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Will Hoylake end up like Parkgate?

Hoylake and Parkgate are in very different locations. Parkgate is 15km from the mouth of the Dee estuary, whilst Hoylake directly faces Liverpool Bay. This means that Hoylake has conditions of high salinity and extremely high levels of wind-blown sand and very low levels of water carried silt. Parkgate has much fresher conditions and no sand delivery. All the sediment deposited is carried by the river and occasional tides that still flood the area. Parkgate is an estuarine salt marsh. 

Hoylake has the potential to develop into coastal salt marsh or dunes. The dominant factor that will determine what forms at Hoylake is the relative delivery of wind-blown sand and water deposited silt. As beach levels continue to rise, we can expect Spartina to appear in areas that are still flooded by tides and in receipt of silt. In areas above the mean high water mark, where sand continues to blow in, we can expect Puccinellia, which benefits from being buried in sand (1), and other dune specialists to take over. In contrast, Spartina is killed off by being smothered.(2)

There are studies underway which should provide a definitive answer, but in lieu of the findings being released, the following points are relevant:-

• Mean high watermark (MHWM) is retreating at a rate of approximately 20ft a year and the upper beach is now above the astronomical high tide mark(3)
• The entire stretch from Red Rocks to New Brighton was dunes historically, strongly suggesting that conditions favour dune formation (4-6)
• Spartina is restricted to the pioneering zone east of Hoyle Rd, around Hilbre point and well off-shore between Kings Gap and Hoyle Rd, closer to shore, above MHWM, it has already been replaced by a wide range of dune specialists which have not been recorded at Hoylake since the late 1800s (7)
• Conditions at Hoylake mimic those at Birkdale, where dunes are forming rather than Southport where a coastal saltmarsh is forming.
• Dunes, fixed with Lyme grass have already formed on the western edges of the New Lifeboat station.

Hoylake cannot end up as an estuarine salt marsh and it is now extremely unlikely that coastal saltmarsh is the destination.

References

1. Langlois, E., Bonis, A., & Bouzillé, J. (2001). The Response of Puccinellia maritima to Burial: A Key to Understanding Its Role in Salt-Marsh Dynamics? Journal of Vegetation Science, 12(2), 289-297 https://www.jstor.org/stable/3236613

2 Hammond, M, 2001, The experimental control of Spartina anglica in estuarine salt marsh http://issg.org/…/ref…/spaang/MarkHammond_PhD_Thesis.pdf

3. Interim data collected by WBC https://sustainablebeach.org.uk/…/12/PROFILE_EX_02.jpg

4. Van Keulen’s Map or the Dee, 1715 https://www.dropbox.com/s/daj5pn0v47vj0fc/sandhills.png?dl=0

5. Photograph showing a dune ridge on Market Street, in approximately the location of the Cottage Hospital https://www.dropbox.com/s/v1c3fi132mc09oe/market%20st.png…

6. Young, H.E, A Perambulation of the Hundred of Wirral, Henry Young and Sons, Liverpool p196 https://twitter.com/…/status/1407069297168596992/photo/17. Stiles, J. Pers comm. https://twitter.com/joshual951/status/1278783380482654210, https://twitter.com/joshual951/status/1310205046794190848

The effect on wading birds raking/dune and saltmarsh succession at Hoylake Beach – RSPB and CAWOS response

Currently, waders that feed at Hoylake feed on marine invertebrates that are exposed between tides. Since the green beach is above the intertidal zone, whether it is grassed or raked will not affect the available food supply of intertidal marine macroinvertebrates.. Further east, where the grasses are Spartina not Puccinellia, and tidal inundation still occurs, the argument that a vanishingly small c.0.01% of feeding habitat is covered could be made. However, it is also important to remember that coastal terrestrial invertebrates such as Amphipods and salt-tolerant Diptera within saltmarsh can be superabundant and make up a considerable part of the diet of species such as Curlew, Dunlin, Ringed Plover and Redshank. Providing a mosaic habitat is better in terms of providing greater food heterogeneity. Also, waders need roost sites, just as much as feeding sites. The Green Beach at Southport is an excellent comparison. It vegetated quickly and is still used for feeding, as well now being an important roost site for waders. In short, waders are not losing any habitat; they are gaining habitat.

In contrast, mechanical raking has been shown to significantly decrease the biomass of macroinvertebrates in multiple studies eg. [Gilburn 2012, Schooler 2019] This can be expected to have a seriously detrimental effect on wading birds using Hoylake if raking is resumed.

Most arctic wader species are suffering catastrophic declines as a result of climate change affecting their breeding grounds, so any changes need to be viewed in that light. There is a lot of interchange between the Dee, Mersey, Alt, and Ribble Estuaries, and even other sites like the Wash, depending on tides states, exposed intertidal area, weather and localised disturbance. For this reason, WeBS counts are coordinated across the country and the site-specific effects are hard to establish. On the whole waders on the Dee are doing well, because of the mix of habitat mosaic and overall structure. See attached WeBS counts. Taking Hoylake in isolation from the rest of the Estuary, as wind-borne sand as opposed to water-borne silt, continues to be deposited, we can expect to see mudflats replaced with sand flats will alter the relative abundance of different marine invertebrates and we can expect this to have an effect on the balance of species that use Hoylake. Favouring the short-billed surface feeders such as Sanderling which mostly feed on tiny Hydrobia snails [Lourenço 2015], over longer-billed species such as Redshank which specialise in feeding on subsurface invertebrates. The development of a green beach will provide an increase in coastal terrestrial invertebrates.

Initially, the effect will be neutral. Birds use Hoylake beach as a high tide roosting site and their primary concern is to roost and conserve energy. They do use Puccinellia clumps as shelter from strong winds, but as a rule, they just need somewhere to sit undisturbed. Eventually, if the vegetated zone is wide enough, it may put sufficient distance between the roosting birds and potential human disturbance to have a significant benefit. Similarly, we can perhaps expect species such as Ringed Plover to breed on North Wirral once again. There are a few pairs on adjacent coasts [Prater 1988]

Several other species including Snow Bunting, Reed Bunting, Rock Pipit, Meadow Pipit, Linnet, Brent Goose and White and Yellow Wagtails have been observed feeding in the new habitat at Hoylake. Using the green beach at Southport as a likely predictor of the value to a wide range of species, should the natural accretion process we allowed to continue, it is highly likely that there will be significant benefits to bird populations.

Graham Jones, RSPB Site Manager, Dee Estuary Nature Reserves. Jane Turner, Cheshire and Wirral Ornithological Society/BTO Surveyor for Hoylake and Meols tetrads.

References

British Trust for Ornithology Wetland Bird Survey Online Report

References

Gilburn, A Mechanical grooming and beach award status are associated with low strandline biodiversity in Scotland Estuarine Coastal and Shelf Science 107:81–88 https://www.researchgate.net/…/257105673_Mechanical…

Lourenço et al Foraging ecology of sanderlings Calidris alba wintering in estuarine and non-estuarine intertidal areas 2015 Journal of Sea Research, 104 33-40. https://www.researchgate.net/…/279738040_Foraging…

Prater, A.J Ringed Plover Charadrius hiaticula breeding population of the United Kingdom in 1984, Bird Study 36, 154-160 https://www.tandfonline.com/…/10.1080/00063658909477020Schooler, N.K., et al , No lines in the sand: Impacts of intense mechanized maintenance regimes on sandy beach ecosystems span the intertidal zone on urban coasts Ecological Indicators 106 (2019) 105457 https://par.nsf.gov/servlets/purl/10123258#birds

Sand inundation

Hoylake has an existing and increasingly severe issue of sand blowing onto the promenade, blocking drains and requiring expensive clean-ups. Just 15 plants per square meter will reduce the volume of blow sand in a gale by 90% and stop it completely below force 7. see graph(1). Consequently, a band of vegetation just a few centimeters high has the potential to dramatically reduce the volume of sand reaching the promenade. See for an analysis of the risks posed by the inshore migration of the East Hoyle Bank.

This has already avoided what would have been a disruptive delivery of sand in April 2021, when the vegetation caught and held the vast majority of the sand blowing in from the beach after a 3-day spell of strong NNW winds which coincided with a dry beach (2) As sand from each sand blow incident is trapped by the belt of Puccinellia, the height of the foredunes will rise, providing additional protection. In Swansea, an experimental man-made dune gave complete protection from a single sand storm which required a £20,000 clean-up on the unprotected section.

Storm Surges

Despite the rising beach levels, there remains a potential for catastrophic damage to the promenade and seafront properties should a storm surge coincide with a spring tide, as occurred in December 2013. Sand dunes have the potential to provide protection against such incidents, and studies in the USA have shown that the presence of dunes dramatically reduced damage to properties compared to adjacent areas where dune formation had been deliberately suppressed(5,6) See also (7)

References

1. Aeolian transport over a flat surface by Leo C. van Rijvan Rijn 

2. People confused as grass ‘disappears’ from beach after storm, Liverpool Echo 2021 

3. The on-going battle to keep Swansea’s sand on the beach and not on the road

4. Case Study: Swansea Sand Dunes – Nature-based solution 

5. Charbonneau, B (2015) A Review of Dunes in Today’s Society, Coastal Management 43 pp 465-470 

6.Rosenberg, A. 2013. After Destruction of Sandy, Longport Finally Accepting Sand Dunes. The Inquirer. April 12. 

7. Sand dune processes and management for flood and coastal defence