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Shellfisheries Waters Compliance Assessments at Pegwell Bay


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Shellfisheries Waters Compliance Assessments at Pegwell Bay in Kent. MIKE by DHI modelling (FM Series) formed a large part of the study, and Jonathan presents some interesting experiences in the use of the Software (Jonathan Short - URS).

MIKE by DHI 15th UK User Group Meeting - Tuesday 19 March 2013

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Shellfisheries Waters Compliance Assessments at Pegwell Bay

  1. 1. Shellfisheries Waters Compliance Assessments atPegwell Bay, KentDHI User Group Meeting 2013Jonathan Short, BSc MScMarch 19th 2013
  2. 2. OverviewObjective:“ identify future investment which will make a contribution to achievement of compliance with the Shellfish Waters Directive Guideline bacteriological standards and support the client (Southern Water) in delivering waste water improvement schemes around the Pegwell Bay, Kent.”• The investigations are a Southern Water Output of the Environment Agency’s AMP 4/5 National Environment Programme under the S2 Shellfish Driver.• The investigations will inform the Agency’s Pollution Reduction Plans drawn up as part of the UK response to EC infraction proceedings concerning the quality of UK Shellfish Waters.• URS (formerly Scott Wilson) in partnership and Intertek (Metoc), investigated the impact of various sources on water quality at the shellfish beds.• MIKE modelling formed a large part of the study. DHI UGM 2013
  3. 3. Pegwell Bay, Kent DHI UGM 2013
  4. 4. Key Aspects of the Study• The study included: Extensive field survey programme (Titan Surveys Calibration of a MIKE FM HD and AD models to stringent FWR standards. Simulation of effluent discharges and plumes from WwTW and CSO. Simulation of background loads e.g. rivers (Catchment and Network models) Large scale production run modelling phase. Compliance assessment in partnership with Intertek Metoc (STORM IMPACT) including assessment of the relative impact of different point sources on overall water quality. Evaluation of pros and cons of implementing UV treatment at key outfalls. DHI UGM 2013
  5. 5. Extensive Field Survey Programme• Hydrodynamics Water levels - ADCP 30-day period (and Deal Pier - CCO). Currents – ADCP. Meteorological data. River flows - EA gauging.• Water Quality Dye Patch monitoring. Drogues. Water sampling and bacterial load testing. Salinity / Temperature– CTD grid. Tracer from WwTW in river. Bathing water sampling. DHI UGM 2013
  6. 6. Further Water Quality Data• Microbiological survey sampling.• Hourly sampling at the Shellfish Beds – Spring and Neap tides, Winter and Summer conditions.• EA routine monitoring sites.• Bathing water sampling records.• Shellfish Bed monitoring data.• Outfall monitoring. DHI UGM 2013
  7. 7. Hydrodynamic Model – Calibration / ValidationParameter Tolerance Applied Absolute Relative 10% tidal range -spring tideWater Level +/- 0.1m 15% tidal range neap tide +/- 20% of observedCurrent Speed +/- 0.1ms-1 speedCurrent +/- 30 degrees* N/ADirectionPhase +/- 15mins N/A DHI UGM 2013
  8. 8. Water Quality Modelling – Calibration / Validation 1.E-05 Simulation Dye Measurement 1.E-06 Concentration (cc/cc) 1.E-07 1.E-08 1.E-09 05/06/10 04:00 05/06/10 05:30 05/06/10 07:00 05/06/10 08:30 05/06/10 10:00 DHI UGM 2013
  9. 9. Salinity Calibration / Validation Comparison of Depth Averaged Salinities at CTD Site C 36 Measured Modelled 35 34 Salinity (psu) 33 32 31 30 31/05/2010 12:00 31/05/2010 18:00 01/06/2010 00:00 01/06/2010 06:00 01/06/2010 12:00 DHI UGM 2013
  10. 10. Discharges Represented in the AD Model 3 WwTW 21 CSOs 1 River 14 Discharge groups DHI UGM 2013
  11. 11. Technical Challenges / Limitations 0mins 160mins DHI UGM 2013
  12. 12. New DHI Whale Module required?!... DHI UGM 2013
  13. 13. Production Runs•Highly computationallyintensive one month phase ofproduction runs.•Modelling outputs totallingover 100 processor days.•Various wind and seasonalconditions.•Hourly releases over a 12hour tidal cycle for eachdischarge location. DHI UGM 2013
  14. 14. Simulating Decay Rates / Residence Stour Estuary E0001326 T90=30hrs DHI UGM 2013
  15. 15. Compliance Assessment Outputs DHI UGM 2013
  16. 16. Key Findings• Water quality within the Pegwell Bay shellfish waters is considered good, and compliant with current water quality standards.• During periods of high rainfall local CSOs in the Sandwich, Ramsgate and Margate catchments contribute the majority of the bacteria concentration in Pegwell Bay. However these impacts are infrequent and are only significant at high percentiles.• Improvements to the treatment process at Weatherlees Hill A WwTW, i.e. UV disinfection, would be expected to reduce its contribution the shellfish waters of Pegwell Bay.• However, given that shellfish waters meet current water quality standards and the relatively high river load in storm conditions, the provision of UV disinfection at Weatherlees Hill A would not provide significant additional benefit when considered against cost and carbon footprint. DHI UGM 2013
  17. 17. Summary• Study provided additional knowledge and insight into the often complex patterns of water movement in coastal and estuarine waters.• MIKE modelling software provided a suitable predictive tool capable of assessing water quality impacts arising from individual discharges.• Formed part of the wider toolkit for for efficiently assessing the performance of different mitigation options.• Outputs will inform the Agency’s Pollution Reduction Plans drawn up as part of the UK response to improvement of Shellfish Waters.• Targeted investment to minimise storm water storage, treatment and pumping requirements in a sustainable manner.• Ensures minimum overall environmental impact, in terms of meeting receiving water quality standards, balanced against reducing carbon emissions. DHI UGM 2013
  18. 18. Questions? Thank you! Jonathan.Short@urs.comDHI UGM 2013