Porth Hellick Sea Defence Proposals - Winter 2022 - Spring 2023

 
What’s the problem?
Porth Hellick is one of the more remote sites that we plan to protect, with few buildings nearby. At the eastern side of the beach sheds are used by local fisherman. Porth Hellick Pool just to the north is the largest freshwater source on St Mary’s. Porth Hellick Pool is an important source of water for Higher Moors SSSI. The pool is partly protected by the vegetated dune behind the beach. 

There are gaps along the dune (shown below in yellow). At the eastern side the dune is significantly lower and needs repairing (shown below in green). Erosion has been caused by people walking through the dunes along multiple routes, as well as by boats being launched on the eastern side. These low points allow sea water to flood across the dunes during storms. If sea water gets into Porth Hellick Pool it affects local wildlife and St Mary’s water supply.

 

What's the suggested solution?

The proposed work renourishes the dune to fill the gaps and rebuild the dune at the eastern side. The renourishment will use sand similar in colour and size to existing sand, which will be covered by a biodegradable coir matting. This will then be overlaid with topsoil and planted with Fascicularia bicolor, which matches the existing vegetation along the dune. A new ramp about 22 m long by 3.7 m wide will be constructed on the eastern side for vehicles to launch boats. A boardwalk will be installed at the western end of beach (highlighted in orange above) to provide easy access for the public and to protect the dune from erosion. The new dune will blend into the surroundings and will not significantly change how it looks. 

Close up of proposed ramp at Porth Hellick and dune renourishment
 
Proposed boardwalk at Porth Hellick

 

What’s the likely impact?

The work could disturb birds using the Higher Moors area, but this disturbance would be temporary and is likely to have a low impact. A significant archaeological feature at Porth Hellick is the grave marker of Sir Cloudesley Shovell, which would need to be temporarily removed until the work is completed.

Work is expected to start in November 2022 and to be completed by March 2023. The construction compound will be located in the field immediately to the north-east of the beach. Vehicles will access the beach by the farm track off Carn Friars Lane and public access to the beach will be available using the footpath at the western end of the beach. 

Aerial image of proposed Porth Hellick sea defence works
 
Feedback

Thank you to everyone who submitted feedback on the proposals at Porth Hellick. The responses have all been helpful and will inform our planning application. There were a range of questions and opinions submitted and we have summarised these, providing answers below.

Why is the boardwalk necessary?

The boardwalk at the western end of the beach is necessary to prevent the dune being further eroded by the passage of feet and hooves. This erosion has created a gap in the dunes through which seawater can flow into the Higher Moors Pool during storms.

Will the design of the boardwalk will make it harder for people to access the beach, because of potential trip hazards?

The access track at the western end of the beach is already eroding, so a boardwalk will help stop this getting worse. The boardwalk will be designed and constructed to avoid trip hazards and there will be no steps on the boardwalk. We’ll have a look at the materials to be used to make sure it is appropriate for horses as well as people. The boardwalk will be generally 100 mm off the ground, graded to ground level at each end, so sand should not cover it.

Will the boardwalk and ramp make the beach inaccessible for horses?

We’ll look at the materials proposed for both the boardwalk at the western end and the beach access ramp at the eastern end of the beach to try and ensure they’re suitable for horses’ hooves. The British Horse Society provide guidance on surfaces – including for boardwalks – which will be used to guide material choice, material strength and boardwalk width.

Will this work include improving the leat? 

The maintenance of the leat discharge point and the freshwater leat will be discussed with the land managers. The aim of this project is to prevent major storms sending large volumes of water into the Higher Moors Pool all at once.

Won’t the ramp just be a concrete eyesore?

The beach access ramp will be profiled so that it is in line with the surrounding dunes, which will be raised to provide protection against water overtopping at this end of the beach during storms. The concrete block mattress forming the surface of the access ramp will be filled with topsoil and seeded with grass. We may need to change this approach if materials are needed to be more suited for horses.

What purpose will the slip at the eastern end provide? What happens as the sides of the slip? Won’t this encourage water to flow over it and into this corner of Porth Hellick?

The ‘slip’ is a beach access ramp for maintenance of the leat outlet and to provide access for pedestrians, horses and vehicles at this end of the beach. It will be about 0.8 m above existing ground level at its crest. Because the ramp is covered with open concrete blocks filled with gravel underneath and soil on top, water running onto the ramp will percolate through. At the sides of the slip the new dune (also 0.8 m above existing ground level next to the ramp) will have the same cross-sectional profile as the ramp.

Is this water question as important now we have desalination on St Mary's or should we protect what we have?

We’re protecting the freshwater at Higher Moors partly because we have limited fresh groundwater available for our water supply. If the Higher Moors Pool and neighbouring local groundwater get saltier, we may have to rely on the desalination plant more. Water from the desalination plant isn’t as tasty as groundwater, and it’s much more expensive to supply. We’re also protecting the freshwater at Higher Moors because it supports a mostly freshwater ecosystem. If the Pool gets saltier, the ecosystem will be affected.

Are there geological as well as ornithological and botanical (and other) issues here? Are all these issues sufficiently safeguarded?

The Environmental Statement has identified no designated or non-designated sites for geological matters within the working area. We’re aware of Camel Rock as a significant geological feature, but no works will occur near to it. The sand to be used for dune renourishment will be similar in size and composition to existing sand at Porth Hellick.

Where is the sand which matches the existing material coming from?

We’ll use Cornish granite sand, unless we can source local Scilly granite sand.

Will there still be path behind the beach?

Yes, it will remain.

The fascicularia and hottentot fig have stabilised the system very effectively and prove a serious obstacle to overtopping but they are invasive - is there a chance that thrift, camomile and other local 'native' species could be re-established?

We would like to use non-invasive local plant species as much as we can, but whatever we use needs good dune-binding properties. We’ll be talking to the Isles of Scilly Wildlife Trust and others about what might be suitable to use.

If you have any further questions about the proposals please get in touch with us at adaptivescilly@scilly.gov.uk