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Earth Science Conservation Review
| Strangford Lough Intertidal Flats | Down |
| Site number: | 1133 | ||
| ESCC: | IA | ||
| Locality Type: | Coastal section | Status: | ASSI |
| Grid Reference: | J507630,J577680 Centroid, Not Entered | ||
| Google maps: | 54.49347,-5.67415 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Quaternary | ||
| Stages: | Holocene | ||
| Site Description | |
|---|---|
| Highlights: | |
The tidal flats of Strangford Lough form extensive deposits around its northern limits in a partially eroded drumlin and late-glacial landscape. The sedimentary dynamics of the contemporary tidal flats are controlled by exposure to waves and tidal currents and vary from current- to wave-dominated sandy areas to suspension-dominated muddy areas. The tidal flats exhibit subtle shore-normal changes at any given site and are in several locations backed by salt marsh deposits. At a number of locations indicators of former sea levels are preserved which offer the opportunity to define the evolution of the area. | |
| Introduction: | |
Although well known for their faunal attributes (Environment Service, 1993), in particular to migratory wildfowl (Brown, 1988, 1990), the tidal flats of Strangford Lough have, to date, received little geomorphological or sedimentological attention. There is, however, apparent concern at perceived changes in sediment texture and Portig et al., (1994) speculated that there may be a link between avian consumption of sediment-binding vegetation and sedimentation patterns. In Ardmillan Bay a sedimentological study (Kirby et al., 1993) focussed on seasonal changes in muddy intertidal flats. The likely impacts of a proposed tidal barrage and associated electricity generation scheme were reported by Carter & Newboult (1982). The entire area of Strangford Lough and some of the area seaward of its mouth have recently been designated a Marine Nature Reserve (Environment Service, 1993). | |
| Description: | |
Strangford Lough experiences a spring tidal range of over 3.5m and is protected from ocean wave attack by virtue of its narrow entrance. Consequently most energy transmitted within the lough originates from tidal currents or wave action. Waves are internally generated by local winds and the maximum fetch is about 15km. The long axis of the lough roughly corresponds to the dominant wind direction (S-SW) and consequently wave action is maximised on its northern and eastern margins. The tidal flats of Strangford Lough cover an area of 50km2 and are best developed between and within Greyabbey Bay and Ardmillan Bay. They attain a coast-normal extent of up to 2km at Newtownards and historical evidence (Harris, 1744) suggests that they were once more extensive and merged into salt marsh in the area now occupied by the town of Newtownards. Salt marsh is present at the landward extent of the tidal flats in only a few locations, but was probably more extensive in the past. This marsh may occupy the margins of the lough or be deposited on the flanks of former drumlins or drumlin remnants. In the absence of detailed analyses of the tidal flat sediments and topography only a limited description is possible at present. At Greyabbey, the tidal flats occupy a small embayment within which drumlin remnants (locally termed pladdies) and relatively intact drumlins are present. A small remnant of marsh is present at Greyabbey which passes seaward into a steep upper tidal flat section composed of coarse sand and locally pebbles. Seaward this is succeeded by a broad sandy flat dissected by several tidal channels in which shell lags are present. The intertidal sand flat is characterised by current ripples and wave ripples, the latter of which appear best developed near the high tide level. At the spring low tide level at Greyabbey, exposures of peat which contain in situ tree stumps are present and record a phase of lowered sea level. More in situ tree stumps are preserved in the high intertidal zone at Greyabbey and on drumlin islands there. The high intertidal flats here consist of a thin veneer of sand which overlies red late-glacial marine clay. Ongoing investigations of archaeological sites in this vicinity will undoubtedly contribute to palaeoenvironmental reconstructions in the light of Holocene sea level changes. Between Newtownards and the Comber River estuary the intertidal flats reach their greatest extent. Remnants of salt marsh are present west of the Newtownards airfield and around the mouth of the Comber River. The salt marsh contains several steep-sided channels. It is highly eroded on its seaward side and a steep eroded scarp is fronted by a narrow high tide beach composed of coarse sand. This passes seaward into a wide expanse of sandy intertidal tidal flats characterised, at low tide, by wave ripples and features typical of late stage emergence runoff (ladderback ripples, flat-topped and double crested ripples, rill marks and microdeltas). Tidal channels are essentially absent from this section of the intertidal flats. Under strong wind conditions this area may contain unusual washed out ripple structures formed by shallow water erosion of ripple structures. There are several areas in this vicinity where raised beach deposits and late glacial and drumlin phase deposits may be examined. An early examination of Rough Island (Movius, 1944) provided evidence of Late Holocene raised beaches. In Ardmillan Bay the intertidal flats are markedly different and contain varying proportions of mud. The hydrodynamic regime has been markedly altered by causeway construction (Kirby et al., 1984) and this may have reduced the efficiency of tidal currents in eroding and transporting sediment. Nonetheless, the intertidal area is largely characterised by thick deposits of soft mud which appear to undergo seasonal variations between erosion and deposition (Kirby et al., 1984). Salt marsh is intermittently present around Ardmillan Bay where it is sometimes fronted by sandy tidal flats in the upper intertidal zone. Artificial Spartina planting has produced different forms of marsh in this area. | |
| Importance: | |
In terms of their earth science interest, the intertidal flats of Strangford Lough afford an excellent opportunity for the demonstration of sedimentary structures and shore-normal zonation of sediments according to the period for which they are tidally inundated. Their ease of access and proximity to the major urban centre renders them locally important as an educational facility. The evidence present on the intertidal flats of former sea levels (late-glacial clays, peat, submerged trees and archaeological remains) offers the opportunity for elucidation of a sea level curve for the area during the late Pleistocene and Holocene. Although not fully investigated, the setting of the intertidal flats in an eroded and infilled drumlin environment into which little fresh sediment is added, is unusual, perhaps even on an international scale. The influence of sediment-limited conditions on tidal flat stratigraphy and growth has not been investigated. | |
| Interpretation: | |
The intertidal flats show textural and structural variation between the essentially sandy flats in the Greyabbey-Comber section and muddy flats in the Ardmillan area. These areas coincide with locations where the drumlin topography is, respectively, either largely eroded or largely intact. Such a situation may be tentatively linked to the degree of exposure to wind-generated wave attack and commensurate energy levels. The Greyabbey-Comber section is exposed to wave action from waves generated by winds blowing along the maximum fetch of the lough. This high energy section is consequently essentially sandy and its former drumlin topography is highly eroded. The lower intensity of oscillation ripple occurrence compared to current ripples at Greyabbey suggests a reduction in wave energy at that location, but temporal variations in this suggested situation have not been studied. The Ardmillan area is essentially muddy except in tidal channels. Conditions favourable to mud deposition in this area arise from the shelter afforded by the remnant drumlin topography and by the lower exposure to contemporary wave attack, which is itself ultimately responsible for drumlin preservation. The construction of causeways in the Ardmillan area, through its reduction in tidal current efficiency may have promoted mud deposition. In the absence of obvious major fluvial sediment or flood-tidal inputs to the intertidal flat system it appears that the system has arisen through the erosion and redistribution of a former drumlin and superimposed marine clay landscape since the late Pleistocene. The sequence described at Roddan's Port (Morrison & Stephens, 1965) provides a likely impression of the potential infilling sequence which could have accompanied and been assisted by drumlin erosion within Strangford Lough. In such a scenario the present intertidal flats would form the upper section of this sequence. The potential for lateral seaward advance of the tidal flats may be limited by the sediment limited setting in Strangford Lough. | |
| Conclusions: | |
Strangford Lough intertidal flats form an extensive, but poorly studied, system of intertidal flats which exhibit spatial variations as a result of varying hydrodynamic energy levels and types. The area affords an excellent natural laboratory in which to study and demonstrate the sedimentology of sandy and muddy intertidal flats and their stratigraphy. The presence of undocumented indicators of former sea levels and of archaeological remains offer the opportunity for construction of a sea level curve and detailed palaeoenvironmental reconstructions during the Holocene. The influence of sediment limitation on tidal flat development in the Lough has not been studied in comparison to other areas. | |
| Keywords | |
|---|---|
| Relations: | Coastal processes, Tidal Feature |
| Geomorph: | intertidal flat, mudflat, salt marsh, sandflat |
| NonGeol: | The entire area lies within the Strangford Lough M |
| Access | |
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| Management: | |
The entire area with the exception of salt marshes at Newtownards and the mouth of the Comber River lies within the Strangford Lough Marine Nature Reserve which should provide the necessary level of management for preservation of the site. Further designation may be necessary to preserve these salt marsh remnants as an integral component of the intertidal-supratidal continuum. Anecdotal evidence suggests that salt marsh has been eroded from the area fronting a flood protection works at Newtownards since the flood protection was constructed. Care should be taken to preserve remaining salt marsh areas and to prevent additional erosion from taking place as a result of such structures. There is also evidence of alteration of sediment dynamics through causeway construction in the western section of the lough to provide access to islands. The impacts of any future causeway construction should be carefully assessed in terms of potential impacts on the intertidal flat system. | |
| Uses | |
| Uses: | Further studies are ongoing on sedimentology and stratigraphy of the tidal flats (UU), on their archaeology (DoE/QUB) and on their contained sea level indicators (UU). |
| Educ. Level: | Undergraduate / Postgraduate |
| References (10) | |||
|---|---|---|---|
| Brown, R.A., 1988. Is there competition between light bellied Brent Geese (Branta bernicla hrota) and Wigeon (Anas penelope) in Strangford Lough? In Wigeon: current trends and future needs., pp.76-84 B. A. S. C., Rosset. | |||
| Brown, R.A., 1990. Strangford Lough - the wildlife of an Irish Sea Lough. Institute of Irish Studies, Queen's University of Belfast. | |||
| Carter, R.W.G. & Newboult, P.J., 1982. Environmental impact assesment of the Strangford Lough tidal power barrage scheme in Northern Ireland. Water Science and Technology, vol. 16, pp.455-462. | |||
| Environment Service, 1993. Strangford Lough Proposed Marine Nature Reserve: Guide to Designation. H. M. S. O., Belfast. | |||
| Harris,, 1744. On the Antient (sic) and Present State of the County of Down., Dublin. | |||
| Kirby, R., Bleakley, R.J., Weatherup, S.T.C., Raven, P.J. & Donaldson, N.D., 1993. Effect of episodic events on tidal mudflat stability, Ardmillan Bay, Strangford Lough, Northern Ireland. In Nearshore and Estuarine Cohesive Sediment Transport., pp.378-392. | |||
| Morrison, M.E.S. & Stephens, N., 1965. A submerged late-Quaternary deposit at Roddans Port on the north-east coast of Ireland. Philosophical Transactions of the Royal Society, London, vol. B249, pp.221-255. | |||
| Movius, H.L., 1940. Report on a stone age excavation at Rough Island, Strangford Lough. Journal of the Royal Society of Antiquaries of Ireland, vol. 70, pp.111-142. | |||
| Portig, A.A., Mathers, R.G., Montgomery, W.I. & Govier, R.M., 1994. The distribution and utilisation of Zostera species in Strangford Lough, Northern Ireland. Aquatic Botany, vol. 47, pp.317-328. | |||
| Synge, F. & Stephens, N., 1966. Late Pleistocene shorelines and drift limits in north-east Ulster. Transactions of the Institute of British Geographers, vol. 39, pp.101-125. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 21 (Strangford Lough). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Strangford Lough Intertidal Flats, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1133. Accessed on 2026-11-08. |
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