design considerations and modelling approaches focused on marine...
TRANSCRIPT
Roy van Ballegooyen*1, Marthinus Retief *1
Gert Jacobs*1, Brent Newman*2 and G. Fearon*3
*1 Maritime, WSP Group Africa, *2 CSIR, *3 SAEON/DEA
Design considerations and modelling approaches focused on
marine outfall performance assessment and monitoring
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Managing uncertainty and
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collaboration
R. Van Ballegooyen
Tel: +27 21 810 4628
2
Introduction
Progressive change over the past decade in the development of intake and outfall systems includes:
• Technological, modelling and engineering advances of relevance
• Trends in developments requiring intake and outfall infrastructure
• Changes in the regulatory environment
• Resultant evolution in design, assessment & performance requirements
4th WRC Symposium:
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Introduction
Changes in Regulatory Environment
Changes in regulatory authority
Review of Policy And Legislation (Regulations)
Department of Water Affairs
(Dept. of Water & Sanitation)
National Water Act (1998)
Department of Environmental Affairs
Integrated Coastal Management Act
ICMA (2008)
2008
Operational Policy for Coastal
Effluent Discharges
(DWAF, 2004a-c)
i) Policy Document
ii) Implementation Guideline
National Guideline for Coastal
Effluent Discharges (DEA, 2014)
Assessment/Management
Framework for Coastal Effluent
Discharges
(Anchor Environmental, 2015)
+ ~ 6
years + ~ 6
years
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Changes in
Regulatory Environment
4
2014 2015
Policy Guidelines 4th WRC Symposium:
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Changes in
Regulatory Environment
Changes in Regulatory Environment
S A Water Quality Guidelines
(1995-1996) • Natural Environment
• Recreational Use
• Industrial Use
• Mariculture
Sediment Quality Guidelines (London Convention)
S A Water Quality Guidelines • Natural Environment &
Mariculture (2019)
• Vol 2: Recreational Use (2012)
Sediment Quality Guidelines • Review of Sediment Guidelines
(2010) & Regulations (2012)
2012
to
2019?
NEMA (1998)
Clear specification of EIA
process requirements
New Environmental Legislation
Review of Water / Sediment Quality Guidelines
2014 NEMA (2010) & NEMA (2014)
Imposition of stringent time-
scales to expedite EIA
processes
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Changes in
Regulatory Environment
6
Water Quality Guidelines
2019 2012
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Changes in
Regulatory Environment
7
Sediment Quality Guidelines
2010 2012
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Changes in
Regulatory Environment
Trends in RSA marine outfalls
A review of outfalls along the South African coastline and their relative risk profiles (WSP, 2016) suggest a perceptible shift in the nature of marine discharges to the marine environment:
• Few new large deep water (WWTW/Industrial) outfalls planned.
• Trend towards small to medium (some large) desalination plant brine discharges & more modest mariculture facility effluent discharges
• A significant unknown remains the likelihood of (typically high volume) thermal discharges from proposed LNG or nuclear power plants
Outfall discharge volume (MLD)
No
. o
f o
utf
all
s
Pre-2005
4th WRC Symposium:
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Trends in RSA
Marine Outfalls
Outfall discharge volume (MLD)
No
. o
f o
utf
all
s
Post-2005
?
Trends in RSA marine outfalls
A review of outfalls along the South African coastline and their relative risk profiles (WSP, 2016) suggest a perceptible shift in the nature of marine discharges to the marine environment:
• Few new large deep water outfalls (WWTW/Industrial) planned.
• Trend towards small to medium (some large) desalination plant brine discharges & more modest mariculture facility effluent and potentially building cooling water discharges
• A significant unknown remains the likelihood of (typically high volume) thermal discharges from proposed power plants (IPP LNG/Nuclear)
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Trends in RSA
Marine Outfalls
Trends in RSA marine outfalls: Implications
Increased desalination activities have resulted in:
• Greater likelihood of intakes and outfalls being located in multi-user environments (near population centres or in coastal embayments/ports)
• The need for a more comprehensive characterisation of intake water quality
• More accurate assessment of potential impacts of effluents on coastal and marine environments, including pollutants of emerging concern
Coastal modelling has a significant role to play in the design and performance assessment requirements of the resultant intake and outfall systems
4th WRC Symposium:
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Trends in RSA
Marine Outfalls
Technical/Modelling Innovations
There has been a strong development of large-scale modelling and down-scaling of these model results:
4th WRC Symposium:
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Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
• Improved wave and storm surge forecasting (SAWS)
• Intake and outfall structural design
• Intake water quality (nearshore suspended sediments)
• Improved modelling of currents and water column structure and down-scaling of these results in coastal embayments and coastal environments (SAEON/DEA). Predicted currents and water column structure are:
• Critical determinants of near-field effluent plume behaviour.
• Important in quantifying catchment impacts on adjacent coastlines
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Outfall Development: Environmental Variability 4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
Outfall locations
Durban
Richards Bay
Outfall locations
Outfall locations
Improved large-scale & nested ocean modelling
HYCOM 1/12° Model Results
Delft3D-FLOW Nested Model Results
courtesy of G. Fearon, SAEON/DEA
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
A WRC supported initial assessment of the freshwater requirements* was undertaken in 2007 outlining:
• The nature of the freshwater links between coastal enviroments and adjacent catchments;
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
Freshwater Requirements of Marine Environments
* van Ballegooyen, R.C., S. Taljaard, L. Van Niekerk, S. Lamberth, A K Theron and S. Weerts. (2007). Determination of freshwater requirements of the marine environment of South Africa: A proposed framework and initial assessment WRC Report No. KV 191/07, 150pp + 37pp App.
• Regions/environments where such links arelikely to be of importance (e.g. the KwaZulu-Natal Bight)
Near-field: Influence of currents/stratification
Rip currents
Longshore currents
Wave direction
Surf zone discharge
Tidal inflow
Head works
Exposed pipeline
Diffuser
Buried pipeline
Moving waste field-Secondary Dilution & Decay
Rising buoyant plume-Initial Dilution
Current profile
Sea surface Sea surface
Sea surface Sea surface
Stratification
Stratification
Stratification
Temperature Current Temperature Current
Temperature
No currentsNo stratification
No currents
Stagnant unstratified water
Weak currents with stratification Moderate currents with stratification
Stagnant stratified water
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
Catchment influences on coastal environments
Reproduced with the permission of Dr Stewart Bernard and Marie Smith
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
2013-2016
4th WRC Symposium:
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Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
ORESECOM – Orange River Study (UNDP/GEF)
Landsat ETM+ satellite image (Pisces 2008)
Purpose of the study is to provide a relative measure of the influence of various flow scenarios on the offshore environment Sediment supply to
beaches & nearshore habitat
Turbidity fronts Salinity fronts Dissolved reactive silicate
(DRS) Nutrients: Upwelling coast Pollutants: Not a low
retention zone e.g. a coastal embayment bay
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
Impact of damming of the River
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Improved large-scale
modelling & down-scaling
Impact of damming of the River
1988 (1:100 year event - Large Floods) 2010 (1:20 yr event - Small flood)
2009 (Large Freshwater Pulse)
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Technical/Modelling
Innovations:
Biochemical modelling
Biogeochemical modelling
Dissolved oxygen near the seabed Diatom biomass in surface waters
Biochemical Modelling: Suspended Sediment
Biochemical Modelling: Diatom Biomass
Biochemical Modelling: Dissolved Oxygen
24
Outfall Development: Dispersion Modelling Activities
Conceptual
“modelling” &
limited near-field
modelling
Coupled near-field and
far-field modelling
Modelling of
full- range of
scenarios
Detailed near-field
modelling for
diffuser design
”Confirmatory far-
field modelling
(CWDP) Operational
Modelling
Support
Modelling to
support policy
development
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Role of modelling in intake
and outfall development
25
Near versus far-field modelling 4th WRC Symposium:
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Technical/Modelling
Innovations:
Coupling of Near-
and Far-field
26
Near versus far-field modelling 4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Coupling of Near-
and Far-field
27
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Coupling of Near-
and Far-field
Near versus far-field modelling
28
The predicted achievable dilutions of an effluent are quite sensitive to the
nature of the near- and far-field model coupling.
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Coupling of Near-
and Far-field
Distributed Entrainment Sink Approach (DESA)
29
Distributed Entrainment Sink Approach (DESA)
The predicted achievable dilutions of an effluent are quite sensitive to the
nature of the near- and far-field model coupling.
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Coupling of Near-
and Far-field
30
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Impacts close to outfall
Characterisation of Near-field behaviours
31
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Impacts close to outfall
Characterisation of Near-field behaviours
32
Monitoring Design: Near-field Diver Surveys
http://www.cfoo.co.za/buoys/buoystatus_umkomaas.php
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Technical/Modelling
Innovations:
Impacts close to outfall
Pollutants of emerging concern
Modelling needs to improve capabilities to deal with chemicals (pollutants) of emerging concern such as (pharmaceuticals & cleaning products, persistent organic pollutants, etc.).
• Improved modelling of bacteriological components and virus’s
• Presently outfall assessment modelling treats most Chemicals (pollutants) of Emerging Concern (CEC) as a conservative tracer where transformation and break-down of the CEC is not fully understood. This typically, but not in all cases, constitutes a very conservative approach.
• Need to better account for potential cumulative effects in the far-field in assessment studies.
Presently the “Precautionary Approach” is taken when there is uncertainty, resulting in possible overly conservative assessments
4th WRC Symposium:
Innovation in every drop
Technical/Modelling
Innovations:
Chemicals of Emerging
Concern
4th WRC Symposium:
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Technical/ Innovations:
Novel construction
techniques
Intake/Outfall Construction techniques
• Conventional: Open cut trench through surf-zone with temporary jetty to provide access for plant
• Higher environmental impact within close shore areas, albeit temporary
• Higher risk construction through dynamic surf-zone
• Potential for construction delays (weather dependant)
Intake/Outfall Construction techniques
• Novel: Tunnelling or Directional Drilling - Sub-seabed conduits installed with boring machines
• Lower environmental impact within close shore area/ Offshore blasting required for machine retrieval pit
• Lower construction risk (limited weather dependence), but depends on geology
• Potential shorter construction period
• Potential very high plant mobilization cost
• Offshore blasting required for machine retrieval pit
4th WRC Symposium:
Innovation in every drop
Technical/ Innovations:
Novel construction
techniques
Intake/Outfall Construction techniques
Port Alfred HDD outfall route
Port Alfred HDD rig
Port Alfred HDD rig site set-up
Port Alfred desalination outfall
(TRG drilling)
HDD proposed for Lamberts Bay Desalination outfall
Others under feasibility study
4th WRC Symposium:
Innovation in every drop
Technical/ Innovations:
Novel construction
techniques
THANK YOU!
4th WRC Symposium:
Innovation in every drop
Thank You