SSF SCAPA FLOW ECE ESTIMATES 2017 SCOTTISH SEA FARMS SSF) SCAPA FLOW ECE ESTIMATES 2017 Report No. Scapa Flow 013.docx Anton Edwards April 2017 For: Anton Edwards CPhys, FInstP Scottish Sea Farms Ltd Duguid's Wark Laurel House Manse Road Laurel Hill Business Park Caputh Stirling Perthshire FK7 9JQ PH1 4JH 01738 710774 SCAPA FLOW 013.DOCX SSF SCAPA FLOW ECE ESTIMATES 2017 SUMMARY This report outlines the hydrography of the area of Scapa Flow in Orkney, so as to estimate the effect of existing and potential fish farms on local nutrient concentrations via the 'Equilibrium Concentration Enhancement' ( ECE) approach. Tidal and residual flows to Scapa Flow have been estimated by various methods (tide tables, direct observation and water budgets) to be sufficient to dilute the nitrogen released from existing consented sites and potential sites such that the likely ECE of nitrogen concentration is less than 10 µgN.litre-1. This estimate is based on a conservative assumption of 90% recirculation. The recirculation is expected to be much less than 90%, increasing the flushing of Scapa Flow and reducing the predicted overall ECE further to within the lower part of the range 1 to 10 µgN.litre-1. Local increases of ECE in the east of Scapa Flow may reach similar levels. Sites in the east of Scapa Flow such as Hunda, Roo Point and Westerbister are removed from the main flows but are well connected to them by an inferred eddy that circulates the water of Scapa Flow in a matter of days. This eddy exchanges with local coastal bays on a time scale of about a day so that the bays are very unlikely to develop local water characteristics different from the main body of Scapa Flow. An ECE of up to 10 µgN.litre-1 may be compared favourably with various relevant or regulatory standards: typical background concentrations a previous Environmental Quality Standard for available nitrogen of 168 gN.litre-1 OSPAR & Water Framework Directive Reference Conditions: in offshore waters such as these (salinity above 34), the DIN (Dissolved Inorganic Nitrogen) reference value is 10M and the threshold 15M. Increases are therefore limited to 5 M (70 gN.l-1). In the cases and circumstances examined here, predicted ECE increases are therefore insignificant on the scale of the Scapa Flow water body. Displacement modelling shows that water in the neighbourhood of Hunda North that complies with Environmental Quality Standards is unlikely to reach local embayments in any significant quantity, implying that these embayments are at very low risk of EQS non-compliance. Comparison of displacements of water over regulatory time scales shows that waters from sites at Hunda North and Glimps Holm are very unlikely to meet with any local cumulative effect of raising local medicine concentrations to anything above EQS. Comparison of modelled depositional footprints at Hunda North and Glimps Holm shows that in this respect the interaction between the two sites is negligible. SCAPA FLOW 013.DOCX SSF SCAPA FLOW ECE ESTIMATES 2017 CONTENTS 1 INTRODUCTION ........................................................................................................... 4 1.1 SCAPA FLOW REGULATORY ISSUES .................................................................................. 4 1.2 THE ECE APPROACH....................................................................................................... 4 2 PHYSICAL BACKGROUND ......................................................................................... 5 2.1 NON- TIDAL CIRCULATION AND THE FAIR ISLE CURRENT ...................................................... 5 2.2 GEOGRAPHY ................................................................................................................... 6 2.3 HYDROGRAPHY ............................................................................................................... 7 2.3.1 TIDAL RANGE ........................................................................................................................................... 7 2.3.2 THE TIDAL STREAM ATLAS ....................................................................................................................... 8 2.3.3 CURRENTS NEAR GRAEMSAY ................................................................................................................... 9 2.3.4 VOLUME FLOWS ....................................................................................................................................... 9 2.3.5 A TIDAL FLOW BUDGET .......................................................................................................................... 10 2.3.6 CURRENTS WITHIN SCAPA FLOW ............................................................................................................ 10 3 FARM SITES .............................................................................................................. 12 3.1 SITE DETAILS ................................................................................................................ 12 3.2 SITE CURRENTS ............................................................................................................ 13 3.2.1 BRING HEAD CURRENTS ........................................................................................................................ 13 3.2.2 TOYNESS CURRENT DATA ....................................................................................................................... 13 3.2.3 WESTERBISTER CURRENT DATA ............................................................................................................. 14 3.2.4 HUNDA NORTH ....................................................................................................................................... 14 3.2.5 ROO POINT ............................................................................................................................................ 15 3.2.6 ST MARGARET’ S HOPE .......................................................................................................................... 16 3.3 SCAPA FLOW CIRCULATION ........................................................................................... 16 3.3.1 THE INTERTEK MODEL ............................................................................................................................ 16 3.3.2 SITE CURRENT SUMMARY ...................................................................................................................... 17 3.3.3 FLUSHING TIME ....................................................................................................................................... 18 3.3.4 CONNECTION OF EAST SCAPA FLOW ...................................................................................................... 18 3.3.5 COASTAL EFFECTS IN THE EAST OF SCAPA FLOW ................................................................................... 19 4 PREDICTION OF NUTRIENT INCREASE .................................................................. 21 4.1 NUTRIENT INPUTS ......................................................................................................... 21 4.1.1 SSF SITE OPTIONS ................................................................................................................................. 21 4.2 CONCENTRATION ENHANCEMENT ................................................................................... 21 4.2.1 TIDAL FLOWS AND RECIRCULATION ......................................................................................................... 21 4.2.2 RESIDUAL FLOWS ................................................................................................................................... 21 4.3 ECE ESTIMATES ........................................................................................................... 21 4.3.1 ECE ESTIMATION IN SCAPA FLOW ......................................................................................................... 21 4.3.2 WORST CASE ECE AT MAXIMUM BIOMASS .............................................................................................. 22 4.3.3 LOCAL EFFECTS ..................................................................................................................................... 23 4.4 SUMMARY ..................................................................................................................... 23 5 EQS COMPLIANCE NEAR HUNDA NORTH ............................................................. 24 5.1 HUNDA NORTH ............................................................................................................. 24 5.2 GLIMPS HOLM ............................................................................................................... 25 6 DEPOSITIONAL FOOTPRINTS NEAR HUNDA NORTH ........................................... 28 REPORT NO: SCAPA FLOW 001 1 SCAPA FLOW 013.DOCX SSF SCAPA FLOW ECE ESTIMATES 2017 7 CONCLUSIONS .......................................................................................................... 29 7.1 ECE ............................................................................................................................ 29 7.2 EQS ............................................................................................................................ 29 7.3 DEPOSITIONAL FOOTPRINTS .......................................................................................... 29 8 REFERENCES 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