Sand and Gravel Spits by Giovanni Randazzo Derek W.T. Jackson & J. Andrew G. Cooper

Author:Giovanni Randazzo, Derek W.T. Jackson & J. Andrew G. Cooper
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

9.5 Contemporary Spit-Barrier Functioning

Past studies of the dunes-barriers and the other coastal systems in Castlemaine Harbour (Vial 2008; Sala 2010; Duffy and Devoy 1999; Delaney et al. 2012) show these environments are impacted not only by Atlantic wave and tidal action, but also to the influence of strong local wind turbulence and the generation of local wind waves over short fetch distances. Together, these controls have caused significant erosion of the barrier shorelines and of the marshes in the area. Under future climate warming, changes in these controls are likely to happen (Sweeney et al., 2002, 2008; Dunne et al. 2008; Devoy 2008; Dwyer 2012; IPCC 2007, 2014a), but their effects on the dune-barriers and on wider shoreline erosion is unknown. Projections of future bathymetric, RSL, storminess, wave refraction, sediments supply and linked controls from climate warming, and the changes now occurring at Rossbehy, have yet to be completed (O’Shea and Murphy 2013; Kandrot 2014), or even commissioned (O’Dwyer and Gault 2014). However, any increases in wind speeds above critical storm size threshold speeds of c. >17 m/s are likely to create barrier sand blows, dependent on the degree of vegetation cover (Carter et al. 1992; Lozano et al. 2004; Sherman et al. 1994; Houser et al. 2008; Houser and Hamilton 2009; Hickey 2011).

Pressures from recreation and tourism activities are currently minimal in the main dune-barrier areas of Inch, though less so at Rossbehy. People impacts, however, from seasonal and daily recreation on the western beach-front and foredunes of Inch are heavy, especially in the summer months. Much of this activity does not penetrate far into the main dunes (maximum distance of <200–300 m), except through the impacts from beach- dune-buggy vehicles and some walking and horse riding. Access by vehicles and horse-riding into the dunes has grown extensively in recent years (post c. 2,000), particularly in the central sections of Inch, with significant erosional and negative consequences on the vegetation and dune surfaces. Means to limit general public access into the dunes, particularly the prohibition of vehicle and horse riding access is now essential.

How the supply of offshore cobble – sands sized sediments and shell material to these dune sands will alter under the impacts of climate warming is also unknown. It is likely that the warming of coastal waters on this North Atlantic margin will increase local shell productivity, which will have knock-on effects in the sediments supplied from the beach into the dunes (IPCC 2007, 2014a). But, much will depend on whether any of this material is moved actively into the dunes in the future. Its immediate importance will be in affecting the nature of plant communities and the linked ecology on the dunes.

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