 2003)
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 58
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 20 Clerk’s Tunnel Start: 206m 79.0ch (E296024 N75400) HIGH End: 206m 73.0ch (E296032 N75509) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected South Portal for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall
40 Geology (Bedrock and Superficial) T61 Undifferentiated Alphington & Heavitree Breccia 35 Formations - breccia T62 30
25
20
15 Elevation(mOD) 10
Cliff Morphology, Mechanics and Dominant Processes 5 Steep cliffs adjacent to and above tunnel portal. Joint-controlled rockfalls 0 Historical Events (Date and Description) 0 10 20 30 40 50 60 Minor landslide near track in 2002 Distance (m) External Linkages (Surface Water, Groundwater and Beach)
Surface water drainage directed inland, away from the cliff face Existing Stabilisation Measures and Hazard Mitigation Measures Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
Cliff Monitoring Historical Photo (August 1958) None
Cliff Inspection Records Abseiled drops to assess topography, material strength, groundwater seepage and vegetation cover (TGP Phase 4 Cliff Assessment, 2007) May 2015 walkthrough
Geotechnical Data raf_58_2549_psfo_p2_0337 GPR survey (Dawlish Sea Cliffs soils investigation source: English Heritage
reports, 2003)
59 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 21 Clerk’s Tunnel to Start: 206m 73.0ch (E296032 N75509) HIGH End: 206m 68.5ch (E296007 N75612) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Phillot South Portal for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 50 Geology (Bedrock and Superficial) 45 T64 Undifferentiated Alphington & Heavitree Breccia 40 T65 Formations – breccia overlain by sandstone 35 T66 30 25 20
Elevation(mOD) 15 10 5 Cliff Morphology, Mechanics and Dominant Processes 0 Steep cliffs with talus slope at the base 0 20 40 60 80 100 Historical Events (Date and Description) Distance (m) 1855 slip at Phillot’s Tunnel
External Linkages (Surface Water, Groundwater and Beach) Surface water directed parallel to cliff face. Small pocket beach Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
Existing Stabilisation Measures and Hazard Mitigation Measures Passive netting
Cliff Monitoring Historical Photo (August 1958) 1 standpipe piezometer (WYGE Dawlish Sea Cliffs Phase 2 Factual Report, 2003) 1 piezometer (Emerson Moore Factual Report, 2007)
Cliff Inspection Records Visual inspection, including abseil drops and a topological survey (TGP Phase 4 Factual and Interpretative Report, 2007) May 2015 walkthrough raf_58_2549_psfo_p2_0338 source: English Heritage
Geotechnical Data 1 rotary cored borehole; 1 hand-dug trial pit;
1 SPT (WYGE Dawlish Sea Cliffs Phase 2 Factual Report, 2003)
1 rotary cored borehole; 5 shearbox tests (Emerson Moore Factual Report, 2007)
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 60
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 22 Shell Cove (includes Start: 206m 68.5ch (E296007 N75612) MEDIUM End: 206m 63.5ch (E296060 N75667) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Phillot’s Tunnel) for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Shallow slide/washout. Rockfalls are secondary hazard mechanisms 50 Geology (Bedrock and Superficial) 45 T67 Undifferentiated Alphington & Heavitree Breccia T68 Formations – sandstone. Breccias comprise sandy, 40 gravelly silt/clay; silty/clayey snad; and clayey 35 sandy gravels. There is a normal fault with a 30 downthrow of c. 4m to the north. Bedding has a strike of 335o, dip of 32o and spacing of 400mm. 25 20
Elevation(mOD) 15 10 5 0 Cliff Morphology, Mechanics and Dominant Processes 0 20 40 60 80 100 120 Cliff face is set back from the railway that runs along a low embankment. Cliff is sub-vertical and fronted by Distance (m) a talus slope. Drainage from cliff top is directed through a network of pipes to the shoreline, but the talus
remains marshy. The north portal of Phillot’s Tunnel is mantled with thick debris that has seepage and is Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) unstable. The sandstone cliff face is affected by honeycomb weathering. Joint-controlled rockfalls are evident Historical Events (Date and Description) The slope above Phillot’s Tunnel north portal is formed in weathered sandstone and has failed in the recent past (2001 onwards) External Linkages (Surface Water, Groundwater and Beach) Seepage from the lower cliffs. Small pocket beach at base of cliff with impounded stream Existing Stabilisation Measures (i.e. active/passive netting, rock bolts/anchors, dentition etc.) and Hazard Mitigation Measures (i.e. catch fences, walls, drains) Slope above Phillot’s Tunnel north portal is netted 2 discrete netted areas (66ch-65ch), some active Gabion basket wall protects railway from talus slope failures
Cliff Monitoring Historical Photo (August 1958) May 2015 walkthrough
Cliff Inspection Records None
Geotechnical Data None
raf_58_2549_psfo_p2_0339 source: English Heritage
61 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 23 Coryton Tunnel Start: 206m 63.5ch (E296060 N75667) MEDIUM End: 206m 60.5ch (E296078 N75751) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected South Portal for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014)
Rockfall 60 T69
50 T70
40
30
Elevation(mOD) 20
10
0 0 20 40 60 80 100 120 140 Distance (m)
Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT 62
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 28 Riviera Terrace Start: 205m 52.5ch (E296930 N77240) MEDIUM End: 205m 47.5ch (E297004 N77309) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital elevation model (LiDAR 2014) Rockfall 25 Geology (Bedrock and Superficial) T111 Dawlish Sandstone Formation dipping 20° north-east T112 20 to east. Sub-vertical joints and faults observed in field. The bedrock geology is notified as a Site of Special Scientific Interest (SSSI) 15
10 Elevation(mOD)
5
Cliff Morphology, Mechanics and Dominant Processes Embayment with locally overhanging strata and small cavities at base of cliff. Vegetated talus slope at c. 0 55° mantles the lower cliff. Sandstone cliff has no vegetation and exposed jointing. Small joint-controlled 0 10 20 30 40 50 60 rockfalls in the lower sandstone cliff and small falls from the overlying soils Distance (m)
Historical Events (Date and Description)
None recorded Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
External Linkages (Surface Water, Groundwater and Beach) Surface water drainage directed towards the cliff top. Seepage noted from bedding. Narrow sand beach
Existing Stabilisation Measures and Hazard Mitigation Measures 1m wooden debris barrier from previous CBU to 51.0ch (start 53.0ch)
Cliff Monitoring Historical Photo None None available
Cliff Inspection Records None
Geotechnical Data 4 dynamic probes (WYGE Dawlish Sea Cliffs Phase 2 Factual Report, 2003)
63 DAWLISH-TEIGNMOUTH CLIFFS UAV SURVEY INTERPRETATION REPORT
Network Rail Chainage and National Grid Reference Hazard Rating
CBU 29 Rockstone Cliff Start: 205m 47.5ch (E297004 N77309) MEDIUM End: 205m 44.5ch (E297047 N77349) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital Elevation Model (LiDAR 2014) Rockfall
30 Geology (Bedrock and Superficial) Dawlish Sandstone Formation dipping c. 20° north-east 25 to east overlain by thin veneer of terrace gravels and slope wash. Sub-vertical joints and faults observed in 20 field. The bedrock geology is notified as a Site of Special Scientific Interest (SSSI) 15
10 Elevation(mOD)
5
0 Cliff Morphology, Mechanics and Dominant Processes 0 10 20 30 40 50 Sub-vertical sandstone cliff regraded top section and talus slope at base. Talus slope at c. 50° and heavily vegetated. Vertical sections of cliff have no vegetation, widespread jointing and preferential weathering of Distance (m) certain sandstone beds to produce cavities and overhangs. Small joint-controlled rockfalls in the sandstone cliff and small falls from the overlying gravels Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012) Historical Events (Date and Description) None documented
External Linkages (Surface Water, Groundwater and Beach) Surface water drainage directed towards the cliff top. Seepage noted from bedding. Narrow sand beach
Existing Stabilisation Measures and Hazard Mitigation Measures 0.5m wooden debris barrier Dentition at 46ch
Cliff Monitoring Historical Photo None None available Cliff Inspection Records None
Geotechnical Data 4 dynamic probes (WYGE Dawlish Sea Cliffs Phase 2 Factual Report, 2003)
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Network Rail Chainage and National Grid Reference Hazard Rating
CBU 30 Rockstone Start: 205m 44.5ch (E297047 N77349) MEDIUM End: 205m 40.0ch (E297114 N77406) (Low = negligible impact. Medium = line affected for <48 hours. High = line affected Footbridge for >48 hours or potential loss of life) Principal Hazard Mechanism Photograph (March 2015) Slope Transects Map 1: Digital Elevation Model (LiDAR 2014) Rockfall (weak sandstone) 25 Geology (Bedrock and Superficial) T114 Dawlish Sandstone Formation dipping 20° north- east to east overlain by terrace gravels and slope 20 T115 wash. Sub-vertical joints and faults observed in the field. The bedrock geology is notified as a Site of Special Scientific Interest (SSSI) 15
10 Elevation(mOD)
Cliff Morphology, Mechanics and Dominant Processes 5 Joint-controlled embayment in the cliff with sub-vertical sandstone cliff and vegetated talus slope. The sandstone shows preferential weathering and erosion of certain beds, leading to overhangs and cavities. Joint-controlled slab failures and localised failures of the overlying terrace gravels are common 0 Distance (m) Historical Events (Date and Description) 1870 Rockstone footbridge breach
Map 2: Bedrock and Superficial Geology (Based on BGS 1:10,000 data) Map 3: Aerial Photo (2012)
External Linkages (Surface Water, Groundwater and Beach) Surface water drainage directed towards the cliff top. Seepage noted from bedding at track level. Narrow sand beach
Existing Stabilisation Measures and Hazard Mitigation Measures 1m mesh catch fence with 0.5m wooden debris barrier
Cliff Monitoring Historical Photo This cliff has no geotechnical monitoring None available
Cliff Inspection Records None
Geotechnical Data 4 dynamic probes (WYGE Dawlish Sea Cliffs Phase 2 Factual Report, 2003)
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Appendix C: UAV data capture areas
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Appendix D: UAV Survey Scope
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UAV Survey Scope
PREPARED FOR: Simon Woddy (Network Rail)
COPY TO:
PREPARED BY: Roger Moore/Oliver Dabson
DATE: 4 August 2015
PROJECT NUMBER: 657257
REVISION NO.: 1
APPROVED BY: 1. Project Overview CH2M is supporting Network Rail (NR) in a study of the geotechnical resilience of rail infrastructure between Exeter and Newton Abbot in Devon, UK. CH2M is contracted by NR to provide technical support and expertise in cliff instability hazard assessment to identify engineering solutions that will deliver future resilience along this stretch of coastline. The location of the cliff section of interest is shown in the file UAV.kmz (see Appendix C). UAV surveys will be used to assist in the characterisation of cliff litho-stratigraphy and structure alongside the track. The resulting data will also be used to characterise the cliff instability processes that have occurred in the recent past. This will inform design of cliff engineering measures in later stages of the investigation. 2. Scope of Work 1.1.1 2.1 Aerial photography requirements 2.1.1. A flight line and photo control layout map shall be submitted to CH2M for review and approval prior to mobilisation to the site. The flight line and control layout map shall be georeferenced in the British National coordinate system and provided in CAD or ESRI GIS file format and contain the following: Flight line alignments; Exposure centres; Horizontal/vertical control point locations; Vertical only control point locations (if applicable); Planned photo acquisition scale or ground sample distance (GSD); Altitude (or altitudes if multiple) above the mean terrain by flight line; The planned photo control point dimensions and configuration shall be provided on, or as an attachment to the flight line/control diagram map; Note: if requested, the Subcontractor shall be responsible for removing the pre-marks after the aerial photography has been successfully obtained 2.1.2. The aerial imagery shall be flown with strict adherence to the approved flight line and control layout map. The survey must be undertaken during time windows where the solar elevation and lateral position does not cause the survey area to be cast in lengthy shadow or cause glare/washing out of the photographs.
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The optimum time of year for undertaking the survey is February or March when vegetation is least dense and lighting and air quality conditions are good. 2.1.3. Aircraft: Aircraft and flights must comply with all current Civil Aviation Authority (CAA) requirements and guidelines. 2.1.4. The imagery shall be delivered as geotagged JPEGs. 1.1.2 2.2. Description of work requirements 2.2.1. Survey Datum and Coordinate System The horizontal datum is GCS OSGB 1936 and the vertical datum is Ordnance Datum Newlyn. The required projection is British National Grid, Transverse Mercator, metres. The scale factor is 0.99960127. 2.2.2. UAV Survey Areas 1-37 Obtain controlled aerial photography. The production of a photogrammetrically-derived bare-earth Digital Elevation Model (DEM) and orthorectified aerial photograph will be the responsibility of CH2M. Field survey Ground Control Points (GCPs) Provide a total of 10 GCPs per Survey Area (where possible – describe constraints where not possible) Provide GCP elevations based on Differential GPS (dGPS) survey with accuracy ≤±0.03m vertically and horizontally. Position GCPs is both areas that are free from vegetation and areas that are vegetated GCPs shall be distributed throughout the area mapped in a uniform random pattern where possible 1.1.3 2.3 Minimum specifications Aerial imagery requirements: Ground Sampling Distance (GSD): 0.02m Overlap requirements: Target 80% (forward and side overlap) 3. Technical documents The following drawings, specifications and other documents described therein compliment and further define the Scope of Work, and are made a park of the requirements of this Subcontract. Document number Description UAV_area Proposed 2016 survey locations
4. Deliverables 4.1 Daily progress including work completed shall be provided to CH2M personnel via email, to be specified and confirmed in advance of the survey. 4.2 Detailed reports and the deliverables as described in items 5 and below shall be provided within two weeks of completion of the fieldwork.
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4.3 All survey products should be geospatially referenced to the same geodetic datum, as listed in item 2.2.1. 4.4 Deliverables may be provided electronically at an FTP site provided by the Subcontractor. If files are too large to transmit via FTP, the Subcontractor should assume mailing or delivering an external Hard Drive to CH2M’s Swindon office, to be confirmed in advance of the survey. The cost of the Hard Drive will be borne by the Subcontractor should this be required. 4.5 Deliverables shall include a Survey Report narrative description of the work performed, details of the process used to collect the data, a listing of principal equipment (including model and serial numbers of the equipment used), names of personnel used, date survey was performed and survey control report. The report shall also include copies of field notes and documentation of quality assurance/quality control checks performed. 4.6 Final flight line and control layout map in AutoCAD version 2013 and in ESRI GIS shape file or geodatabase format version 10.0 or higher. 4.7 All control network data and GCP survey data shall be provided in (x,y,z) ASCII file format. ASCII file shall include point number, northing, easting, elevation and description. 4.8 Georeferenced aerial photographs shall be delivered in geotagged JPEG format.
5. Site specific information 1.1.4 5.1 Health and safety requirements (in addition to CH2M Agreement) Refer to NR Unmanned Aircraft System [UAS] Framework Agreement and Technical and Safety Summary. 1.1.5 5.2 Utilities Electrical power will not be available at the Site. The Subcontractor shall take responsibility in ensuring that all battery units have sufficient charge to complete the required work on each day. 1.1.6 5.3 Access to work locations The posted speed limits must be obeyed at all times while onsite. Roads and work sites may be slippery, soft and uneven. Compensation will not be provided for lost time or damage to property, however caused.
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Appendix E: Specification of UAV Survey
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UAV Technical Specifications
PREPARED FOR: Simon Woddy
COPY TO:
PREPARED BY: Roger Moore/Oliver Dabson
DATE: 4 August 2015
PROJECT NUMBER: 657257
REVISION NO.: 1
APPROVED BY:
Survey Requirements Date of survey: February/March 2016 Approx 6.3km long, max. width approx. 230m. Site is Dimensions of survey area: to be split into 37 rectangular areas to be surveyed individually Anthony White (Network Rail) Contact details (access): Tel. 01793389723 Email [email protected] Coastal cliffs adjacent to an operational railway. Some of these cliffs are near-vertical, others have a much shallower angle and consequently extend Nature of survey area: further inland. Some landslide morphologies are present. Vegetation cover varies from mature woodland through to bare vertical cliffs Cliff face litho-stratigraphy and structure, characterisation of landslide/rockfall morphology and fabric. Characterisation of faults and joints will be required; these may be approx. 3 cm wide. Principal subject of interest: Identification of clast size variations in sandstone geology will also be required. The full height of the cliffs from cliff top edge, down to the railway line, coastal defence structures and back of beach are to be captured by the survey. If required, can be used to quantify change in 3D Repeat surveys: morphology etc, e.g. following rockfall events Access to cliff face (for GCPs) is extremely limited over much of the site. A public footpath runs on the opposite side of the line to the cliffs for much of the Access: railway. One section (approx 1/3 of the corridor) is not publically accessible and may require access negotiation and/or rail possession
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Technical Specifications Multi-rotor UAV, <7kg max take-off weight. Capable Vehicle required: of pre-programmable flight pattern using satellite navigation system. [To be advised by Subcontractor, based on GSD requirements and site constraints. Appropriateness Sensor required: to be verified by CH2M on receipt of method statement from subcontractor] Ground Sampling Distance (GSD) required: 0.02m [To be advised by Subcontractor, based on GSD, sensor, focal length etc. Appropriateness can be verified by CH2M on receipt of method statement from subcontractor]. In order to assist with the Flying height requirements: elimination of error, imagery of whole (or larger parts of) survey areas should be captured as well as the detailed images that will deliver the required GSD. Local-scale imagery at various capture angles, between vertical and horizontal, normal to the slope to capture detailed slope and cliff features. Capture angle requirements: Vertical and oblique imagery at site and detailed scale to assist with elimination of error and creation of continuous DEMs and mosaicked orthophotos (to be completed by CH2M). Overlap requirements: 80% (forward and side overlap) 10 GCPs per survey area (where possible). “Uniform Ground Control Point requirements: random” pattern. GCPs to be surveyed in with dGPS Geotagged jpgs Flight line map documents Products required: Photographs of GCPs Survey report File type: geotagged jpgs Other deliverable requirements: Flight path, GCP details (ESRI Arc Shapefile)
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Additional Points Vegetation cover in some areas, even in the winter months, may be too dense to allow for the creation of a DTM (see below)
CBU Relative chance of successful modelling from imagery 1 Poor 2 Good 3 Good in north, poor in south 4 Good 5 Poor 6 Good 7 Poor 8-12 Reasonable, particularly where cliff is exposed 13 Good 14-15 Good Headland and 16 Good in lower, vertical cliff 17-21 Good 22-23 Poor Coryton Tunnel Good 24-25 Lower exposed cliff good, vegetated upper cliff poor Kennaway Tunnel Good 26 Good 27-34 Good
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