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Water quality modelling
- f the River Almond,
Scotland, UK
IAHS-IAPSO-IASPEI joint assembly, Gothenburg
Atkins Lectures
of the River Almond, Scotland, UK IAHS-IAPSO-IASPEI joint - - PowerPoint PPT Presentation
of the River Almond, Scotland, UK IAHS-IAPSO-IASPEI joint - - PowerPoint PPT Presentation
Atkins Lectures Water quality modelling of the River Almond, Scotland, UK IAHS-IAPSO-IASPEI joint assembly, Gothenburg Vera Jones, senior environmental scientist, Water and Environment 25 July 2013 Introduction Background to the project
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Introduction
Background to the project
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River Almond, SE Scotland Large part of the flow from wastewater discharges and untreated discharges from combined sewer overflows Pollution from septic tanks and other private discharges Diffuse pollution pressure associated with historic mining A number of surface water outfalls – industrial estates.
Catchment understanding at the start of the project
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Key objectives of this study
Water quality survey and development of a modelling tool Help to assess the impact of Scottish Water assets on the water quality of the River Almond and its tributaries Development of strategic options to meet requirements of the Water Framework Directive and the Urban Wastewater Treatment Directive.
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Summer 2011 survey
Upper boundary Cramond Weir
Study area
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Modelling
Model development, calibration and validation
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Model description (Mike 11 Ecolab by the DHI Group)
Advection/dispersion Biogeochemical interactions Heat Hydraulic model
Time Space Time Space Advection Dispersion Time Space Time Space Time Space Time Space Advection Dispersion
d[BOD]/dt= - BOD Decay - Sedimentation + Resuspension Photosynthesis = Pmax*suninp/depth Respiration= DO2/(DO2+ mdo)*resp* teta2(TEMP-20)/depth
Air temperature, air humidity, wind speed
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Determinants modelled: Dissolved oxygen Temperature Ammonia Nitrate Ortho-phosphate Particulate phosphorus Biochemical oxygen demand
Model description
Advection/dispersion Biogeochemical interactions Heat Hydraulic model
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Boundaries: 31 rural sub- catchments Seven wastewater treatment works Six private discharges ~120 combined sewer overflows – modelling by MWH
Model description
Advection/dispersion Biogeochemical interactions Heat Hydraulic model
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Calibration and validation summary
temperature ( ºc)
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Calibration and validation summary
Excellent match when considering daily average temperature
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Key parameter in this study: overall good match with observed data
Calibration and validation summary
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Calibration and validation summary
Some spikes in the model record – potentially high values not picked up by the monitoring
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20 40 60 80 100 120 140 160
15/08/2011 20/08/2011 25/08/2011 30/08/2011 04/09/2011 09/09/2011 14/09/2011 19/09/2011 24/09/2011
DO%
- bserved
modelled
Model Observed
Max: day Min: night Crucial to fish Many interactions with other parameters
DO% saturation
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Methodology for the needs assessment
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Results extracted and processed for every model node:
- Water Framework Directive standards
- 99th percentile (99thile) standards*
- Fundamental Intermittent Standards (FIS)*
Two years selected for further scenario testing : ‘poor’ and ‘average’ water quality
*FWR (2012). Urban Pollution Management Manual http://www.fwr.org/UPM3/
Urban Wastewater Treatment Directive
Methodology for needs assessment
10-year runs – stochastic ‘baseline’
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High Good Moderate Poor Bad
For all results analyses: Good or High Status is required.
Methodology for needs assessment
Programme developed for processing results at every node against the relevant standards. Output in a suitable format to produce maps of classification at model node.
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Needs assessment: stochastic ‘baseline’ runs
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Summary of 10-year baseline stochastic runs:
- No FIS failures
- WFD failures for ortho-phosphate
and ammonia
- 99thile failures for ammonia and
BOD
High Good Moderate Poor Bad
Ammonia – WFD assessment (10-year)
Results of needs assessment: summary
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Needs assessment: scenarios runs
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Results of needs assessment: analysis against WFD standards
Ortho-phosphate 2024 - baseline Ortho-phosphate 2024 – no waste water treatment works scenario
Works are a key cause of failure to meet the Water Framework Directive standards
High Good Moderate Poor Bad
Wastewater Treatment Works (WwTW) discharges
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Wastewater Treatment Works (WwTW) discharges
BOD 2024 - baseline BOD 2024 – no waste water treatment works scenario
Results of needs assessment: analysis against 99thile standards
Works dilute intermittent untreated combined sewer overflow inputs
High Good Moderate Poor Bad
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Results of needs assessment: analysis against WFD standards
Ortho-phosphate 2024 - baseline Ortho-phosphate 2024 – no combined sewer overflows scenario
Small improvement – combined sewer overflows have a small effect
- n compliance with Water Framework Directive standards
High Good Moderate Poor Bad
Combined Sewer Overflows
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Results of needs assessment: analysis against 99thile standards
Combined Sewer Overflows
BOD 2025 - baseline BOD 2025 – no combined sewer overflows scenario
Combined sewer overflows have a noticeable impact on compliance with 99thile standards
High Good Moderate Poor Bad
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Results of needs assessment: analysis against WFD standards
“Best Available Technology”
Ortho-phosphate 2025 - baseline Ortho-phosphate 2025 – ‘best available technology’ scenario
Best available technology treatment at WwTW is not sufficient to achieve required status
High Good Moderate Poor Bad
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Summary and Conclusion
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Summary and Conclusion
- The results of the modelling portray a complex picture of water quality dynamics in
the River Almond system
- Key parameters of concern with regards to the Water Framework Directive and
Urban Wastewater Treatment Directive compliance – ortho-phosphate and BOD
- Most significant cause of poor water quality: continuous discharges from
wastewater treatment works
- However wastewater treatment works also have a beneficial effect - diluting the
intermittent untreated combined sewer overflow inputs
- Operation of key wastewater treatment works at ‘Best Available Technology’
treatment levels: not sufficient to bring the whole system to the required status – key for strategic decisions
- Assuming the current wastewater load to the system, achieving requirements
through investment in wastewater treatment work will be challenging
- Model currently being used to test different options – in discussion with the
regulator (Scottish Environment Protection Agency) – aiming to achieve best possible ‘balance’ of compliance, also considering impacts on flow.
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For more information contact:
Vera Jones vera.jones@atkinsglobal.com
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