Journal of Maps ISSN: (Print) 1744-5647 (Online) Journal homepage: https://www.tandfonline.com/loi/tjom20 Geomorphology and substrate of Galway Bay, Western Ireland Denise McCullagh, Sara Benetti, Ruth Plets, Fabio Sacchetti, Eimear O’Keeffe & Kieran Lyons To cite this article: Denise McCullagh, Sara Benetti, Ruth Plets, Fabio Sacchetti, Eimear O’Keeffe & Kieran Lyons (2020) Geomorphology and substrate of Galway Bay, Western Ireland, Journal of Maps, 16:2, 166-178, DOI: 10.1080/17445647.2020.1717656 To link to this article: https://doi.org/10.1080/17445647.2020.1717656 © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps View supplementary material Published online: 29 Jan 2020. Submit your article to this journal Article views: 105 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tjom20 JOURNAL OF MAPS 2020, VOL. 16, NO. 2, 166–178 https://doi.org/10.1080/17445647.2020.1717656 Science Geomorphology and substrate of Galway Bay, Western Ireland Denise McCullagha, Sara Benettia, Ruth Pletsa,b, Fabio Sacchettic, Eimear O’Keeffec and Kieran Lyonsc aSchool of Geography and Environmental Sciences, Ulster University, Coleraine, Northern Ireland; bFlanders Marine Institute, Ostend, Belgium; cMarine Institute of Ireland, Oranmore, Galway, Ireland ABSTRACT ARTICLE HISTORY A combination of multibeam bathymetry and backscatter, LiDAR altimetry and bathymetry, Received 18 July 2019 satellite images, and hydrodynamic model outputs were used to map the seafloor and Revised 14 January 2020 coastline of Galway Bay (western Ireland). This is the first time these multiple datasets have Accepted 14 January 2020 been integrated into a single combined geomorphological and substrate map. The substrate KEYWORDS of the bay is predominantly mud and sand with bedrock outcropping extensively around the Seafloor; geomorphology; coastline. The main depositional features are dunes, while the main erosional features are hydrodynamics; habitat scours and outcropping bedrock. Hydrodynamic model outputs show good correlation mapping; Ireland between the direction and intensity of prevailing currents and the location and shape of the features in the bay. This indicates that although Galway Bay was shaped glacially through the passage of the British-Irish Ice Sheet across the bay and ensuing glacial and marine sediment deposition, many of the mapped seafloor landforms are modern and current-induced. 1. Introduction energy, storm-dominated system, protected from the Extensive seabed mapping was carried out in Ireland as full force of the Atlantic Ocean by the Aran Islands part of government-funded initiatives to map its Exclu- (Inis Mór, Inis Meáin and Inis Óírr) (Figure 1). The sive Economic Zone: the Irish National Seabed Survey bay encounters strong semi-diurnal tides, with a (INSS, 1999–2005) and the Integrated Mapping for the mean spring tidal range of >4.5 m (Booth, 1975; Mar- Sustainable Development of Ireland’s Marine Resource ine Institute, 2017). Hydrodynamic models show cur- project (INFOMAR, 2005-present). To date, marine rent speeds (both surface and tidal) between the Aran −1 geophysical data have been collected in a large portion Islands above 45 m/s in the ebbing spring tide, of Ireland’s territorial waters. The ability to map the while wave models, based on wind speeds from the seabed at high-resolution continues to improve our atmospheric research station at Mace Head, show win- understanding of coastal and marine environments ter wave heights above 2.5 m in the north and south ff and processes. This is essential to implement practical sounds and mid-bay areas (Joshi, Du y, & Brown, fl management of marine resources and to promote sus- 2017). The primary in ow of Atlantic water into Gal- fl tainable development (Barnard, Erikson, Elias, & Dart- way Bay is through the South Sound, with out ow nell, 2013; Li & King, 2007; Poppe, DiGiacomo-Cohen, through the North Sound, creating a counter-clockwise Smith, Stewart, & Forfinski, 2006). In this paper, geo- gyre (Harte, Gilroy, & McNamara, 1982; Lei, 1995). physical datasets are combined with satellite images, The primary freshwater source at the head of the bay fl seafloor samples and hydrological data and integrated is the river Corrib, with volumetric ow rates usually 3 into a single geomorphology and substrate map, pro- exceeding 311 m s(OPW, 2016). Other freshwater viding for the first time a coherent picture of the coast- inputs include submarine groundwater drainage line and seabed features of Galway Bay, located on the streams along the northern shore and the rivers to western Irish seaboard (Figure 1 and Main Map). The the east and south of the bay (Smith & Cave, 2012; geomorphological map (Main Map) provides a com- Cave & Henry, 2011)(Figure 1). plete image of the submarine landscape and gives an The geology of the northern side of the bay is domi- insight into the processes active in Galway Bay. nated by granite of Caledonian orogeny age, with the rest of the area (including the Aran Islands) made of Carboniferous Viséan limestone (GSI, 2007). The land- scape to the north and east of the bay is flat and low 2. Study area lying, with the majority of areas within 5 km of the Galway Bay is a large (62 km long, 32 km wide) marine coastline generally below 30 m. In contrast, to the embayment on the west coast of Ireland. It is a high south, the landscape is hillier with peaks above CONTACT Denise McCullagh [email protected] © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF MAPS 167 Figure 1. Topo-bathymetric image of the study site from LiDAR and MBES data showing the 0 m contour line in black and sub- divided into 3 geographical areas: inner bay, mid bay and outer bay. Examples of features identified in the bay and discussed in the text are outlined in black. 100 m, allowing for a steeper coastline. A fault runs azimuth biasing, features were considered with numer- across the northern side of the bay (mapped by Clarke, ous illuminations as well as without azimuth (Hillier & 2014) (Main Map). During the last glaciation Ireland Smith, 2008; Smith & Clark, 2005). This, alongside sub- was covered by the British-Irish Ice Sheet (BIIS) strate identification, contour lines (10 m spacing) and (Clark et al., 2018). This ice sheet extended as far as slope angle (inset in main map) were used to aid geo- the shelf edge west of Ireland and resulted in a wide morphological classification and interpretation. range of glacial landforms across the landscape. Along the inner bay coastline, drumlins are found ff onshore (GSI, 2013). O shore, a large morainic com- 3.2. Substrate mapping plex has been mapped at the mid-shelf (Peters, Benetti, fi Dunlop, & Ó Cofaigh, 2015). The substrate classi cation included in the main map is derived from the interpretation of MBES bathymetric and backscatter data for subtidal depths >20 m and 3. Methods the interpolation of biological samples and subtidal and intertidal data traced from orthoimagery and 3.1. Geomorphological mapping LiDAR datasets. Rock outcrops have been traced Multibeam echo-sounder (MBES) bathymetric and from orthoimagery, LiDAR data and MBES bathy- backscatter data were acquired by the INSS and INFO- metric shaded relief data. MAR projects between 2006 and 2014 on board the RV The seabed classification of Galway Bay done by Celtic Voyager using a Kongsberg Simrad EM3002D INFOMAR combined automated and manual methods MBES (300 kHz). These data were processed and tid- of classification. The data were collected in 6 survey ally corrected using CARIS HIPS & SIPS and gridded legs from 2006 to 2014 and the data types include at 5 m resolution by INFOMAR. LiDAR (Light detec- MBES and LiDAR. As a result, the seabed classification tion and ranging) altimetry data were collected for work has been done in stages and has incorporated INFOMAR between 2006 and 2010 by Tenix LADS more than one technique. The software used to classify Corporation. These datasets were combined to create the MBES data was QTC Image Multiview. a detailed altimetric/bathymetric map of Galway Bay The next step was to classify the first MBES dataset (Main map and Figure 1) that was used, together (CV07_01) using an automated software called QTC with backscatter classification and satellite images Multiview. The processing strategy of QTC Multiview from Google Earth (2017 images), to identify and has been described in principal and demonstrated in map submarine features and coastline type (following the literature (Preston, Christney, Collins, & Bloomer, Ashley, 1990; Duarte, 2017; Fairbridge, 2004; Huggett, 2004; McGonigle, Brown, Quinn, & Grabowski, 2009). 2011; Livingstone & Warren, 1996; Ó Cofaigh, Dunlop, In summary, the software applies image-based classifi- & Benetti, 2016; Van Rijn, 1984; Whitehouse, Harris, cation techniques to MBES backscatter imagery. The Sutherland, & Rees, 2011). Shaded relief with vertical data are cleaned and depth filtered to produce a com- exaggeration (×10) and different illuminations were pensated backscatter image for classification. Rectangu- generated in ESRI ArcGIS 10.1. In order to avoid lar patches of the compensated backscatter imagery are 168 D. MCCULLAGH ET AL. interrogated using a suite of algorithms to extract a waters in the northeast Atlantic at a resolution of series of (132) variables. These are then reduced by prin- 0.025 degrees and is available at three-hourly intervals cipal components analysis to three values (Q-values), (Marine Institute, 2018). The model outputs use one which best summarise the variance for each rectangular year of data and provide an overview of the general patch.