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Rd, around Hilbre point and well off-shore between Kings Gap and Hoyle Rd, closer to shore, above MHWM, it has already been replaced by a wide range of dune specialists which have not been recorded at Hoylake since the late 1800s (7)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