Dredging and nature conservation: one problem – many issues

Dredging is an inevitable and necessary part of port management and is essential for free flowing trade between nations; and yet it causes considerable controversy in many places. In Europe it is one of the more challenging aspects of port interactions with nature conservation. There must be very few major ports in northern Europe where there is no tension between dredging and nature conservation legislation. Examples include Antwerp, Hamburg and Southampton.

The degree to which dredged channels have been included or excluded from sites designated under the EU Habitats Directive has caused great concern in the UK. Differing interpretations have been given to the application of Article 6(3) of the Habitats Directive to maintenance dredging, and the variation in national approaches has been used to illustrate the perception of an uneven playing field. There can be no doubt that there are differences in approach, although recent rulings by the European Commission have sought to harmonise the approach to site designations. Meanwhile case-law has been established that helps to clarify concerns about interpretation of Article 6(3). Progress has been made, and solutions to some of the issues have been found, but circumstances change and new legislation emerges to complicate an already challenging environment. This is what has happened in the case of dredging as ports in Europe now need to satisfy two separate pieces of critical legislation: the Habitats Directive and the Water Framework Directive (WFD), together with the Priority Substances Directive which follows from the WFD. This establishes a challenging legislative framework for port managers and potentially an even more challenging environment for regulators. There is considerable scope for confusion, misinterpretation and misapplication of precedents. This article looks at some of the issues as they pertain to northern Europe and highlights some of the conundrums that decision-makers and their advisers will have to resolve.

No two ports are the same

It is easy to think that issues in one port will be the same as issues at another. For example, dredging is constantly ongoing in northern European ports in Germany, the Netherlands, Belgium and the UK. There are places where sediment load within the water column is very high, and there is ample scope for sediment transport as bed load. But, these ports share common ground that is not universally experienced. In places such as Milford Haven in south-west Wales and Truro in south-west England, dredging is likely to be far more intermittent as the water column is largely free of sediment and deposition rates are much slower. But, the rocks of the southwest contain high levels of heavy metals, mining spoil from a previous era continues to disperse and so in some localised places sediment can be naturally contaminated. Conversely, estuaries such as the Rhine continue to be fed with contaminants of anthropogenic origin far inland, whilst others suffer from re-mobilisation of contaminated sediment within the tidally influenced sections.

 These differences provide an indication of range and variation in a very small part of Europe. For example, the Baltic or Mediterranean have virtually no tide, whereas the Severn has a tide of 12-14 metres! Sediment sources in northern Europe are mainly from marine sources whilst in southern Europe they mainly arise from riverine sources. Water quality such as the impact of diffuse pollution or point source pollution raise further problems. Not all of the complexities occur in all places, but they can lead to misconceptions that some ports are being treated more leniently than others when in fact the issues between them are very different.

This variation means that solutions found in one port may not be applicable at another, and vice-versa. For example, on the Humber Estuary, the ports of Hull, Grimsby and Immingham rely on a process of dredge disposal within the estuary at locations within close proximity of the dredged channels and berths. This process of circulatory sediment movement is actually beneficial to the port because the estuary itself needs the sediment to maintain favourable condition for its Special Protection Area and Special Area of Conservation. That is not to say that dredging is required for wildlife management, but the technique used ameliorates its detrimental effects.

Sediment cycling would not be appropriate for a port in a clear-water estuary such as Milford Haven or Falmouth, however. In these estuaries the wildlife interest reflects the low sediment load and high water clarity. Creation of dredge plumes and sediment dispersal in these clear water estuaries would be highly detrimental to the wildlife interest that is vulnerable to smothering in particular.

These two examples are just the start of the problem. Add to the mix conflicting demands from geomorphologically-based conservation management and from water and sediment quality based conservation and the problem can become even more complex.

 For example, in many places in England, there is a growing awareness that sea level rise is impacting on inter-tidal habitats, causing erosion through coastal squeeze (the loss of accommodation space that is needed to absorb wave energy), and the corresponding need to maintain or even increase sediment loads within the water column if saltmarshes and mudflats are to be maintained. Yet, increasing sediment loads by techniques such as over-spilling or water column placement may be regarded by water quality and fisheries specialists as undesirable. What is good from a geomorphological perspective may not be helpful to the fishery manager who is concerned about impacts on salmonids (salmon and sea trout).

Multiple legislative frameworks

 The issues described above are just the tip of an increasingly complex problem. For example, the Priority Substances Directive sets quality standards for contaminant loads within sediments. It could potentially lead to a clash between the need to retain sediment within a system for sound geomorphological reasons and the legislative requirement for contaminated sediment to be removed to landfill. Each set of arguments is perfectly valid, but at the moment there is great uncertainty that is likely to provide work for lawyers and consultants but may not fully resolve environmental concerns.

 Decisions may seem to be perverse and some solutions even more so. For example, a port may maintain its navigation channels by dredging sand. That sand might be a viable commercial commodity that would offset dredging costs, but it has been interpreted by one regulator as waste material that requires disposal licenses that preclude use of resultant landfill for specific building projects.

 There is an alternative argument that dredged sand should be retained within the system. If the dredge site were to be proposed as a source of aggregate under aggregate licensing arrangements it probably would not be consented, at least in the UK. This is because there is a need to ensure that aggregate dredging does not affect coastal processes in such a way that the integrity of coastal defences is compromised, and so it is confined to much deeper water. Aggregate dredging is currently viewed by the public as potentially detrimental to coastal defences (for good historic reasons) but the same issue is unlikely to be raised for navigation dredging. Yet, channel deepening can raise tidal propagation considerably as experienced at Hamburg, and loss of sediment can lead to failings in wave energy attenuation as first exemplified by aggregate dredging off Hall Sands in Devon (it led to the village being washed away in a storm in 1917).

This brings us to the requirements of the various Directives, all laudable in their own right and important tools to safeguard the natural environment. Where complex local situations lead to conflicting impacts on different attributes, dredging must inevitably become a matter of far greater significance to regulators and their advisors, whilst delays and additional costs must be recognised as a likely impact on the ports industry and on national economies.

 Some examples of variable practice

Dredging is a practice whose implications are poorly understood by all concerned. For example the nature conservation adviser frequently has little concept of what a dredger does or how it does it. This is exemplified by dredging being restricted to particular time windows to avoid possible noise disturbance to shorebirds. Presumably this particular case officer assumed that a bucket dredger would be used. Even if a bucket dredger were to be used, the distances from the shore would greatly reduce the noise and studies of pile-driving in the Humber Estuary for South Humber Bank Power Station in the mid-1990s showed how rapidly shorebirds habituate to ongoing noise.

This contrasts with the operator who regards the removal of sediment from an eroding system as inconsequential to wildlife and flood defense management and not the business of a wildlife advisor. Or, the Harbour Master who would willingly agree to land sediment for soil conditioning but blames environmentalists for stopping him from entering into such an agreement. In this case there is a basic failure to understand that loss of sediment can be a critical issue both for wildlife and for coastal defences.

 On a more positive note, there are estuaries such as the Stour and Orwell (Harwich & Felixstowe) where the Harbour Authority has taken a leading role in developing sediment by-passing schemes to counter accelerated erosion arising from channel deepening. In this, Harwich Haven Authority are exemplars of good practice.

 Disposal of dredged material at sea is often looked upon as getting rid of a waste material. In the North Sea, this is far from the case. Disposal at sea where this sediment adds to the existing background levels is far better than landing sediment that would otherwise have contributed to the overall resource of marine sediment. This is because sea-borne sediment is the fundamental building block for coastal evolution in the southern North Sea from Germany to the UK.

Similarly, avoiding dredge plumes in a sediment laden estuary may be an irrelevance but raised as an issue. The value of increasing over-spilling to help sediment re-mobilisation may be therefore be missed as a possible management tool. Meanwhile, the use of over-spilling to assist geomorphological management may be promoted by one advisory body on nature conservation grounds and challenged by another for fisheries management reasons.

In the UK agitation dredging has not been controlled in the past, and there have been instances of plough dredging used in some marinas to disperse highly contaminated sediment. This may appear to be a good idea to the commercial interests of that marina, but its impact may have more far-reaching consequences – perhaps increasing contaminant levels within otherwise clean sediments in maintained channels and greatly increasing costs for the port concerned. In this case, synergy may be found between the port engineer and the nature conservationist for different but equally valid reasons.

Unfortunately, oversights or a lack of understanding of regulatory processes can also raise tensions and mistrust. For example it is not uncommon for ports to submit applications for renewal of licenses for maintenance dredging at the last moment, placing licensing authorities in an impossible position. If the dredge does not go ahead the port cannot operate, and this quickly becomes a high profile lever to force a decision. It usually leads to a panic and other cases are dropped to make sure a calamity is avoided. This in turn delays other ports who have submitted their applications in good time. These incidents can lead to suspicion and mistrust amongst NGOs and wildlife advisors, and on the odd occasion they might be right; but more frequently it is just a genuine mistake. Ports, meanwhile, often do not realise that regulators and their advisors do take calculated risks and make use of the legislative regime to accommodate risk. For example, where maintenance dredging licenses are of short duration, the likely geomorphological implications are equally short-lived as it is possible to respond quickly to issues when they are detected and develop mitigation strategies. If the legislation is adjusted to provide much longer licenses, scope for pragmatism and risk management is greatly reduced, especially where the precautionary principle needs to be applied (as is the case with the Habitats Directive).

 At the same time, there will be the NGO or wildlife advisor who fails to realise that ports have legal obligations to maintain declared depths and of course that they cannot operate on an intermittent basis according to demands for narrow maintenance windows. The frustration this causes is immense and is not the basis for problem solving.

 All of these examples, which are based on real cases, illustrate the factors that generate tension between ports, regulators and management of the natural environment. Unfortunately, even if 99% of the ports behave, the 1% of miscreants will be cited as the justification for more rigorous legislation, whilst the occasional unreasonable or ill thought out requirement from a regulator or wildlife group will be seen as indicative of deliberate bias against ports. Neither is true but they don’t help matters when they emerge.

 An example of problem solving

In England the Habitats Directive and Environmental Impact Assessment Directive led to a major problem for ports, regulators and advisors such as English Nature (now Natural England). The problem was that in some places there were multiple requirements for consent for maintenance dredging within a single estuary. Applications arrived in a random way and each had to be accompanied by an environmental statement. Most involved consents that lasted for one year or a maximum of three years. Meanwhile, multiple applications needed to be evaluated “in combination” with other plans and projects, especially other dredging proposals that quite possibly had a bearing upon each other. So, for example two applications of vastly different scales might be under consideration at the same time; say one for half a million cubic metres and the other for 5,000 cubic metres. One had the potential for major impact on sediment budgets, whilst the other was unlikely to be of particular consequence, yet the combined effects of these and other dredges over a ten-year time-frame might reasonably be concluded to have a potentially profound impact on inter-tidal habitats. The result of such situations was frequently impasse, demands for more studies, delays, frustration and administrative overload. Pragmatic regulation was not possible and the regulatory system was being drawn into disrepute. A solution was sought by all involved. The ports disputed that maintenance dredging should be assessed under Article 6(3) of the Habitats Directive. Case-officers from the Department for Transport (DfT), the Department for Environment, Food and Rural Affairs (Defra) and English Nature were unable to service all of the demands to turn around environmental statements in the statutory timescales. The solution involved compromises on all sides, but this critical situation spawned the Maintenance Dredging Protocol (http://www.defra.gov.uk/wildlife-pets/ wildlife/protect/bird-habitat/mdpe.htm). The Protocol established a framework for recording and describing existing dredging commitments and the level of current understanding of its implications, together with an evaluation process that allowed regulators to take an overview of the issues and to put individual dredges into context. This was the “Baseline Document” that forms the foundation of the process. It is a product that requires input from both the port and from the wildlife adviser (English Nature – now Natural England). The Maintenance Dredging Protocol established a streamlined system for regulation without exceptionally onerous evaluation processes for each dredge (evaluation of sediment quality remains mandatory). It ensures that geomorphological issues relating to sediment budgets are evaluated and reviewed in a manner that was acceptable to all of the signatories. The system is voluntary but there is a strong incentive for ports to work together to develop a baseline document for their estuary: if they don’t, an environmental statement will have to accompany each dredging application.  

A constantly evolving environment

When the ports-regulators working group first discussed the Maintenance Dredging Protocol, the most pressing issue was sediment management. Issues of water quality and fisheries management were of limited concern as casework noted by the regulators and English Nature did not refer to these issues. Perhaps this too was due to narrow spheres of expertise? Since then, the use of specific sediment management techniques, such as water column placement and over-spilling have encountered separate problems. A geomorphological solution now emerges as a possible water quality and fisheries problem. Furthermore, application of the Water Framework Directive has meant that impacts on benthic organisms have become a more prominent issue as they are contributory attributes to Good Ecological Potential. The one-size fits all solution is again seen to require modification.

This analysis illustrates just a few of the complexities of finding a path through regulatory frameworks used to manage maintenance dredging. It also illustrates the tensions between different wildlife attributes and the factors that need to be taken into account to meet the objectives of various European Directives. Furthermore, it highlights potential tensions between different regulators and the need to establish common ground and prioritisation of impacts and solutions. In addition, it shows how relationships can be forged and strained. Yet, let there be no doubt, that maintenance dredging does have wider environmental implications that are a matter of concern and this is why it is regulated.

The Maintenance Dredging Protocol remains a valid tool for managing some aspects of maintenance dredging, but there are clearly arguments for a more comprehensive approach. It might be applied elsewhere in Europe, but there is a need to adapt to local conditions and not to try to apply all of the principles in the same way across Europe. For example, the sediment management issues that are so fundamental to maintaining inter-tidal habitats in North West Europe almost certainly differ from river-borne sediment budgets elsewhere. Dredging management plans are an essential component of modern port governance but their scope and objectives may vary according to local conditions.

Perhaps the most important lesson emerging from this brief account involves the technical competency of decision makers and wildlife advisers. The conventional model of the decision-maker and advisor role in England has been to use what might euphemistically be called “broad and shallow” technical competency. Advisors such as case officers in Natural England often cover a wide range of terrestrial and coastal issues and have limited depth and breadth of experience of dredging or physical processes. Their qualifications are often predominantly terrestrial ecology and conservation management which requires a very different skill base. Dredging will be one of many issues they cover, even though it demands expertise ranging from the fundamentals of estuarine geomorphology through to water quality and fisheries matters as well as an understanding of dredging techniques. Perhaps therefore it is time to have a bit of sympathy for those case officers who don’t always have access to the right technical backup and to ask more searching questions about the degree of backroom support they get. This is an issue that combines science, policy and regulation, and solutions are rarely achieved by political fixes. One of many issues will almost certainly emerge in due course: foreshore erosion, sub-tidal smothering, water quality and disruption of fish movement are all possible, but they rarely occur together.

At the moment these very complex issues are poorly understood by decision-makers and regulators across Europe and conflicting approaches that are appropriate to local conditions run the risk of being endorsed or rejected without full understanding of the local circumstances. Perhaps an inventory of port-estuaries, their physical parameters and water quality issues could be combined to assist decision-makers and ports to understand range and variation so that local solutions are better fitted to the prevailing conditions?