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Dublin Bay and Approaches
Cuan Bhaile Átha Cliath

Overview

Dublin Bay is located on the east coast of Ireland. It can be defined as the area of water from Howth Head in the north to Dalkey Head in the south. It is approximately 10 kilometres across the mouth of the bay and narrows to the mouth of the River Liffey which enters the Irish Sea in Dublin Bay. A large portion of the inner bay is affected by the rise and fall of the tides, with large areas of sand and mudflats exposed at low tide.

Photographs showing the coastline of Howth Head (left) and Bray Head (right) taken during INFOMAR surveying and ground truthing of Dublin Bay and Approaches.

Within the bay, the North Bull Island is a prominent physical, man-made feature which developed due to sedimentation accumulation after the construction of the North Bull wall in 1821 to ameliorate the problem of siltation in Dublin Harbour. Along with the seawalls protecting Dublin Harbour, the pier walls at Dun Laoghaire Harbour are an impressive feature in the south of the bay. The upland areas of Howth Head, Dalkey Head with the Wicklow Mountains to the south and the Poolbeg chimney stacks dominate the sky line of Dublin Bay.

Location of Dublin Bay in Co. Dublin on the east coast of Ireland.

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INFOMAR Survey History

INFOMAR surveys of the area include both Dublin Bay and the approaches in the Irish Sea. Work to survey these areas began 2003 when the Celtic Voyager surveyed a large area outside the mouth of the bay but also a significant portion of the seabed east of Dun Laoghaire. In 2004, the Celtic Voyager again mapped an area to the north around Howth.

In 2008, surveying around the area of the Kish bank commenced and coverage of a large portion of seabed to the east of the bank was achieved. Surveying was concentrated to an area north of the Ben of Howth and to Skerries. CV_09_UCC_Gael was carried out in conjuction with University Colledge Cork. The CV0905 survey was conducted along the north dublin coast. The aim of the leg was to complete remaining unsurveyed areas that will allow data from three earlier survey legs to be merged together. Since late July 2009, the Geological Survey of Ireland's new survey vessel, RV Keary has been making steady progress in completing the shallow water areas of Dublin Bay on survey leg KRY09_02 that were not covered by previous surveys by the Celtic Voyager. The main areas of surveying have been concentrated close to the coastline around inner Dublin Bay and on top of the shallowest areas of the Kish Bank, surveying at high spring tides to ensure safest draught clearance.

In 2010, the Celtic Voyager surveyed a large area. The survey area is situated in the Irish Sea Priority Area as designated in the INFOMAR scope of work. It stretches from offshore County Louth in the north to offshore County Wicklow in the south and is bounded to the east by the limit of the priority area. It includes the Wicklow Reef and parts of the Kish and Codling Banks. In 2010, the RV Keary survey operations were focused in Dublin Bay and Approaches extending from the Howth Head in the north of the bay to Dalkey Island in the south. This survey was conducted under INFOMAR standards while doing trials on the new vessel.

The Celtic Voyager returned to survey an area east of Lambay Island, parts of the Codling Bank, and west of Kish Bank in 2012. The M.V. Cosantóir Bradán and RV Geo surveyed around Lambay Island and the shallower waters on the coast north of Howth in 2013. The RV Keary, RV Tonn & RV geo surveyed some gaps in coverage to the south in 2016.

Coverage from survey legs undertaken to survey Dublin Bay and Approaches for the INFOMAR project to date (2016).(Click image for a more detailed map).

Survey Coverage polygons can be downloaded as a shapefile from our Interactive Web Data Delivery System (IWDDS).

Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

Read more about some of the survey legs on our Blog by clicking on the links below.

RV Keary progress in Dublin Bay

CV09_05 Survey off North Dublin coast

CV10_01 Irish Sea Priorty Area

Lambay Island Survey

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Bathymetry (Water Depth)

Water depth varies from 0 to 150 m.

Detailed .pdf charts of the bathymetry of Dublin Bay can be downloaded by clicking here

You can download Bathymetry xyz data from IWDDS

(Data Type: Vector Datasets, Region: Offshore, Theme: Bathymetry (Survey Leg) entire survey leg or Bathymetry (Survey Line) for individual tracklines. Take note of the survey names in INFOMAR Survey History.

You can also download the bathymetry data in ArcGIS GRID format

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Shaded Relief

The 3D appearance is achieved using software called Fledermaus. By using some vertical exaggeration, artificial sun-shading (usually as if there is a light source in the nw 315°) and colouring the depths using various colour maps, it is possible to highlight the subtle relief of the seabed. This helps us to quickly understand the variation in depths. View the 3D Map of Dublin for a more spectactular image.

A shaded relief image of the seabed at the mouth of Dublin Bay with the Burford Bank in the centre of the bay, which was and is a significant hazard to marine traffic in the Dublin Harbour area. From a geological perspective, the sand waves at the northern and southern ends of the bank illustrate the strong tidal currents moving in the area which created and maintain this stunning seabed feature. Also visible is the Frazer Bank, south of Dalkey Island which again shows the dynamic sedimentary processes operating in the Irish Sea. (Click image for a more detailed map)

Shaded relief of Dublin Bay.

Detailed .pdf shaded relief charts of the bathymetry of Dublin Bay can be downloaded by clicking here

Download Shaded Relief Bathymetry Geotiffs from our Interactive Web Data Delivery System (IWDDS)

Select your area of interest.Offshore Geotiffs - Bathymetry Shaded Relief Geotiffs.

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Backscatter

Multibeam Systems also collect additional information, including the strength of the acoustic signal (or return) from the seafloor. This is known as Backscatter. Differing seafloor types, such as mud, sand, gravel and rock will have different Backscatter values depending on the amount of energy they return to the sonar head. Rocky areas will typically have high returns while soft sediments like mud are more likely to absorb energy and have low Backscatter returns. These differing values are used to generate a grey-order image (i.e. dark for high returns, bright for low returns) of the seabed which can be used to examine the nature of the seafloor.

Backscatter image draped on the multibeam shaded relief image showing the Burford Bank and area south of Howth Head in image on left. The strong backscatter areas (dark areas) are generally representative of coarser grained sediments such as gravels and coarse sands. Interestingly, the light area of low backscatter intensity, corresponding to the Burford Bank, suggests that the bank is composed predominantly of sands with little coarse fraction present. (Click image for a more detailed map)

Detailed .pdf backscatter charts of Dublin Bay can be downloaded by clicking here

Download Backscatter Geotiffs from our Interactive Web Data Delivery System (IWDDS)

Select your area of interest.Offshore Geotiffs - Backscatter Geotiffs.

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Ground Truthing/Seabed Sampling

To verify the results of remotely sensed sonar data, it is important to collect physical sediment samples from the seabed. These may be from the surface where grabs are used or may penetrate through the seabed and retain the vertical structure of the sediment by using various coring methods. These samples are also critical for the confirming seabed classifications.

A range of seabed sampling has been undertaken in Dublin Bay under the INFOMAR project. These include grab samples. The locations of the grab samples have been mainly determined by the seabed classification made from the multibeam data.

Seabed sampling locations in Dublin Bay (Click image for a more detailed map)

Sediment sample recovered from the seabed on the Burford Bank as part of the ground truthing of the Dublin Bay seabed classification.

Sample locations can be downloaded as a shapefile from our Interactive Web Data Delivery System (IWDDS).

On the IWDDS Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

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Seabed Classification

Seabed classification is an advanced process in which a backscatter image is interrogated using special software in order to divide it into areas which have similar characteristics. Areas which have a similar nature are grouped together and divided into separate classes. These classes are colour coded and developed into seabed classification charts.  

The classification of the multibeam dataset from Dublin Bay resulted in the creation of a 5 class classification divided into two types of rock, reflecting the different textures observed from rock outcrops in the bay. Three more classes divided the sediments into Gravels and Coarse Sand, Coarse to Medium Sand and Fine Sand to Mud.

Seabed Classification Chart for an area around Dalkey Island, Co. Dublin. (Click image for a more detailed map)

Seabed Classification Chart for the East Coast (Click image for a more detailed map)

For a more detailed chart of the seabed classification of surveyed areas of the East Coast click here

Further information about the classification process can be found in the Data Processing section.

You can download the Seabed Classification in ArcGIS GRID format data from IWDDS

(Data Type: ArcGIS GRIDS, Region: Offshore ArcGIS, Theme: Seabed Classification ArcGIS GRID

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Geology

The main rock types along the coast of Dublin bay are limestone and granite. The limestone, called the “Calp”, is the blue expanse on this map and was formed in a warm shallow sea many millions of years ago – it is composed of the remains of tiny, ancient aquatic life. The granite, however, represented by the pink colour, is an igneous rock, which means it originally rose from deep within the Earth as molten rock (magma), which then cooled slowly to form this hard, crystalline rock. It did not reach the surface at that time, but was later exhumed over millions of years through erosion of the overlying landscape – it forms part of the mountainous landscape of Wicklow. Note that the northern and southern points of Dublin Bay (Howth and Dalkey) protrude into the sea – this may be because the granite and the rocks of Howth are harder than the limestone, and so perhaps the limestone was eroded more by the sea to form the bay.

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3D Map of Dublin

Find out more here

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INFOMAR in Google Earth

To view and download datasets in Google please click here

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Shipwrecks

To view the shipwrecks in Google and to download Shipwreck Information Sheets please click here.

Shipwreck locations can be downloaded as a shapefile from our Interactive Web Data Delivery System (IWDDS).

On the IWDDS Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

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WW1 Shipwrecks in the Irish Sea Storymap

A whistle stop tour of world war one shipwrecks in the Irish Sea.

Click Here to view the Story Map

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Data Access

Full details outlining the process to gain access to datasets for the bay above or all INFOMAR data can be found in the INFOMAR | Data page of this website.

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Return to Survey Details Map

Follow these links to your area of interest on the INFOMAR website:

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