Sand Dunes
Sand dunes are a familiar sight at beaches across the Iveragh Peninsula, and are particularly prominent at Rossbeigh, Derrynane, and Waterville. These mounds of sand form at the top of the beach, above the maximum reach of the waves. Dunes mainly form through wind action. Once formed, they are critical for supplying sediment to beaches and protecting coastal zones. Dunes are highly dynamic. They are constantly changing because of once-off bursts of winds or unusually high waves, periodic storms, and long-term climate variation.
Dune system at Derrynane. Provided by knowledge gatherer, Anna Collyer.
Sand dunes require certain conditions to form. Firstly, there must be a large supply of sand, such as expansive tidal flats with a large range between high and low tide. This large intertidal range allows enough time for sand to dry. The second condition required is a strong and continuous wind to move the sand grains. This happens at beaches that face the prevailing winds, such as Rossbeigh, Derrynane and Waterville, which all face the dominant southwesterlies.
Dune initiation occurs when wind blows and transports sand up the beach towards an obstacle such as a pebble, a lump of seaweed or a piece of driftwood. This barrier intercepts the wind, so the sediment is dropped. Sand continues to build up on the windward side of the obstacle to form a ridge. Eventually, the sediment pile becomes steep and unstable and collapses, with the smaller particles cascading down the more sheltered slip face away from the wind. As more sand grains accumulate and this process is repeated, embryo dunes develop.
Characteristics of sand dune.
Once the initial embryo dunes form, vegetation starts to grow, which is key in the development, stabilisation, and protection of the dunes. Marram grass is particularly important for Iveragh’s dunes. Marram grass naturally thrives in the saline environment of the seashore. The root systems of the Marram grass bind the sand grains together and restrict movement in the sand, preventing the dunes from blowing away [1]. The long, coarse, and prickly blades of Marram grass also play a role, acting as a wind break, catching suspended sand grains, and allowing them to settle at the grass base.
Marram grass and dune system at Rossbeigh. Provided by knowledge gatherer, Anna Collyer.
Embryo dunes may only be a few metres high, but dunes tend to grow taller and more chaotic moving further inland and can reach heights of over 15m. Moving inland, the environmental conditions also change, particularly with regards to the soil pH. These changes mean that the combination of plant and animal species changes across the dune system. Sand dunes close to the beach tend to be more yellow in colour but get progressively greyer further inland, due to the increasing abundance of humus and bacteria from plants and animals.
Importance, Erosion and Protection
Dunes perform a range of ecosystem functions, acting as a protective barrier for coastal areas, providing an important habitat for plants and animals and acting as freshwater aquifer.
Dunes provide a vital habitat for a variety of animal species including the Common Lizard (Laghairt choteann), Hares (Giorria) and a range of insects. The dunes of Derrynane are important sites for Ireland’s rarest amphibian, the Natterjack toad (Cnádán). The Natterjack toad is Ireland’s only toad and can be distinguished from the common frog by the stripe running down its back . The Natterjacks hibernate in burrows dug into the sandy soil and lay toad spawn in the pounds found in the dune slacks at Derrynane.
Castlemaine Harbour is sheltered by the dunes at Rossbeigh and Inch and is a Special Area of Conservation (SAC) (https://www.npws.ie/protected-sites/sac/000343) and a Special Protection Area (SPA) (https://www.npws.ie/protected-sites/spa/004029). Here the protection provided by the dunes has allowed several critically important habitats to develop which now host a large population of protected bird species, including thousands of wetland birds such as Brent Geese (Cadhan), Dunlin (Breacóg) and Curlew (Crotach) who spend the winter here.
The sand dunes of Iveragh are also home to many plants which are adapted to the harsh environmental conditions. Marram grass helps to hold nutrients and freshwater in the sand, which facilitates other plants to grow. Common species found on Iveragh’s dunes include Orchids (Magairlín), Sea Spurge (Bainne léana), Rock Samphire (Craobhraic), Sea Bindweed (Plúr an phrionsa), Thrift(Rabhán), and Kidney Vetch (Méara Muire).
Sea Bindweed and Sea Spurge at Inny Strand. Provided by knowledge gatherer, Anna Collyer.
Dunes act as a physical protective barrier against severe wind, powerful waves, and storm events, protecting low lying regions from erosion and flooding. But dunes themselves are extremely vulnerable to the elements and their highly mobile nature means that conservation can be challenging. Breaching and damage of dune systems can occur during brief extreme weather events in just a few hours, but recovery may take years. Climate change impacts such as increased storm frequency and sea level rise are growing concerns for dune habitats, as many lack the space to move further inland. Clean Coasts and CARO work to raise awareness of the importance and fragility of our dune systems.
Rossbeigh is the perfect example to illustrate the impermanence of dunes in our landscape. A major breach of the sand dunes at Rossbeigh occurred in December 2008 and since then the sand spit has been eroding rapidly [4]. The winter of 2014 brought heavy storms which had devastating impacts to the dune system. In addition to shifting hundreds of thousands of tonnes of sand, these storms wreaked havoc on the beachfront, obliterating large stretches of road, destroying the playground and hurling rocks and boulders across the area. The Rossbeigh spit and dune system offers considerable protection to the Castlemaine area and there is local concern about the erosion.
Although this erosion is a natural process, governed by relentless action of the wind, waves and tides, human influences have created additional pressures. Some of the biggest pressures on fragile dune systems include the construction of roads, car parks, and piers. Recreational pressures such as walkways, campsites and golf courses also exacerbate dune destruction. Of particular concern is the trampling of plants by both humans and livestock. Trampling can expose grass roots leaving the dunes vulnerable to strong winds and blowout. Good management practices, such as the construction of footpaths to limit the trampling of plants and fencing off areas to prevent people wandering onto the dunes, can minimise damage. The planting of marram grass is widely employed to restore dunes, while boulders and concrete blocks are used to mitigate erosion while still allowing water to flow out of the dunes, preventing them from becoming muddy.
Large boulders used as rock armour to protect dune at Inny Strand. Provided by knowledge gatherer, Anna Collyer
Despite concerns over dune and beach erosion, the removal of large volumes of sand occasionally reveals interesting artefacts. In Derrynane, middens, which were used as dumping sites for shellfish remains, dating from the Medieval Period to more recent times have been exposed after storm events [5]. Sand removed from beaches sometimes exposes peat and tree stumps. In Iveragh, these ‘drowned forests’ were flooded in the Mid-Holocene period, about 4,000 years ago, as sea levels rose along the western seaboard. These deposits were later buried beneath layers of sand deposited by the wave and tides.
Famously, Rossbeigh hosts the wreck of a wooden schooner known as the Sunbeam. The Sunbeam ran aground at Rossbeigh in January 1904 on a voyage from Galway to Cork. For decades the ships lay on the strand partially buried by the sands as an iconic part of the seascape at Rossbeigh but was torn from its position by the wind and waves and moved hundreds of metres towards the dunes by the power of superstorm Christine in January 2014. The CHERISH project has been monitoring the movement of the Sunbeam since 2017 and have recorded the wreck having moved a remarkable 3km along the strand.
