SUSTAINABLE SEDIMENT MANAGEMENT IN THE UK

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1 Presentation for Tidal River Elbe Conference 6-7 November 2006 in Hamburg: Integration von Verkehrlicher Nutzung und Umweltzielen an der Tideelbe. Hamburg Port Authority and Wasser-und Schiff-fahrtsdirection Nord. SUSTAINABLE SEDIMENT MANAGEMENT IN THE UK Roger K.A. Morris Natural England, Northminster House Peterborough PE1 1UA Summary Sediment management is an underlying principal that governs the way in which the coastline of the UK, and in particular England, is managed. Muds and sands are the foundations for sand dunes, saltmarshes and mudflats that support a vast array of important wildlife, and many wildlife designations are concentrated upon soft-sediment systems. As a consequence much has been done to develop mechanisms for sustainable sediment management and our focus centres upon ways in which we can keep sediment within the system as far as possible. This paper briefly describes four examples of positive sediment management and briefly examines procedures developed to ensure sediment management is achieved sustainably in relation to maintenance dredging. Introduction The coastline of the United Kingdom is hugely variable in its form and in the nature of the sediments that are encountered. These differences reflect the changing age of the geological strata across the country and in the degree to which the drift or superficial geology overlies older strata. Thus, the age and strength of rocks increase as one travels to the west and towards the north-west. Scotland, Cumbria, Wales and south-west England are ancient and very hard hence they support some of the most dramatic coastlines with high cliffs and seas with low sediment loads. These coastlines generally have sandy or coarser sediment beaches and reflect a generally more active wave climate influenced by their proximity to the Atlantic Ocean. There are exceptions in more sheltered locations such as the Dee and the Mersey, but many are the coastlines where sand-dunes are prevalent on lower-lying stretches of coast. The further east one travels up the English Channels, the concentration of suspended sediment generally increases. Much of this sediment arises from eroding soft cliffs of clays and sands, including Jurassic and Cretaceous strata such as the lower Greensand, the Lias and the Gault Clay. More recent deposits from the Eocene and Pleistocene outcrop in various places and are important sources of silts, sands and clays. Once into the North Sea, the geology is dominated by recent strata, especially clays, sands and boulder clays which are readily eroded and contribute significantly to the sediment load in eastern English estuaries (most of the sediment entering UK estuaries arises from marine sources rather than from fluvial sources). Today, the estuaries of southern and eastern England are the focus of much attention because they are low-lying and highly vulnerable to the twin impacts of sea level rise and isostatic adjustment (south-east England is sinking by about 1mm year -1 as western Scotland rises now that it is no longer underneath the ice cap of the last glaciation). These twin impacts are the cause of much concern because the coastline is showing signs of responding in ways that are worrying both for nature conservation and for flood risk management.

2 Sediment management is the key to resolving many of the problems we are experiencing on the English coast, whilst it is far less of a problem in Scotland and is generally less of an issue in many parts of Wales. As a consequence I will concentrate the remainder of my presentation on the issues that pertain to eastern England and will only briefly skim those affecting western and northern areas. Where is the greatest port activity in the UK? UK ports have generally evolved as a response to local needs and as a consequence there are a great many ports in the UK (650 according to the Department for Transport 1 ). Many are extremely small, but even so there are 35 ports handling over 2 million tonnes pa. The biggest include the ports of London, Grimsby and Immingham, Tees and Hartlepool, Felixstowe and Southampton. For all of these ports, and many more, dredging is a significant activity and a major cost to the port. In addition, channel deepening has emerged as an important challenge and we have seen proposals for deepening at various ports (Harwich & Felixstowe, Poole Harbour, Southampton Water, London Gateway and Tees & Hartlepool). Dredging has a number of impacts, including changes to tidal propagation, draw-down of inter-tidal sediments and interception of marine derived sediments such that they do not reach the mudflats and saltmarshes that rely on them to maintain their position in the tidal frame. Where dredging occurs in an already eroding environment such as that of the Stour and Orwell Estuaries (Harwich and Felixstowe) existing problems can be exacerbated. There is therefore a close relationship between determination of dredging consents and management of the coast for wildlife and for people. Sediment and coastal management in the UK sediment cells Sediment management takes a variety of forms. We have recognised that it needs to be undertaken in a holistic manner and that on the open coast the way in which we manage sediment at one location can profoundly affect the coast elsewhere. We have therefore set up a process of shoreline management planning 2 and the development of management proposals that should make sure that the law of unintended consequences is avoided as far as possible 3. These plans are based on the concept of sediment cells and the need to consider the ways in which sediment moves as an underpinning component of the management. The first generation of shoreline management plans had many problems and there were many places where it proved difficult to agree appropriate actions. These plans are now undergoing the first 5- year revision and new guidance and greater understanding of what is sought should yield better solutions. The Shoreline Management Planning approach has also been adapted to dealing with estuaries where a co-ordinated approach is also required. This has important implications for sediment management because it is possible to plan in advance how we might wish estuaries to evolve and to look in detail at the inter-action between sediment management and mudflat and saltmarsh evolution. This is best illustrated on the Humber Estuary where the Humber Estuary Shoreline Management Plan has dovetailed with an understanding of dredging activity and its significance in relation to the sediment budget of the estuary. 1 DETR Focus on Ports. The Stationary Office, London. 86pp. 2 Defra, Shoreline Management Plans: A guide for coastal defence authorities. Department for Environment, Food & Rural Affairs, London. 71pp 3 This is the situation where one action has an equal and opposite reaction, but that reaction has not been expected because no thought has been given to what might happen.

3 Nature Conservation designations A very considerable part of the UK coastline is designated for its wildlife interest, as is illustrated by the map of Natura 2000 sites in England. These sites coincide with nearly all of the major estuaries and consequently with the majority of the major ports (Table 1). As a consequence of the Natura 2000 designations accorded to the majority of estuaries where ports are located, attention has closely focussed upon the need to manage sediment and to consider ways in which ports might contribute to sustainable management. There are two sets of circumstances where sediment management has formed a significant component of sustainable coastal management. Firstly, where capital projects lead to detrimental morphological changes there has been a need to consider ways in which damaging impacts can be offset, mitigated or compensated. Secondly, maintenance dredging is usually an activity that requires particular consents and as such it is judged to be a plan or project under Article 6(3) of the Habitats Directive. As a consequence of investigations into impacts of port developments, a variety of novel solutions for sediment management have been developed. Table 1 Natura 2000 sites in England with significant associated port infrastructure SAC/SPA Thames Estuary & Marshes SPA Medway Estaury SPA Stour & Orwell Estuaries SPA Humber Estuary SPA and psac Teesmouth and Cleveland Coast SPA Morecambe Bay SAC & SPA Mersey Estuary SPA Severn Estuary SPA and psac Plymouth Sound & Estuaries SAC Solent Maritime SAC Portsmouth Harbour SPA Port Port of London Port of Sheerness Thamesport Felixstowe Harwich Ipswich Grimsby & Immingham Hull Goole Tees & Hartlepool Barrow Heysham Fleetwood Liverpool Garston Bristol Newport Plymouth RN Devonport Southampton Portsmouth RN Portsmouth Case study 1: Harwich Haven Capital Dredge (1998) When proposals for capital dredging at Harwich Haven were evaluated, it was concluded that without mitigation there would be adverse affects on the integrity of the Natura 2000 interest through accelerated sediment loss. As a consequence, it was agreed that the port would undertake a programme of sediment feeding that effectively made it possible for sediment to by-pass the port and travel upstream to deposit on mudflats. This process was achieved by a variety of measures including rainbowing of dredged material onto mudlflats, and placing sediment in the water column at suitable locations to allow sediment to move up onto the mudflats. Levels of sediment feeding have increased over time and today some 500,000 m 3 year -1 are placed in this way.

4 At the time, this was a totally novel approach and we were not sure that it would work. As a precaution, it was therefore necessary to create 16.5 ha of new habitat as well (partly to offset oneoff losses and partly to provide some assurance that ongoing losses were accommodated whilst the sediment feeding programme was developed and monitored). Today, we are reasonably assured that current levels of sediment feeding are working and the predicted increase in erosion has been arrested. Case study 2: Felixstowe Trinity III Modelling of this 270 metre extension of the port at Felixstowe indicated that there would be increased wave activity on the opposite bank and a serious risk that the flood defences would be breached. To provide time for a strategy to be developed to manage these flood banks (ideally they need to be realigned landward) a variety of temporary measures was put in place. Actions included the creation of clay bunds behind which dredged material was placed. This sediment was expected to consolidate to form new mudflats and even saltmarshes, but it was also expected to erode over a period of 20 years. The sediment placement has been very successful and although it is eroding this is part of the plan as the eroded material contributes to the sediment load in the estuary. Importantly, however, this approach was developed specifically to address the flood risk management issues and not those of nature conservation. The approach was made possible because the foreshore involved had already eroded down to consolidated clays and was therefore of very limited interest to wildlife. Case Study 3 Wallasea Island Managed Realignment In the 1990 s the UK Government allowed two port developments to progress without compensatory measures (at Fagbury Flatts and Lappel Bank). Faced with infraction proceedings, Government sought a site to create 120ha of compensatory habitat comprising a mixture of saltmarsh and mudflat. Creation of higher level land for saltmarsh was not possible without importation of sediment and as a consequence a low bund was created, behind which some 500,000 m 3 of sediment dredged from Harwich Haven was placed. This sediment was allowed to consolidate before the walls were breached and now forms a first line of defence in front of the new sea wall. Already, it is developing saltmarsh vegetation and is expected to develop fully into saltmarsh in about 5 years. The Maintenance Dredging Protocol Maintenance dredging in the UK often requires a range of consents and as such it has been concluded that the consents must be treated as plans and projects under Article 6(3). Our ports have argued that the UK is out of step with Europe because elsewhere in Europe maintenance dredging is treated as an ongoing operation. Everybody involved with maintenance dredging agrees that there is a need for a streamlined process, because as it stands the yearly consents have become very onerous and run the risk of putting some smaller ports out of business because of the cost of environmental submissions. A working group comprising the ports, Defra 4, DfT 5 and Natural England 6 have developed a protocol for streamlining maintenance dredging consents. This protocol involves: 4 Department for Environment, Food and Rural Affairs 5 Department for Transport 6 The new body that includes the functions of English Nature

5 Preparation of a baseline document that describes what is currently known about morphological evolution of the affected estuary. Details of the past ten years dredging activity are described and it is made clear where dredging occurs and who does it. The implications of dredging in relation to management of the SAC/SPA are evaluated in relation to current condition monitoring and any possible links between dredging and the condition assessment are highlighted. Where the site is currently in favourable condition and the implications of maintenance dredging are believed not to be having an adverse affect on site integrity, a judgement is made that, provided the dredging programme broadly conforms to the parameters of the past ten years, there will be no adverse affect on site integrity. The protocol document must be updated by any developer whose activity changes the way in which the estuary functions, or whose activity adds a further load on the dredging regime. Their proposals will be evaluated, taking account of the existing dredging regime and it is for them to ensure through the consents process that their project meets the costs of any changes. Through this approach, new developers are not allowed to disadvantage existing users. The maintenance dredging baseline document will be linked to condition reporting for Natura 2000, and where any decline in condition is detected, then an investigation will be made to determine whether any impacts can be attributed to dredging and in which case operating procedures may need to be revised. So far, we have trialled this approach in three estuaries, the Humber, Medina and Fal. The trials have illustrated a range of issues but have largely shown that the approach will work. However, there are questions about how best to manage issues relating to the impact of dredge plumes in some estuaries where migratory fish are present and where it is thought by some that dredging may have an impact. This aspect of the protocol is likely to develop further as the range of estuaries covered expands. Several ports are waiting to roll-out their baseline documents and the process has been designed to avoid administrative overload, so there has been prioritisation to ensure development of a baseline where it is most needed in the first instance. We expect the overall process to take in the order of four years. Case Study 4 ABP dredging on the Humber Estuary Associated British Ports dredge between 10 and 15 million m 3 of sediment from the sunk dredged channel each year. This sediment is transported a short distance away before disposal within the estuary. As a consequence most, if not all of the sediment stays within the estuary. This process of sediment recycling means that the estuary is not denuded of sediment and therefore the authorities have been able to conclude that the dredging will have no adverse affect on the Natura 2000 interest. Concluding comments Sustainable sediment management has become an integral part of the approach to securing sustainable port activity within and adjacent to Natura 2000 sites on the coast. The value of this sediment is considerable because it is the building block for sand dune development and mudflat and saltmarsh accretion that underpins much of the important coastal wildlife asset. However, the

6 role sediment plays in the lives of the human population and in the economics of living on the coast is probably under-emphasised. Keeping sediment in the system is also the key to sustainable flood risk management and as such programmes of sediment management for nature conservation have important implications for flood risk management, and vice-versa.