DINGLE FISHERY HARBOUR CENTRE COUNTY KERRY BATHYMETRIC AND GEOPHYSICAL SURVEY. September 2016 REPORT

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1 Doc. Ref DINGLE FISHERY HARBOUR CENTRE COUNTY KERRY BATHYMETRIC AND GEOPHYSICAL SURVEY September 2016 REPORT Client: Report by: Marine engineering Division Blennerville Tralee, Co. Kerry Irish Hydrodata Ltd. Ballygarvan County Cork Report date: October 28 th 2016

2 Contents Section Page 1. Introduction 1 2. Survey Areas 2 3. Survey Works Programme 4 4. Project Personnel 7 5. Survey Equipment 8 6. Survey Results 12 Appendix A Survey Equipment A.1 Appendix B Swath Bathymetry B.1 Appendix C Sidescan Sonar C.1 Appendix D Magnetometer D.1 Appendix E Sub-bottom profiling E.1 Appendix F Topography F.1 List of drawings accompanying this Report 1253_16_01 - Dumpsite Sidescan Sonar & Magnetometer Survey Trackplot 1253_16_02 - Dumpsite Magnetometer Profiles 1253_16_03 - Harbour Basin Magnetometer Survey Trackplot 1253_16_04 - Harbour Basin Magnetometer Profiles 1253_16_05 - Channel Magnetometer Trackplot 1253_16_06 - Channel Magnetometer Profiles 1253_16_07 - Harbour Basin & Channel Bathymetry (1:1000) 1253_16_08 - Sub-bottom Profiles 1253_16_09 - Harbour Basin Bathymetry (1:500) 1253_16_10 Harbour Shoreline Topography Digital data accompanying this report 2mx2m bathymetric data ITM_CD Topographic data ITM_ODM Units: All horizontal positions are on Irish Transverse Mercator (ITM) Marine charts are to Chart Datum and follow nautical convention, ie +ve soundings are below datum. (Chart Datum is 2.7m below OD Malin Head) The topographic survey drawing is to OD Malin Head and follows land survey convention, ie +ve heights are above datum. Date Revision Purpose October 28 th 2016 Issue Report i

3 1. Introduction 1.1 Background to survey The Department of Agriculture, Fisheries and Marine (DAFM) are proposing to bring larger vessels into Dingle Fishery Harbour Centre (FHC), County Kerry, than can currently access the facilities. The Consulting Engineer is Nicholas O Dwyer Ltd., Dublin. A series of surveys has been planned to provide various data. Irish Hydrodata Limited (IHD) has been awarded the bathymetric and geophysical survey contract. 1.2 Main Works Proposed and Purpose of Contract The survey works were to comprise the following:- Approximately 14,150m 2 of topographic survey Approximately 185,100m 2 of bathymetric survey Production of level profile sections from combination of the above surveys Geophysical survey (over water) at the Harbour, Dredged Channel and Dump at Sea sites The surveys were to be undertaken to provide ground/bed level and stratigraphy information in order to finalise the design of the proposed dredging within Dingle Harbour, incorporating works along the existing north to south channel and within the turning basin and to determine the proposed Dump at Sea location (hereafter referred to as the dump site). Topographic survey was carried out on the piers and revetments. Multibeam bathymetric survey took place in the inner harbour basins and dredged channel. Magnetometer survey was undertaken in the inner harbour basins and dredged channel. Magnetometer and sidescan sonar surveys were carried out at the dump site. Sub-bottom profiling took place outside (to south of) the inner harbour basins. 1.3 Report Content This report describes the survey and the data acquired. The interpretation of the data from an archaeological perspective was carried out by Laurence Dunne Archaeology and is contained in a separate report. A Marine Mammal Observer (MMO) was present before and during the sub-bottom profiling element of the work. The MMO s function is to ensure that the area is clear of marine mammals at the time of the survey. On completion of the survey, a report was produced and is contained under separate cover. Page 1

4 2. Survey Areas 2.1 Dump Site The proposed Dump Site is located in Dingle Bay to the south-east of the entrance to Dingle Harbour (Figure 2.1). The survey area is a roughly rectangular corridor of approximately 1140m x 465m. The survey area co-ordinates were supplied by the Engineer as WGS84 Lat/Long and were converted to Irish Transverse Mercator using OSI GridInquest software. They are listed in Table 2.1. Sidescan sonar and magnetometer surveys were carried out in this area. Figure 2.1 Proposed Dump Site Point ID LAT (WGS-84) LONG (WGS-84) ITM East ITM North NW N W NE N W SW N W SE N W Table 2.1 Proposed Dump Site co-ordinates 2.2 Dredged Channel The survey area for the dredged channel to Dingle Harbour is shown shaded in Figure 2.2. The survey area co-ordinates were supplied by the Engineer on Irish Transverse Mercator. This comprised a large listing of 71 points, the main ones of which are provided in Table 2.2 below. Swath bathymetry and magnetometer surveys were carried out in this area. Sub-bottom profiling survey took place along the approximate lines coloured red in Figure 2.2. Page 2

5 Figure 2.2 Dredged channel Point ID ITM East ITM North Table 2.2 Dredged channel co-ordinates 2.3 Survey Equipment Details of the survey equipment are presented in Appendix A 2.4 Survey Personnel Mr. Jim Walshe. BE, M.Eng.Sc, CEng. Mr. Tom Bruton BE, M.Eng.Sc. MMO: Mr Paddy O Dwyer BSc Page 3

6 3. Survey Works Programme Mobilisation to site was on September 15 th Field survey works were completed on September 22 nd The works programme is summarised in Table 3.1 below. Date Sept. 15 th 2016 Weather good Sept. 16th 2016 Weather fair Sept. 17 th 2016 Weather fair Sept. 20 th 2016 Weather fair Sept. 21 st 2016 Weather poor in a.m. Good in p.m. Sept. 22 nd 2016 Weather good. Sept. 23 rd to Oct. 18 th 2016 Item Mobilised to site. Commenced topo survey on revetments and piers Launched survey boat Blue Fin at Dingle Marina slip. Fitted vessel with singlebeam echosounder, DGPS positioning system and magnetometer. Carried out part of magnetometer survey in dredged channel. Although not a survey requirement, singlebeam echosounder was also used over these survey lines. Mobilised sidescan sonar system on survey vessel. Completed survey of Dump Site with sidescan sonar, magnetometer and singlebeam echosounder. Emma Delia acted as safety boat during this survey. Completed magnetometer survey in dredged channel area. Also included singlebeam echosounding. Demobbed sidescan and magnetometer from Blue Fin. Mobilised to Dingle with Geoswath and C-Boom and fitted out Blue Fin with Geoswath and POS/MV inertial navigation system. Initiated calibration. Calibrated Geoswath in a.m. Completed Geoswath survey in required area in p.m. Demobbed Geoswath to Cork. Mobilised C-Boom on Blue Fin Completed Boomer survey. MMO in attendance during survey. Demobilised C-Boom. Demobbed survey vessel. Returned to Cork Preliminary data processing Draft deliverables supplied to Archaeologist & Marine Mammal Observer Table 3.1 Works Programme Page 4

7 4. Survey Results 4.1 Swath Bathymetry Survey Method The swath bathymetry survey was carried out on September 21 st 2016 in the harbour basins and dredged channel. Survey lines were run such as to provide full coverage of the survey area. Additional survey was also undertaken in the inner basin area at the request of the client. Results Data was post-processed using Geoswath GS4 software. The bathymetry was reduced to Chart Datum at Dingle using tide data measured at the main pier. Data was output on a 1m x 1m grid. This datafile was subsequently input to the Triangulated Irregular Network (TIN) module of Hypack hydrographic software and a thinned dataset was output on a 4m x 4m grid for use in the preparation of a bathymetric chart. The thinned dataset was required for legibility. The bathymetric chart consists of 2no. drawing sheets which plot at 1:000 scale on A1-sized media. Reduced-scale versions of the drawings are shown in Appendix B (Figs. B.1 and B.2). Deliverables An AutoCAD drawing of the survey area bathymetry (chart referenced to Chart datum) was provided to the client (Drg No: 1253_16_07). An enlarged chart of the basin area was also provided (Drg No: 1253_16_09). All bathymetric data was provided in an xyz data file (ITM and Chart datum). Figure 4.1 Extract from MB survey showing basin area Page 5

8 4.2 Sidescan Sonar Survey Method The sidescan sonar survey was carried out simultaneously with the magnetometer survey at the Dump Site on September 17 th Survey lines were steamed at 40m line spacing in an E-W direction. The sidescan towfish was towed off the aft quarter at a layback of 15m. The layback distance and times were noted for use in post-processing. The sidescan range was set to 75m port and starboard to ensure better than 100% overlap and good data beneath the towfish. Data from the 100kHz and 500kHz frequencies were logged simultaneously. Results Preliminary post-processing of the data was achieved using Klein SonarPro software. A survey trackplot was produced (to plot at 1:1500 scale on A1-sized media) and is shown at a reduced scale in Appendix C in Figure C.1. A sidescan mosaic was also prepared and is shown in Figure 4.2. Deliverables The original sidescan data without slant-range correction was provided to Laurence Dunne Archaeology to assess the archaeological potential. The digital data was provided in both XTF and SDF formats. The survey position data are embedded in the sidescan data files allowing targets to be located. Layback positions and times were provided and are required to be applied in post-processing. An AutoCAD drawing comprising a survey trackplot (Drg No: ) was provided along with a 1m x 1m resolution sidescan sonar mosaic in TIF format. Figure 4.2 Dump site sidescan mosaic. Page 6

9 4.3 Magnetometer Survey Dump Site Method The magnetometer survey of the Dump Site was carried out simultaneously with the sidescan sonar survey and over the same planned survey lines, on September 17th Thus, the survey lines were steamed at 40m line spacing in an E-W direction. The magnetometer towfish was towed off the aft quarter at a layback of 12m. Data was logged to hard disk using Hypack hydrographic survey software. Results Preliminary post-processing of the data was achieved using Hypack software. A survey trackplot with corresponding event marks was provided (Appendix D, Figure D.1). Magnetic signature profiles with survey event marks were plotted (Figures D.2, D.3). This enables any potential target to be located in plan. The layback has been accounted for in the survey trackplot. Deliverables The magnetometer profile data with associated trackplot were provided in AutoCAD format (Drg Nos: & ) to Laurence Dunne Archaeology to assess the archaeological potential. The magnetometer data was also provided digitally in georeferenced format Harbour Basins and Dredged Channel Method The magnetometer survey of the Harbour basins and dredged channel was carried out on September 16th and 17th The survey lines were steamed at 10m line spacing in an E- W direction in the dredged channel. The lines were run N-S in the harbour basins. The magnetometer towfish was towed off the aft quarter at a layback of 12m. Data was logged to hard disk using Hypack hydrographic survey software. Results Preliminary post-processing of the data was achieved using Hypack software. Magnetic signature profiles with survey event marks were plotted. Examples of a magnetic signature indicating a potential magnetic target are presented in Fig Survey trackplots with corresponding event marks were produced. This enables any potential target to be located in plan. The layback has been accounted for in the survey trackplots. Contours of magnetic intensity were also plotted in plan on the survey trackplots to give an indication of the location of possible magnetic targets. For the Harbour Basins, the survey trackplot consists of 1no. drawing sheet which plots at 1:000 on A1-sized media. A reduced-scale version of the trackplot is shown in Appendix D, Page 7

10 Figure D.4. The magnetic profiles are provided on 3no. drawing sheets at 1:1000 scale. Figures D.5 to D.7 show a reduced-scale version of these profiles. For the Dredged Channel, the survey trackplot drawing consists of 2no. drawing sheets which plot at 1:000 on A1-sized media. A reduced-scale version of the trackplot is shown in Figures D.8 and D.9. The magnetic profiles are provided on 9no. drawing sheets at 1:1000 scale. Figures D.10 to D.18 show a reduced-scale version of these profiles. Deliverables The magnetometer profile data with associated trackplots were provided in AutoCAD format (Drg Nos: , 04, 05, 06) to Laurence Dunne Archaeology for archaeological assessment. Figure 4.3 Extract from magnetometer data record showing anomalies Page 8

11 4.4 Sub-bottom Profiling Survey Method The sub-bottom (C-Boom boomer) profiler survey was carried out on a series of lines in the dredged channel and at the entrance to the inner harbour basins (Figure 4.4) on September 22 nd The catamaran was towed off the aft quarter at a layback of 5m. Data was logged to hard disk in Coda format. The survey trackplot is presented in Appendix E, Figure E.1. Results Post-processing of the data was achieved using Coda software. All survey lines have been processed and data are presented as profiles in the survey drawings that accompany this report. A reduced scale version of the profiles is presented in Figure E.2. Reflectors, representing changes in acoustic impedance in the bed materials have been digitised and where possible, traced across survey lines. The geophysical sweep time has been converted into depths using an assumed speed of sound in sediment of 1600m/s. Examples of the original sub-bottom data is presented in Figure 4.5 and 4.6. Good data quality was achieved in the outer channel area where coherent reflectors were identified at up to 10m below the seabed. These represent detailed layering in the fine sediments and are evident over a distance of 600m. Within this region the acoustic basement reflector shoals from 11m to 6m CD. This reflector is believed to represent the top of a coarse glacial till which overlies bedrock. Further to the north and closer to the basin the reflectors become intermittent and less well defined. The sub-bottom materials become coarser. Between cross-sections B9 and B11 the basement rises locally to 4m CD. Interpretation is difficult because glacial till and bedrock may produce similar reflectors. Local point diffractions are indicative of boulders and possible rock pinnacles. Frequent discontinuities suggest bedrock. Within the basin data quality is poorer due to shallower water and spurious reflectors. Horizons are generally present within 2m of the seabed. The interpretation is of locally finer material overlying glacial till or bedrock. Rock outcrops are present on the eastern shoreline where the surface material consists of a coarse gravel and cobble. Reflectors that are consistent with this rock can only be traced for a short distance from the shoreline. The interpretation is preliminary and is subject to verification and further assessment once borehole data is available. Deliverables The geophysical profile data with associated trackplots were provided in AutoCAD format (Drg No: 1253_16_09). Page 9

12 Figure Subbottom Profiler Track Locations Figure Line 12 Cross-section through channel form west to east Page 10

13 Figure Line B15, longitudinal profile along channel from south to north 4.5 Topographic Data Method Shoreline topography within the survey area was surveyed using RTK gps. The survey was referenced to existing survey station data provided by the client (Figure 4.7). Only three of the points were positively located (B002, B007 and B008). Figure Survey Stations Deliverables An AutoCAD drawing of the survey topography chart to Malin Head datum was provided to the client (Drg No: 1253_16_10). Page 11

14 APPENDIX A Survey Equipment 1. Survey Equipment A.1 Survey Vessel IHD s own survey vessel Blue Fin was used for the work. The vessel is a 21 launch with cabin and is fully equipped with safety equipment including in-hull singlebeam echosounder transducers. It holds a current Dept. of Transport P4 License for survey works and is ideal for shallow water work. The vessel was towed to the site and launched at a slipway in Dingle harbour marina. The vessel operated out of dingle Marina. A.2 Horizontal Positioning For all water-based survey except Geoswath multibeam survey, positioning of the survey vessel was achieved using Trimble Ag132 DGPS with OMNISTAR corrections. This provided sub-meter horizontal accuracies. Positioning was on Irish Transverse Mercator (ITM). A.3 Vertical Control/Tide Measurement A Hobo water level recorder was deployed at the main pier in dingle Harbour for the duration of the field works. The tide data was reduced to datum (OD Malin and Chart Datum) based on a series of manual observations taken at a TBM on the pier during the course of the works. The TBM was surveyed in as part of the topographic survey. The tide data was used for reduction of the bathymetric data to datum. The instrument was set to record at 10-minute intervals. A( 1)

15 A.4 Bathymetric Survey (singlebeam) A Knudsen 320M simultaneous dual frequency (33kHz, 210kHz) precision survey echosounder was used to acquire the depth information. Speed of sound in water was measured using an Odom Hydrographics Inc. Digibar. The survey was managed using the latest version of the hydrographic survey software package Hypack. A.5 Sidescan Sonar Survey An L3-Klein System 3000 simultaneous dual frequency digital sidescan sonar system was employed for the survey. The system comprises a Klein 3110 Transceiver Unit (TPU) and a Klein 3210 Towfish. The operating frequencies are 100kHz and 455kHz simultaneously, thereby providing a greater possibility of detecting objects and providing a clear image of the seabed. Data from both frequencies was logged digitally using SonarPro software, for post-processing by ADCO. Data was logged in both SDF and XTF formats. The L3-Klein System 3000 is described in detail in Appendix A. A.6 Magnetometer Survey A Geometrics G882 marine magnetometer was employed for this aspect of the survey. It is an extremely high resolution Caesium vapour, small size, system for professional surveys. The G882 is focused for operation in small boat, shallow water surveys. Data was logged in ASCII format. Equipment data sheets are provided in Appendix A. A( 2)

16 A.7 Sub-bottom Profiling Survey A C-Boom boomer sub-bottom profiling system was used to acquire sub-bottom data. The system includes a deck power supply, lightweight tow cable and a catamaran assembly. An Applied Acoustics AH360/8 Hydrophone is also employed. The power supply output voltage range is Volts and its power consumption is 800W. The catamaran assembly comprises a transducer, electronics module and frame. The energy discharge per pulse is 100joules. The acoustic output (re 1uPa@600V) is -200dB. The dominant frequency is 1760Hz. Data was collected using a CodaOctopus DA4G 2000 Acquisition System. Data was recorded in SEG-Y format for post-processing. Equipment data sheets are provided in Appendix A. A.8 Swath Bathymetry Survey A Kongsberg Geoswath Plus compact swath bathymetry system was employed to acquire bathymetric data. A POS/MV WaveMaster inertial navigation system was used to provide accurate attitude, heading, heave, position, and velocity data, representing the latest in state-of-the-art inertial/gps technology. Equipment data sheets are provided in Appendix A. The full system system comprised the following:- Kongsberg Geoswath Plus Compact Deck Unit; Kongsberg Geoswath 500kHz Integrated Compact Transducer Head Assembly; Valeport Mini SVS (for speed of sound); Applanix POS/MV Wavemaster Type 45 IMU (for heave, pitch, roll); Applanix POS/MV Surface Unit c/w RTK and Marine Star options (for positioning). A( 3)

17 APPENDIX B Results Swath Bathymetry in Dredged channel B(1)

18 Fig. B.1 Bathymetric Chart Sheet 1 of 2 B(2)

19 Fig. B.2 Bathymetric Chart Sheet 2 of 2 B(3)

20 APPENDIX C Results Sidescan Sonar at Dump Site C(1)

21 Fig. C.1 Sidescan sonar survey trackplot at Dump Site C(2)

22 Fig. C.2 Sidescan sonar mosaic at Dump Site C(3)

23 APPENDIX D Results Magnetometer at Dumpsite D(1)

24 Fig. D.1 Magnetometer survey trackplot at Dump Site D(2)

25 Fig. D.2 Magnetometer profiles at Dump Site sheet 1 of 2 D(3)

26 Fig. D.3 Magnetometer profiles at Dump Site sheet 2 of 2 D(4)

27 Results Magnetometer in Harbour Basins D(5) EPA Export :03:03:51

28 Fig. D.4 Magnetometer survey trackplot at Harbour Basins D(6) EPA Export :03:03:51

29 Fig. D.5 Magnetometer profiles at Harbour Basin sheet 1 of 3 D(7) EPA Export :03:03:51

30 Fig. D.6 Magnetometer profiles at Harbour Basin sheet 2 of 3 D(8) EPA Export :03:03:51

31 Fig. D.7 Magnetometer profiles at Harbour Basin sheet 3 of 3 D(9) EPA Export :03:03:51

32 Results Magnetometer in Dredged Channel D(10) EPA Export :03:03:51

33 Fig. D.8 Magnetometer survey trackplot in Dredged Channel sheet 1 of 2 D(11) EPA Export :03:03:51

34 Fig. D.9 Magnetometer survey trackplot in Dredged Channel sheet 2 of 2 D(12) EPA Export :03:03:51

35 Fig. D.10 Magnetometer profiles in Dredged Channel sheet 1 of 9 D(13) EPA Export :03:03:51

36 Fig. D.11 Magnetometer profiles in Dredged Channel sheet 2 of 9 D(14) EPA Export :03:03:51

37 Fig. D.12 Magnetometer profiles in Dredged Channel sheet 3 of 9 D(15) EPA Export :03:03:51

38 Fig. D.13 Magnetometer profiles in Dredged Channel sheet 4 of 9 D(16) EPA Export :03:03:51

39 Fig. D.14 Magnetometer profiles in Dredged Channel sheet 5 of 9 D(17) EPA Export :03:03:51

40 Fig. D.15 Magnetometer profiles in Dredged Channel sheet 6 of 9 D(18) EPA Export :03:03:51

41 Fig. D.16 Magnetometer profiles in Dredged Channel sheet 7 of 9 D(19) EPA Export :03:03:51

42 Fig. D.17 Magnetometer profiles in Dredged Channel sheet 8 of 9 D(20) EPA Export :03:03:51

43 Fig. D.18 Magnetometer profiles in Dredged Channel sheet 9 of 9 D(21) EPA Export :03:03:51

44 APPENDIX E Results Sub-bottom profiling E(1) EPA Export :03:03:51

45 Fig. E.1 Sub-bottom profiler trackplot E(2) EPA Export :03:03:51

46 E(3) EPA Export :03:03:51

47 Fig. E.1 Sub-bottom profiler survey trackplot E(4) EPA Export :03:03:51

48 APPENDIX F Results Topography Fig. F.1 Topographic survey plan map F(1) EPA Export :03:03:51