Pipeline construction and reinstatement monitoring: current practice, limitations and the value of airborne videography

The Science of the Total Environment 186 (1996) 221-230

the Science of the TOtal Environment A.--*-~)o.he-udb-*~~~

Pipeline construction and reinstatement monitoring: current practice, limitations and the value of airborne videography Jung-Sup Urn *, Robert Wright Centre for Remote Sensing and Mapping Science, Department of Geography, University of Aberdeen, Aberdeen AR9 ZUF, Scotland, UK Received 11 December 1995; accepted 22 February 1996

AbbtlWt A largepipelineconstructedacrossseveralcountriesaffectsa variety of landownersand environmentsin its path. One of the critical issues influencingthe approvalof pipelineconstructionby governmentagenciesisthe ability of the developerto demonstratehow the pipeline right of way (ROW) will be revegetated.This paper presentsthe environmentalsignifiice of pipelinedevelopmentin termsof the presentlegalframeworkin the United Kingdom(UK) and of its particular linearcharacteristics. Current practice for restorationmonitoring,drawn from an exampleof a recentlyconstructedpipeline,ispresentedto demonstratethe limitation of on-sitefield sampling.In an attemptto identify the optimalremotesensingsystemfor restorationmonitoring, an overview is provided of the applicationrequirementsand the technology currently available for restoration monitoring of operational pipelines.The relative limitationsof traditional remotesensing systemsarebriefly discussed and the strengthsof videographyfor sucha linear applicationare highlighted.Major differencesbetweentypical remotesensors andvideo systems areidentifiedandtheir consequences evaluatedin the context of a linearapplication.The paperconcludesby suggesting that thereis a need for future studiesto developa techniquefor the applicationof video remotesensingto the restorationmonitoringof a narrow corridor, in a morepractical and automaticway. Keywords: Pipelinereinstatementmonitoring; Corridor monitoring; Remotesensing;Airborne videography

1. Introdaetion Over the past two decades, an increasing environmental awareness among the general public has led to greater care for areas of particular ecological and aesthetic importance. Environmental Impact Assessment (EIA) regulations were rapidly established in most countries of the world l

following the United States National Environmental Policy Act (NEPA) of 1969. In Europe, since the European Community (EC) Directive on EIA was approved in 1985, Member States have already taken the necessary legal measures in their own countries to comply with its requirements. There is virtually no large scale development activity which is not subjected to environmental impact assessment in almost all countries of the world.

Corresponding author.

0048-%97196/$15.00 0 1996 Elsevier Science B.V. All rights reserved PII SOO48-9697(96)05 115-7

Pipeline construction in general is one among

222

J.-S. ,Um. R. Wright / The Science of the Total

many development activities that can produce significant environmental impacts. The number of pipelines installed for the economic transport of natural gas, oil and chemicals (such as ethylene) has increased substantially in the last few decades. The stark linear boundaries of pipeline easement have the effect of breaking up the natural habitat visually, immediately after the disturbance [l]. In particular, linear developments (including roads, railways, pipelines, canals and overhead transmission lines) tend to occupy the most convenient routes between centres of population or sources of supply and demand. Such a prominent impact made environmentalists more eager to maintain the protection of any natural ecosystem which was disturbed and, furthermore, landowners required that their property should be restored as early as possible. Recently, there has been a trend towards a strict enforcement of government environmental regulations concerning the environmental impact of pipeline construction. In particular, during the past 20 years or so, much international interest has focused on Scotland because of North Sea oil and gas discoveries. Continuing oil/gas discoveries have provided Scotland (and the rest of the UK) with extensive land-based oil and gas pipeline systems in a comparatively short time. Under the Electricity and Pipeline Works Regulations (1990), cross-country pipelines for the transmission of hazardous materials, when over 16 km in length, require an EIA for Construction Authorization from the Secretary of State for Energy. In addition, ‘many of the pipeline landfalls in Scotland were required by the planning authorities to achieve an appearance that was compatible with the adjacent surface’ [2]. When granting the Pipeline Construction Authorization (PCA), the Secretary of State requires the developer to agree the Method Statement with the relevant Local Planning Authority over environmentally sensitive crossings, such as moorland. The Method Statement specifies the methods of reinstatement and also the requirement for subsequent environmental monitoring. Based on this requirement, the developer undertakes monitoring of the environmental effects of the projects and provides the rele-

Environment

186 (19%)

221-230

vant local planning authorities and nature conservation bodies with the monitoring results. 2. Envirolmlental stNetion

siw

of pipe&le

con-

All pipelines result in varying degrees of surface disturbance depending on a number of factors, including the diameter of the pipe, topography, soil condition, equipment used and access requirements during the construction [3]. Because of their particular linear form, the construction work associated with a large-scale corridor can have significant effects upon both terrestrial and aquatic ecology, exerting influence on the landscape at a variety of different scales. For example, a pipeline trench may have to be dug through terrain features such as moorland, agricultural land and woodland, and traverse streams and rivers [4]. Concern for the environment does not stop once the transmission line has been built and placed into service. Progressive restoration is regarded as a reliable indicator of the return to former physical, chemical and hydraulic ground characteristics after the disturbance of a development project. A visible scar on the moorland, woodland, agricultural land or grassland is considered a major environmental aspect of pipeline construction. Furthermore, as Ritchie [2] has observed, ‘the quality of ground restoration is often regarded as the index of environmental success. The public’s suspicion of a new pipeline magnifies itself in the appearance of the bare ground shortly after the pipeline has been laid’. Disturbance of the ground during construction usually results in a change from the previously vegetated area to bare ground. The length of time the impact lasts for depends on the ability of the original vegetation to recover after the construction. Reinstatement of a moorland area, with slowly regenerating species, requires several growing seasons over 5-10 years or so. As a result, moorland habitats may show visible signs of disturbance for a number of years while impacts on agricultural or grassland areas tend to be small and of short duration. Moorland habitats are often considered the most important in terms of

J.-S. Urn. R. Wright/The Science of the Total Environment 186 (19%) 221-230

landscape quality and, due to their sensitivity, are the most susceptible to impact from pipeline constructioll [4]. 3. Present monitorhlg corridor

practice for the disturbed

Traditional methods for monitoring of revegetation can be exemplified by current practice in relation to Shell’s North Western Ethylene Pipeline (NWEP), constructed in 1991 in the UK. The NWEP consists of approximately 411 km of 25-cm

diameter pipeline. The Pipeline Construction Authorization (PCA) required the monitoring of the environmentally sensitive sites (most of them are moorland sites). Shell undertook to monitor the successof reinstatement over the 5-year period following construction. They also undertook to make the results of the monitoring available to the relevant Local Planning Authorities and to the statutory nature conservation organizations: English Nature and Scottish Natural Heritage [5]. A series of progressively detailed field surveys were carried out and detailed qualitative ecologi-

RAILWAY

CARNWATH

North Western

Fig.

223

1. Example of community and transect map.

224

J.-S.

Urn, R. Wright / The Science of the Total

Environment

I86 (i9%)

221-230

Table1 Percentage estimation of vegetation recovery for Community A at Carnwath Moss (1989-1995) ‘89

‘92

‘93

‘94

‘95

20 25

15 10

15 10

20 20

20 20

Moss Yorkshire fog (Holcus lanorur)

70 10

25 10

20 10

20 10

30 5

Bare peat and stones

30

60

35

20

15

Heather (C&M vulgaris) Ha&s-tail cottongrass (Eriopkorwn

vaginaturn)

No data for MO-1991

during the pipeline construction.

cal data were collected in 1989 and 1990 (before the pipeline construction) along the pipeline route. These were to be used as a baseline against which the success of reinstatement could be measured along the route, and to determine any shorter or longer-term disturbance effects [a]. After the pipeline construction, starting in 1992, an annual

field survey has been done in summer. The results were compiled, with maps drawn to indicate position and extent of the communities. Such field monitoring can be demonstrated by a practical case of Camwath Moss, selected from the NWEP. Fig. 1 shows the location map of communities A and B at Camwath Moss. An overall estimate for

Table 2 Quadtrat recordings for Transect 2 NE outside of the ROW

Heather Hare’s-tail cottongrass Moss Yorkshire fog Bare soil

1

2

3

4

5

AV

30 0 65 0 0

2 20 90 0 0

15 15 70 0 0

15 15 65 0 0

40 10 40 0 0

20.4 12 66 0 0

Over the pipeline ROW

Heather Hare&-tail cottongrass Moss Yorkshire fog Bare soil

6

7

8

9

10

11

12

13

AV

10 50 35 0 0

25 20 80 0 5

5 20 25 0 50

2 15 0 0 80

30 10 40 2 0

0 0 12 20 15

20 0 20 20 10

15 10 50 10 2

13.38 15.63 32.75 6.5 20.25

SW

Heather Hare’.+tail cottongrass MOSS

Yorkshire fog Bare soil

outside of the ROW

14

15

16

17

18

AV

45 15 80 0 0

50 5 65 0 0

45 5 50 0 0

30 10 10 0 0

30 10 10 0 0

40 9 43 0 0

AV, average of quadrat recordings for individual species.

J.-S.

Urn. R Wright/The

Science

of the Total Environment

the revegetation has been made by a subjective visual assessment (by percentage) as presented in Table 1 (51. At certain ecologically important sites, transects were recorded across the pipeline. These were marked out with one or more wooden stakes, so that recording may be repeated along a similar line in future years. The transects are generally 40 m in length, with the vegetation recorded at 2-m intervals. Fig. 1 shows transect 1, 2 and 3 in the Carnwath Moss area. Records were made by percentage of cover in l-m by l-m quadrats as shown by the example of Transect 2 in Table 2. Fig. 2 is a photograph which shows the scene to locate the existing field transect, followed by quadrat recording of vegetation recovery at the Camwath Moss during the 1995 annual field survey for the NWEP. Such information from the vegetation transect recording was used to compile a set of histograms (Fig. 3). These indicate average cover of recovered plant taxa (represented by heather and moss), weed dispersal (represented by ha&s-tail cottongrass and Yorkshire fog) and bare soil. Both ‘inside’ and ‘outside’ sections of the

186 (19%)

221-230

225

graphs have been subdivided, where appropriate, to indicate areas where the transect crosses a change in vegetation type [5]. The survey results are followed by general comments on the state of the vegetation both inside (20 m) and outside the spread. The comments on the reinstatement, for the example of Community A at Camwath Moss, are as follows: ‘Vegetation growth and cover remain good along the eastern boundary fence. Recovery in other areas is variable. The bare patches associated with the waterlogging appear to the south of this, with the worst areas to the north and south of Transect 2. Growth of heather and hare’s-tail cottongrass, while good along the eastern fence, remains slow over the pipe. The main growth here is of common cottongrass and ‘pool’ species of Sphagnummoss. Growth on the buried road is improving, possibly assisted by site management at the end of November, 1994 (the breaking up of hard unvegetated peat surface with a spade). Overall cover of higher plant species remains similar to 1994, with heather and hare’s tail cottongrass at 2O?h. The grazing has reduced Yorkshire fog cover

Fig. 2. Photograph which shows scene to locate the existing field transect and the following quadrat recordings of vegetation recovery.

226

J.-S. Urn, R Wright/The Science of the Total Environment I86 (1996) 221-230

Fig. 3. Histogram

for Average

Vegetation Cover at Transect (derived from Table 2.)

2, Carnwath

Moss.

70 66

-

0 0 -4

0

NE Mean

ROW

X (individual

Mean

ground

SW Mean

class) -

Fig. 3. Histogram for average vegetation cover at Transect 2, Carnwath Moss.

to 5%. Moss cover has increased to 30%, and bare soil has declined from 20% to 15%. Transects 1 and 2 were recorded in community A’ [5]. 4. Limitatioos of present monitoring system and of tdItioml remote sensing tecbdqaes 4.1. Limitations

of present monitoring

system

In general, current monitoring programmes for disturbed pipeline sites have been based on the attributes of an area at one point in time, reflecting the emphasis on the small number of in-situ data [2,7]. One of the major disadvantages of traditional field monitoring is that it is costly, laborious and time consuming due to the large number of sam-

ples required. Nevertheless, sampling errors can be quite large, especially where the ground vegetation is not uniformly distributed in the field. Furthermore, point observations have the disadvantage that they provide only limited information on historical trends and spatial distribution of the vegetation recovery, which is possible through comparison among scenes of different dates. Until recently, the investigations of a shifting mosaic and patch dynamics in a pipeline corridor remained largely theoretical because the field survey technique has diffkulty in assembling multi-temporal images simultaneously. Present ground-based regular inventories are not practical in terms of either cost or scientific reliability. For revegetation monitoring using remote sens-

J.-S. Urn, R. Wright / The Science of the Total Environment 186 (19%) 221-230

ing techniques, it is necessary to acquire detailed aerial survey dam for a narrow pipeline corridor and to collect such data regularly as an integral part of the ecological monitoring process at relatively low cost. Depending upon the size of the pipe, the pipeline operator should maintain a ROW of 20-100 m wide and should assess the effectiveness of restoration and recovery along the route. For hundreds or thousands of kilometres of pipelines such monitoring can be quite a costly activity. The expense, limited temporal resolution, and the lack of a permanent record of the information captured using traditional field methods have led the pipeline operator to explore remote sensing technology for monitoring of revegetation. It is certain that more pipelines will be constructed in many places in the near future and it is also apparent from recent global trends that concern for environmental impacts of such pipeline development may be of world-wide importance. There is, therefore, an imperative need to identify an appropriate practical technique for monitoring restoration of vegetation along pipeline routes. 4.2. Limitations techniques

of traditional

remote sensing

Remote sensing techniques, in order to be practical, must be part of a methodology to deliver the most useful information at as low a cost as possible to the potential user. For the requirements of corridor monitoring, various sensors can be deployed from satellite or aircraft (from photographic cameras to scanners and complex imaging spectrometers). Satellite image resolution is still limited to a minimum mapping unit of 10 m per pixel. This is too coarse a resolution for monitoring pipeline corridors as narrow as 20 m. It will still be necessary to have to use aerial photography to get specific fine details at the larger scales. Aerial photography is one of the oldest and most widely applied sensors, capable of recording information in the visible and near infrared wavelengths onto photographic film. Large-scale photography has often been used for this type of

227

application to investigate detailed ground features [f&9]. However, the cost of processing and scanning conventional aerial photography can still be relatively high for a long pipeline route. Furthermore, manual handling of hundreds or thousands of hard-copy aerial photographs may prove to be unmanageable. Traditional sensors are basically designed for site-by-site assessment for a specific ground target. They do little to address the overall impacts of such linear developments on the landscape. Furthermore, if large areas are to be covered to detect suRicient ground detail, the cost disadvantage will apply to the whole coverage. To fultil the data requirements of corridor monitoring it is sufficient to have information along a line in the vicinity of the corridor disturbed. There is much recording of redundant information in linear applications using traditional area-based sensors. Clearly, economic factors hinder the use of standard area-based remote sensors in this type of application. This is why most of the information for linear features at lower level is currently gathered from ground survey. Corridor monitoring represents a potential application for remote sensing which is largely unfulfilled. 5. Value of videogqhy

in corridor monitoring

Airborne video remote sensing can be applied in a fairly cost-effective manner to linear feature monitoring (requiring a narrow swath) because angular coverage of the video camera is much narrower than for conventional photographic cameras, Unlike pushbroom-type airborne scanners, stereo coverage is achieved with airborne video in each single flight line, by covering a very large number of individual frames within a very short time interval. Thousands of aerial photographs would be required to provide the same stereo coverage as recorded on one hour of video tape. Video is physically and conceptually easier to handle for a linear application. The high cost of photo acquisition, particularly for a scattered linear target, is a significant disadvantage of the pho-

228

J.-S. Urn, R. Wright / The Science of the Total Environment 186 (19%) 221-230

tographic survey method. With airborne video, the linear extent of hundreds of kilometres of a pipeline can be recorded all on the same day. Additionally, videography is much less expensive than most other remote sensing systems [IO]. Due to such low-cost data acquisition, this technology may have a particular value in highly changeable areas, such as the revegetating corridor of a pipeline ROW, where year-to-year and seasonal changes are common. Large-scale changes in ROW could be monitored and thus annual survey results could be updated on a site-specific basis. In a temperate region such as the UK, there are only a few months in the year with the necessary bright light conditions for aerial photography. On the whole, the reduced illumination conditions of winter do not favour aerial photography. The almost all-weather capability of video, due to the high light sensitivity of the CCD (Charge Coupled Device) sensor, could assist the multi-seasonal monitoring requirement for the ROW. Even with a wider angle of view, it is difficult to ensure coverage of the 20 m swath of the ROW target using aerial photography at low altitude (especially when checks on ground coverage must await processing of the film). Such target navigation problems can be much less troublesome with videography since it is possible to review an image strip and correct for any gaps in coverage while the aircraft is still in the vicinity [lo]. Also, the time and cost of photographic processing are virtually eliminated by providing instantaneous video-taped imagery, much more quickly than with photography. Furthermore, the electronic format of video data can be readily converted to digital format, facilitating computer-based image enhancement and analysis. The uncertainties introduced by photographic emulsions and processing are avoided, and radiometric and geometric corrections are simplified. Such advantages of video imaging for remote sensing purposes indicate promise, but problems with resolution, formatting and electronic noise have delayed widespread acceptance of the technique. However, significant improvements have been realized in video equipment within the past few years. Many of the limitations inherent in

aerial videography can be reduced or overcome by current technology. The drawback of poorer spatial resolution than photography may be compensated to an extent by low level data acquisition. Moreover, the spectral sensitivity of new CCD video cameras covers the full range of visible light and can extend well into the near infra-red (NIR). Video cameras have better light sensitivity than film cameras, and this permits imaging within narrow spectral bands. Also, video images should provide colours of higher purity than with film (which has extensive spectral overlap) because of the use of optical elements to spectrally separate the light results in distinct spectral bands. The high photon efficiency and wide spectral response video cameras provide a potential capability for multi-spectral imaging. Given sufficient spatial information, multi-spectral remote sensing may offer an effective alternative to conventional aerial photography in monitoring of pipeline corridors. For the video imagery to be useful in a Geographic Information System (GIS) environment, it must be georeferenced to a map projection and coordinate system. However, it is often difficult to locate identifiable features due-to the narrow tield of view of video cameras. The current emergence of satellite-based Global Positioning Systems (GPS) offers the possibility of georeferencing each video frame in real-time [ 1l- 13). Furthermore, the advent of high resolution digital frame cameras (DFC) and the possibility of capturing analogue video in digital form can facilitate airborne acquisition of terrain imagery of high quality at low cost [14]. Consequently, one area of remote sensing application that could benefit From these advances in technology is environmental monitoring of corridor development. Fig. 4 shows a digitized video frame and a digitized portion of an aerial photograph taken over the Camwath Moss of NWEP in August, 1995. (The original colour video and aerial photograph are presented here in black and white.) The two kinds of imagery have considerably different image characteristics in terms of tone and texture. The slightly blurred appearance of the video image is primarily caused by the poorer spatial resolution of the video sensor and recording tape compared

J.-S. Wm. R. Wright/The

Science of the Total Environment 186 (19%) 221-230

with that of photographic film. However, the distribution of the main plant communities are generally as distinguishable in the video image as in the photographic image. The video imagery

Pipeline

Sk

Undisturbed

cl

Sparsely Revsgetated with Grass Species

Fig. 4. Example

clearly separates revegetated areas, bare peat, waterlogged areas and recovered heather commu&y, which is the minimum information required for successful monitoring of revegetation

0

ROW Aeather

of video

Area

frame

(upper)

229

Recovered

A

Waterlogged

0

Bars

Peat

and aerial photography

Heather area

230

J.-S. Urn. A. Wright / The Science of the Total

(the information content and image clarity are even better on the original colour video image). This example demonstrates that the Video system has potential to achieve an acceptable compromise between resolution parameters and cost in the design of a remote sensor system for revcgetation monitoring. 6. COEC~~~ Video remote sensing offers a number of unusual characteristics which can be highly advantageous for imaging and monitoring of linear features. Video systems for use in remote sensing are rapidly evolving as the technology advances and additional improvements will further enhance their capabilities. The rapid development of increasingly high quality video cameras and recording tape (including digital video tape) will significantly aid this progression in the near future. However, it is important to understand fully the video medium in order to make the best use of its advantages. It is concluded that the postulated advantages of videography for corridor application should be further tested through more rigorous experiment and assessment before widespread adoption of videography as a rapid, low-cost remote sensing method.

Acknowledgements

Environment

186 (19%)

221-230

111 British Gas, Heathland Restoration: A Handbook of Techniques, Environmental Advisory Unit, University of Liverpool, 1988, p. 160. W. Ritchie, Restoration of Pipeline Landfalls and Routes. Proc. Seminario o Impacte Ambiental de Introducao do Gas Natural em Portugal. Vimiero (Portugal). Centre for Environment and Planning, 1989, p. 9. f31 R. Seager, Environmental impact of pipelines on polar and tropical environment. Paper presented at a seminar on Pipelines and Environment, 3-10 March. Organized by Pipes and Pipelines International and Centre for Environmental Management and Plarming, University of Aberdeen, 1988, p. 14. 141 A.A. Ryder, J.B. Kenworthy, and M.P. Heape, Impacts on the landscape and the cultural heritage. Paper Presented at a Seminar on Natural Gas and Environment, Lisbon, Portugal, l-2 June 1989, p, 17. I51 RSK Environment Ltd., NWEP Ecological Monitoring Results (Year 4), Shell UK Downstream Ltd., 1995, p. 274.

161 Shell Chemicals UK Ltd., Environmental Management Plan: The North Western Ethylene Pipeline, 1992. p. 198. C. Gimingham and P. Lane, Botanical Report on the St. Fergus Vegetation, Centre for Environmental Management and Planning, Aberdeen University, 1991, p. 42. Is1 R.E. Cooper and R.J. Stedwill, Right-of-way rehabilitation monitoring using oblique aerial photography, in F.A. Crabtree (Ed.), Proceedings of the Third Intemational Symposium on Environmental Concerns in Rightof-Way Management, San Diego, CA, 15-18 February 1982, Published by Mississippi State University, 1984, pp. 285-289. IQ1 M.A. Jadkowski. P. Convery, R. Birk and S. Kuo, Aerial image databases for pipeline rights-of-way management. Photogrammetric Eng. Remote Sens., 60(3) (1994) 171

347-353.

1101 R. Wright, Airborne Videography: Principles and PracThe authors would like to acknowledge RSK Environment Ltd., who provided the ecological knowledge and expertise discussed in this paper. We also wish to thank Sky Vision International (UK) Ltd. and Shell UK Chemicals Ltd. for their assistance with the pilot project. Thanks go to Dr S. Rapson of RSK for her comments on the manuscript and to Mr Jim Livingston for assistance in preparing the illustrations. We are also grateful to the British Council, the Ministry of Science and Technology (Korea) and the Committee of ViceChancellors and Principals (UK) for funding the scholarship which made this research possible. Thanks are also extended to J.S. Urn’s employer, the Ministry of the Environment (Korea), who nominated him for this study.

tice, The Photogrammetric Record, 14(81) (April, 1993) 447-457.

1111 T. Bobbe, Real-time differential GPS for aerial surveying and remote sensing. GPS World, 3(7) (1992) 18-22.

1121 R. Wright, Airborne videography and satellite GPS for mapping and monitoring International Workshop GIS for Mediterranean Management’ held at Thessaloniki, Greece,

in forestry, in Proceedings of on ‘Satellite Technology and Forest Mapping and Fire the Aristotelian University, 4-6 November, 1993, pp.

467-475. 1131

R.D. Cooper, T. McCarthy and R. Raper, Airborne videography and GPS. Earth Obs. Mag., 4(11) (1995) 53-55.

r141

J. Raper and T. McCarthy, Using airborne videography to assesscoastal evolution and hazards, in Fifth European Conference and Exhibition on Geographical Information Systems (EGIS), Paris, France, March 29-April 1, 1994, pp. 1224-1228.