Category: Guide 1

Can we predict if dunes or Salt Marsh will develop at Hoylake?
 

Intertidal Zonation:

 If you have ever looked at a steep rocky shore at low tide, you can see bands of animals and plants at different heights. This is because different organisms are adapted to the gradient of conditions (dominated by time spent in the air and under water).  The same processes work on flatter muddy and sandy shores, though the bands are much wider due to the shallow gradients.

Salt marshes:

 A salt marsh begins when mud and silt are deposited along a sheltered part of the coastline. This is because rates of deposition are greater than transportation due to the lack of energy in the waves. The deposition builds up over time meaning that the mud breaks the surface to form mudflats. Some plants then begin to grow. The first plants are typically Spartina (Cord Grass) and Salicornia (Samphire), which are tolerant to saltwater. Due to the sediment and material accumulating, it gets covered by the tide for shorter periods. This and rain will leach (wash out) some of the salt. As the salt is now lower in concentration, it means more plants can start to grow. Puccinellia (Salt Marsh Grass) is an early coloniser The ranges of salt marsh plant populations are generally limited in the seaward direction by their ability to withstand marine inundations. In the landward direction, they tend to be limited by competition, particularly shading by other plants.

Dune Systems:

Dunes form when sand is deposited along a coastline faster than wave action can remove it. As with salt marshes, the initial pioneer plants are typically Spartina and Salicornia, with Puccinellia following when the accretion is sufficient to reduce the amount of time spent under seawater. Puccinellia with its preference for being buried in sand, and Elymus (Sand Couch) colonise early, followed by a wide range of dune specialist species, until Marram or Lyme Grass establish above the reach of the sea in all but exceptional conditions, and fix the dunes.

What is the crucial decider in predicting dunes or salt marsh?

It all comes down to the sediment, specifically the rate of sediment delivery and the balance of sediment type delivered. This means that the relative contribution of wind and water delivery of sediment and tidal scour play a role. It is important to remember that the plants are just an indicator of the changes in beach level, not the cause of it, though of course their roots will reduce tidal scour and accelerate the accretion process. Unless the beach level are rising and producing conditions where it is possible for pioneer plants to establish, there can be no vegetation. Both the Sefton coast and the Fylde coast demonstrate the subtleties of the processes. Marshide and Southport are forming saltmarsh, Birkdale and Crosby are forming dunes, while Formby isn’t accreting at all its eroding (and adding to the accretion to either side of it.) On the Fylde coast St Annes is still receiving huge amounts of sand and is still forming dunes, but a few km away, Lytham has virtually no sand delivery and the Ribble is still delivering mud and silt, so it has formed saltmarsh. 

So what is going to happen at Hoylake?

The environmental conditions at Hoylake resemble those at Birkdale in terms of sand supply, lack of silt supply, rising beach levels and relative exposure. The plant species establishing include many dune specialists and the entire coast was dunes previously so if the sand keeps blowing in, it’s pretty much certain that there will be impressive dunes at Hoylake again. If you look at the seaward side of the main vegetation band, you can see Puccinellia doing its trick of building hummocks.

References:

For now these are general (the area is so well established I’ve used teaching materials). So far the only primary research isn’t UK/Europe specific. 

I will add additional resources as and when I find them

How do salt marshes form?

 

How do dunes form 

Is zonation on coastal sand dunes determined primarily by sand burial or by salt spray? A test in New Zealand dunes 

Does Natural England have enforcement powers or is it only advisory?

To long? Short version is that the law is clear thay are more than just advisory.

There is a claim that natural England is only advisory, The evidence provided for this is is here. https://www.gov.uk/…/organisations/natural-england/about

We are open to any other evidence anyone has to support the case that Natural England is only advisory.

In the mean time we’ve done some digging as our understanding was that Natural England had enforcement powers. Though I have to admit before we went to look I was only basing this on two things.

1: The signs on the prom which explain a bit about the SSSI and that it’s an offence to damage it.

2: The advice that Natural England gave to the council in March 2020 and the later statement they made when the decision to stop raking was challenged by our local councillors. In the statement/advice Natural England said that they could take enforcement action agains the council.

Advice from NE to the council in March 2020 can be found here https://democracy.wirral.gov.uk/…/Natural%20England…

Statement from NE to the council in August 2020 can be found here https://democracy.wirral.gov.uk/…/Natural%20England…

So let us dig deeper because the claim they are only advisory isn’t going away so maybe we have made a mistake.

First the advice document that explains the statutory duty of the council in relation to the SSSI and includes this paragraph:

“Further guidance on public bodies responsibilities for SSSIs can be found from the following webpage: https://www.gov.uk/…/sites-of-special-scientific… “

the link contains, amoungst other sections,

“You could be fined £20,000 in a magistrate’s court or get an unlimited fine in the Crown Court if you:

* do not give Natural England notice of your intention to carry out or approve an activity likely to damage a SSSI

* act before you get Natural England’s response”

“You do not need Natural England’s assent for works that you’ve decided are unlikely to damage a SSSI. You could be prosecuted and fined if you damage a SSSI. Contact Natural England if you’re unsure.”

“You could be prosecuted and made to restore the features of a SSSI if you:
* fail to notify Natural England of the works

* do not take account of Natural England’s advice

* cause more damage than necessary”

and

“If you decide to go ahead without assent

You can still carry out works if:
* Natural England refuses to give its assent
* you believe the conditions attached to an assent are unacceptable You must give Natural England written notice at least 28 working days before the start of the works if you intend to go ahead without assent. You must show that you’ve:

* taken into account any advice Natural England gave you
* considered alternatives that could reduce the impact on the SSSI, such as using lighter vehicles to carry materials

* weighed the balance between conflicting interests, including the special interests of the SSSI Natural England may refer a case to the Secretary of State for Environment, food and rural Affairs if it still has serious concerns about the potential damage to a SSSI. This can lead to a judicial review of the public body’s decision to go aheadwith the works.”

So the council can proceed without assent but it has to have asked for it and it has to notify Natural England and explain why they are going ahead however, they must return the SSSI to its original condition and crucially they are still open to prosecution.

Whilst these documents go some way to explain the situation you really have to look at the law.

Natural England was set up by the Natural Environment and Rural Communities Act 2006 which can be found here https://www.legislation.gov.uk/ukpga/2006/16/contents

You can see there is a section on “Advisory functions” in it it states that Natural England must give advice to public bodies if they request it and that at the request of Natural England, the public authority must inform Natural England in writing whether the advice has been rejected and, if so, why.

But we need to keep reading.

You can see there is also a section on “Other functions” which include Power to bring criminal proceedings.

Further in Part IV Sites of special scientific interest Section 55 is Offences in connection with SSSIs which amends Section 28P of the Wildlife and Countryside Act 1981 so see that for the detail.

The whole act can be found here https://www.legislation.gov.uk/ukpga/1981/69/contents

Section 28P is found here https://www.legislation.gov.uk/ukpga/1981/69/section/28P…

The relevant parts are sections 28P 2 and 3. As the council is a section 28G authority (see section 28G for an explanation).

So it’s an offence if the council don’t comply with Section 28H and is liable on summary conviction, or on conviction on indictment, to a fine.

So it’s clear that Natural England have enforcement powers too.

However, why the confusion over whether the council have to take the advice or not etc?

Well this takes us to Section 28H which is the section the assent is given or withheld under. Let’s take it a by subsections

“(1) A section 28G authority shall give notice to Natural England before carrying out, in the exercise of its functions, operations likely to damage any of the flora, fauna or geological or physiographical features by reason of which a site of special scientific interest is of special interest.”

The council have to notify NE before doing anything that is likely to damage the SSSI “ by reason of which a site of special scientific interest is of special interest” which means it has to be damage to something which is part of the reason the SSSI exists.
You can find the designation of the SSSI details here https://designatedsites.naturalengland.org.uk/SiteDetail.aspx?SiteCode=S1003676&SiteName=wirral&countyCode=&responsiblePerson=&SeaArea=&IFCAArea=

clicking on “citation” takes you to why it was designated an SSSI https://designatedsites.naturalengland.org.uk/…/1003676…

the first section of this is

“Description and Reasons for Notification:

North Wirral Foreshore is located between the outer Dee and Mersey Estuaries. This site is an area of intertidal sand and mudflats and embryonic saltmarsh which is of considerable importance as a feeding and roosting site for passage and wintering flocks of waders, wildfowl, terns and gulls.
The embryonic mixed saltmarsh is formed principally from common saltmarsh-grass Puccinellia maritima and glasswort Salicornia europaea, together with some common cord-grass Spartina anglica.“

There’s more to it but as we’re talking about raking/spraying vegetation we can for now stop there.

So anything which may damage the embryonic mixed salt marsh needs to be notified to Natural England or the council are liable on summary conviction, or on conviction on indictment, to a fine.

There is also a list of operations which may damage the SSSI https://designatedsites.naturalengland.org.uk/…/1003676… this covers things like spraying herbicides/rotovating/ploughing/cutting etc amongst other things.

The council had done this when asking for assent and for changes to the assent in 2010 and 2015. The Natural England response is covered in subsection 3.

“(3) In response to the notice referred to in subsection (1), Natural England may send a notice—
(a) saying that they do not assent to the proposed operations, or
(b) assenting to them (with or without conditions),
but if they do not send a notice under paragraph (b) within the period of 28 days beginning with the date of the notice under subsection (1) they shall be treated as having declined to assent.”

So previously the council had got the assent for some activity though this ran out in March 2021 and the natural England advice was

“Due to the presence of other species it is now difficult to undertake spraying and raking in a way that is legally compliant with the Assent; non-compliance with the Assent poses risks of enforcement by Natural England.“

So where are we now?

Well the council have no assent and would have to notify the council before they did anything which might damage the salt marsh, specifically the saltmarsh-grass Puccinellia maritima and glasswort Salicornia europaea (known as samphire) and Spartina anglica.

Then Natural England have to reply as per subsection 3 above within 28 days or they are deemed to have declined to give assent.

So what happens if Natural don’t give assent?

If you check the Natural England advice/statements at the top you’ll see Natural England said they are unlikely to give assent for raking the whole beach but that

“ Vegetation control across the whole coast would not be acceptable as this is likely to be contrary to the site’s conservation objectives, it is also unlikely to be economic or sustainable. Smaller areas of vegetation control may have scope to be consented but there should be clear justifications for requests to control vegetation establishment.”

also

“ There needs to be a thorough ecological survey of any areas to be proposed for targeting of vegetation control. “

So if the council don’t do what they are currently doing (surveys) then they are unlikely to get assent.

But what happens if the council acts without assent?

Well we’ve seen from subsection 1 above they have to notify Natural England or they are liable on summary conviction, or on conviction on indictment, to a fine. If Natural England don’t give it we drop into subsection 4.

“(4) If Natural England do not assent, or if the authority proposes to carry out the operations otherwise than in accordance with the terms of the Council’s assent, the authority—

(a) shall not carry out the operations unless the condition set out in subsection (5) is satisfied, and

(b) shall comply with the requirements set out in subsection (6) when carrying them out.”

So if the council are either going to act without the consent or they are going to do something agains the conditions of the assent then they need to comply with subsections 5 AND 6.

“(5) The condition is that the authority has, after the expiry of the period of 28 days beginning with the date of the notice under subsection (1), notified Natural England of (note a typo here in the website) —

(a) the date on which it proposes to start the operations (which must be after the expiry of the period of 28 days beginning with the date of the notification under this paragraph), and

(b) how (if at all) it has taken account of any written advice it received from Natural England, before the date of the notification under this paragraph, in response to the notice under subsection (1).”

This is the council must notify Natural England of their intention to proceed without assent which must be at least 28 days later and it must state how if at all it considered the assent/conditions/advice.

AND subsection 6

“(6) The requirements are-

(a) that the authority carry out the operations in such a way as to give rise to as little damage as is reasonably practicable in all the circumstances to the flora, fauna or geological or physiographical features by reason of which the site is of special interest (taking account, in particular, of any such advice as is referred to in subsection (5)(b)); and

(b) that the authority restore the site to its former condition, so far as is reasonably practicable, if any such damage does occur.”

So when then doing whatever the council decide to do without assent, they must do it in a way to minimise any damage and to restore the damage.

In short if the actions the council do damage the SSSI, as above this includes damaging Spartina/puccinella etc, then they must re-instate it afterwards. eg if you take away the spartina you must then put it back.

If not the council are liable on summary conviction, or on conviction on indictment, to a fine.

So they can ignore the assent but they can’t damage the SSSI without restoring it or they may face enforcement action.

Sorry this is a long detailed post but it’s more nuanced than Natural England is advisory or not. Naturaal England has a duty to advise and it’s possible to ignore the advice so long as you don’t damage the SSSI or re-instate it after you’ve done whatever you are planning on doing, if you fall foul then they can use their enforcement powers.

It’s a bit like saying a police officer can’t physically prevent you speeding but ignoring that if you do they can fine you.

What can be done about the drains?

This is the opening “gambit” on a discussion that I am hoping will start to crystallise some suggestions – for now it’s a few statements and questions for debate. Which I will correct/update as things are clarified.

1. Statement: There are two intended and one unintentional source of water reaching the beach.

(i) Added by Nigel Blacow: Road gullies (that take surface water from adjacent public roads and footpaths) and the associated drainage are the responsibility of Wirral Council, via the Highways dept, not United Utilities (UU are responsible for most other public /shared sewers but they are not responsible for private drains/soakaways that only serve one property. These are the responsibility of the property owner). When the Promenade was built in the 1890’s the outlets were probably nearer the top of the wall than the bottom but now because of rising sand levels they are either close to the bottom of the visible wall or buried under the sand (Kings Gap end of the prom, in particular). The gullies are designed to ‘trap’ solid debris, in the surface water running off the road surfaces and so need to be regularly cleaned out by a tanker using a suction hose. Because sand blows onto North Parade and surrounding roads and ends up in these road gullies, they tend to block up more quickly and as I believe Wirral only own one suitable tanker they arent cleared as frequently as required. When they are cleared the drainage outlet pipe to the sea wall is also frequently blocked, so this has to be cleared using a high pressure water jet and this can inevitably result in some dark silty residue being left on the beach. The possible contaminants in the surface water and/or this debris are many and their impact on the beach flora and fauna are unknown. In March 2020 Natural England advice to Wirral council said – ‘Natural England advises that the water quality should be tested to understand the contamination risks, better managed and regulated.’
There are approx. 23 road gullies on North Parade and there are currently 10 visible outlets through the sea wall, these outlets generally coincide with the roads leading down to North Parade. At the Kings Gap end of the prom the council have confirmed that some of the surface water outlets are so deep under the sand that they have been unable to locate them, with the limited resources available, and that trying to keep these clear is no longer practical or viable!
(ii) Rainwater from the seaward side of North Parade properties [lanwdard feeds into the main sewers], some of which are soakaways and some have outlets onto the road and some may drain onto the beach Added by Nigel Blacow The council have said they intended to map as many of the surface water drainage points and pipes as possible but due to covid and lack of resources this doesn’t appear to have been completed.

(iii) General water table from the soakaways mentioned, and broken drains and possibly water from further afield [Hoylake Carrs] building up behind the sea-wall and leaking through in places. I heard that the foundations for the new flats on the site of the old fire station hit water unexpectedly high and that council test bores on the promenade did likewise 
Added by Nigel Blacow Given the age of these drains, it is highly likely that some are broken or leaking but this is unlikely to be a major factor and will just add to the general groundwater. From close observation of the beach over some years it is apparent that in addition to the surface water from the roads etc. there is also an element of groundwater, from many sources, that finds its way to the beach. The majority of this groundwater probably come from the fields and golf courses behind the developed area of Hoylake, which tend to flood following long periods of heavy rain. This groundwater must percolate under the ‘built up’ section of Hoylake down to the beach, which is at a lower level and it is probable that this is the main source of seepage through the sea wall. With regard to the prom and sea wall it is a historic fact in the past Wirral have injected cement grout under the concrete surface of the prom to fill the voids caused by water movement and minimise any resultant settlement.

2. Question: Where can the drainage water be taken?

Is the only choice further out towards the sea, where there is still sweeping? Drainage from the houses could be diverted to the sewers, but the drainage from the roads would have to flow uphill to go anywhere else.

Added by Nigel Blacow There are a number of possible alternatives, so far –
a)Natural England, in their March 2020 report said – Natural England advises that it would be better for the local environment for land drainage/ run off to be collected, treated and then discharged via a regulated discharge point. There may be opportunities for wetland creation landward of Hoylake or further along the coast and these areas could receive this treated water.
b)Divert the surface water into the combined public sewer that runs along the landward side of North Parade. It is unlikely that UU would be very receptive to this suggestion. It would add a large volume of surface water to the sewage going to the treatment plant and this is undesirable for a number of reasons, practical and financial. It would also be a major civil engineering project and have significant costs.
c)The surface water could be ‘managed’ using SuDS (Sustainable Drainage – susdrains.org) principles. This is a nationwide initiative to better manage surface water, by allowing it to be dealt with close to its source, rather than piping it elsewhere. This generally involves use of correctly designed, engineered and constructed soakaways, reed beds and/or attenuation tanks. The recently published ‘Masterplan’ (i.e. a record of development in Hoylake and some ideas for the future, based on local consultation) produced by AECOM consultants for Hoylake Vision, outlines some details of how this solution might be incorporated into a remodelling of North Parade and the promenade.
Added by Steve Taylor: In Liverpool in the eighties a massive interceptor sewer was constructed from Garston to Bootle which intercepted all of the old Victorian sewers that were previously discharging directly into The Mersey. This sewage was then pumped to I think Sandon Dock treatment works. Perhaps a similar interceptor sewer could run the length of the promenade at Hoylake gathering all of the surface water and road drains to a more suitable outlet point east of Meols? A big and expensive undertaking.

3. Question: What are the contaminants in the water?

The current assumption is that is heavy metals, inorganic salts, aromatic hydrocarbons, and suspended solids from road runoff plus pesticides, fertilisers and plant waste from gardens.

4. Question: Could the developing green beach form part of the solution?

For example is there any way to use reed-bed water purification before discharging the water into the sea?

5. Question: How much is it likely to cost to fix the drainage issues, and are there any grants still available now we are not EU members? 

The Landfill Communities Fund could be a potential source of funding  [thanks Lisa]. 

REFERENCES

https://hoylakevision.org.uk/hoylake-vision-progress-report-regarding-surface-water-discharges-onto-hoylake-beach-august-2020/?fbclid=IwY2xjawNbrMVleHRuA2FlbQIxMABicmlkETAxd2g3dUo5VUptd3ltWVd5AR5VOlVzUTi_OeWowgPkGH7fx7QJmEZPnrdPGza2FuAZUiC-WfSsjyh60mvLvQ_aem_4HH2OLWLRYRZ1HKzkGHepg

Who is the decision maker when it comes to managing the beach?

Who is the ultimate decision-maker? 

The section of beach within the scope of this discussion is wholly within the North Wirral SSSI [site of special scientific interest] (1) Consequently, any activity that affects the habitat must be approved in advance by Natural England. Specifically, it is an offence to carry out any activity that may likely damage the SSSI without consent from the relevant conservation agency. (2) Furthermore the site is also designated as part of the Dee Estuary Special Area of Conservation which grants still higher levels of protection to any habitats classes as Annex 1 under that citation.  

Why has the management of Hoylake Beach been halted?  

Natural England’s formal Assent that permitted the management of Hoylake Beach expired on the 31st March 2021. Prior to that, at the end of the 2019 season, they advised against spraying or raking They have not renewed the licence, consequently, it is currently illegal to rake or spray the beach. [3]

What needs to happen before and raking of the beach can start?  

Natural England have indicated that it might be possible to replicate the approach they have adopted at Southport, ie. identify an area of the foreshore that can be retained as a managed amenity area, however, they will not agree to anything prior to a comprehensive botanical and geomorphology study. This will identify the least harmful location and determine if the damage resulting to nationally important habitat is justifiable. Nothing can happen without Natural England’s specific say-so.

Issues to consider:

If the council were to resume raking without first obtaining permission from Natural England, they would be liable to prosecution and fines.

EVIDENCE:

Link to the citation for the North Wirral Foreshore SSSI https://designatedsites.naturalengland.org.uk/SiteDetail…

Link to the Environmental Law covering SSSIs http://www.environmentlaw.org.uk/rte.asp?id=303

Link to a letter confirming that Assent to rake/spray Hoylake beach has been withdrawn by Natural England, and evidence that raking is likely to result in prosecution of the Council https://democracy.wirral.gov.uk/…/Natural%20England…

In the 1600s, the Hyle/Hoyle “lake” was a channel, 30ft deep at the Dovepoint end, and 15ft deep at the Hilbre end. It was deep enough for the largest ships using the coast to moor at low water. Silt from mostly the Dee but also the Mersey was deposited in the channel over time and it gradually filled. By the late 1800s there was still enough water close off shore to allow the substantial Hoylake fishing fleet to anchor there. (1)

When the promenade was built, only the eastern part of the channel was water at low tide, but there was still a channel around 200m from the promenade, filled with water twice a day and protected the promenade from sand blowing in from the East Hoyle bank. (2) 

That channel continued to fill with silt, though water with a heavy load of silt would still arrive from east and west each tide. This too acted as a barrier to windblown sand, though the beach level continued to rise and become flatter.

Today the beach level measured at 200m offshore is around 6-7m higher. It is almost flat (a 1 in 400 gradient). Sand has finally covered over the silt, at least to level with the Old Baths, and there is no gutter to bring silt in from the Dee. The mean high tide mark is retreating seaward at an astounding 7m a year and the upper beach is now above the astronomical high tide mark (which is why dune plants are able to establish).

As sand continues to blow in, some of it will be trapped by the seaward edge of the green beach which will rise into a ridge, further protecting the upper beach from seawater. (3)

The height and position of those dunes will be determined by the relative contribution of sand delivery and tidal scour but an equilibrium will be found. They will start on the outer edge of the main vegetation line and adjust outwards. A dune slack will form behind.

References

1. Hoylake’s fishing fleet at anchor, dunes and bathing machines prior to the promenade, Young, D, More pictures from the past. 
2. Children paddling in the Hoyle Gutter, showing the proximity if water and the steep profile of the beach Young, D Ibid. 
3. Sand dune formation and succession: Short video tutorial Universities of Cambridge/Derby 

More on saltation and how slipways give us an insight into what will happen if we do not have a solution to sand-blow

The attached diagram explains why at Hoylake, most aeolian (by wind) transport of sand is by saltation and what determines how much sand can be carried by the process. Most people will have seen saltation in action or felt it on their shins if out on the beach. Here is a video from Hoylake beach on Youtube 

The following is noteworthy:

• the grains seldom reach more than 25cm above the beach before gravity pulls them back down, though in extreme conditions 1.5m jumps are known. This has implications for the design of artificial or natural on beach barriers to prevent sand from reaching the promenade and is why saltation only gives us issues when the promenade is over-topped or the sand can blow up a slipway
• A phenomenal amount of sand can be transported like this. 10.9 metric tons of sand per meter per day can be delivered in an onshore Force 8-9 gale. That is 5.5 metric tons per minute across the zone from Kings Gap to the Lifeboat station in a NW gale if the beach is dry
• Anything that lowers the drag force of the wind or increases the lift needed to overcome gravity, will reduce the amount of sand transported. The energy to raise each grain of sand up a slipway is about 0.6J [0.004g per grain and a 1.5m rise] Consequently the carrying capacity of the wind is greatly reduced on slipways.

In the last few days a steady, but not excessively strong WSW wind has been blowing more or less parallel to the promenade, with frequent rain showers damping down the saltation process. There is a relatively narrow band of free sand (compared to the huge East Hoyle Bank), close to the sea wall, and this has been able to saltate sand up the new slipway by the lifeboat station. The outcome is the familiar build up of sand around the Hoyle Rd slipways and near the Parade School wall [see the posts below for examples]

Now imagine this was the whole width of the beach providing sand and there was less than 20cm from the sand to the top of the wall, rather than the need to carry sand up the slipway and lose most of its lifting power. This video is a clue – from when a limited overtopping occurred in two small sections, at the King’s Gap steps and the Alderly Rd slipway.  .

How wind moves sand

At Hoylake, most windblown sand is moved by three main methods which depend on the wind speed and especially the size of the sand grains.

At Hoylake,  >95% of sand moves by saltation a sort of hopping action – when a sand grain “hops” and when it lands dislodges more grains and they dislodge more, until a cascade of sand starts moving in the wind a few cm above the beach – see Figure 1

Saltation can start with wind speeds as low as 5m/s (11mph) but if the beach is wet, after a tide or rain, it takes stronger winds to start the sand moving.

If the prevailing winds blow over a large expanse of sand, there is more chance of it drying out and the conditions for saltation to occur.

Once in motion, the saltating sand will continue moving until:

• The sand particles are in the lee of a raised object
• The wind drops
• The sand particles meet an uphill gradient that is too steep for the wind
• The sand particles hit a wet patch or an area bound with silt or a salt crust

Increasing average winds, a greater expanse of sand or less frequent coverage by the tide will increase the amount of sand delivered to the promenade.

Why there is a greater risk of sand blowing onto the promenade

• In the 1660s when the 1st map in figure 2 was created, the Hoylake lake was less of a lake and more of a channel, 5m deep at the Hilbre end and 10m deep at the Dovepoint end.
• It was used as a sheltered [by the East Hoyle bank] deep-water anchorage
• Kings Gap, was a small and managed gap in the huge dune system on N Wirral that allowed convenient access to horse-drawn traffic.
• Tidal forces have redistributed the sands of the E.Hoyle since the last Ice Age, gradually filling in the Hoyle “lake” The second map is from an 1899 survey and shows that the channel was now a gutter reaching about ½ the original length
• As recently as 10 years ago the mud and silt of the Hoyle Lake was easy to encounter just by walking seawards, though the permanent gutter had gone.
• Before about 1850, there was only around 70-700m of exposed sand that could saltate offshore, but that was enough to build dunes. Figure 3
• Even when the “Lake” filled the wet sand and mud of the remnant gutter protected the promenade from the bulk of sand blow in from the East Hoyle bank because it broke the sand transport pathway for saltation.
• Now there is no protection from the vast expanse of the East Hoyle bank’s wind-blown sand and a direct sand transport pathway has developed
• Mean High water mark is retreating at up to 75m/decade, so more of the bank is dry more often
• Climate change makes extreme weather events more likely.

Consequently, we can expect a lot more sand to be delivered a lot more frequently.

How much sand has arrived (and where is it)

One of the benefits of undertaking that enormous analysis of the LiDAR data is that its now possible to examine the changes to the beach in huge detail.

• You can see from the first graph that the highest build-up of and isn’t close to the promenade – it’s 100-200m out on the beach. This explains why it’s no longer a muddy slippery, impassable quagmire out there – that’s under close to a meter of fresh sand
• The second graph shows build-up is much greater at the RNLI end of the beach (and this isn’t the effect of the old baths – it has happened out way past them too).
• Looking at the profiles of different locations over time, the areas which are accreting are mostly accreting at a steady rate i.e. the changes we have seen are still going on and the beach is getting higher and higher
• HOWEVER there are locations (currently in the model as linear projections based on accretion 1985-2020 that actually fit better as passing a tipping point and now are accreting much more rapidly. This means there might actually already be a lot more sand arriving now, and the rate of delivery is accelerating. These are further out on the beach and may well be a foretaste of things to come.

Studies on the control of Spartina have shown mechanical removal leads to a 42.8% increase in plant density in subsequent growing seasons compared to control areas that were left unmanaged. [1] This is because this grass propagates via underground rhizomes and any activity which fragments and redistributes those rhizomes will increase the rate at which it can spread compared to natural expansion. 

How could Spartina be controlled?

• Chemical spraying will slow the expansion of Spartina, though the effect is short-lived and recovery to 100% of former density occurs within 1-2 years. (1,2)
• Smothering with dredged substrate or covering with plastic sheeting for a complete growing season has been shown to be effective in controlling Spartina (3,4)
• Complete removal of substrate containing the rhizomes which extend 30-40 cm underground is an effective treatment [2]

What will happen if we do nothing?

As noted in https://www.facebook.com/groups/353912892854904/posts/353920626187464 the Spartina growth on the North Wirral foreshore is constrained within a zone with specific conditions of salinity and silt delivery. That zone is moving as the accretion continues. Now that that raking and spraying has stopped favouring Spartina over its competitors, it is more or less irradicated from the upper beach. That process will continue to happen as the beach profile changes.

References

1. First record of Spartina alterniflora in southern Africa indicates adaptive potential of this saline grass 

2. A systematic review of the effectiveness of management techniques used in the control of invasive estuarine cordgrass Spartina species 

3 The Effects of Smothering a Spartina alterniflora Salt Marsh with Dredged Material 

4. Hammond, M, 2001, The experimental control of Spartina anglica in estuarine salt marsh #spartina