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Avoiding a big bang for your buck
Renewable Energy Focus Volume 16, Number 5–6 December 2015
www.renewableenergyfocus.com
SPECIAL FEATURE
Avoiding a big bang for your buck David Appleyard Unexploded ordnance presents an on-going challenge for offshore renewable energy project developers and as some have found to their cost, getting it wrong can be very expensive. With new guidelines on UXO management set to be published, best practice means a better understanding of the risks. It may seem unlikely in the politically calm waters of modern European seas, but for those installing and servicing equipment offshore, armed conflict nonetheless represents a very real risk. For beneath the surface hidden dangers lurk in the deep. Not some radioactive rubber-tentacled 1950s fiend, but something far more sinister and dangerous: unexploded ordnance (UXO). Far from any current war zone, UXO is an obvious and unwelcome legacy of historical naval conflict, for example sea mines that have slipped moorings or been otherwise lost – only an estimated 30-70% of the millions of sea mines laid during world wars one and two were ever recovered. But there also are munitions-carrying shipwrecks, military aircraft both crashed and dumping munitions ahead of landing, materiel washed overboard, naval bombardments and so forth. There’s a huge range of UXO too, from 9 mm pistol rounds, through ship-busting mines and torpedoes, incendiaries, chemical weapons and on up to 2000 lb bombs. Another significant source of UXO is the dumping of stockpiles that have reached the end of their service life – it seems explosives to have a best before date. One infamous site is Beaufort’s Dyke between the west coast of the UK and Ireland, which, according to Ramora UK Managing Director David Welch, is the watery grave of more than one million tonnes of World War II ordnance. Even marked dumpsites are often vague in their extent. Simon Cooke, CEO of 6 Alpha Associates, explains: ‘‘Dumping is a significant off-shore activity in Britain, France, Holland, Germany, between and after the wars up until the late 1980s of shelf-life expired munitions. ‘‘There are many mini dump sites around the UK, a lot of vessels were incentivised for speed of dumping, not for accuracy. Not only are those dump sites not accurately logged, but some munitions were short dumped, in the region – but not actually at the dump site. They might have also drifted on the sea bed.’’
Imparting enough kinetic energy to detonate perhaps a 500 kg bomb or torpedo filled with a high explosive such as Amatol or Torpex during the installation of an offshore wind or marine energy site is thus a clear risk – the consequences potentially catastrophic. Even if no injuries result, a trenching tool alone can cost of the order of £5 million (US$7.7 million).
UXO: A major operational risk With the potential for significant injury or death from UXO detonation, European project developers are bound by health and safety legislation to effectively manage and reduce this risk.
Sea mine: a significant source of UXO is the dumping of stockpiles that have reached the end of their service life or lost sea mines, but their location is often uncertain (image courtesy of 6 Alpha Associates). 1755-0084/ß 2015 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ref.2015.10.018
138
Three 50 kg wartime bombs were discovered at Gwynt y Moˆr last year after storms disturbed the seabed (image courtesy of Siemens).
Company directors in the UK, who can even be jailed, should a preventable death or serious injury occur. There is also the potential for fines and reputational risk should workers be exposed to such obvious danger. Discovering UXO during on-site work typically results in costly delays as local site operations are halted whilst the items are made safe. With the hire of a single big lift barge running to many tens of thousands of dollars daily, expenses can soon rack up when as many as 60 vessels of various types may be working at peak load on a typical offshore wind project. Indeed, early in 2014 following the discovery of three WWII bombs by a Remotely Operated Vehicle (ROV), RWE Innogy UK was forced to set up a 250 m exclusion zone during the developˆ r project 8 miles (12 km) off the ment of its s2 billion Gwynt y Mo coast in Liverpool Bay. A series of severe storms had disturbed the seabed, revealing the 50 kg bombs, which were discovered during a survey and were eventually destroyed by controlled explosion – the usual disposal method for UXO. Although RWE said work continued elsewhere on the 160 turbine site, explosives have certainly presented significant problems at a number of offshore wind farm projects. Perhaps most notorious is the 108 MW Riffgat project in the North Sea off Germany. This project suffered more than 6 months of delays when the cable route had to be cleared of significant volumes of munitions. Constrained by German legislation to a very particular route, developers Tenet were reportedly required to spend at least £50 million (US$77 million) to sweep seabed of metallic objects.
Managing UXO risk Although even a decade ago offshore encounters with UXO were largely limited to the oil and gas industry, as the development of offshore wind sites has accelerated, so has the likelihood of exposure. In the USA, the Army remains responsible for disposal of ordnance but another shift – witnessed in the UK waters for example around a decade or more ago – has been the withdrawal of military ordnance disposal services from the commercial environment.
SPECIAL FEATURE
With high profile examples making developers more aware of the risks, they have been on a steep learning curve, as Welch explains: ‘‘We went from a situation where people weren’t expecting to find anything and didn’t know what to do when they did and had very poor survey data to base it on, to a situation now where everyone is concerned about ordnance data before they start spending too much money. ‘‘People have recognised that there is a risk and if measured properly the processes and technologies that are now available to developers will locate 99% of the items that maybe in their [development] area. Disposal mechanisms are well proven and items can easily be relocated or disposed of in a very short time scale, therefore the impact on development is minimal from a disposal perspective.’’ Echoing this view, Cooke says: ‘‘In our experience, those developers that have been caught out by this, they’re very much attuned to this now.’’ But he also adds that as much as 20% of offshore wind developers have not yet fully explored UXO risks: ‘‘Generally most developers are good at developing technical risk, they’ve just not been exposed to this unexploded ordinance risk, therefore it’s not been dealt with, they just haven’t thought about it.’’ Cooke breaks down 6 Alpha’s staged approach to UXO management, which is based on a probability and consequence approach summed up as an ALARP (As Least As Reasonably Practicable) approach to risk. ‘‘There’s a phased approach that developers need to take and it’s very much about gaining intelligence, an understanding what’s on their sites and the risk. It’s procuring good quality throughout the risk assessment, which focuses on that element that you’re about to undertake: installation, operations, whether that’s a foundation for wind turbine generators, infrared cabling, or export cabling. It’s focusing on that site and working on what the prospective sources of unexploded ordinance threat might be.’’ Starting with an initial desk study assessment of potential risks, for example known military activities in the area, a key part of the approach is a thorough assessment of developers’ plans and modes of operation. Says Cooke: ‘‘One of the most important things to ask a developer is: ‘What are you going to be doing and where?’ If it’s in the region there might be some UXO you need to look at the nature of the activity and the sort of thing that could make the ordinance explode, it’s usually some sort of aggressive interaction. Things like piling, cable plough activity, driving mono piles or anchoring.’’ He continues: ‘‘It depends on the nature of the encounter and how aggressive it is, which is one half, the other half is the consequence. Whilst the probability of detonation is slim, it’s a high consequence event. Its consequence drives the risk, rather than its probability.’’ Investigation of those areas where there is a potential risk of a significant UXO encounter follows the desk analysis – most likely through a thorough geophysical survey using a range of sonar and magnetometry-based geophysics techniques [see Box panel]. ‘‘You need to know how far away you need to be from a prospective item of UXO in order to prevent it detonating, so a technical analysis of your precise installation methodology, whether its cable or rock armour, etc. It’s important to 139
SPECIAL FEATURE
Renewable Energy Focus Volume 16, Number 5–6 December 2015
SPECIAL FEATURE
SPECIAL FEATURE
undertake that technical analysis because that will then set an avoidance distance and that will also set your geophysical survey, you need to undertake the minimum survey that’s appropriate.’’ Cooke suggests an example may include increasing resolution to 5 m line spacing, rather than the more typical 30 m for many geophysical applications, which is likely to yield the vast majority of potential threat items in operational areas. With an accurate survey revealing likely threats, where possible installations and aggressive operations should be re-routed or moved to an appropriate location away from suspect items. However, for a number of technical, engineering or regulatory constraints, this is not always possible, desirable or appropriate. As Cooke explains: ‘‘The second point is that inevitably you won’t be able to avoid all these things, and therefore you need to investigate those things that are effectively in the cable’s way or in the foundations. It’s an expensive process, reducing to the minimum number of targets you need to have a look at is an important plank of the strategy.’’ While often the vast majority if not all signals will turn out to be benign items such as chain, anchors or other metallic debris, those which are suggestive of munitions should be investigated further. This typically means an ROV or diver investigating suspicious objects, some of which are potentially buried metres below the surface of the seabed. Welch offers a typical strike rate of around one in 100 items revealing UXO, however, he notes that a recent site produced a strike rate of closer to 10%, suggesting site specifics are everything. Concluding, Cooke sums up the management of UXO as a ‘Goldilocks’ approach to risk mitigation. ‘‘It’s just enough in the right time and space, to manage the risk in accordance with and not only the best practice, but in accordance with the law the legislation and in the jurisdiction in which you operate in.’’ He adds though: ‘‘A lot of money has been burned going too far. No-one can afford the 100% site clearance approach, but EU law requires developers to mitigate risks for projects, and getting it wrong is going to cost you a lot of money.’’ A set of guidelines concerning UXO in the offshore sector are due to be published by the Construction Industry Research and Information Association (CIRIA) as Refocus goes to press.
Developers Tenet were required to spend tens of millions of Euro clearing UXO from the site of the 108 MW Riffgat project in the North Sea off Germany (image courtesy of Enova). 140
Renewable Energy Focus Volume 16, Number 5–6 December 2015
Co-authored by 6 Alpha Associates ‘Assessment and Management of Unexploded Ordnance (UXO) Risk in the Marine Environment’ provides guidance to organisations involved with the planning, design, delivery, operation and maintenance, decommissioning or regulation of projects in the marine environment on UXO risks. Welch, who notes the absence of specific rules concerning UXO in the UK, evidently supports such a move: ‘‘One key improvement that can be made is that developers can be consistent not only in the way that they approach it but also in the information that they receive from various consultants. Only then will they have a degree of trust in the industry so that they adopt a consistent approach and it has got to be moved, and the costs are the costs and that it can be done very quickly. ‘‘A greater level of understanding of the actual risks is required,’’ added Welch.
Future UXO management Any offshore installation requires regular maintenance, including checking for cable movement, possible dumping and so on. However, as a result of wave and tidal forces, as well as human activities such as fishing, UXO can also migrate over time, making their presence an on-going O&M risk as well as risk during the project development phases. Indeed, at the end of project commissioning some objects with known UXO signatures may well remain on-site and un-investigated, should they fall outside of work areas. While predicting the path and migration rates of such objects is an emerging field, observations are clearly key. One potential development concerns advances in both magnetometry arrays and data analysis. Wolfgang Suess, spokesperson for Germanybased sensor company SENSYS Sensorik & Systemtechnologie GmbH explains that the next development stage in sensor systems are likely to see increased automation, with systems that can sweep areas remotely and potentially even exclude numerous objects as benign, leaving only high probability objects for further consideration by human operators. ‘‘Always trying to acquire as much data [as possible], so not only using one probe but a whole series of probes, generating more data than you do today, this is hopefully the trend.’’ Suess also envisages combining various sensor techniques into one single platform so that the results of multiple modes of investigation can be overlaid. Welch also picks up on automation: ‘‘You get to a point with technology where humans can’t go any faster. I think if we’re still working off ships, divers and ROVs, we’re near the end of the technology for the disposal bit, but we’re into systems which can operate up to one kilometre away, thereby further reducing risk etc.’’ Cooke summarises the benefit of a UXO strategy: ‘‘A lot of money is being spent on delay because of the encounter of unexploded ordnance, of course there is a health and safety aspect of this, the other benefit is that you won’t waste money on the inevitable delays that will occur if unexploded ordinance is discovered on your site.’’ Or as Welch says: ‘‘Are you prepared to spend that money for the benefit of having a clear site or are you prepared to shoulder the risk of not having a clear site.’’
Renewable Energy Focus Volume 16, Number 5–6 December 2015
SPECIAL FEATURE
German parachute mine disposal on an offshore wind farm site (image courtesy of Remora).
Side scan sonar can produce detail images of objects on the seabed, such as the Russian submarine seen here; picture courtesy of Swedish Sonar.
The first step in managing UXO risk is to determine the location of any suspect objects. There are a number of complementary approaches. Side Scan Sonar uses ultrasonic sound waves reflected off solid objects to build an accurate high resolution picture of the seabed and any objects which lie upon it. Such a system will pick up objects such as larger munitions on the surface of the sea bed, shipwrecks and other sunken vehicles, for example. Such as system is typically towed behind a boat and can rapidly cover significant areas of the seabed. Objects discovered in this way can be characterised in terms of both size and density. For buried objects, techniques such as magnetometry and electromagnetics are required. Typically used in big arrays with multiple probes and towed by a vessel or an ROV, magnetometry uses a passive sensor to record the Earth’s magnetic field. Objects which have magnetic characteristics, such as iron bomb casings, will influence the Earth’s magnetic field and these anomalies can be plotted to reveal buried objects. Electromagnetics is similar to onshore metal detecting. A pulsed inductive field is projected into the seabed, any conductive objects within this field will create a magnetic field by induced current. Again, this anomaly can be detected and analysed. These electromagnetic geophysical techniques can detect objects buried 2-4 m beneath the seafloor, slightly less than magnetrometry, but explains Suess: ‘‘The advantages you can also catch not only iron or magnetic objects but also aluminium, gold, copper, many different materials and a lot of ammunition was also made of aluminium.’’ Welch also highlights the improving performance of sonar and geotechnical investigative techniques: ‘‘On some of the sonar system, you can get really good resolution – you can almost see what it is – generally speaking we have magnetometry that will enable you to assess it’s got the right characteristics of UXO.’’ He continues: ‘‘You can pick up everything, but then you’ll also be searching for horse shoes in the mud and the time it would take to clear that site would be mammoth, so in terms of the larger items you can get some really nice magnetometry indications and imagery and they’ll say on the basis of a good assessment that could be an item of ordnance of a certain size.’’ ‘‘The picture available to enable sound decision making has never been better and it means a developer can be in charge of his own destiny to a degree, some sites spend a few million getting the surveys done and then actually nothing is found, but then they’ve got a clear site and they can push on and build it, so there is a balance to be had.’’
ABOUT THE AUTHOR David Appleyard is a freelance journalist focused on the energy, engineering and technology sectors.
141
SPECIAL FEATURE
Detecting underwater UXO
www.renewableenergyfocus.com
SPECIAL FEATURE
Avoiding a big bang for your buck David Appleyard Unexploded ordnance presents an on-going challenge for offshore renewable energy project developers and as some have found to their cost, getting it wrong can be very expensive. With new guidelines on UXO management set to be published, best practice means a better understanding of the risks. It may seem unlikely in the politically calm waters of modern European seas, but for those installing and servicing equipment offshore, armed conflict nonetheless represents a very real risk. For beneath the surface hidden dangers lurk in the deep. Not some radioactive rubber-tentacled 1950s fiend, but something far more sinister and dangerous: unexploded ordnance (UXO). Far from any current war zone, UXO is an obvious and unwelcome legacy of historical naval conflict, for example sea mines that have slipped moorings or been otherwise lost – only an estimated 30-70% of the millions of sea mines laid during world wars one and two were ever recovered. But there also are munitions-carrying shipwrecks, military aircraft both crashed and dumping munitions ahead of landing, materiel washed overboard, naval bombardments and so forth. There’s a huge range of UXO too, from 9 mm pistol rounds, through ship-busting mines and torpedoes, incendiaries, chemical weapons and on up to 2000 lb bombs. Another significant source of UXO is the dumping of stockpiles that have reached the end of their service life – it seems explosives to have a best before date. One infamous site is Beaufort’s Dyke between the west coast of the UK and Ireland, which, according to Ramora UK Managing Director David Welch, is the watery grave of more than one million tonnes of World War II ordnance. Even marked dumpsites are often vague in their extent. Simon Cooke, CEO of 6 Alpha Associates, explains: ‘‘Dumping is a significant off-shore activity in Britain, France, Holland, Germany, between and after the wars up until the late 1980s of shelf-life expired munitions. ‘‘There are many mini dump sites around the UK, a lot of vessels were incentivised for speed of dumping, not for accuracy. Not only are those dump sites not accurately logged, but some munitions were short dumped, in the region – but not actually at the dump site. They might have also drifted on the sea bed.’’
Imparting enough kinetic energy to detonate perhaps a 500 kg bomb or torpedo filled with a high explosive such as Amatol or Torpex during the installation of an offshore wind or marine energy site is thus a clear risk – the consequences potentially catastrophic. Even if no injuries result, a trenching tool alone can cost of the order of £5 million (US$7.7 million).
UXO: A major operational risk With the potential for significant injury or death from UXO detonation, European project developers are bound by health and safety legislation to effectively manage and reduce this risk.
Sea mine: a significant source of UXO is the dumping of stockpiles that have reached the end of their service life or lost sea mines, but their location is often uncertain (image courtesy of 6 Alpha Associates). 1755-0084/ß 2015 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ref.2015.10.018
138
Three 50 kg wartime bombs were discovered at Gwynt y Moˆr last year after storms disturbed the seabed (image courtesy of Siemens).
Company directors in the UK, who can even be jailed, should a preventable death or serious injury occur. There is also the potential for fines and reputational risk should workers be exposed to such obvious danger. Discovering UXO during on-site work typically results in costly delays as local site operations are halted whilst the items are made safe. With the hire of a single big lift barge running to many tens of thousands of dollars daily, expenses can soon rack up when as many as 60 vessels of various types may be working at peak load on a typical offshore wind project. Indeed, early in 2014 following the discovery of three WWII bombs by a Remotely Operated Vehicle (ROV), RWE Innogy UK was forced to set up a 250 m exclusion zone during the developˆ r project 8 miles (12 km) off the ment of its s2 billion Gwynt y Mo coast in Liverpool Bay. A series of severe storms had disturbed the seabed, revealing the 50 kg bombs, which were discovered during a survey and were eventually destroyed by controlled explosion – the usual disposal method for UXO. Although RWE said work continued elsewhere on the 160 turbine site, explosives have certainly presented significant problems at a number of offshore wind farm projects. Perhaps most notorious is the 108 MW Riffgat project in the North Sea off Germany. This project suffered more than 6 months of delays when the cable route had to be cleared of significant volumes of munitions. Constrained by German legislation to a very particular route, developers Tenet were reportedly required to spend at least £50 million (US$77 million) to sweep seabed of metallic objects.
Managing UXO risk Although even a decade ago offshore encounters with UXO were largely limited to the oil and gas industry, as the development of offshore wind sites has accelerated, so has the likelihood of exposure. In the USA, the Army remains responsible for disposal of ordnance but another shift – witnessed in the UK waters for example around a decade or more ago – has been the withdrawal of military ordnance disposal services from the commercial environment.
SPECIAL FEATURE
With high profile examples making developers more aware of the risks, they have been on a steep learning curve, as Welch explains: ‘‘We went from a situation where people weren’t expecting to find anything and didn’t know what to do when they did and had very poor survey data to base it on, to a situation now where everyone is concerned about ordnance data before they start spending too much money. ‘‘People have recognised that there is a risk and if measured properly the processes and technologies that are now available to developers will locate 99% of the items that maybe in their [development] area. Disposal mechanisms are well proven and items can easily be relocated or disposed of in a very short time scale, therefore the impact on development is minimal from a disposal perspective.’’ Echoing this view, Cooke says: ‘‘In our experience, those developers that have been caught out by this, they’re very much attuned to this now.’’ But he also adds that as much as 20% of offshore wind developers have not yet fully explored UXO risks: ‘‘Generally most developers are good at developing technical risk, they’ve just not been exposed to this unexploded ordinance risk, therefore it’s not been dealt with, they just haven’t thought about it.’’ Cooke breaks down 6 Alpha’s staged approach to UXO management, which is based on a probability and consequence approach summed up as an ALARP (As Least As Reasonably Practicable) approach to risk. ‘‘There’s a phased approach that developers need to take and it’s very much about gaining intelligence, an understanding what’s on their sites and the risk. It’s procuring good quality throughout the risk assessment, which focuses on that element that you’re about to undertake: installation, operations, whether that’s a foundation for wind turbine generators, infrared cabling, or export cabling. It’s focusing on that site and working on what the prospective sources of unexploded ordinance threat might be.’’ Starting with an initial desk study assessment of potential risks, for example known military activities in the area, a key part of the approach is a thorough assessment of developers’ plans and modes of operation. Says Cooke: ‘‘One of the most important things to ask a developer is: ‘What are you going to be doing and where?’ If it’s in the region there might be some UXO you need to look at the nature of the activity and the sort of thing that could make the ordinance explode, it’s usually some sort of aggressive interaction. Things like piling, cable plough activity, driving mono piles or anchoring.’’ He continues: ‘‘It depends on the nature of the encounter and how aggressive it is, which is one half, the other half is the consequence. Whilst the probability of detonation is slim, it’s a high consequence event. Its consequence drives the risk, rather than its probability.’’ Investigation of those areas where there is a potential risk of a significant UXO encounter follows the desk analysis – most likely through a thorough geophysical survey using a range of sonar and magnetometry-based geophysics techniques [see Box panel]. ‘‘You need to know how far away you need to be from a prospective item of UXO in order to prevent it detonating, so a technical analysis of your precise installation methodology, whether its cable or rock armour, etc. It’s important to 139
SPECIAL FEATURE
Renewable Energy Focus Volume 16, Number 5–6 December 2015
SPECIAL FEATURE
SPECIAL FEATURE
undertake that technical analysis because that will then set an avoidance distance and that will also set your geophysical survey, you need to undertake the minimum survey that’s appropriate.’’ Cooke suggests an example may include increasing resolution to 5 m line spacing, rather than the more typical 30 m for many geophysical applications, which is likely to yield the vast majority of potential threat items in operational areas. With an accurate survey revealing likely threats, where possible installations and aggressive operations should be re-routed or moved to an appropriate location away from suspect items. However, for a number of technical, engineering or regulatory constraints, this is not always possible, desirable or appropriate. As Cooke explains: ‘‘The second point is that inevitably you won’t be able to avoid all these things, and therefore you need to investigate those things that are effectively in the cable’s way or in the foundations. It’s an expensive process, reducing to the minimum number of targets you need to have a look at is an important plank of the strategy.’’ While often the vast majority if not all signals will turn out to be benign items such as chain, anchors or other metallic debris, those which are suggestive of munitions should be investigated further. This typically means an ROV or diver investigating suspicious objects, some of which are potentially buried metres below the surface of the seabed. Welch offers a typical strike rate of around one in 100 items revealing UXO, however, he notes that a recent site produced a strike rate of closer to 10%, suggesting site specifics are everything. Concluding, Cooke sums up the management of UXO as a ‘Goldilocks’ approach to risk mitigation. ‘‘It’s just enough in the right time and space, to manage the risk in accordance with and not only the best practice, but in accordance with the law the legislation and in the jurisdiction in which you operate in.’’ He adds though: ‘‘A lot of money has been burned going too far. No-one can afford the 100% site clearance approach, but EU law requires developers to mitigate risks for projects, and getting it wrong is going to cost you a lot of money.’’ A set of guidelines concerning UXO in the offshore sector are due to be published by the Construction Industry Research and Information Association (CIRIA) as Refocus goes to press.
Developers Tenet were required to spend tens of millions of Euro clearing UXO from the site of the 108 MW Riffgat project in the North Sea off Germany (image courtesy of Enova). 140
Renewable Energy Focus Volume 16, Number 5–6 December 2015
Co-authored by 6 Alpha Associates ‘Assessment and Management of Unexploded Ordnance (UXO) Risk in the Marine Environment’ provides guidance to organisations involved with the planning, design, delivery, operation and maintenance, decommissioning or regulation of projects in the marine environment on UXO risks. Welch, who notes the absence of specific rules concerning UXO in the UK, evidently supports such a move: ‘‘One key improvement that can be made is that developers can be consistent not only in the way that they approach it but also in the information that they receive from various consultants. Only then will they have a degree of trust in the industry so that they adopt a consistent approach and it has got to be moved, and the costs are the costs and that it can be done very quickly. ‘‘A greater level of understanding of the actual risks is required,’’ added Welch.
Future UXO management Any offshore installation requires regular maintenance, including checking for cable movement, possible dumping and so on. However, as a result of wave and tidal forces, as well as human activities such as fishing, UXO can also migrate over time, making their presence an on-going O&M risk as well as risk during the project development phases. Indeed, at the end of project commissioning some objects with known UXO signatures may well remain on-site and un-investigated, should they fall outside of work areas. While predicting the path and migration rates of such objects is an emerging field, observations are clearly key. One potential development concerns advances in both magnetometry arrays and data analysis. Wolfgang Suess, spokesperson for Germanybased sensor company SENSYS Sensorik & Systemtechnologie GmbH explains that the next development stage in sensor systems are likely to see increased automation, with systems that can sweep areas remotely and potentially even exclude numerous objects as benign, leaving only high probability objects for further consideration by human operators. ‘‘Always trying to acquire as much data [as possible], so not only using one probe but a whole series of probes, generating more data than you do today, this is hopefully the trend.’’ Suess also envisages combining various sensor techniques into one single platform so that the results of multiple modes of investigation can be overlaid. Welch also picks up on automation: ‘‘You get to a point with technology where humans can’t go any faster. I think if we’re still working off ships, divers and ROVs, we’re near the end of the technology for the disposal bit, but we’re into systems which can operate up to one kilometre away, thereby further reducing risk etc.’’ Cooke summarises the benefit of a UXO strategy: ‘‘A lot of money is being spent on delay because of the encounter of unexploded ordnance, of course there is a health and safety aspect of this, the other benefit is that you won’t waste money on the inevitable delays that will occur if unexploded ordinance is discovered on your site.’’ Or as Welch says: ‘‘Are you prepared to spend that money for the benefit of having a clear site or are you prepared to shoulder the risk of not having a clear site.’’
Renewable Energy Focus Volume 16, Number 5–6 December 2015
SPECIAL FEATURE
German parachute mine disposal on an offshore wind farm site (image courtesy of Remora).
Side scan sonar can produce detail images of objects on the seabed, such as the Russian submarine seen here; picture courtesy of Swedish Sonar.
The first step in managing UXO risk is to determine the location of any suspect objects. There are a number of complementary approaches. Side Scan Sonar uses ultrasonic sound waves reflected off solid objects to build an accurate high resolution picture of the seabed and any objects which lie upon it. Such a system will pick up objects such as larger munitions on the surface of the sea bed, shipwrecks and other sunken vehicles, for example. Such as system is typically towed behind a boat and can rapidly cover significant areas of the seabed. Objects discovered in this way can be characterised in terms of both size and density. For buried objects, techniques such as magnetometry and electromagnetics are required. Typically used in big arrays with multiple probes and towed by a vessel or an ROV, magnetometry uses a passive sensor to record the Earth’s magnetic field. Objects which have magnetic characteristics, such as iron bomb casings, will influence the Earth’s magnetic field and these anomalies can be plotted to reveal buried objects. Electromagnetics is similar to onshore metal detecting. A pulsed inductive field is projected into the seabed, any conductive objects within this field will create a magnetic field by induced current. Again, this anomaly can be detected and analysed. These electromagnetic geophysical techniques can detect objects buried 2-4 m beneath the seafloor, slightly less than magnetrometry, but explains Suess: ‘‘The advantages you can also catch not only iron or magnetic objects but also aluminium, gold, copper, many different materials and a lot of ammunition was also made of aluminium.’’ Welch also highlights the improving performance of sonar and geotechnical investigative techniques: ‘‘On some of the sonar system, you can get really good resolution – you can almost see what it is – generally speaking we have magnetometry that will enable you to assess it’s got the right characteristics of UXO.’’ He continues: ‘‘You can pick up everything, but then you’ll also be searching for horse shoes in the mud and the time it would take to clear that site would be mammoth, so in terms of the larger items you can get some really nice magnetometry indications and imagery and they’ll say on the basis of a good assessment that could be an item of ordnance of a certain size.’’ ‘‘The picture available to enable sound decision making has never been better and it means a developer can be in charge of his own destiny to a degree, some sites spend a few million getting the surveys done and then actually nothing is found, but then they’ve got a clear site and they can push on and build it, so there is a balance to be had.’’
ABOUT THE AUTHOR David Appleyard is a freelance journalist focused on the energy, engineering and technology sectors.
141
SPECIAL FEATURE
Detecting underwater UXO