design considerations and modelling approaches focused on marine...

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

4th WRC Symposium:

Innovation in every drop -

Managing uncertainty and

building capacity through

collaboration

R. Van Ballegooyen

Tel: +27 21 810 4628

[email protected]

[email protected]

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:

Innovation in every drop.

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

4th WRC Symposium:

Innovation in every drop

Changes in

Regulatory Environment

4

2014 2015

Policy Guidelines 4th WRC Symposium:


Changes in


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


6

Water Quality Guidelines

2019 2012

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Changes in


7

Sediment Quality Guidelines

2010 2012

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Changes in


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:


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)

4th WRC Symposium:


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

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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:


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:


Technical/Modelling

Innovations:



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:


Technical/Modelling

Innovations:



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;

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Technical/Modelling

Innovations:



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:


Technical/Modelling

Innovations:



Catchment influences on coastal environments

Reproduced with the permission of Dr Stewart Bernard and Marie Smith

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Technical/Modelling

Innovations:



2013-2016

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Technical/Modelling

Innovations:



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

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Technical/Modelling

Innovations:



Impact of damming of the River

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Technical/Modelling

Innovations:



Impact of damming of the River

1988 (1:100 year event - Large Floods) 2010 (1:20 yr event - Small flood)

2009 (Large Freshwater Pulse)

4th WRC Symposium:


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:


Technical/Modelling

Innovations:

Role of modelling in intake

and outfall development

25

Near versus far-field modelling 4th WRC Symposium:


Technical/Modelling

Innovations:

Coupling of Near-

and Far-field

26

Near versus far-field modelling 4th WRC Symposium:


Technical/Modelling

Innovations:

Coupling of Near-

and Far-field

27

4th WRC Symposium:


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:


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:


Technical/Modelling

Innovations:

Coupling of Near-

and Far-field

30

4th WRC Symposium:


Technical/Modelling

Innovations:

Impacts close to outfall

Characterisation of Near-field behaviours

31

4th WRC Symposium:


Technical/Modelling

Innovations:


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:


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:


Technical/Modelling

Innovations:

Chemicals of Emerging

Concern

4th WRC Symposium:


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)


• 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

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Novel 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:



Novel construction

techniques

THANK YOU!

4th WRC Symposium:


Thank You

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