Greater Dublin Drainage Project Irish Water Environmental Impact Assessment Report: Volume 3 Part A of 6 Chapter 9 Biodiversity (Marine) June 2018 Envir onmental Impact Assessment Report: Vol ume 3 Part A of 6 Irish Water Environmental Impact Assessment Report: Volume 3 Part A of 6 Contents 9. Biodiversity (Marine) ................................................................................................................................. 1 9.1 Introduction .................................................................................................................................................. 2 9.2 Methodology ................................................................................................................................................ 4 9.2.1 Desktop Study ............................................................................................................................................. 4 9.2.2 Field Surveys ............................................................................................................................................... 4 9.2.3 Underwater Noise Modelling ....................................................................................................................... 8 9.2.4 Impact Assessment Methodology ............................................................................................................... 9 9.2.5 Non-Statutory Consultation ....................................................................................................................... 13 9.3 Baseline Environment ............................................................................................................................... 16 9.3.1 Designated Sites for Nature Conservation ................................................................................................ 16 9.3.2 Geomorphology and Seabed Sediments .................................................................................................. 17 9.3.3 Sediment Chemistry .................................................................................................................................. 18 9.3.4 Marine Benthos ......................................................................................................................................... 22 9.3.5 Water Quality Profiling, Sampling and Plankton ....................................................................................... 32 9.3.6 Baldoyle Estuary Walkover ....................................................................................................................... 36 9.3.7 Marine Mammals ....................................................................................................................................... 39 9.3.8 Fish and Shellfish ...................................................................................................................................... 45 9.3.9 Summary Evaluation (Importance) of Key Marine Ecological Receptors and Habitats ............................ 51 9.4 Impact of the Proposed Project – Construction Phase ............................................................................. 53 9.4.1 Construction of the Microtunnelling Compounds Adjacent to the Baldoyle Estuary and Construction Works Upstream of Marine Environment with Potential for Contaminated Runoff ................................... 54 9.4.2 Tunnelling Underneath Baldoyle Bay and Tunnelling Compounds ........................................................... 55 9.4.3 Dredging of Proposed Outfall Pipeline Route (Marine Section) ................................................................ 63 9.4.4 Piling for Tunnel Interface and/or Fibre Optic Cable ................................................................................. 69 9.4.5 Installation of the Proposed Marine Diffuser ............................................................................................. 70 9.5 Impact of the Proposed Project – Operational Phase ............................................................................... 72 9.6 ‘Do Nothing’ Impact ................................................................................................................................... 78 9.7 Mitigation Measures .................................................................................................................................. 78 9.7.1 Construction Phase ................................................................................................................................... 78 9.7.2 Operational Phase ..................................................................................................................................... 82 9.8 Residual Impacts ....................................................................................................................................... 82 9.9 References ................................................................................................................................................ 83 32102902/EIAR/9 ii Environmental Impact Assessment Report: Volume 3 Part A of 6 9. Biodiversity (Marine) This Chapter of the Environmental Impact Assessment provides a characterisation of the receiving environment and an assessment of the impacts of the Proposed Project on estuarine, coastal and marine ecology. The key areas of the Proposed Project boundary which may be particularly sensitive are Baldoyle Bay and Rockabill to Dalkey Island Special Areas of Conservation (SAC). In particular, the sub-littoral reefs close to the proposed outfall pipeline route (marine section) and the presence of designated marine mammals in the waters surrounding the outer end were of concern and have received a significant level of assessment. A large number of estuarine and marine surveys were undertaken between 2012 and 2017. This included a walkover survey over the mudflats, Salicornia and Atlantic salt meadows of the Baldoyle Bay Estuary SAC beneath which the proposed outfall route (marine section) will pass using micro tunnelling. The potential for impact in this area relates to bentonite or air breakout during construction along with possible contamination from runoff from the proposed temporary construction compounds. These possible impacts can be mitigated through a Construction Environmental Management Plan, preventing discharges to the estuary and detailed control of bentonite flow and air pressures where needed. The proposed outfall pipeline route (marine section) area was surveyed using multiple geophysical and benthic surveys between 2012 and 2017. Benthic data shows a diverse population based on sands to the west and mixed sandy gravels to the east at shelf break with no contaminants found in surface or dredge sediment depths. These habitats are not particularly sensitive to construction impacts and no significant impact is predicted. The proposed marine diffuser will be located within Rockabill to Dalkey Island SAC (designated for Reefs at Ireland’s Eye and the harbour porpoise over the greater area). The reefs were assessed in 2015 using camera and divers and these showed a diverse habitat with a naturally high silt content. The Construction Phase presents a minor risk of plume effects during dredging whilst near the proposed marine diffuser location during spring tides, but no mitigation other than monitoring and control of dredging operations is needed to keep this to a negligible impact on this feature. Harbour porpoises were assessed by an extensive monitoring survey between 2015 and 2017 using both acoustic and observational techniques in the vicinity of the Proposed Project. Results showed some of the highest densities recorded in Ireland and moderate levels of activity throughout the year with numbers increasing in late summer. This was coincident with the presence of calves and may be due to seasonally abundant food sources such as sprat, herring and Trisopterus and gadoid species. Numbers then reduced during late spring/early summer which may be associated with an offshore movement of this species before calving. No impacts are expected for dredging operations outside the SAC, but passive acoustic monitoring and marine mammal observations will be carried out to limit proximity during high noise construction operations (i.e. piling). Operations will also be restricted to outside peak population periods to reduce a potential minor impact to a negligible impact within the SAC. Fish surveys showed mostly nursery areas of limited importance but with a few sensitive/important fish species were present. The shellfish fishery is also important commercially but not sensitive ecologically. No impact from construction other than restriction of fishing grounds and loss of habitat at the proposed marine diffuser location are predicted. No operational impacts of the Proposed Project and no predicted significant residual effects upon estuarine, coastal and marine ecological receptors are predicted. 32102902/EIAR/9 Chapter 9 – Page 1 Environmental Impact Assessment Report: Volume 3 Part A of 6 9.1 Introduction This Chapter of the Environmental Impact Assessment Report (EIAR) provides a characterisation of the receiving environment and an assessment of the ecological impacts of the Greater Dublin Drainage Project (hereafter referred to as the Proposed Project) on marine ecology. The marine ecology impact assessment addresses the potential impacts on the benthos (animals living on or within the seafloor), marine mammals, fish, plankton and water