Gwynedd Council Pwllheli Harbour maintenance dredging strategy Updated strategy report

Transcription

1 Pwllheli Harbour maintenance dredging strategy Issue 5 January 2016 This report takes into account the particular instructions and requirements of our client. It is not intended for and should not be relied upon by any third party and no responsibility is undertaken to any third party. Job number Ove Arup & Partners Ltd 4 Pierhead Street Capital Waterside Cardiff CF10 4QP United Kingdom

2 Document Verification Job title Job number Document title File reference Document ref Revision Date Filename 2015_Mar_Strategy_Report.docx Draft 1 10 March 2015 Description First draft Prepared by Checked by Approved by Name PA KG/RG CW Signature Draft 2 25 Mar 2015 Filename Description 2015_Mar_Strategy_Report_Issue_V2.docx Prepared by Checked by Approved by Name PA RG CW Signature Issue 5 Jan 2016 Filename Description 2016_Jan_Strategy_Report_Issue_V3.docx Prepared by Checked by Approved by Name PA GM RG Signature Filename Description Name Signature Prepared by Checked by Approved by Issue Document Verification with Document Issue 5 January 2016

3 Contents 1 Introduction 1 2 Description of existing strategy and considered areas 2 3 Coordination with regional strategies West of Wales Shoreline Management Plan Pwllheli Pilot Project 9 4 Impact of Climate Change 10 5 Methodology for the development of the strategy Review of existing information Development of solutions Stakeholder management 14 6 Proposed new design dredge levels and widths Comparison of dredging volumes for different depths Proposed new dredge design 23 7 Dredging frequency and expected volumes Proposal for dredging campaigns Analysis of historic accretion rates and forecast Expected annual dredge volumes 26 8 Proposed dredging system to be used in each area Harbour entrance: Marina approach Marina basin 30 9 Strategy for disposal of materials Short term options Medium/Long term options Measures for reduction of accretion rates in the harbour Short term options Medium/Long term options Cost estimation Annual estimated dredging cost Disposal of materials 38 Page Issue 5 January 2016

4 12 Expected impact of proposed measures and required consents Short term measures Medium/Long term measures Conclusions and next steps 40 Appendices Appendix A Technical focus workshop presentations Appendix B Drawing 1001 Dredge design Appendix C Groyne structure reinforcement outline design Appendix D Groyne structure outline design assumptions Appendix E Extent of Pwllheli Harbour Act Issue 5 January 2016

5 1 Introduction In the early 1990 s the then local Authority Cyngor Dosbarth Dwyfor commenced the development of Pwllheli Harbour to include a 400 berth marina. The capital dredging was undertaken by a cutter suction dredger and the plant was of a size that dictated that a significant over dredge of both the channel and marina basin was conducted. Over the period there has been a programme of maintenance dredging undertaken in varying forms in different areas of the Harbour and since 1997 the responsibility for the management of dredging operations within the marina being transferred to CGC. The most recent Dredging Strategy for Pwllheli Harbour was prepared for Gwynedd Council (GC) in January In April 2014 Arup was commissioned by Gwynedd Council to review the current dredging arrangements in light of changing circumstances and prepare a Maintenance Dredging Strategy including an assessment of viable options for the maintenance dredging management and a proposal for a sustainable strategy including costs for the period The mentioned changes include: The development and ongoing implementation of the Welsh National Sailing Academy and Events Centre in Pwllheli The implementation of the 2013/14 dredging works, including land reclamation and landscaping within the harbour area West of Wales Shoreline Management Plan 2 (SMP2) Formulation of the Local Flood Risk Management Strategy for Pwllheli (Pwllheli Pilot Climate Change Adaptation Strategy) Climate Change and Sea level rise Relevant legislation Increased budgetary pressures facing local authorities in Wales (and uncertainty regarding the availability of previous Welsh Government funding toward moving material to Traeth Crugan) Following submission of the Draft Strategy in March 2015 it was reviewed by GC and the Harbour Committee members. The comments were received in July 2015 and incorporated to this final version of the document. In the same way, copies of the Draft Strategy Report and the Shadow HRA Report were provided to NRW in March Comments to the HRA and the Strategy were received in August 2015, followed by a teleconference between GC, Arup and NRW. The HRA report has been accordingly amended and issued to NRW as Final Version in December This is the final version of the Strategy Report including amendments in relation to NRW s comments. Issue 5 January 2016 Page 1

6 2 Description of existing strategy and considered areas The current strategy was produced by Marina Projects in 2009 and the main issues found that were to be addressed by the proposals in the strategy are: - The high number of constraints that make dredging activities complex and expensive. - The main accretion within the harbour caused by the coastal processes and not by materials carried by the rivers flows. - When the marina was originally formed there was a significant over dredge in the main Access Channel to create access for the dredger. This created a perception of an enhanced tidal access window by leisure vessels using the harbour and berthed in the marina. However full tidal access to the marina was not envisaged by the original design (-3.00m below OD,- 0.56m below CD, for the entrance and Access Channel). The design width proposed for the channel was also very generous, with 80m. - There were clear indications that a wide Entrance/Access Channel increased the level of accretion throughout the Harbour. - The deepest areas of the Access Channel had drifted towards the exterior of the curves and the navigation marks do not currently show the position of the channel. - The design depth in the marina basin that had been used in previous dredging campaigns provided additional depth beyond what was required for the majority of vessels (-3m below CD). The main objective of the strategy was to reduce the maintenance dredging to the minimum practical level. The strategy included the design of the proposed revised dredging levels in the marina basin, adapted to the draft required for the vessels actually moored in each area (-3.94m, -4.44m and -5.44m below OD; -1.5m, -2m and -3m below CD). Issue 5 January 2016 Page 2

7 Figure 1: Current strategy proposed design levels, including the area of new capital dredging for the WSAEC undertaken in 2014 The main recommendations included in the strategy for each area of dredging were: - Keep undertaking hydrographic surveys every year to understand the siltation processes within the marina. - Longer term aspirations would be to increase depth at Harbour Entrance and Access Channel down to -3.50m OD (-1.06m CD) and width from 25m to 30m, positioning the channel to reflect the natural deeper water. - Retain the current method of dredging for the Harbour Entrance using land based plant with arising material being either stockpiled or taken directly for beach recharge. - The most appropriate method to dredge the Access Channel and the Marina Basin was considered to be use of an appropriately sized cutter suction dredger with the dredged spoil being discharged into the stilling lagoon. The Access Channel was top priority in the next dredging campaign. - Review the basis of existing Shoreline Management Plan and update all assessments and secure appropriate Licences and Consents. - Engage a suitable contractor to undertake the maintenance dredging. Therefore Council owned equipment was no longer considered suitable for operational service in Pwllheli Harbour. Since the production of this strategy, GC has: - undertaken dredging of the Harbour Entrance annually to guarantee the access of the vessels to the marina; Issue 5 January 2016 Page 3

8 - levelled the Access Channel bed approximately every two years (allowing to remove high spots that may pose a risk for navigation without generating material to deal with) and - undertaken maintenance dredging campaigns in the Marina Basin and Channel approximately every 5 years. The areas considered in the 2009 strategy (Marina Basin, Access Channel and Harbour Entrance, shown in Figure 2) where modified in the Factual Sedimentation report produced by Civil Engineering Solutions in 2014 to improve accuracy having reviewed the coverage of the survey data. The areas used in this strategy are coordinated with these latest ones and, in the same way as the previous strategy, this does not include actions for the inner harbour. Figure 2: Image taken from 2009 Strategy showing the considered dredging areas Figure 3: Modified analysis areas Issue 5 January 2016 Page 4

9 3 Coordination with regional strategies There one main regional strategy that this document has been produced to align with that is the West of Wales Shoreline Management Plan 2. The Pwllheli Pilot Climate Change Adaptation Strategy was produced in line with the mentioned SMP2 but it hasn t currently been officially adopted by GC as its flood management strategy. Its contents has been considered in this study as recommendations for short, medium and long term strategies in coastal management. 3.1 West of Wales Shoreline Management Plan 2 The strategies included in the Pwllheli Pilot Project are aligned with this regional management document that assesses the risk of flooding along the Welsh Coast and draws the policies to address those risks to people and the developed and natural environment in a sustainable way. Figure 4: General shoreline geomorphological processes (source SMP2) The drift along the Traeth Crugan frontage tends to be towards the east. The western end is an area of erosion and is only maintained by the higher foreshore. The areas of higher sea bed to the eastern end of Traeth Crugan do tend to support sediment accumulation in the centre of the bay but this can be variable, and the dunes are vulnerable to erosion. Abererch tends to be an area of sediment parting, with sediment moving to the east and to the west. There can be periods of accretion. Based on the essential coastal processes described in the SMP 2 document (and shown in Figure 2) we can say that the main source of accretion in the harbour is Issue 5 January 2016 Page 5

10 coastal and that the harbour is susceptible to receive sediments from both Traeth Grugan and Abererch. Pwllheli is a key area of flood risk and the sea level rise will have a significant impact on the extension and level of risk. In an unconstrained scenario (assuming no intervention has been done in the area, therefore the harbour, other structures or flood protection works were never done) the natural behaviour of Abererch is to roll back. It seems quite probable that a breach would occur and that the area of the Afon Erch would form a new tidal inlet. In the absence of the harbour entrance structures, the entrance is likely to widen, there could be increased sediment moved into the entrance and there would be increased erosion along Glan y Don as the shape of this frontage changes. In a do-nothing scenario (it is taken that no further defence measures would be taken to manage the erosion and set back of the shoreline) the probable initial failure or breach of the dunes at Abererch would be to areas adjacent to the current rock defence to the dunes. There would then be a period of readjustment as the beach develops at the main entrance to the valley behind to establish an ebb tide bank system that would tend to hold the natural bay forward. As such, a breach in this part of the bay would not be to the significant detriment of the natural defences along other sections of the frontage shape forward, but it would mean a significant loss of railway line and increased risk of flooding for Abererch. Something similar would happen to Traeth Crugan, where a breach would form a natural entrance for Afon Penrhos. Along South Beach there would be a roll back of the shoreline with sea level rise. Under this scenario, without management, the dunes might degrade over time. Overall, this scenario for the whole area creates opportunity for significant gain in nature conservation value as the whole area reverts to a naturally functioning barrier saltmarsh system. However, there would be very substantial losses in terms of infrastructure, flood damage to properties, loss of the golf course, loss of navigation to the harbour and to harbour facilities. The defence of the core part of the town relies upon maintaining defences at the Cob and maintaining defence from coastal flooding along the Penrhos Valley. There is also significant flood risk, while these defences are maintained from fluvial flooding. There is flood risk in the longer term to the operation of the harbour and navigation to the harbour relies upon control and dredging of the harbour channel Issue 5 January 2016 Page 6

11 Figure 5: Conceptual geomorphological process ( extract from the Geomorphological Baseline Report - v15draft, Halcrow 2010) Figure 6: Conceptual geomorphological process at Abererch ( extract from the Geomorphological Baseline Report - v15draft, Halcrow 2010) If the strategy was to maintain the present management, hold the Line along Traeth Crugan frontage by sustaining the current linear defence would require substantial raising and reinforcing of the rock revetment. This defence has needed to be reinforced and extended significantly over the last 30 years and would continue to do so into the future. The frontage is subject to significant erosional Issue 5 January 2016 Page 7

12 pressure and, overtime there is seen as being a general loss of sediment and width for sediment retention along the frontage. The eastern end of this frontage, along South Beach is naturally retained by the presence of Carreg Imbill. Historic evidence indicates that this section is relatively stable. The key area of concern in terms of flood risk management is the railway and the village of Abererch. However, the key issue is the sustainability of managing the coastal frontage. According to SMP2 the current management practice would result in the need to extend the current defences laterally along the shoreline or to shift to an approach where the vulnerable area of the shoreline is managed as a new headland. Both options are considered unsustainable in the long term either Proposals for short, medium and long term measures Based on the described scenarios, the proposed strategy by SMP2is summarised in the table below, obtained from Section 4 of the document, Coastal Area D PDZ13: Policy Unit Policy Plan Comment Abererch HTL MR MR Subject to national consideration of railway Glan Y Don HTL HTL HTL Allow buffer zone for natural behaviour of the dunes Pwllheli Harbour entrance Pwllheli centre HTL HTL HTL HTL HTL HTL Spatial planning for potential long term adaptation South beach HTL HTL HTL Golf course HTL MR MR Traeth Crugan HTL MR MR Table 1: Short and long term strategies for flood management in the area of Pwllheli Harbour, proposed in the SMP2 HTL Hold the line MR Managed Re-alignment Issue 5 January 2016 Page 8

13 3.2 Pwllheli Pilot Project Pwllheli Pilot Project is a proposal for sustainable flood management plan for Pwllehli that combines structural defence works with wider flood management measures and environmental and social considerations. Traeth Crugan and Abererch constitute the main coastal flood protection for Pwllheli area. There are signs of erosion along the dunes, especially at Abererch, where protection measures such as rock revetments, dune fencing and plastic sheet piles. The plastic sheet piles placed in 2006 give a fixed line of defence designed to last 10 years. There were major repairs to this structure in 2011 as there was significant erosion to the east earlier in the year. Emergency works have been required in 2014 at Abererch Sands caravan park after the storms occurred during the previous winter. No beach nourishment has been undertaken in Abererch as part of the works undertaken recently. Dredge material from the harbour has been used for beach recharge on the Traeth Crugan frontage until The placed material acts as a buffer between the dune face and the erosion face of the beach Coastal flood risk in Pwllheli It is known that the 90% of the siltation material in Pwllheli Harbour is originated in the coast and carried by the coastal drift parallel to Traeth Crugan. Therefore beach nourishment using dredge material from Pwllheli has been keeping this material in the natural system. Although a tidal breach has not yet occurred in Pwllheli and according to the Pilot Project it has low probability, the consequences to the town would be severe if it did happen. The likehood of tidal flood is expected to increase with time and, considering that the risk is based on the probability and the severity of the consequences, the risk will also increase. The dunes have been identified as being vulnerable to breaching at Abererch within the next 5 years with no further management and at Traeth Crugan within the next years (with no further management). Therefore an adequate management of these two elements will become more critical for Pwllheli over the time Flood Risk Management Plan for Pwllheli The recommendation of the Pilot Project in the short term (between 2005 and 2025) is to continue with the present management of existing coastal defences on Traeth Crugan and Abererch to maintain current levels of protection, and maintain beach control structures and recharge in Abererch. In the medium term (between 2025 and 2055) the managed realignment on Golf Course and Traeth Crugan and Abererch would be recommended, and to raise the level of the wall along the Cob, North Quay and Morfa Carreg. The approach to the management in the long term (between 2055 and 2105) would be to continue to hold the line for Glan y Don, Pwllheli Harbour and Issue 5 January 2016 Page 9

14 entrance, Pwllheli Centre and South beach, and the managed realignment of the two sand frontages, letting the coastal process progress in a controlled way Coordination with Pwllheli Maintenance Dredging Plan It is important to highlight the influence of the SMP2 and the recommendations from the Pilot Project in this Maintenance Dredging strategy. The materials dredged from the entrance and channel may be suitable for beach nourishment at Traeth Crugan and Abererch, in the short/medium and long term of this strategy, as the considered time-frame is 10 years. This allows for an adequate coordination with the regional strategy. Going beyond that, a different sustainable disposal option would required, as the trend for the dunes is to retreat and if this would happen in a controlled way, no additional material would be required in this area. 4 Impact of Climate Change Over the last years, presumably due to human activity, the global temperature has increased, which is commonly linked to increased levels of carbon dioxide within the earth s atmosphere. The predominant direct effects that climate change will have on coastal regions are sea level rise, increased salinity and changes in storminess. As temperatures have risen globally sea levels have also risen. If the sea level rise is not taken into account by the design it may have impact on the assets and activities held in the marina, especially flooding and wave overtopping. Recent scientific reports estimate global sea level rise by 2100 between 1 and 2m. But it is important to note that sea level rise is not uniform around the world and high level estimates are not useful for design of infrastructures. The IPCC 4th Assessment Report 2007 on climate change is generally well thought of, except for its predictions on sea level rise. Widely regarded as too low, the values given (18cm to 59cm by cm for other factors such as sliding ice) were almost instantaneously considered as out of date from the moment the report was published. Indeed two recent reports (2009) have attempted to update the science in the IPCC report. However, many countries continue to use these values as the basis of their national recommendations as much of the research that was included is agreed upon. But these high level estimates are not particularly useful for designs as the width of their ranges illustrate the current uncertainty about what may happen in the next 100 years. What is noticeable is that the values tend to get larger with time. A comparison between sea level measurements over the past 10 years and those predicted by earlier models show that the current rate of change in sea level is at the upper bound of what was predicted. Though it is possible that rate will converge with the projected values these values would suggest that the upper bound values are quite likely while it is unlikely that lower bound estimates will be correct. Issue 5 January 2016 Page 10

15 Figure 7: Recent observations show the observed sea levels from tide gauges (blue) and satellites (red) are tracking near the upper bound (black line) of the IPCC 2001 projections (grey shading and black lines) since the start of the projections in 1990 (Rahmstorf et al. 2007) The red curve shows annual sea level since 1970 based on tide gauges (the thick red line is a non-linear trend). The blue curve shows satellite sea level from 1993 to the end of 2008; the thick blue line is the linear trend (3.2 mm/year) over this period. For comparison, the projections of the 2001 IPCC report are shown (dashed lines and grey uncertainty range). Most countries do provide guidance on what should be included within a design to allow for sea level rise. For the UK, UKCIP (UK Climate Projections, 2009) provides projections of the future climate based on global and regional models. The very unlikely H++ scenario range gives a rise of 93cm to approximately 190cm relative to 1990 mean sea levels by the end of the 21st century. In Wales, the Technical Advice Note (TAN)15, 2004 (DAPs updated in 2015), recommends to consider an allowance of 5mm per annum over the life of any coastal defence scheme, considering projections that estimate that around the Welsh coast, increases will be in the range of 25 to 30 cm by 2050, slightly more in the south than the north. Pwllheli Pilot Strategy document has used for the hydraulic models the 2006 Defra climate date, included in the following table: Net Sea Level Rise (mm/year) relative to 1990 Issue 5 January 2016 Page 11

16 Table 2: Net sea level rise estimated by Defra (2006) For the period considered in this project ( ), the estimated sea level rise (between 120mm and 175 mm) may have some impact on maintenance dredging in Pwllheli Harbour. Although the increase in average sea level may indicate that less maintenance dredging may be required, other studies have also confirmed that Climate Change will have impact on the frequency and intensity of storms and wave heights (the Department for Environment, Food and Rural Affairs (DEFRA) suggests an assessment based on increases to wave height and wind speed by +5 to -10%). These are expected to increase over the time. For the particular case of maintenance dredging in Pwllheli Harbour, this will likely cause an increase of the material carried by waves overtopping the groyne and by the coastal drift. This effect of the climate change is difficult to quatify at this stage, and considering that it will be oppose to the sea level rise, the reduction associated to the last one has not been included in the calculations. 5 Methodology for the development of the strategy The approach to this commission is multidisciplinary, including coastal processes, environmental constraints, social issues and economic factors. The main objectives of this strategy are: - Adjust the dredging design to optimise costs and at the same time providing an adequate service to the marina users. - Sustainable options for dredge material disposal - Outline design of potential measures to reduce the accretion rates in the harbour. - Recommendations for dredging systems. - Review of licence / consents required for the proposed measures. - Review the current dredging arrangements based on the changes introduced by the development and ongoing implementation of the Welsh National Sailing Academy and Events Centre in Pwllheli, the implementation of the 2013/14 dredging works, including land reclamation and landscaping within the harbour area and the West of Wales Shoreline Management Plan 2 (SMP2). 5.1 Review of existing information The team based the proposals included in this strategy on the knowledge they acquired on the current situation of Pwllheli Harbour and main issues related to Issue 5 January 2016 Page 12

17 the maintenance dredging from the site visits and the following provided information: Maintenance dredging strategy and history of dredging activities in the harbour - Pwllheli Climate Change Pilot Adaptation Strategy (2011), including the geomorphological baseline report that updates the knowledge on the hydrodynamics of this area of the coast. - Factual Sedimentation report produced by Civil Engineering Solutions (2014). - General arrangement and Environmental Statement of the Welsh National Sailing Academy and Events Centre project (2013). - Traeth Crugan - Pwllheli Coastal Defence Options Study (2008). - Hydrographic Surveys undertaken from 1997 to the latest one, done in September 2014 after the most recent dredging campaign. - Current dredge disposal costs. - Geometry drawings of the stilling lagoon. - List of vessels moored in the harbour. - Pwllheli Harbour Act Development of solutions The design of an updated dredging scheme for the marina has been obtained by comparing the costs associated to different depths and widths and taking in consideration the impact on the access to the harbour for different sizes of vessels. The annual accretion rates have been revisited by comparing the hydrographic surveys from the different years, together with the volumes dredged every year and in each campaign, obtaining updated values that have been used in the rest of the strategy. Based on the information obtained from previous reports, provided by the harbour management team, and the feedback received from the local stakeholders, different measures for dredge material disposal, dredging systems and timing and measures to reduce accretion have been analysed and proposed for: - Short term: to be implemented in 3 years or less. - Medium/long term: to be implemented in less than 10 years. This classification is based on the expected planning times and costs required to put in place each of the proposals. The liaison with Natural Resources Wales (NRW) has been key to determine the viability of each of the proposals considering the potential impacts on the SAC and SSI that surround the harbour and the additional studies required to justify the adequacy of the measures. Issue 5 January 2016 Page 13

18 5.3 Stakeholder management Technical focus workshop A technical focus workshop was held on the 11 th July 2014 in the Marina premises with local stakeholders and members of the Harbour Committee. Members of the Harbour Committee, Berth Holders Association, Plas Heli board, Pwllheli Sailing Club, Hafan Pwllheli management team, and Marine Traders Association were invited to this workshop that didn t aim to be a public consultation but to explain the objectives of the project and the progress made to date and gather valuable feedback from stakeholders that are closely involved in the activities of the marina. Presentations on the main issues to be addressed by the strategy, as well as the available information and progress of the project were given to the attendees in sessions focused on specific topics. Copies of the presentations are included in Appendix A. Figure 8: Image taken during one of the workshop sessions The main conclusions from the workshop sessions are summarised below: Session 1: Introduction and general problems encountered The apparent lack of planning in previous dredging campaigns, where the dredging works started when the sea bed levels already exceeded the design. There is a necessity to set up a trigger level to alert on the necessity of dredging works. The timing of the campaigns should be coordinated with the activities of the marina (commercial, recreational, boat yards, maintenance and competitions). At the commencement of the marina activities the harbour was (over) dredged and the access from sea was granted 24hrs, but currently that cannot happen in all tidal conditions. Issue 5 January 2016 Page 14

19 It was expressed by a majority of the attendees that returning to the initial situation would be desirable. Therefore, for example, visitors can have access without having to forward plan when they can enter the harbour (as is the current situation). This will be also favourable for local investments in Business in the Harbour and Town. The also attendees showed the perception that when the harbour was first created (at the beginning) the equipment was bigger and more efficient, and used on a more regular basis. Currently the dredging campaign is not annually planned and dredging is not done regularly. Another aspect to improve, according to some users of the marina, would be the communication of the dredging campaigns to the users about when and where the works are undertaken. The expectations of the majority of the attendees to the workshop for the new strategy was that was easily understood by all, so that everyone knows what the expectations are. It needs to be a predictable and manageable solution. The preferred improvement would be to increase the available access time, up to 24/7 if feasible. Dredging should be publicised early (Feb / March) so that berths are filled. The attendees also expressed their concern for the recent bad press that the marina has had. Session 2: Dredge depth options and associated cost After the presentation of the four alternatives analysed a discussion on the stakeholders preference, based on their knowledge of the harbour was held. Regarding the design levels, it was propose to relate them to future or potential use (size of boat) rather than current modern boat 2.5m. A wider entrance was preferred, 30metres instead of 25metres, to allow better access to the harbour. And the focus should be on key settlement areas corners internal of channel. There was the suggestion of an alternative option, annually maintained, to achieve: - Mouth/Entrance 30m width. - Channel 4m OD depth (considering an annual Build Up 0.5m) - Basin 5.5m OD Depth The cost of dredging should be analysed against income generated. It has to be considered that there are currently empty births (110 approximately). The levels considered in the design should be based on Low Spring Tide Level. Values in the report need to be in chart data rather than ordinance survey so that the users of the harbour can understand. During the discussion regarding navigability and access to the harbour it was raised that the navigation marks will need to be re-located and that the navigation entrance should be amended as there is a problem adjacent to the sand stockpile. Issue 5 January 2016 Page 15

20 Session 3: Method and timing of dredging works It was understood during this session that October to March is the best time to undertake dredging works and the ideal sequence is this: - Oct Dec Basin - Jan Mar Approach - March - Entrance The seasons when it is not possible are spring and September (fishes going up and down the river). From previous consultation with NRW it is known that there is not an ideal time to dredge the harbor due to the overlap of migrating seasons for different species. It is understood that in summer the agitation is quieter. The timing comes down to what is the method of dredging. Water injection would be one method to clean out channel and entrance, with pipes to support this in the actual harbour. The preferred methods of dredging would be: - Cut-suction for Marina Basin - Potentially injection for channel and entrance. Injection has resulted very effective in the past for the area localised at the travel lift, but it has environmental issues that need to be analysed further. - Bed levelling that has been happening by ploughing in the channel area. Main restraint on the dredging regime is the method of disposal. Injection method is better for the sand (injecting the silt will muddy the water). Jetting up the channel was an option to be considered and discussed with NRW. The preferred strategy is to try to reduce the amount of material deposited in the harbour followed by a regular maintenance. If the accretion rate could be reduced by a half, it would be easy to keep the proposed depths. It is estimated by the management team is that 7,000m3 silt brought into the harbour each year. An important idea developed during the workshop was the public interest for this dredging campaign to go ahead (economic benefit for residents of Pwllheli) and how to obtain a balance with the environmental issues. It was suggested to build this into the Flood strategy & coastal defence for Pwllheli to get funding for disposing the sediment to support the flood defence (release sediment back into the system). Session 4: Dredge material disposal options There are two separate materials to consider for disposal. Silt and sand/gravel. It was agreed that re-use of the material should be investigated further. There were proposals to keep disposing materials within the harbour. For example, to spread the silt that is removed through dredging, at the end of the training wall to academy. Fill that area with silt (back of the industrial estate). Issue 5 January 2016 Page 16

21 It was agreed by the majority that it was necessary to look at the cause of the problem and not the symptoms. The question of the ownership of the material dredged by the Crown State was raised, if re-use was proposed. Proposals that were made during this discussion were: agriculture, off-shore disposal, use as construction material, in a barrier. Double-handling should be avoided, and keeping the material in the same hydrographic system (e.g. beach nourishment) is viewed as a positive option. Session 5: Reduction of accretion within the harbour. Preliminary engineering options It was agreed that this strategy needs to be considered within a broader picture for Coastal Protection management led by GC, NRW and Welsh Government (WG). Sand Trap/River Silt Traps good idea, emptied by land-based excavator. Also pumping sand for beach nourishment (Removes double handling/cost implications/waste). When harbour was originally built there was a sump that took the silt that travelled down from the river, there was a suggestion to reinstate that element. It was also suggested to pump sand for beach nourishment (removing double handling/cost implications/waste). I was agreed that ultimately modelling is required: The Model for different shapes / orientation of groynes should look at the effect on the caravan park (coastal defence). Other considered proposals were increasing the crest of the training wall and groyne, to build offshore submerged structures. The first step should be to repair the existing groyne to original height and see if it has a better effect (as it did in the past). It requires a height that will stop it overtopping. Further actions to the groyne configuration will require modelling to verify the impact on the coast. Session 6: Consents It was agreed that an early conversation with NRW would be required, also to communicate a compelling economic argument on the benefits that the marine activities bring to the town. The first step is to develop sustainable and technically sound solutions to be included in the strategy report, and the business case needs to be built Then discussions must be held with external partners, such as NRW. The final solution needs to be developed on a collaborative basis Liaison with NRW As part of the development of the strategy, a meeting was held with NRW on 14 October 2014 at Bangor NRW offices. The topics discussed are exposed below: Disposal of materials on the short term. Issue 5 January 2016 Page 17

22 Part of the dredge material might be disposed behind the bund, in the same way as the dredge material from the Welsh National Sailing Academy capital dredging The disposal of arisings from the Welsh National Sailing Academy (WNSAES) dredging works behind the bund was and, as part of the licencing, a biodiversity benefit needed to be established in response to the loss of mudflat under the bunded area. Therefore a condition of planning permission is for the settled dredged arisings to become a wildlife area. Disposal of additional materials to backfill completely the area might need a waste disposal permit. If the maintenance dredging is necessary to provide an adequate service to the WNSAEC, the current permit obtained for this project could be still used. Beach nourishment. The required characteristics of the sand depend on the destination beach. Materials from the approach channel were refused previously for the use in Abererch beach (content in silt 17% was higher than allowed 15%). In case any material from the harbour dredging works is proposed to be placed at Traeth Crugan (where the sand from the harbour entrance has been historically used) or Abererch beach, specific analysis will need to be undertaken. It was confirmed that flood management at Traeth Crugan is responsibility of Gwynedd Council whereas coastal defence responsibility at Abererch beach corresponds to NRW. Both frontages have suffered of erosion in the recent years: the area on the West of Pwllheli harbour was nourished with dredge materials by GC by means of a loan from WG. The eastern area of the port has been subjected to various measures to reduce erosion such as zigzag fences or a bank of cobbles. In 2000 this area received approximately 4,000m3 of sand from the stockpile. The area considered under the Harbour Act covers great part of Traeth Grugan and the western end of Abererch beach. Disposal at beach within the harbour act area willnot initially need marine licence, but this had to be confirmed with the Marine Licence (ML) team in Cardiff. Arup agreed to send a letter to the ML team with the relevant legislation and our approach to the strategy proposals. This consultation with the ML team was undertaken in November 2014 with confirmation that Marine Licence will not be required for such activities within the Harbour Act Area. The extent of Pwllheli Harbour Act area is included for information in Appendix E. Some repair works are currently being carried out at Abererch beach where additional sandy material may be required. Arup agreed to contact Dafydd Roberts (NRW) to enquire on the possibility to dispose at least art of the material in the stockpile at Abererch beach were the repairs. In the long / medium term, dredging will be done in an annual basis, so ideally the beach nourishment should be done in the same way. The marine licence has a valid period of 3 years. This needs to be confirmed by monitoring of both Traeth Crugan and Abererch to avoid overloading the system. Issue 5 January 2016 Page 18

23 Modifications to the groyne / training wall height. A modification in the level of these elements initially will not require a marine licence (location within the Harbour Act area). The HRA included in the strategy must determine the level of expected impact of this actions on the SAC. How far can we assess this without modelling? Disposal of materials: Habitat creation During the meeting, it was mentioned that some of the flood protection strategies (mentioned in the Pwllheli Pilot Climate Change Adaptation Strategy) for Afon Erch and Afon Ddu might require the creation of new habitat areas. Constraints to Water Injection as dredging method The main concern of NRW is the lack of good understanding of the impact on the SAC. A very important information are the expected annual volumes of material to be dredged from the harbour. Arup was to extrapolate the historic values to obtain an average annual expected volume. The lack of baseline information in the area to evaluate the impact of the particles in suspension is an additional problem. The turbidity caused by the WID may be similar to the one caused by a storm, but that cannot be proved at the moment. It was stated that NRW would require from GC to monitor turbidity levels in the bay. Due to the uncertainties regarding the impact of WID if used in the channel it is considered more adequate to continue to undertake bed levelling in the Marina Approach by ploughing, that has been used successfully so far to flatten high areas in the area. Off-shore disposal The application for a new location, outside of the SAC, but closer to Pwllheli Harbour than the disposal area at Holyhead is feasible. GC must consider that, if they decide to go ahead with this, other port authorities in the area will be allowed to use the disposal location. No other port facilities undertaking dredging activities on a regular basis are located in the area. Additional information on the complete process was to be requested by Arup to the NRW Marine Licence team in Cardiff. Modifications to the groyne / training wall layout A modification of these elements initially will not require a marine licence (location within the Harbour Act area). The HRA included in the strategy must determine the level of expected impact of this actions on the SAC. No modelling will be done for the strategy, but this will be requested as part of the development of this proposal. Next steps and coordination with NRW team The HRA needs to be developed in parallel to the strategy. More detailed information about the SAC needs to be requested to NRW. Once the draft strategy is produced, a copy will be sent to NRW for comments. Issue 5 January 2016 Page 19

24 6 Proposed new design dredge levels and widths 6.1 Comparison of dredging volumes for different depths The main concern expressed by the stakeholders during the workshop was the reduction in access times over the years, due to siltation build-up of the sea bed, in comparison with the initial depths after the construction of the marina. The dimensions of the channel and the depths achieved after the first capital dredging respond to the over-dredge required for practical reasons and not the intended design. The proposed design (for the entrance and access channel mainly) must be balanced, giving the users adequate access to the marina with an acceptable dredging volume and subsequent cost. Three options where compared based on operational issues and dredging volumes Operational factors: channel depth The list of vessels moored in Pwllheli provided information on the distribution of drafts required: The average draft of the vessels in Pwllheli is 1.5m, with a 93% of them less or equal to 2m. The 60% of vessels listed in the marina have a draft less or equal to 1.5m. Figure 9: Tidal restrictions for Marina Approach design depth of -3.0m OD (-0.56m CD). The conclusions of the analysis of the tidal range at Pwllheli Harbour for -3.0m OD (-0.56m CD) and -3.5m (-1.06m CD) are: - For a design depth of -3.0m OD (-0.56m CD) at the Access Channel the mean vessel (draft 1.5m) could access the marina approximately 80% of the time. The vessels with draft 2.0m could access the harbour over the 70% of the time. - For a design depth of -3.5m OD (-1.06m CD) at the Access Channel the mean vessel (draft 1.5m) could access the marina approximately 90% of the time. The vessels with draft 2.0m could access the harbour over the 80% of the time. Issue 5 January 2016 Page 20

25 Figure 10: Access restrictions for spring high tide with a design depth of -3.0m OD (- 0.56m CD) Operational factors: channel width The channel width was approximately 80m after the first capital dredging in 1991, due to the size of the equipment used. The design vessel will be the one with the second largest draft: B (beam) 4.9m, L (length) 13.1m and D (draft) 2.7m. The optimal widths, recommended by different guidelines and based on the design vessel considered, are shown in Standards/ Recommendations Australian Standards (AS ) 30.0 Design of Marina Structures and Facilities 30 Guidelines for Marina Berthing Facilities 23 Design of breakwaters for yacht harbours 36 Unified Facilities Criteria Design: Small Craft Berthing Facilities 30.0 Guidance on facility and management specification for marine yacht harbours and inland Recommended design width (m) Issue 5 January 2016 Page 21

26 waterway marinas with respect to user requirements The Yacht Harbour Association: A Code Of Practice For The Design, Construction and Operation of Coastal and Inland Marinas and Yacht Harbours The Institution of Civil Engineers: Dredging design and Practice Guide Based on these recommendations and the issues raised during the stakeholders workshop it would be recommendable increasing the design width from 25m to 30m. This width, combined with different depths and proposals for the marina basin is included in the analysis of options described in the next section Design options and associated dredging volumes Four options have been analysed to compare the improvements in navigation and operation of the marina versus the required volumes to dredge, that are described in the following table: Marina Basin m OD (mcd) Depth of entrance and channel m OD (mcd) Width of entrance and channel (m) Option 1 Same as 2009 strategy See Figure 1 Option 2 Same as 2009 strategy See Figure 1 Option 2B Same as 2009 strategy See Figure 1-3 (-0.56) 25-3 (-0.56) (-1.06) 30 Option 3-5.5m (-3.06m) -3 (-0.56) 25 Table 3: Design options analysed The latest full hydrographic survey available at the time that these calculations were done (June 2014) was the one undertaken in June This 3D information was compared with the proposed levels and the dredge volumes required to reach those levels were obtained by using the ACAD software Civils 3D. Issue 5 January 2016 Page 22

27 It is important to highlight that the volumes obtained in this section are based on a hydrographic survey that was carried out before the latest dredging campaign in 2014, therefore the volumes from this campaign were not deducted. For the purpose of this exercise, that is comparing the options, the deduction was not done, and the results are still valid. Option 1 corresponds to the design proposed by the Strategy from 2009 and it is the current geometry used for the dredging at the Marina Basin and Marina Approach. It would require to dredge approximately 60,000 m³ in the marina basin and 2,000 m³in the Marina Approach. Option 2 only proposes to widen the channel. The improvement in navigation is considered low, and the volume to dredge is effectively the same as currently. Option 2B maintains the design in the basin, increasing the depth and width at the Marina Approach and Harbour Entrance, providing better conditions to the access from the sea, solving some of the problems described by the marina users. The increase in volume (and cost) is approximately 20% higher than the current design. Option 3 proposal is to lower all the levels at the marina basin down to -3.06m CD. This would make easier the operations in basin and more flexible berths. But the increase in the volume to dredge is 100%, that makes this option not viable. 6.2 Proposed new dredge design Based on the analysis undertaken in previous section of this report. It is proposed to adjust the dredge design in the following way: Maintain the variable depths in the marina basin, that optimises the works in that area, deepen the channel to -3.5m OD (-1.06m CD) and widen it to 30m. That depth and width are also recommended also for the harbour entrance. This is already achieved by removing the sand deposited at the entrance by a land based equipment. The additional volume to dredge to adapt the design to this proposal, was obtained by comparing the proposed levels with the 3D hydrographic survey provided in December 2014 that was undertaken just after the 2014 dredging campaign, which covered the whole area (Marina Basin, Marina Approach and Harbour Entrance) and it is the latest available at the moment this report is produced. It will be recommended to over-dredge a buffer of approximately 300mm in the Marina Approach and Harbour Entrance, if navigation issues (similar to the ones declared by the users in the workshop) happen before the next year s campaign. However, the improvements to the geometry of the channel should help to solve those issues. Some of the Harbouor Committee members expressed their preference for a deeper Marina Approach and Harbour Entrance (up to 1.5m CD), to facilitate access to larger vessels, make the marina more attractive to new users and anticipate future required depths. Taking into account the constraints of the harbour, the proposal of this strategy is to maintain that as aspitational objective, for inclusion in the strategy in the future, subject to improvement in the conditions for disposal of materials. Issue 5 January 2016 Page 23

28 Based on this, the estimated dredge volumes to adjust (difference between the surface of the latest hydrographic surface and the desired design surface) the design are: - Marina basin: 5,648.49m³. - Marina Approach: 3,306.61m³ (6,200m³ if 300mm buffer is considered). - Harbour entrance: m³ (1,300 m³ if 300mm buffer is considered). Drawing no.1001, included in Appendix B, show the proposed design. The design of the channel has been adapted to the deepest areas that have been displaced towards the outside of the bends by the water dynamics. In particular, the section of channel located in front of the lifeboat station has been shifted towards South. At that location, part of the circular piles used for berths have been removed, allowing the relocation of the channel at the deepest area in that section. Figure 11: Removal of circular steel piles general arrangement of (2012) 7 Dredging frequency and expected volumes 7.1 Proposal for dredging campaigns It was agreed during the workshop and conversations with Pwllehli Harbour management team that carrying out one dredging campaign in the marina basin every 5 year caused a lot of disruption. All the vessels needed to be relocated during the weeks of dredging works to allow the dredger to reach all the areas of the basin. It was agreed that more regular and planned dredging works would be preferable. Currently, excavation works at the entrance occur every year after the winter storms and the channel bed is levelled every two or three years. The proposal is to undertake the same activities in combination with additional work in the marina basin every year. The volumes to dredge will be lower than previous campaigns and will allow to use smaller equipment managed by the Harbour staff. Issue 5 January 2016 Page 24

29 As mentioned in the workshop, the best time to undertake the dredging works is October to March, taking into account the fishes migration and the elevated use of the marina in summer. The use of a small and simpler equipment will allow to undertake some dredging also in summer if necessary, giving the harbour operations team more flexibility. 7.2 Analysis of historic accretion rates and forecast To determine the average accretion rate per year that will be expected during the 10 years of the strategy, 14 hydrographic surveys provided by GC were compared, and the difference in volumes considered. The areas considered to compare the successive surveys to obtain the siltation rates are shown in Figure 12(coordinated with the areas from the Factual Sedimentation report produced by Civil Engineering Solutions in 2014) and they were adjusted to be covered by all the surveys, so complete surfaces were compared each time. Figure 12: Areas considered for calculation of siltation volumes These areas are: Marina Basin: 81,086 m² Marina approach: 19,842 m² Harbour entrance: 23,623 m² The average accumulated siltation rates (average of all the previous years for each hydrographic campaign), and the comparison with the values obtained in the Factual Sedimentation report produced by Civil Engineering Solutions (2014). Issue 5 January 2016 Page 25

30 Table 4: Accumulated siltation in the harbour, by area 7.3 Expected annual dredge volumes The design considered is the one described in Section 6.2 and shown in drawing no.1001, included in Appendix B. The areas of the design are shown in Figure 13 and the expected volumes that will increase the bed level, based on the annual siltation are included in Table 5 below. Figure 13: Areas of the proposed design Issue 5 January 2016 Page 26

31 Table 5: Expected volumes to be removed annually from the three considered areas Both Marina Basin and Marina Approach volumes are to be removed by dredging techniques (bed levelling will be undertaken when necessary to remove high spots). The materials from the Harbour Entrance are proposed to be extracted by land based equipment. 8 Proposed dredging system to be used in each area Dredging in its basic form is the operation of removing material from underwater. It is generally used for construction activities, creating greater depths of water generally to improve navigation and accommodate bigger vessels. In the case of Pwllheli Harbour the purpose is to maintain adequate depths to allow to undertake the activities in the marina in a safe way. For any dredging campaign there are a number of restrictions which can influence the project, and adequate dredging techniques according to the specific conditions: Potential restrictions in a dredging campaign Channel width Draught Sediment type (sand, silt, clay, boulders, rock) Chemical composition (contamination) Weather & sea state Working environment (port, harbour, marina, offshore) Services Debris/ foreign matter (UXO) Sensitive structures Environmentally sensitive areas (SAC/ SPA/ NHA/ spawning grounds) Aquaculture Interaction with other navigation, moorings Legislation, licences and permits Table 6: Potential restrictions in a dredging campaign Disposal of the material Issue 5 January 2016 Page 27

32 Haul distance Availability of plant/ equipment In Pwllheli the systems to use are dictated by the nature of the material, the location (marina basin, marina approach and harbour entrance), the cost and the impact on the SAC. The capital dredge done in 1989 was undertaken by a large cutter suction dredger. The harbour entrance suffers from littoral drift (west to east) and requires regular dredging. The entrance was formed by cutter suction dredger in 1989/90. Dredging has been done annually from a land-based plant. No significant dredge was done in the access channel since it was created until recent years. It was designed to be 80m wide entrance (too generous for the size of the vessels) with depth -3.00m below OD,-0.56m below CD. Accretion has reduced depths and the width of the channel deeper water on outside of bend. Plough dredging has been employed to remove localised hot spots to localised low spots within the harbour The marina basin was formed using cutter suction dredging (capital dredge) and dredging pumped ashore for reclamation. Shortly after completion of the marina an area of deposition to the north of the marina basin created operational problems: heavy deposition of sands, gravels and silts to the north of the marina basin and NW corner. Dredge of this area was recommended / Maintenance dredging was carried out in the 2 northern bays and capital dredging was undertaken to the north of the existing marina basin to provide additional capacity to receive river channel erosion material from Afon Erch. No dredging was required until winter of 1999/2000. In1999 GC bought their own vessel (Council owned Nessie N8DX portable cutter suction dredger) used to conduct dredging between 1999 and The material was pumped to a bunded area (stilling lagoon) 225m long capacity of 22,000m3 in the harbour. 6 consecutive dredging campaigns were undertaken between 1999 and 2006 (generally between October and March and generally last 3 months). Since the production of the 2009 strategy, GC has: Available budget - undertaken dredging of the Harbour Entrance (land-based plant) annually to guarantee the access of the vessels to the marina; - levelled the Access Channel bed approximately every two years and - undertaken maintenance dredging campaigns in the Marina Basin and Channel approximately every 5 years. This has been done by contractor, as the small dredger owned by GC was sold. Based on previous activities and our understanding of the issues from the marina users, the proposals for the dredging method for each area are: Issue 5 January 2016 Page 28

33 Gwynedd Council 8.1 Harbour entrance: Sediment and location are appropriate for a land based plant or floating plant, such as small trailing suction hopper dredger that could transport thematerial along the coast or pump it to the use location. Considering the depth and width of the working area, a land based plant is still considered the most adequate system for this area. Furthermore, in case a new small dredger is purchased for the work in the marina basin, it could be a multipurpose plant that could work from land and from water in the different areas, similar to the one in Figure 14 and Figure 15. Figure 14: Multipurpose small dredger (land based) Figure 15: Other use of multi-purpose dredger (work in water) 8.2 Marina approach This area has been re-levelled approximately every 2-3 years since the issue of the 2009 strategy. Ploughing is the system used. Issue 5 January 2016 Page 29

34 Water Injection (WID) was used to dredge a small area around the travel lift quay, with satisfactory results. This is considered a suitable system to maintain the levels in the channel, once it has been dredged down to the designed levels. The annual volume to be removed from the channel is expected to be around 1,000m³. The use of this system is conditioned by the potential effects on the SAC and NRW requirements. Uncertaities around these issues make WID less straightforward to use than ploughing, that has been used for bed levelling to date, with good results and no impact in the area. While WID is not approved as system for the marina approach, ploughing, in the same conditions agreed previously, is to be used to level the channel. The implications of the use of this system for the SAC and surrounding area have been assessed in the HRA produced for this strategy. 8.3 Marina basin Currently, the maintenance dredging works in the basin are held every 4-5 years and GC procures an external contractor to undertake the works. The volumes to remove are large and the disruptions caused to users and management (that need to relocate all the vessels during the campaign for the contractor to undertake the works) are important. If a small modern plant is to be acquired by GC that can be used by the harbour staff with simple training, the works can be undertaken annually, reducing the volumes to handle and the disruption to the users, as different areas could be targeted each year. The works could be also planned outside of the initial frames (Oct-Dec) if the equipment was permanently available in the harbour, and coordinated with other activities in the marina. There is a range of commercial plants that can be used for this purpose. The Watermaster multipurpose dredger shown in Figure 14 and Figure 15 that could be used also as land-base plant for the excavations at the harbour entrance. This can be equipped with a cutter pump (discharge distance 1.5km) to carry out dredging in the marina basin. There are also remote controlled pumps suitable for the work in the basin, similar to the one in Figure 16. Issue 5 January 2016 Page 30

35 Figure 16: Remote controlled solids removal pumping system 9 Strategy for disposal of materials 9.1 Short term options Marina Basin Dredge material associated with the Welsh National Sailing Academy and Events Centre (WNSAEV) was being disposed of within a bunded area of Pwllheli Harbour. Firstly it is required to determine the remaining capacity behind the rock armour bund. It is proposed that the materials dredged from the marina basin within the next three years are deposited there. It will be necessary to deposit the material in the stilling lagoon to settle, dewater and reduce volume before backfilling the landscape area. The strategy considers the cost of double-handling this material for disposal (see Section 11). If the combined volume of the stilling lagoon and the landscape area behind the bund is not sufficient, additional disposal options are considered such as disposal at landfill or at the existing offshore disposal location at Holyhead. The number of landfills that would accept material from dredging in Gwynedd is reducing, and the material arising from the WNSAEV capital dredging has not been accepted by any landfill within Gwynedd. The Marine Management Organisation (MMO) register shows that the two main options chosen by other ports are landfill and offshore disposal. The costs for these three options have been assessed and included in Section Marina Approach and Harbour Entrance The stockpile of sand situated at the Harbour Entrance, together with the materials extracted from the entrance in subsequent years, need to be removed. The existing Issue 5 January 2016 Page 31

36 stockpile material is a contributing factor to rapid accretion in the Harbour Entrance. This material has previously been used in beach nourishment activities along Traeth Crugan. Coastal protection works and flood management at Traeth Crugan are responsibility of Gwynedd Council, whereas NRW deals with Abererch frontage. Both frontages have suffered of erosion in the recent years. The area on the West of Pwllheli harbour was nourished with dredge materials, by means of a loan obtained from Welsh Government. The area to the East of the harbour at Abererch has been subject to various measures to reduce erosion such as zigzag fences or a bank of cobbles. In 2000 this area received approximately 4,000m3 of sand from the stockpile. Ideally, the material from the Harbour Entrance would continue to be used for beach nourishment, as identified within the coastal protection strategies in the West of Wales Shoreline Management Plan 2 (SMP2), Pwllheli Pilot Project and Traeth Crugan Pwllheli Coastal Defence report. Initial discussions regarding the use of materials from the Harbour Entrance or Marina Approach for coastal protection works were held with NRW, as part of this study (see Section5.3.2). The potential financial support by NRW to transport the material to its final destination was also discussed. The requirements for the sand depend on the characteristics of the destination beach. Materials from the approach channel were refused previously for use in Abererch beach (content in silt 17% was higher than allowed 15%). In case any material from the harbour dredging works is proposed to be placed at Traeth Crugan (where the sand from the harbour entrance has been historically used) or Abererch beach, specific analysis will need to be undertaken. The levels of the Abererch frontage have dropped in recent years. Significant damage to the dunes occurred during the recent winter storms. A capital scheme of emergency works was commissioned to reinforce a 400m section of dune with plastic piling and rip-rap. Subsequent storms demolished this defence leaving a vertical face of plastic piling. Consequently, the dune was further reinforced with c. 7,000 tonnes of rock armour, extending the protection over 700m to protect the adjacent caravan park. The current estimated stockpile volume is 30,000m³, owned by GC and available for either GC or NRW to be used in coastal protection works. Further discussion was held with the NRW responsible for the emergency coastal protection works following the extreme winter storms at Abererch frontage. In brief, he was supportive of beach nourishment works along Abererch and would welcome the opportunity to use or purchase the sand fraction from dredging campaigns and the extant stockpile. The access to the area in Abererch was poor, by a low-class B-road through the caravan park. The route was not sufficient to accommodate a heavy plant. The proposal is to use a barge to ferry materials from the stockpile to Abererch. Transport costs could amount to approximately one third of the project costs and could potentially be met by NRW but would require internal bid for Grant Aid support. Issue 5 January 2016 Page 32

37 9.2 Medium/Long term options Marina Approach and Harbour Entrance The use of materials from the Marina Approach and Harbour Entrance for beach nourishment and coastal protection is considered acceptable as part of the strategy for the period , which is the limit of the long term in this strategy. The materials to be used are to be tested to determine the adequacy of the grain sizes to the intended destination. This is important specifically for the materials extracted from the Marina Approach, with some content of silt. But it may only be a temporary measure in the longer term, in line with the Shoreline Management Plan (SMP2) recommendation to change from Hold the Line (HTL) to Managed Realignment (MR) in this area from 2025, and this needs to be considered in subsequent strategies Marina Basin But for the materials arising from the Marina Basin, that are mainly silty and not suitable for beach nourishment, several options were discussed during the workshop and in the meeting with NRW. The application for a new Offshore Disposal location, outside of the SAC, but closer to Pwllheli Harbour than the disposal area at Holyhead may seem time demanding and difficult to achieve due to environmental requirements. However this option may be feasible (detailed assessment is required) and it will be costeffective in the long term because it beats the costs of other viable long term options (landfill and Holyhead disposal location) once the application process is passed. Only GC must consider that, if it is decided to go ahead with this, other port authorities in the area will be allowed to use the disposal location. However, no other port facilities are known to be undertaking dredging activities on a regular basis are located in the area. Use of dredge material for habitat creation: During the meeting with NRW, it was mentioned that some of the flood protection strategies (mentioned in the Pwllheli Pilot Climate Change Adaptation Strategy) for Afon Erch and Afon Ddu might require the creation of new habitat areas. However this option is not considered a long term sustainable solution as it depends on particular one-off projects that may not coincide with dredging programme. 10 Measures for reduction of accretion rates in the harbour 10.1 Short term options Some options have been analysed and discussed with the users of the marina. We consider as short options those that can be undertaken immediately and that would be implemented within a 3 years period. Those would be the proposals that don t Issue 5 January 2016 Page 33

38 require a Marine Licence and those that are expected not to have likely significant effects on the coastal processes and the SAC. Potential effects of the options considered have been assessed separately within the accompanying Habitats Regulations Assessment (HRA) report, which will be subject to consultation with NRW. Proposal 1: Sand stockpile The stockpile of dredged sand is currently placed very close to the harbour entrance. With no protection, the Eolic transport may accelerate the siltation process at the harbour entrance. It is therefore an urgent measure to remove this material from the harbour entrance. Initial discussions have been held with NRW for the purchase of the sand that GC should follow up. In addition to that, this proposal is aligned with the strategies for coastal management included in the Pwllheli Pilot. Proposal 2: Sand trap at the entrance channel This is a usual system to capture sediments in channels and basins. It is a deeper area that allows the material suspended in water to be deposited in a controlled area. It would catch most of the sand drifting, thus preventing the Marina Basin and Approach channel areas from filling up and siltation. Issue 5 January 2016 Page 34

39 This system can help to increase the periods between dredging campaings, but not the total volume that needs to be extracted, either to create the trap or to maintain the depths in the marina, that remains the same. Figure 17: Schematic showing the performance of a sand trap Proposal 3: Changes to the harbour entrance structures There is a short bull-head rail crib groyne to the south of the entrance to control the littoral drift material. Crest level of the bull-head rail grib groyne is +4.8m OD at the highest point and -3m OD at the lowest. Built-up material at the structure creates a source of sand and boulders that are washed into the harbour during storms and deposited in the Access Channel and Marina Basin. Maintenance work is also currently required on the groyne. The short term proposal is the addition of rock armour in the groyne and increase of the crest level of the bull-head rail crib to provide both: Additional protection. Reduce overtopping by material that can then be washed into the Harbour. Issue 5 January 2016 Page 35

40 An outline proposal is include in Appendix B to raise the level of the groyne structure above the current ground to the initial level considered in The ground around the groyne has built up approximately 1.8 2m and this is the additional height to be provided to the structure. Figure 18: Long section. Initial design of the groyne structure (1985) As this is an action undertaken within the limits under the Pwllheli Harbour Act 1983, no marine licence is expected to be required. Potential effects from this option have been assessed separately within the accompanying HRA report, which will be subject to consultation with NRW. No likely significant effect on the SAC is anticipated from this option; primarily as the levels of the groyne above ground are restored to its initial design, and this will only affect materials carried by storms onto the harbour entrance. However, this would be confirmed by a specific HRA following completion of further study and detailed design Medium/Long term options Currently, the length of the crib groyne does not prevent the entrance of material, carried by currents and waves, to the Harbour. It is likely that an extension of this structure would reduce the annual volume of materials accrued within the harbour. This options should be assessed in conjunction with raising the top level. Besides, the direct impact that such extension could have on Abererch frontage should carefully be assessed. In the same way, other actions such as including additional structures like groynes will need detailed assessment via hydraulic modelling, to determine if they bring an actual improvement in maintenance of levels at the harbour entrance, and any impact on the coastal processes. A hydraulic model with the adequate detail will also help to understand how the training wall is performing under the coastal processes (siltation levels at the back side and overtopping frequency) and the potential need to increase its top level. The possibility to extend the existing groyne structure or add other structures will require: - An assessment of the impact of these changes on Abererch beach by means of the development of an hydraulic model - To follow the environmental process described in the attached HRA. Issue 5 January 2016 Page 36