Managing flooding in Pwllheli

Shoreline Management Plans (SMP2s) are policy responses to environmental changes. They provide the framework for managing the long-term impact of tidal flooding across Wales.

They break the coastline down into smaller sections known as ‘policy units’ and explain how each unit should be managed in the short, medium, and long term, taking into account the sustainability of flood risk management activities and assets and priorities for flood protection.

Coastal Squeeze

Where man-made structures have been built to protect communities and land from coastal flooding and erosion, such as sea walls or rock revetments, the habitat may be prevented from moving landward as sea levels rise whilst it continues to be lost from the lower shore. This is known as ‘coastal squeeze’.

Coastal squeeze means that the saltmarsh size and function is reducing over time, along with the habitats and species that it supports.

A lot of saltmarsh habitat is legally protected therefore we are required to create new saltmarsh to offset losses in the future with sea level rise.

Livelihoods

Landowners and farmers may have noticed that the environment is changing and we want to hear your adaption concerns and ideas.

Natural Environment

The study area forms an important blend of coastal and wetland habitats that act as green corridors into surrounding countryside.

The environmental importance of this area is reflected in the large number of protected habitats and species.

Many of these are of National and International importance and these too are being threatened by the effects of flooding and climate change.

Recreation

This study area offers many opportunities for diverse recreational pastimes. These too will be carefully considered, as they are of vital importance for people’s health and wellbeing, and also bring income to the community.

Historic Environment

The area surrounding Pwllheli has a long and fascinating history. Pwllheli itself has been a settlement since the 13th Century with a strong association with the sea, having been the main fishing port of the Llyn.

The coastline here has however changed considerably over time. Over the last 150 years there has been significant human intervention and development. These actions will have affected the shoreline development during this period and will continue to do so into the future. For example, the construction of the railway enclosed the marsh areas along the east coast, and in doing so has restricted any landward movement of the dunes themselves.

There have been extensive changes to the Pwllheli South Beach, with land reclamation having taken place during the 19th century. The railway was extended across the north quay to Pwllheli in 1910, which effectively fixed the position of the shoreline at Pwllheli itself.

In 1813 the Pwllheli embankment (Embankment Road) and tidal flood gates were constructed connecting the main town with the South Beach. This created the basic structure of the inner and outer harbour that exist today as well as having a marked impact on how the land west of here has adapted.

Landscape

The outstanding natural beauty of the area with its close association with the Eryri National Park needs careful consideration when project planning.

View the information board for Pwllheli – the wider context

Natural Resources Wales is Wales’s largest environmental body. As well as managing flood risk, we have many legal duties and responsibilities to ensure we protect the outstanding environment we live in both now and in the future.

To achieve this, we have started carrying out a number of specialist surveys to help us understand the current state of nature.

We call this our baseline. Environment assessments will be used to ensure that all necessary approvals are in place for any work we carry out.

We must: protect the natural and historic environment, use natural resources in a sustainable way, seek ways to avert the Climate and Ecology Emergencies.

The Project

We have created a computerised flood model to calculate potential flood extents and water depths from storms. We are using this to understand the problem at Pwllheli and have carried out environmental surveys as part of evidence gathering.

We have been assessing a Long List of options to reach a proposed Short List, prioritising flood risk reduction to people and homes.

Outside the scope of the Project, but ongoing:

• We inspect, operate and maintain flood defences working with asset owners and other organisations.
• We fulfil conservation and regulatory duties to protect the environment.
• We currently maintain the three main rivers entering Pwllheli (Erch, Penrhos & Rhyd-hir)
• We issue flood alerts and flood warnings for the coast, as well as fluvial flood warnings for the Erch and the Rhyd-Hir.
• We will continue to perform our ongoing response functions during a flood.

View the information board for Our work in the area

Several flood defences exist in the Pwllheli study area. These include embankments, harbour wall and mechanical gates at key locations.

Through this study, we are developing our understanding of the flood risk and the function of the defences so we can continue to protect homes and businesses in the long-term.

View the information board for Flood defence structures 

Flood Risk along the coast is influenced by the coastal processes. Increased erosion is putting pressure on the existing defences, with this comes an increasing risk of breaches and consequently tidal flooding.

Holding the line in the areas of current erosional pressure increases the potential for erosion on areas either side of the protected area. Therefore, the options taken forward are focused on managing the realignment of these areas in line with the Shoreline Management Plan.

Options proposed for the shortlist:

• Raised Harbour walls - Increase defence heights around the harbour where needed to manage the risk of flooding from future storm events.
• New Harbour Gates - A regulated barrier at the harbour entrance to create capacity within the harbour to manage river flooding and equally to manage tidal flood risks from storm surges.
• Realign Defences (Inland) - New coastal defences to the west of the town, perpendicular to the coastal frontage allowing the coastline to move back.
• Realign Defences (Coastal) - New coastal defences moved marginally inland but remaining consistent with the current alignment along the western coastal frontage, allowing the coastline space to move back.

Options not proposed for the shortlist:

• Groynes and Breakwater - Hard barriers (typically rock or timber) designed to help trap sediment and preserve the beach, improving protection from flooding and erosion.
• Beach/Sand Replenishment - Introducing significant volumes of sediment or sand along the western frontage to increase the extent to which the dunes and shore can act as a barrier to storm events.
• Hard Engineering Defences - Hard engineered defences such as rock armour or rip-rap to protect the shoreline against scour and wave erosion.

View the information board for Coastal flood risk

There are several watercourses and areas of interest to the west of Pwllheli. Here three main rivers the Afon Rhyd-hir, the Afon Penhros and Afon Ddwyryd merge as they approach the western edge of Pwllheli. They continue towards the town as the Afon Rhyd-hir which enters the harbour through tidal gates below Embankment Road.

Flood risk from these watercourses primarily arises from the rivers becoming “tide-locked” when the gates close during high tides. When this coincides with high river flows from prolonged or heavy rainfall, water levels in the rivers increase, overflowing into the surrounding floodplain. This can result in flooding to people, property and the A499.

Options proposed for the shortlist:

• New Harbour Gates - A regulated barrier at the harbour entrance to create capacity within the harbour to manage river flooding and equally to manage tidal flood risks from storm surges.
• River Diversion - A reprofiling of the gradient to diverts flows to the coast at a new location west of the town.

Options not proposed for the shortlist:

• Upstream Storage - Introducing changes in the upstream land to create greater capacity for flood water to be stored there.
• Overpumping on the Afon Rhyd-hir and Afon Penrhos - High volume pumping stations to be constructed in Pwllheli, designed to pump high river flows to the sea when high tides would otherwise cause a backing up effect.
• New Flood Defences - Localised defences within the town centre where they can provide direct protection from river flooding.

These are additional options that will be taken forward for consideration in conjunction with the main options that are shortlisted.

• Dredging - Significant ongoing dredging and channel reprofiling of the rivers to improve flows and capacity.
• Localised Road Raising - Increasing the height of the roads above predicted flood levels to lessen risk of road closures through flooding.
• Natural Flood Management - when natural processes are used to reduce the risk of flooding through restoring bends in rivers, changing the speed water flows in rivers and the way land is managed so soil can absorb more water.
• Property Flood Resilience - measures that can help to prevent flood water ingress into a building or aid rapid recovery following a flood event.

View the information board for Flood risk from rivers - West

To the east of Pwllheli the Afon Erch flows from Abererch village towards the town. This river enters the harbour on its eastern side, after passing through the tidal gates adjacent to Abererch Road.The main area of flood risk from the Afon Erch is within Abererch village.

There are existing flood defence structures here including an embankment which helps to protect the village. However, there remains a flood risk from over topping of the banks in extreme events which could become more frequent with climate change.

Options proposed for the shortlist:

• Direct Defences (Flood Walls/ Embankments) - Raised flood defences in Abererch providing a direct line of defence against flooding from the Afon Erch.

Options not proposed for the shortlist:

• Upstream Storage - Introducing changes in the land upstream, north of Abererch tocreate capacity for flood water to be stored there.

These are additional options that will be taken forward for consideration in conjunction with the main options that are shortlisted.

• Dredging - Significant ongoing dredging and channel re-profiling of the Afon Erch to improve flows and capacity.
• Natural Flood Management - when natural processes are used to reduce the risk of flooding through restoring bends in rivers, changing the speed water flows in rivers and the way land is managed so soil can absorb more water.
• Property Flood Resilience - measures that can help to prevent flood water ingress into a building or aid rapid recovery following a flood event.

View the information board for Flood risk from rivers – East

Critical Success Factors

These are the project outcomes that are crucial to the successful delivery of the project and differ from the Objectives which identify aspirational outcomes.

Strategic Fit and Business Needs - The option should substantially reduce flood risk from sea and main rivers. It should align with the relevant flood risk management strategies, policies, guidance and deliver wider benefits to the locality.

Potential Value for Money - The option should achieve a positive cost benefit ratio. It should deliver efficiencies and minimise costs associated with future maintenance and operational requirements.

Supplier Capacity and Capability - The option must match the capacity and capability of potential suppliers to deliver it.

Potential Affordability - The option must meet the requirements and deliver outcomes to be eligible for funding via Welsh Government Flood Risk Management Grant in Aid. The option should consider opportunities to provide benefits to potential funding partners.

Potential Achievability - The option must be physically possible to construct within the constraints in the area. The relevant consents and permissions must be securable. The Risk Management Authority must be able to meet the long-term management and maintenance needs of the option.

Investment Objectives

The project investment objectives have been established through early dialogue with stakeholders and are presented in the following table. These investment objectives are aspirational and set out ‘where we want be’ or ‘what we want to achieve’ and are not so narrowly defined so that they set limits on what is possible.

1. Anticipate the effects of climate change and seek to reduce the flood risk and impact to properties, transport infrastructure and risk to life associated with fluvial and tidal flooding from the Erch, Rhyd-hir and overtopping and breaching of Pwllheli’s Coastal frontage.
2. Increase performance of the existing flood defences and control structures, including reducing the short to long-term operational maintenance and health and safety liabilities.
3. Understand evolution of coastal processes and the timeframe and trigger points for SMP policy implementation. Put forward solutions that will deliver against the SMP2 policies for the various Pwllheli frontage sections that will be adaptable to wider strategies set out by NRW and Cyngor Gwynedd.
4. Seek to deliver a flood risk solutions that can demonstrate delivery against SMNR principles and benefits. Supporting Welsh Government climate and biodiversity emergency priorities.
5. Seek to maintain and enhance biodiversity and ecosystem resilience, through working with Natural Flood Management and identifying wider opportunities in the catchment.
6. Through effective engagement consider the needs and views of the local community and stakeholders.
7. Seek to support amenity and regeneration in Pwllheli and where possible enhance, natural, historic, visual and built environments in order to support local culture and the Welsh language.
8. Seek to promote sustainable management of the dunes (a priority habitat), whilst improving access and improving social and recreational cohesion.
9. Identify options within a ‘Coastal Adaptation Plan’ for habitat creation, restoration and enhancement in support of Sustainable Management of Natural Resources (SMNR) and conservation priorities.
10. In conjunction with the public and stakeholders, support the planning and communication of a ‘Coastal Adaption Plan’ for the western and eastern Pwllheli coastal flood plain.

View the information board for Appraising the options

View the Longlist options appraisal table - Word document 

View the information board showing the Longlist options appraisal table - PDF

There are multiple areas of flood risk in the study area that require mitigation from both fluvial and coastal sources. Therefore, the location specific options have been joined to create a shortlist of compatible options that cover the whole study area.

The proposed combinations may be subject to change pending the final results of the Strategic Outline Case (SOC) assessment.

Combination A:

• Rivers West - Business as usual
• Coastal West - Managed realignment (coastal)
• Harbour / Central - New harbour gate
• Rivers East - New flood walls / Upgrade existing assets
• Coastal East - No active intervention

Combination B:

• Rivers West - River diversion
• Coastal West - Managed realignment (coastal)
• Harbour / Central - Raised harbour walls
• Rivers East - New flood walls / Upgrade existing assets
• Coastal East - No active intervention

Combination C:

• Rivers West - Business as usual
• Coastal West - Managed realignment (inland)
• Harbour / Central - New harbour gate
• Rivers East - New flood walls / Upgrade existing assets
• Coastal East - No active intervention

Combination D:

• Rivers West - River diversion
• Coastal West - Managed realignment (inland)
• Harbour / Central - Raised harbour walls
• Rivers East - New flood walls / Upgrade existing assets
• Coastal East - No active intervention

View the information board for Shortlist Option Combinations