appendix g-1

Browse LNG Precinct

Browse Liquefied Natural Gas Precinct Strategic Assessment Report

(Draft for Public Review)February 2011

Appendix G-1Marine Wastewater

Discharge Modelling Study

Final Report: Modelling study of the operational discharges DHI WATER & ENVIRONMENT PTY LTD of the Browse LNG Precinct

Browse LNG Precinct Modelling Study of the Operational Discharges of the Browse LNG Precinct Woodside Energy Ltd

Final Report: Modelling study of the operational discharges of the Browse LNG Precinct

Page 2 of 66 DHI WATER AND ENVIRONMENT PTY LTD

Final Report January 2011

PO Box Z5543 PerthWA 6831 AUSTRALIA Tel: +61 8 9321 1555 Fax:+61 8 9321 3555

Client Woodside Energy Ltd

Client's representative Craig Gosselink

Project

Browse LNG Precinct Operational Discharges During Development of the Browse LNG Precinct. Modelling Study

Project No

43800080

Authors

Dr Paul van Gastel Dr Michael Meuleners

Date 24 January 2011 Approved by Tony Chiffings

A For review PVG,MJM

OSP TWC 24/1/11

Revision Description By Checked Approved Date

Key words Browse Downstream

MIKE 21 Advection Dispersion Model Brine Water Process waste Water

Classification

Open

Internal

Proprietary

Distribution No of Copies

Woodside Energy Ltd. Craig Gosselink 1 (PDF)



© DHI Water and Environment Pty Ltd 2011 The information contained in this document produced DHI Water and Environment Pty Ltd is solely for the use of the Client identified on the cover sheet for the purpose for which it has been prepared and DHI Water and Environment Pty Ltd undertakes no duty to or accepts any responsibility to any third party who may rely upon this document. You may download, store in cache, display, print and copy information in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. You may not commercialise the material without the prior permission of the copyright owner except as permitted under the Copyright Act 1968 (as amended). Requests for further authorisation should be directed to DHI Water and Environment Pty Ltd, Level 5, 67 Astor Terrace, Spring Hill, QLD 4000.



CONTENTS EXECUTIVE SUMMARY

1 INTRODUCTION .............................................................................................. 10 1.1 Objectives................................................................................................... 10 1.2 Structure of this Report .............................................................................. 11

2 PROJECT OVERVIEW .................................................................................... 12

3 STUDY APPROACH........................................................................................ 14 3.1 Overview .................................................................................................... 14 3.2 Modelling Scenarios ................................................................................... 16

3.2.1 Process Waste Water Scenarios ...................................................................16 3.2.2 Brine Water Scenarios...................................................................................17 3.2.3 Ambient Environmental Parameters ..............................................................17

4 PHYSICAL ENVIRONMENT ............................................................................ 18 4.1.1 Wind, Waves and Currents ............................................................................18 4.1.2 Water Levels .................................................................................................19 4.1.3 Tidal Currents ................................................................................................19 4.1.4 Regional Processes Summary ......................................................................22

5 MODEL DESCRIPTION AND SETUP ............................................................. 24 5.1 Near-field model setup ............................................................................... 24

5.1.1 Ambient Environmental Conditions ................................................................24 5.1.2 Sensitivity Test of the Diffuser Design ...........................................................25

5.2 Far-field Model Setup ................................................................................. 25 5.2.1 Hydrodynamic Model Resolution ...................................................................26 5.2.2 Advection – Dispersion Modelling ..................................................................26 5.2.3 Model Setup ..................................................................................................26

5.3 The Integration of the CORMIX and MIKE21 AD Results .......................... 27

6 MODEL VALIDATION ..................................................................................... 28

7 CORMIX NEAR-FIELD MODELLING RESULTS ............................................ 29

8 FAR-FIELD MODEL RESULTS ....................................................................... 34 8.1 Background ................................................................................................ 34 8.2 Results ....................................................................................................... 34



9 SUMMARY AND CONCLUSIONS .................................................................. 48

10 REFERENCES ................................................................................................. 50

B1 SELECTION AND SET-UP, CALIBRATION OF 2D MIKE 21 HD MODEL AND THE VALIDATION OF THE COMBINED HD MODEL ............................................. 63

B1.1 General ........................................................................................................ 63 B1.2 Overview of Two Dimensional Models ......................................................... 63

B1.2.1 DHI’s Two Dimensional Models .....................................................................63 B1.2.2 Model setup...................................................................................................63 B1.2.3 Model calibration ...........................................................................................64



APPENDICES A Winter dilution plots B Model calibration report C MIKE 21 Description FIGURES Figure 2-1: Modelled outfall locations showing the precinct boundary as the red dotted line. .... 12 Figure 3-1: Conceptual diagram showing modelling approach .................................................. 15 Figure 4-1: Water depth and water current speeds measured through the water column by an

upward looking Acoustic Doppler Current meter in 18 m depth (AHD) of water off James Price Point, July-Nov 2008 The top graph shows the sea-surface height (SSH) with the peak of the spring tide reaching a magnitude of approximately ±4 m, and the bottom plot the through-water column current speed, over the depth range of valid data .............................................................................................. 20

Figure 4-2: A comparison of the magnitude and phasing of the easting and northing depth-averaged velocity components. The top plot shows the spectral density and the dominance of the diurnal tidal peak (M2) and the semidiurnal solar (S2) peak tidal energy dominating the current meter record. The bottom plot shows a direct time series comparison of the velocity components and the ~5 hrs phase ................... 21

Figure 4-3: The 2D model output of currents showing predicted direction and strength of flows at James Price Point coastal area during a flood spring tide, 18/10/08. The red cross indicates the location of the field mooring. The precinct boundary is presented by the mauve line. .............................................................................. 21

Figure 4-4: Observational data extracted from the Acoustic Wave and Current (AWAC) located offshore from James Price Point showing the significant wave height over a 100 day period commencing the end of August 2008. ................................................ 22

Figure 5-1: The integration of the CORMIX and MIKE 21 AD model dilution results. The red ellipse ideally represents the boundary of the near-field mixing zone determined by the CORMIX model results. ............................................................................ 28

Figure 8-1 Maximum predicted summer extent of process waste water dilution zone, Scenario 1, location 1.The precinct boundary is presented by the black line. ....... 37

Figure 8-2: Maximum predicted summer extent of process waste water dilution zone, location 1, Scenario 2. The precinct boundary is presented by the black line. ....................... 38



Figure 8-5: Maximum predicted summer extent of process waste water dilution zone,location 2, Scenario 2. The precinct boundary is presented by the black line. ....................... 41


Figure 8-7: Maximum predicted summer extent of brine water dilution zone, location 3, Scenario 1. The precinct boundary is presented by the black line. ....................... 43







Figure A-1: Maximum predicted winter extent of process waste water dilution zone, Scenario 1, location 1.The precinct boundary is presented by the black line. ...................... 52

Figure A-2: Maximum predicted winter extent of brine water dilution zone, location 4, Scenario 4. The precinct boundary is presented by the black line. ...................................... 61

TABLES

Table 2-1: UTM Coordinate listing of the assumed notional outfall locations ............................. 13 Table 3-1 Summary of Wastewater discharge Scenarios (Woodside) .................................. 16 Table 5-1: Diffuser configurations examined for Sensitivity Test................................................ 25 Table 7-1: Proposed release rates & summer static current speeds at location 1 (14.8m depth) 29 Table 7-2: Proposed release rates & summer static current speeds at location 2 (12 m depth) . 29 Table 7-3: Proposed release rates & summer static current speeds at location 3 (7.5 m depth) 30 Table 7-4: Proposed release rates & summer static current speeds at location 4 (9 m depth) ... 30 Table 8-1: Scenario 1: Minimum dilution rate at the edge of the far-field mixing zone. ............... 34 Table 8-2: Scenario 2: Minimum dilution rate at the edge of the far-field mixing zone.. .............. 35 Table 8-3: Scenario 3: Minimum dilution rate at the edge of the far-field mixing zone. ............... 35 Table 8-4: Scenario 4: Minimum dilution rate at the edge of the far-field mixing zone. ............... 35



EXECUTIVE SUMMARY

A dispersion modelling study was carried out to simulate the discharge of process waste water and potential brine water streams in order to inform the strategic assessment of the Browse LNG Precinct. To examine the potential range of environmental outcomes in terms of the size of mixing zones and dilution levels, four different scenarios were assessed under summer and winter conditions with different discharge rates corresponding to a 25mtpa and 50mtpa LNG production at the Browse LNG Precinct. These were:

• Scenario 1, process waste water with discharge rate of 265 m3/hr and salinity of 0.7 ppt

• Scenario 2, process waste water with discharge rate of 550 m3/hr and salinity of 0.7 ppt

• Scenario 3, brine water with discharge rate of 1100 m3/hr and salinity of 70 ppt

• Scenario 4, brine water with discharge rate of 2200 m3/hr and salinity of 70 ppt

Modelling of the scenarios was carried out in integrated stages. Firstly, the near-field discharge CORMIX model was used to assess the dilution of the plume at the near-field mixing zone under a range of ambient summer and winter conditions. A validated fine-mesh coastal model (MIKE21 HD) was used to generate two-dimensional current data for the study region. Secondly, MIKE21 AD was used to estimate the extent and shape of mixing zones in the far-field. The dilution levels at the end of the near-field mixing zone were integrated into the far-field model outputs.

In the near-field, the CORMIX model showed that for process waste water the length of the near-field mixing zone increases with increasing depth, decreasing discharge rate and decreasing ambient current speed. For process waste water, the footprint of the near-field mixing zone varies between 40 – 300 m and dilution rates range from 1:124 to 1: 1,428. In the case of brine water, the footprint of the near-field mixing zone varies between 75 – 300 m and dilution rates range from 1:116 to 1: 1,398.

The far-field model results indicated that the plume was spreading in a north-south direction due to the oscillating tidal flow. The plume appears to disperse rapidly in this well-mixed environment. Using the 14-day far-field modelling results, dilution rates were defined at the edge of predefined mixing zones enclosing the proposed LNG processing facilities. Minimum dilution rates of 1:600 and 1:350 were found for respectively for a 265 m3/hr and 550 m3/hr discharge of process waste water.

Minimum dilution rates of dilution rates of 1:250 and 1:150 were found for respectively or a 1100 m3/hr and 2200 m3/hr discharge of brine waste water.

The model indicated seasonal variability doesn’t play a significant role in the mixing or advection of the plume. The size and orientation of dilution contours are similar for summer and winter seasons and dilution rates are comparable in most cases.



From a strategic-level assessment perspective, the study findings indicate that waste water discharges are subject to rapid dilution and dispersion in the receiving waters of the James Price Point coastal area.

With a continual discharge of waste water at a constant rate, unacceptable low dilution levels are never reached in the James Price Point coastal area due to the ambient strong flows and tidal mixing. Strong flows across an outfall diffuser give rise to high dilution rates. For these reasons, the discharge of process waste water and brine water, if required, is expected to be readily manageable through the adoption of appropriate treatment technologies, where required, and engineering design of outfalls.



1 Introduction The State of Western Australia, through the Department for State Development, proposes to develop an onshore, common user liquefied natural gas (LNG) precinct to process natural gas from the Browse Basin gas fields, north of Broome. The Browse LNG Precinct (BLNG Precinct) would consist of multiple proponent LNG processing facilities and associated infrastructure, and would be located at James Price Point, approximately 60 km north of Broome, on the Dampier Peninsula of Western Australia (WA).

Woodside Energy Ltd (Woodside), as Operator of the Browse LNG Development, proposes to construct and operate a Liquid Natural Gas (LNG) processing facility located at the proposed BLNG Precinct in the vicinity of James Price Point.

The BLNG Precinct will generate waste water streams from several sources (refer to Part 2 Section 5.13.5 of the SAR for details), which after treatment, will be discharged into coastal waters in the BLNG Precinct via one or more ocean outfall(s). Waste water will be derived from liquid effluent from processing such as process waste water, ancillary equipment such as condensed water, surface runoff from process areas, sewage and grey water. The combination of these waste water streams is herein referred to as process waste water, which is characterised as being positively buoyant on discharge into the marine environment. In addition, the BLNG Precinct may generate brine water if a desalination plant is required. Brine water is negatively buoyant on discharge into the marine environment.

This report provides technical documentation of marine discharge modelling used to inform the SAR through inclusion in the Supplementary Information Document (SAR Supplement).

1.1 Objectives

The study was undertaken to meet the following key overall objectives:

• To present the modelling process undertaken for waste water discharges under various discharge scenarios at 25mtpa and 50mtpa LNG production;

• To determine the near-field mixing zone and far-field mixing zone footprints (size and scale) and dilution levels for mixing zones during a spring-neap cycle for both winter and summer. The modelling also included investigation of the sensitivity to the following:

o Location of outfall (i.e. depth and distance from shore);



o Waste water discharge type; and

o Flow rate of the waste water stream.

It may be noted that characterisation of the extent of the mixing zone is of key importance because trigger values at a selected species protection level, as defined under the ANZECC/ARMCANZ (2000) Australian and New Zealand national water quality guidelines, will be determined at the boundary of the active mixing zone (Ref /1/).

1.2 Structure of this Report

The remainder of this report is structured as follows: • Section 2 describes an overview of the BLNG Precinct in terms of its waste

water discharges;

• Section 3 introduces the study approach used to model waste water discharges and details the modelling scenarios;

• Section 4 characterises the pertinent physical/hydrodynamic conditions and processes of the receiving environment at the James Price Point coastal area;

• Section 5 provides a technical account of the model setup of CORMIX and MIKE 21 2-D hydrodynamic model;

• Section 6 presents details on model validation;

• Section 7 presents CORMIX-based near-field modelling results;

• Section 8 presents MIKE 21-based far-field modelling results; and,

• Section 9 presents a summary and the overall conclusions of the study.



2 Project Overview During its operation phase, the BLNG Precinct will generate an estimated 15 GL/yr of waste water (process waste water and brine) if it is a 25Mtpa LNG facility and an estimated 30 GL/yr of waste water if it is a 50Mtpa LNG facility (refer to Part 2 Section 5.13.5 of the SAR for details). Discharge of treated process waste water and brine will be via ocean outfall(s). For the purposes of this strategic-level assessment four notional locations were selected in order to allow examination of any differences in plume dispersion (Figure 2-1, Table 2-1). In this way, outfall discharge points were selected at shallow waters closer to shore and deeper waters further from shore. Positioning of outfall discharge points also included northern and southern locations in relation to the BLNG Precinct. It was also assumed that the outfall(s) will be equipped with a multiport diffuser to increase initial mixing and dilution of discharged waste water in the receiving waters. A multiport diffuser is a linear structure consisting of closely spaced ports which inject turbulent jets at high velocities into the receiving waters. In this study, it was conservatively assumed that waste waters will be discharged through an 8 port diffuser with 30 mm port diameter and a 60° vertical angle of discharge, 3 m port spacing and with all ports pointing in one direction following the diffuser line.

Figure 2-1: Modelled outfall locations showing the precinct boundary as the red dotted line.



Table 2-1: UTM Coordinate listing of the assumed notional outfall locations

Location Easting (MGA94, Zone 51)

Northing (MGA94, Zone 51)

Water depth

1 407275 m 8063425 m 14.8 m 2 407937.5 m 8063625 m 12 m 3 408575 m 8063625 m 7.5 m 4 408100 m 8065625 m 9 m



3 Study Approach 3.1 Overview

In order to provide an understanding of the dilution and dispersion of the waste water discharges, a two-stage modelling approach was adopted. The modelling approach is conceptualised in Figure 3-1. This approach takes into account near-field effects relating to the definition of the near-field mixing zone, and far-field dilution and advection processes relating to secondary mixing, where: • Near-field mixing refers to dilution dynamics of the waste water discharge as it

enters the marine environment in a jet-like flow as determined by the diffuser design and the properties of the waste water (e.g. buoyancy / density). Near-field mixing occurs due to coupling of the entrainment of the surrounding ambient water into the jet-like flow from the diffuser with the additional dispersive mechanism from the ambient current field. In this document, the active mixing zone is referred to as the near-field mixing zone.

• Far-field mixing refers to where the plume dynamics are governed by the local movement of water induced predominantly by the tides. Far-field mixing and dilution occurs due to the tidal movement of ambient water and wind and wave induced turbulent mixing of the discharge with the surrounding waters.

The first modelling stage (near-field) involved the use of the Cornell Mixing Zone Expert System (CORMIX) model (a jet/plume model) to predict the geometry and dilution characteristics of the near-field mixing zone. CORMIX v.6.0 is used in this modelling approach, which is the most recent version. CORMIX is a standard and widely-accepted tool for accurate and reliable point source near-field mixing analysis. The CORMIX modelled plume is assumed to be at steady state. CORMIX calculates the jet-like flow of the waste water discharge based on multiport diffuser design including average vertical angle of discharge, average height of the port centres, number of ports and port spacing and average diameter of the discharge ports. The second modelling stage (far-field) involved the use of DHI’s MIKE21 Advection Dispersion (AD) model in order to take account of dynamic mixing processes induced by the movement of water over undulating bathymetry under the influence of tidal and wind driven currents. The far-field modelling using MIKE21 AD was undertaken with the previously developed fine resolution 2D coastal sediment mesh (Ref /2/). To ensure a conservative approach, see section 5.0, the port layout was excluded to ensure that the extent of the dilution field was determined by ambient flow conditions and not exacerbated by increased current speeds induced by such a layout. The modelling outputs of the CORMIX model, which predicts the near-field



dilution and plume extent is integrated with the model solution from DHI’s MIKE21 AD model in order to provide a representative prediction of the far-field dilution field. This integration of CORMIX and MIKE21 AD solutions are described in Section 5.3.

Figure 3-1: Conceptual diagram showing modelling approach

Using this modelling approach, the effects of different meteorological and oceanographic conditions, the diffuser design, and varying discharge rates of waste water can be modelled.

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3.2 Modelling Scenarios

Scenarios were developed by Woodside to inform the potential range of environmental outcomes due to waste water discharges in terms of the size and shape of the resultant waste water plumes. As such, the scenarios were developed to examine and test differences depending on outfall location and depth as well as a range of flow rates to examine any differences in the size of the mixing zone so as to inform strategic assessment of the BLNG Precinct. A summary of modelling scenarios and assumptions is presented in Table 3-1. A total of 22 scenarios have been investigated. Table 3-1 Summary of Wastewater discharge Scenarios (Woodside)

Input Scenario 1 Scenario 2 Scenario 3 Scenario 4 Flow rate of waste water stream

265 m3/hr 550 m3/hr 1100 m3/hr 2200 m3/hr

Locations of discharge 1, 2 and 3 1, 2 and 3 1, 2 and 3 3 and 4

Waste water type

Process waste water

Process waste water Brine water Brine water

Salinity of waste water 0.7 ppt 0.7 ppt 70 ppt 70 ppt

Temperature of waste water

ambient ambient ambient ambient

3.2.1 Process Waste Water Scenarios For Scenario 1 and 2, separate simulations were run to examine the fate of different flow rates (Scenario 1: 265 m3/ hr, Scenario 2: 550 m3/ hr). These were of continuously discharged process waste water over the course of a 14 day spring- neap tidal cycle at 3 outfall locations (Locations 1 to 3), located at water depths of 14.8, 12 and 7.5 m (



Table 2-1). The discharged process waste water was assumed to be freshwater with salinity levels much lower than ambient seawater, nominally at 0.7 ppt (Table 2-1). Flow rates for Scenario 1 and 2 correspond to BLNG Precinct production rate scenarios of 25 Mpta and 50 Mpta respectively. Both scenarios were run in the summer and winter seasons to examine any seasonal differences.

3.2.2 Brine Water Scenarios For Scenario 3 and 4, separate simulations were run to examine the fate of continuous brine water discharges at a range of flow rates (Scenario 3: 1100 m3/ hr, Scenario 4: 2200 m3/ hr). Again, these scenarios were run over the course of a 14 day spring- neap tidal cycle at two off the four outfall locations (Table 2-1). Salinity of brine discharges were conservatively assumed to be 70 parts per thousand (Table 2-1). Flow rates for Scenario 3 and 4 correspond to BLNG Precinct production rate scenarios of 25 Mpta and 50 Mpta respectively. Both scenarios were run in the summer and winter seasons to examine any seasonal differences.

3.2.3 Ambient Environmental Parameters Environmental parameters used by the model were set as follows:

• Discharge temperature is equal to the ambient seawater temperature, which was assumed to be 29 C during the summer months and 26 C during the winter months;

• The ambient salinity was assumed to be 34 ppt; and,

• The air temperature was assumed to be 29 C during summer and 23 C during winter.



4 Physical Environment

It is essential that the physical processes that determine the advection and mixing and dispersion of routine marine discharges are identified and understood. This enables the processes that dominate/force the transport and dispersion of a discharge to be identified and verified so that they are accurately reproduced in the hydrodynamic and environmental modelling. This, in turn, gives confidence in the environmental modelling output. Finally, this understanding is important to the interpretation of the modelling results.

4.1.1 Wind, Waves and Currents The physical processes that typically drive water movement in coastal marine environments are tidal and wind induced currents. Waves are also an important feature, for while they do not contribute to net transport, they are very important to vertical mixing and in shallow water environments, material re-suspension. Density differences as a result of temperate changes (seasonal heating effects) or salinity differences (freshwater plumes for example) can be important in some situations as well. On the NW Shelf dominant currents are a product of tidal movements, although wind pushing on the surface of the water, and differences in water density as a result of differences in both temperature and salt concentrations (salinity) also contributes at an oceanographic scale. Small differences in water level heights as a result of differences in atmospheric pressure across gradients at scales of hundreds of kilometres may also be a factor. Winds in the region tend to be local or synoptic, that is, land - sea breezes with spatial scales of 100s of kms that vary on a daily basis driven by differential heating over land and water or monsoonal winds with spatial scales of 1000s of kms that vary on scales of days or months driven by upper atmosphere pressure gradients. Additionally, cyclones occur every year in northern waters of Western Australia. Hydrodynamic modelling of cyclones for use in the environmental modelling has not been included in the present scope. While waves are important for turbulent mixing processes, they do not contribute significantly to net horizontal movement of fluid particles (rather causing fluid particles to undergo a closed orbital trajectory) leaving winds and tidally induced currents as the principal contributors to the advection of ocean water.



4.1.2 Water Levels Water levels at the James Price Point coastal area vary significantly due to the large tides. Given the large scale of the intertidal zone both horizontally and vertically, the actual water level acts as a significant control on the volume, duration and direction of transport of materials in this region, including the water and materials in marine discharges. The tides at Broome, the site of the nearest long term tidal record to James Price Point coastal area, are semi-diurnal with a lowest to highest astronomical range of 10.5 m. The mean range is 8.27 m at spring tide and 2.11 m at neap tide. Estimated tides at James Price Point have a reduced tidal excursion, with a lowest to highest astronomical range of 8.34 m. The mean range is 6.9 m at spring tide and 0.93 m at neap tide. Tropical cyclones, when they occur, can also have a strong effect on water levels. However, it should be noted that this modelling did not include any reference to tropical cyclones as they are effectively a transitional event that has very little consequence on the routine nature of discharges and management consequences would be very difficult to predict.

4.1.3 Tidal Currents It is possible to examine current meter records to identify key oceanographic processes that occur at that site. While there has been several metocean measurement campaigns across the Browse basin in the last three years, data from a metering site in immediate vicinity of JPP is presented here and provides important insight into currents in the region. Analysis of the records from a current meter deployed from 27th July 2008 to 5th November 2008 off shore from JPP in 18 m water depth (Latitude 17.471°S, Longitude 122.084°E) is shown in Figure 4-1 and provides a temporal view of the mechanisms generating the nearshore flow field at a single point. Specifically, the data collected consisted of 3 months of horizontal and vertical current speed measurements recorded in up to 18 vertical sections (bins). The analysis shows that the tides in the James Price Point coastal area are semi-diurnal, with tidal sea-surface height variability in excess of ±4 m (the upper graph in Figure 4-1). The lower graph shows the current speeds recorded through the water column. These data shows that a phase difference of ~1.5 hrs exists between the sea-surface height and the maximum observed current speed for both flood and ebb tide where the maximum current velocity is reached after the peak in the surface water elevation, corresponding with the highest potential for tidal current induced mixing and transport. In addition, a high resolution Laser Airborne Depth Survey (LADS) of the nearshore area around James Price Point showed the seabed bathymetry to be highly undulating. This combination of strong tide, undulating topography and year-round



strong solar heating generates a water column that is vertically well mixed with strong topographical forcing that has a highly barotropic (2-D) structure.

Figure 4-1: Water depth and water current speeds measured through the water column by an upward looking Acoustic Doppler Current meter in 18 m depth (AHD) of water off James Price Point, July-Nov 2008 The top graph shows the sea-surface height (SSH) with the peak of the spring tide reaching a magnitude of approximately ±4 m, and the bottom plot the through-water

column current speed, over the depth range of valid data The examination of the observed phase shift and magnitudes of the depth averaged easting and northing velocity components from the current meter record on the nearshore dynamics (Figure 4-2) shows the depth average tidal velocity components are of similar magnitude indicating a near circular anticlockwise flow pattern. The observed phase shift of ~5 hrs implies that at no time during the spring tidal period does the depth averaged current speed drop to zero. During the peak of the spring tide the tidal currents range from ~0.3 m/s to 0.6 m/s. Tidal ellipse parameters show a preferentially orientated alongshore flow, induced by tides of < 0.25 m/s. The hydrodynamic model results show that during the flood tide the onshore flow is topographically steered northward and southward in the vicinity of JPP. The northward flow enhances the anti-clockwise rotating tidal flow, generating a predominantly northerly propagating flow with an excursion length of ~6 km. The southerly flow acts to oppose the anti-clockwise rotating tidal flow, reducing the magnitude of the tidal circulation in the region south of James Price Point. This process is confined to within ±20 km of James Price Point. A similar review of the circulation dynamics during the neap tide shows that the weaker tidal forcing produces a weaker rotational response with no flow separation.



Figure 4-2: A comparison of the magnitude and phasing of the easting and northing depth-averaged velocity components. The top plot shows the spectral density and the dominance of the diurnal tidal

peak (M2) and the semidiurnal solar (S2) peak tidal energy dominating the current meter record. The bottom plot shows a direct time series comparison of the velocity components and the ~5 hrs phase

. Figure 4-3: The 2D model output of currents showing predicted direction and strength of flows at James Price Point coastal area during a flood spring tide, 18/10/08. The red cross indicates the location of the field mooring. The precinct boundary is presented by the mauve line.



The harmonic analysis of the current speed showed the orientation of the semi-major axis of the tidal ellipse is about 343 degrees, indicating that any contaminant that enters the nearshore environment will have a tendency to be transported in an alongshore direction. The current data extracted from the Acoustic Wave and Current (AWAC) instrument also showed that lower frequency flows, i.e. flows with a period of motion greater than 3 days, persist within the region. These flows have a characteristic mean magnitude of ~0.04 m/s (maximum 0.09 m/s) and move in a predominantly southerly direction. When compared to the stronger and more highly variable tidal flows the low frequency flows are an order of magnitude less and will therefore play a secondary role in the dispersion and advection of plumes and have therefore been omitted from the study. Also omitted from the study is the impact of surface wave breaking. The mean significant wave height (Hm0) of the James Price Point coastal area is ~ 0.4m, with periodic wind induced events increasing that to above 1m for periods of less than 5 days (Figure 4-4). The induced mixing associated with the breaking of these waves is proportional to Hm0

2 and therefore is considered to play only a minor role in the plume dispersion in this area. Further, the exclusion of wave induced mixing ensures a more conservative estimate of the dispersive characteristics of the plume.

Figure 4-4: Observational data extracted from the Acoustic Wave and Current (AWAC) located offshore from James Price Point showing the significant wave height over a 100 day period

commencing the end of August 2008. The final physical process to be considered is the action of the wind. Time series analysis of the wind field at James Price Point over a five year period (2004-2008,) shows the wind to be highly variable in direction, with a mean magnitude of 4.5 m/s. It was therefore included in the study.

4.1.4 Regional Processes Summary In summary, the James Price Point coastal area is dominated by tidal driven currents which are topographically steered into a northward and southward propagating flow



particularly during spring tides. Largest currents are found when tidal forcing is strongest but even at tidal low amplitudes a residual current persists. The regional and coastal hydrodynamic processes for the James Price Point area can be summarised more specifically as follows: • Tides along the North West shelf dominate water movement and near the

James Price Point coastal area they are semi-diurnal (two highs and two lows each day).

• The springs tidal range at James Price Point is approximately 7.8m, with tidal forcing dominating the current regime for the James Price Point coastal area, even at low tidal amplitudes.

• During the peak of the spring tide the tidal currents range from ~0.3 m/s to 0.6 m/s, with a corresponding maximum tidal excursion of ~6 km.

• The combination of strong tide, undulating topography and year-round strong solar heating generates a water column that is vertically well mixed with strong topographical forcing resulting in strong variability in current velocities.

• James Price Point and the associated nearshore bathymetry cause a ‘split’ in the tidal movement of water with flood tides heading north and south respectively either side of the Point and conversely flowing outwards from these directions on the falling ebb tides.



5 Model Description and Setup In this study, CORMIX has been applied for near-field analysis and the MIKE 21 Advection - Dispersion model was used to predict the far field solution. To represent the plume’s dilution characteristics across both mixing zones the CORMIX near-field dilution results have been applied or coupled to the MIKE21 AD far-field dilution results. The details are described below.

To ensure a conservative model setup was utilised for the purposes of a strategic level assessment it was assumed that firstly, the outfall(s) will be equipped with a multiport diffuser to increase initial mixing and dilution of the discharged wastewater which is predicted to comfortably fall within the ANZECC guidelines (1992) and by using this simple diffuser design provides for maximum flexibility for future changes in the location and efficiencies of the outfall(s). Secondly, the port layout was excluded to ensure that the extent of the dilution field was determined by ambient flow conditions and not exacerbated by increased current speeds induced by such a layout. While the Port will generate some areas of low flow, the overall effect in areas where a waste water discharge will be located would be an area of greatly increased flow (a non conservative estimate). Modelling results from the Coastal Processes Study (Appendix G4 in) where a Port layout was included show the magnitude of the currents at Loc 2, Loc 3 and Loc 4 in Figure 2-2 can be expected to increase by as much as 25% and for Loc 1 no change will occur.

5.1 Near-field model setup

CORMIX computes the plume characteristics in the near-field mixing zone within which the fluid motion and dispersion are dominated by the discharge properties such as mass flux and buoyancy flux of the outfall jet. Results of CORMIX are extracted at the end of the near-field mixing zone which is defined as the zone where strong initial mixing occurs as a result of momentum and buoyancy. Required input data for near-field analysis in CORMIX are geometry, discharge, salt concentration of discharged flow in outfall position, depth of outfall and ambient current conditions. The major outputs of CORMIX are specifications of jet plume including length and width of the diffused plume, its trajectory and dilution rates along the centreline trajectory of the plume.

5.1.1 Ambient Environmental Conditions CORMIX requires the specification of typical ambient environmental conditions, including vertical density structure, water temperature and background currents. The variability in the background currents were extracted from the field measurements at



the 5th and 95th percentile (refer to Section 3). The 5th percentile equated to a current speed of 0.04 m/s and the 95th percentile to a current speed of 0.43 m/s. The 5th percentile current speed reflects weak currents and a corresponding low dilution rate, which is representative of a neap tide. The 95th percentile current speed corresponds to strong currents and a high dilution rate that is representative of the movement of the plume under spring tidal conditions.

5.1.2 Sensitivity Test of the Diffuser Design The mixing in the near-field is sensitive to the discharge design configuration. Before selecting the diffuser design for this strategic level examination of waste water discharge, a two diffuser sensitivity test was conducted to ensure conservative modelling assumptions were adopted. The sensitivity test examined the different multiport diffuser configurations presented in (Table 5-1). Table 5-1: Diffuser configurations examined for Sensitivity Test

Number of

ports Port diameter

(mm)

Port spacing

(m)

Vertical angle of discharge (degrees)

8 30 3 60 16 30 3 60

Sensitivity tests undertaken on both outfall configurations showed that a longer diffuser (16 ports) increases the dilution by a factor of 2. However, as a conservative modelling approach has been adopted, the 8 port diffuser was selected to model the near source near-field mixing zone.

5.2 Far-field Model Setup

To simulate the spatial advection and dispersion of the discharged waste water, it is necessary to predict the regional currents driven by the winds and tides. DHI’s two-dimensional ocean/coastal circulation model, MIKE21 HD, was used to predict the circulation of the receiving waters. MIKE21 simulates the 2-D flows of ocean waters within a model region due to forcing of the tides, wind stress and bottom friction (Appendix B). Higher resolutions are used for areas with complex bathymetry and areas of interest. To simulate the ocean circulation over the area of interest, the model was provided with the following input data:

• Measured bathymetry for the area, which defines the shape of the seafloor. Bathymetry was defined by Laser Airborne Survey and has a horizontal resolution of 5 m.

• The amplitude and phase of tidal constituents, which were used to calculate the sea surface heights over time at the open boundaries of the model domain. Tidal forcing was extracted from the global KMS model with a horizontal resolution of 0.25 degrees.



• Wind data to calculate the wind shear at the sea surface. Satellite blended wind from the Bureau of Meteorology (BOM) were used with a horizontal resolution of 0.125 degrees.

5.2.1 Hydrodynamic Model Resolution The finest grid resolution in the area of interest was set at 25 m. This very fine resolution can be assumed to accurately reproduce the key hydrodynamic processes which is driving the movement of the plume. The model predictions compared very well with the measured data (see Figure B1). This confirms that winds and tides used as input are capable of replicating the currents in the study area (see Appendix B for a description of the Model setup and calibration). The 2-D model was used for two reasons, the first is that the waters off James Price Point are tidally driven and therefore predominantly 2-D in structure, see section 4.1.3, and secondly, given the number of modelling scenarios performed, 22 in total, the computational requirements of a 2-D model is significantly less than that of a fully 3-D simulation.

5.2.2 Advection – Dispersion Modelling The MIKE21 AD model was used to simulate the spreading of the plume subject to currents and wind in the coastal region. The discharge rate and salinity associated with the different scenarios are used as input in the model. The simulation period was set to 14 days, which covers one neap and spring period. The model predicts the transport and dilution of the plume by ambient currents within the model domain and therefore can accurately predict the ‘rate of dilution’ of the far-field mixing zone where tidal and wind induced currents determine the plume’s spreading characteristics, that is, the main limitation of the MIKE21 AD model in this application is that it under predicts the spreading characteristics of the plume within the near-field mixing zone by as much as 70% and therefore under predicts the absolute dilutions across both the near and far-field mixing zones.

5.2.3 Model Setup The 2D hydrodynamic solution is used to drive the AD module. For this purpose, a coastal unstructured grid domain has been setup and validated around James Price Point extending to beyond the 30 m depth contour. The unstructured mesh for the model was generated using 40280 triangular and quadrangular elements applying Mike Zero Mesh Generator. In order to have a proper examination from salinity dispersion in the vicinity of the project site, a mesh resolution of 25 m has been used around outfall locations.

The timestep integration was set so that the maximum Courant number was 0.8. The horizontal dispersion coefficient was specified through the spatially varying Smagorinsky formulation. A Smagorinsky coefficient of 0.28 m2/s was used.

The bed resistance controls water surface elevation and current speed for each point and can be introduced to model through both Chezy and Manning formula. Although,



there are some laboratory based relationships for calculation of bed resistance for the current study a calibrated Manning coefficient of 32 was used.

The format of the wind data is specified as varying in both time and space. The wind friction is specified as a constant value of 0.001255.

The contribution of the outfall location to the continuity equation is taken into account by specifying the magnitude of the source (in m3/s). The AD module sets up additional transport equations for temperature and salinity. The calculated temperature and salinity are feed-back to the hydrodynamic equations through buoyancy forcing induced by density gradients. The source flux is calculated as Qsource

.Csource where Qsource is the magnitude of the source and Csource is the temperature/salinity of the source. The time integration of the transport equation is performed using an explicit scheme. The time step interval for the transport equations is synchronized to match the overall time step for the shallow water equations.

5.3 The Integration of the CORMIX and MIKE21 AD Results

To better represent the plume’s dilution characteristics across both mixing zones the CORMIX near-field dilution results (Table 7-1 column six) have been applied to the MIKE21 AD far-field dilution results. This was achieved by simply determining the difference in dilution between the CORMIX and MIKE21 AD results at the boundary of the near-field mixing zone and applying this difference to the MIKE 21 AD dilution results that lay outside the extent of this zone. This approach is best represented in Figure 5-1, which shows an idealised ellipse (in red), that is representative of the CORMIX near-field mixing boundary location, superimposed onto the MIKE21 AD model grid. Along the boundary of the ellipse the difference in the dilutions between the CORMIX and MIKE21 AD solutions (∆dilution) were determined. For all cells inside the ellipse the dilution field was determined by CORMIX. For all grid cells outside the boundary of the ellipse, representing the far-field mixing zone, the dilution = MIKE21 AD dilution + ∆dilution.



Figure 5-1: The integration of the CORMIX and MIKE 21 AD model dilution

results. The red ellipse ideally represents the boundary of the near-field mixing zone determined by the CORMIX model results.

A critical aspect of the integration of the two model solutions was to ensure the orientation of the semi-major axis of the ellipse (Figure 5-1) coincided with dominant flow direction.

6 Model Validation

The 2D model domain was validated against reliable field measurements (refer to Appendix B for details) located offshore of James Price Point located offshore from James Price Point (Latitude 17.471°S, Longitude 122.084°E) in a water depth of 18 m. The model validation consists out of the following data comparisons:

• Time series of depth-averaged current speed; and,

• Time series of depth-averaged current direction.



7 CORMIX Near-field Modelling Results The results from the CORMIX model were interrogated to provide predictions of dilution levels and footprints of the near-field mixing zone. Plume characteristics of the near-field mixing zone for each the four outfall locations are shown in Table 7-1 (location 1), Table 7-2 (location 2), Table 7-3 (location 3) and Table 7-4 (location 4). Each table lists the results for each of the scenarios performed at the stated location. Table 7-1: Proposed release rates & summer static current speeds at location 1 (14.8m depth)

Scenario Flow rate

(m3/hr)

Current speed (m/s)

Distance to

achieve 1:10

dilution level

Distance to

achieve 1:100

dilution level (m)

Dilution level at edge of near-field

mixing zone

Footprint of near-

field mixing zone (m)

1 265 0.04 < 1 m 18 203 167 1 265 0.43 < 1 m < 1 1428 85 2 550 0.04 < 1 m 27 168 306 2 550 0.43 < 1 m 1 732 91 3 1100 0.04 < 10 m 27 198 300 3 1100 0.43 < 1 m 5 398 106

Table 7-2: Proposed release rates & summer static current speeds at location 2 (12 m depth)

Scenario Flow rate

(m3/hr)

Current speed (m/s)

Distance to

achieve 1:10

dilution level

Distance to

achieve 1:100

dilution level(m)


mixing zone

Footprint of near-


1 265 0.04 < 1 m 20 174 158 1 265 0.43 < 1 m < 1 1230 70 2 550 0.04 < 1 m 21 172 171 2 550 0.43 < 1 m 2 560 79 3 1100 0.04 < 10 m 26 152 221 3 1100 0.43 < 1 m 6 325 93



Table 7-3: Proposed release rates & summer static current speeds at location 3 (7.5 m depth)

Scenario Flow rate

(m3/hr)

Current speed (m/s)

Distance to

achieve 1:10

dilution level

Distance to

achieve 1:100

dilution level

Dilution level at edge of

near-field mixing zone

Footprint of near-


1 265 0.04 < 1 m 26 126 151 1 265 0.43 < 1 m <1 703 42 2 550 0.04 < 1 m 26 124 156 2 550 0.43 < 1 m 3 367 57 3 1100 0.04 < 10 m 30 116 221 3 1100 0.43 < 1 m 10 200 75 4 2200 0.04 < 10 m 28 116 233 4 2200 0.43 < 1 m 18 140 113

Table 7-4: Proposed release rates & summer static current speeds at location 4 (9 m depth)

Scenario Flow rate (m3/hr)

Current speed (m/s)

Distance to

achieve 1:10

dilution level

Distance to

achieve 1:100

dilution level


mixing zone

Footprint of near-


4 2200 0.04 < 10 m 28 128 238 4 2200 0.43 < 1 m 18 161 117

After discharge of process waste water, the effluent density is less than the surrounding ambient water density at the discharge level. Therefore, the effluent is positively buoyant and will tend to rise towards the surface. The plume is vertically well mixed within the near-field mixing zone.

After discharge of brine water, the plume is negatively buoyant and will tend to sink towards the bottom. The plume will spread laterally along the bottom while it is being advected by the ambient current. The plume thickness might decrease during this phase. The effect of ambient velocity on the mixing rate is relatively strong:

• 95th percentile velocity: the plume is vertically mixed fully mixed within near-field, but restratifies later. The plume becomes vertically fully mixed again at > 2000 m downstream.

• 5th percentile velocity: the plume is not mixed in the near-field and far-field.

The results for each scenario can then be summarized as follows: • Scenario 1 Process waste water with discharge rate of 265 m3/ hr. The

footprint of the near-field mixing zone varies between 42 – 85 m during strong



currents and between 151- 167 m during weak currents. Dilution ranges from 1: 126 to 1: 203 during weak currents and from 1:703 to 1:1428 during strong currents.

• Scenario 2 Process waste water with discharge rate of 560 m3/ hr. The

footprint of the near-field mixing zone varies between 57 – 91 m during strong currents and between 156 – 306 m during weak currents. Dilution ranges from 1: 124 to 1: 178 during weak current and from 1:367 to 1:732 during strong current.

• Scenario 3 Brine water discharged at a rate of 1100 m3/ hr. The footprint of the

near-field mixing zone varies between 75 – 106 m during strong currents and between 221 – 300 m during weak currents. Dilution ranges from 1: 117 to 1: 152 during weak current and from 1:200 to 1:398 during strong current.

• Scenario 4 Brine water discharged at a rate of 2200 m3/ hr. The footprint of the

near-field mixing zone is around 115 m during strong currents and 235 m during weak currents. Dilution ranges from 1: 116 to 1: 128 during weak currents and from 1:141 to 1:161 during strong currents.

The key findings of the CORMIX modelling were that:

• For process waste water discharges, an increase in discharge rate decreases the dilution rate at the edge of the near-field mixing zone and increases the footprint of the near-field mixing zone.

• For brine water discharges, an increase in discharge rate causes a decrease in dilution rate at the edge of the near-field mixing zone and increases the footprint of the near-field mixing zone.

• An increase in ambient current speed significantly increases the dilution rate at the edge of the near-field mixing zone and decreases the footprint of the near-field mixing zone.

• The distance to achieve a 1:10 dilution level is less than 1 m in most cases.

• The distance to achieve a 1:100 dilution level is less than 10 m during strong currents and less than 30 m during weak currents.

The dilution level at the 5th percentile, current speed of 0.04 m/s, has been used for integration into the far-field modelling. The reasons are twofold: firstly, the 2 week model simulation starts at the bottom of the neap tide when mixing with ambient waters is significantly reduced; secondly, this is a conservative approach as it decreases the dilution rates by almost an order of magnitude. To illustrate the CORMIX results, Figures 7-1 to 7-4 show a plan view of the solution set for location 3 (408575 E, 8063625 N, water depth of 7.5 m). Each figure shows the dispersive length scales for a set of dilution contours of the simulated near-field CORMIX plume.



Figure 7-1: Process waste water discharge at a rate of 265 m3/hr at a depth of 7.5 m: Predicted plume dimension and dilution rate in the near-field mixing zone during weak

current

Figure 7-2: Process waste water discharge at a rate of 550 m3/hr at a depth of 7.5 m: Predicted plume dimension and dilution rate in the near-field mixing zone during weak

current



Figure 7-3: Brine water discharge at a rate of 1100 m3/hr at a depth of 7.5 m: Predicted plume dimension and dilution rate in the near-

field mixing zone during weak current

Figure 7-4: Brine water discharge at a rate of 2200 m3/hr at a depth of 7.5 m: Predicted plume dimension and dilution rate in the near-field mixing

zone during weak current



8 Far-field Model Results

8.1 Background

To quantify the likely far-field mixing and dispersion, detailed modelling was carried out using Mike 21 AD model integrated with the near-field CORMIX results. The method of integration of the two models is described in Section 5.3. The integrated model simulated the wastewater discharge as a conservative tracer into a time-varying current field taking into account the initial dilution set by the near-field modelling described in Section 7. The main objective of the far-field modelling was to predict the extent and shape of mixing and to quantify the dilution levels at the boundary of the predefined far-field mixing zone. The far-field modelling augments the near-field work by allowing the time-varying nature of currents to be included, together with the potential for recirculation of the plume back to the discharge location. In the latter case near-field concentrations can be increased due to the discharge plume mixing with the remnant plume from an earlier time.

8.2 Results

The integrated modelling results are presented as a mosaic of 11 images (Figures 8-1 to 8-11). Each image shows the maximum spreading extent of the waste water plume over the two week simulation period for the different scenarios and outfall locations (see Table 4-2). It is important to note that the results represent a composition of the minimum dilution for the period under consideration and does not represent a snapshot in time. The modelling period from 6 November to 20 November has been selected for the seasonal discharge during summer. The winds during this period originate from a north easterly direction with a mean wind speed of 4 m/s.

The period from 2 May to 16 May has been selected for the waste water discharge during winter. Winds during this period originate from a south easterly direction with a mean wind speed of 5 m/s. It was found that the difference between summer and winter conditions was minimal and therefore only the summer scenarios for each location are presented. The winter dilution plots can be found in Appendix A.

The results from the far-field integrated model approached, see Section 5.3, were interrogated to provide predictions of dilution field at the edge of the far-field mixing zone for each of the scenarios. The extent of the far-field mixing zone was set to the James Price Point Precinct Boundary (Figure 2-1). A summary of the results is shown in Table 8-1 to Table 8-4.

Table 8-1: Scenario 1: Minimum dilution rate at the edge of the far-field mixing zone.

Scenario 1 (265 m3/hr)

Dilution rate Location 1 Location 2 Location 3

Far-field mixing zone

1:2000 1:1700 1:600



Table 8-2: Scenario 2: Minimum dilution rate at the edge of the far-field mixing zone..




1:1200 1:900 1:350





1:700 1:600 1:250



Dilution rate Location 3 Location 4


1:200 1:150

The key findings for each of the scenarios are summarized as follows: • Scenario 1 (Process waste water with a discharge rate of 265 m3/ hr). The

model indicated dilution rate at the edge of the far-field mixing zone increases by a factor of 3 by discharging at a depth of 15 m compared to a shallow discharge at 7.5 m ( Table 8-1 to Table 8-4.

• Table 8-1). • Scenario 2 (Process waste water with discharge rate of 560 m3/ hr). The model

indicated doubling the discharge rate of process waste water has a proportional effect on the dilution rates for all discharge depths (

• Table 8-2). • Scenario 3 (Brine water discharged at a rate of 1100 m3/ hr). The model

indicated that the discharge depth played a role in the rate of dilution as the



minimum dilution rate of 1:250 occurred at location 3 - the shallowest outfall location (Table 8-3).

• Scenario 4 (Brine water discharged at a rate of 2200 m3/ hr). The model

indicated the minimum dilution levels of 1:150 occurred at the edge of the far-field mixing zone after discharge at the northern-most notional outfall location (Location 4). Doubling the discharge rate of brine water at location 3 (depth of 7.5 m) did not significantly affect the dilution rate.

The key findings of the far-field modelling simulations were that:

• The dominant factor influencing the spread of the salinity plume is the advection by the tidal current. The plume is directed along the coastline in the direction along 343 degrees, corresponding to the orientation of the tidal semi-major axis.

• For all scenarios examined and the winds play a secondary role in the advection of the negatively buoyant salinity plume.

• The dilution rate is found to be sensitive to the discharge rate and depth of discharge.

• The seasonal variability doesn’t play a significant role in the advection of the plume, indicating that tidal circulation is the dominant forcing mechanism.

• The size and orientation of dilution contours are similar for the winter and summer seasons and dilution rates are comparable in most cases.



Figure 8-1 Maximum predicted summer extent of process waste water dilution zone, Scenario 1, location 1.The precinct boundary is presented by the black line.

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Figure 8-2: Maximum predicted summer extent of process waste water dilution zone, location 1, Scenario 2. The precinct boundary is presented by the black line.

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Figure 8-5: Maximum predicted summer extent of process waste water dilution zone,location 2,

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Figure 8-7: Maximum predicted summer extent of brine water dilution zone, location 3, Scenario 1.

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Figure 8-8: Maximum predicted summer extent of brine water dilution zone, location 3, Scenario 2. The precinct boundary is presented by the black line.

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Figure 8-10: Maximum predicted summer extent of brine water dilution zone, location 3, Scenario 4.

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9 Summary and Conclusions The conceptualized mixing dynamics of an effluent continuously discharging into a water body can be segregated into a near and far-field mixing region. In the near-field region, the initial jet-like discharge characteristics of the diffuser dominate. As the plume travels further away from the outfall, the diffuser characteristics become less important and the dispersive characteristics of the plume are best described by the underlying hydrodynamic conditions. This region is referred to as the far-field mixing zone.

The key to this study was the integration of the model results that best reproduced the dispersive characteristics for each region. To do this a three stage modelling approach was undertaken. The first stage involved the use of the CORMIX model to simulate the dispersive characteristics of the near-field region. The second stage involved the use of the MIKE21 advection-diffusion (AD) model to simulate the far-field mixing. The final stage was to integrate the modelling results from stage 1 and stage 2 to produce a representative plume across both the near and far-field regions.

The modelling study investigated the near and far-field mixing regimes by predicting the dilution levels based on the:

• Location of the outfall (i.e. depth and distance from shore);

• Waste water discharge type;

• Flow rate of the waste water stream, and

• Seasonal variability.

A conservative approach has been used throughout this study by:

• Use of the 8-port design instead of the 16-port design (decreases the dilution rate by a factor of two);

• Adoption of the 5th percentile velocity for the CORMIX calculations (decreases the dilution rate by a factor 3 to 7); and,

• Starting the far-field simulation at the bottom of neap tide.

Overall, key conclusions based on near-field CORMIX model simulations were that:

• The results of the near-field model provide predictions of dilution levels and footprints of the near-field mixing zone. Depending on the scenario, the near-field mixing zone would remain within 300 m of the discharge location. Modelling indicates a range between 40-300 m from the point of discharge, with an upper extent of 200-300m;



• Increasing the discharge rate decreases the dilution rate at the edge of the near-field mixing zone and increases the footprint of the mixing zone. Minimum dilution rates of 1:116 were found at the edge of the near-field mixing zone for the 2200 m3/hr brine discharge;

• Increasing the ambient current speed significantly increased the dilution rate at the edge of the near-field mixing zone and decreased the size of this zone. The increase in dilution rate was higher for process waste water then the brine water;

• Increasing the depth of discharge increases the footprint of the near-field mixing zone and decreases the dilution rate at the edge of the near-field mixing zone;

• The distance to achieve a 1:10 dilution level is less than 1 m in most cases, and

• The distance to achieve a 1:100 dilution level is less than 10 m during neap tide or weak ambient currents and less than 30 m during the spring tide or strong ambient currents.

The key conclusions of the integrated near-field CORMIX and MIKE21 AD far-field model simulations were that: • The dominant factor influencing the spread of the salinity plume is the advection

by the tidal current. The winds play a secondary role in the advection of the salinity plume;

• The dilution rate is found to be sensitive to the discharge rate and depth of discharge. For process waste water, doubling the discharge rate has a proportional effect on the dilution rate and discharging at a depth of 15 m compared to 7.5 m leads to a 3-fold increase in dilution rate. For brine, the dilution rate is also sensitive to the depth of discharge. The minimum dilution rate of 1:700 were modelled while discharging at a depth of 15 m. Conversely, the maximum dilution rate of 1:250 was found while discharging at a depth of 7.5 m. It was also found that increasing the discharge rate doesn’t significantly affect the dilution rate at a discharge depth of 7.5 m.

• The model indicated seasonal variability doesn’t play a significant role in the advection of the plume. The size and orientation of dilution contours are similar for summer and winter seasons and dilution rates are comparable in most cases.

From a strategic-level assessment, the study findings indicate that waste water discharges are subject to rapid dilution and dispersion in the receiving waters of the James Price Point coastal area. The model results show that by the use of an eight diffuser design the strong tidal forcing quickly dilutes the waste water well within the marine precinct boundaries. The discharge of process waste water and brine water, if required, is expected to be readily manageable through the adoption of appropriate treatment technologies, where required, and engineering design of outfalls.



10 References /1/ ANZECC/ARMCANZ (2000): A guide to the Application of the

ANZECC/ARMCANZ Water Quality Guidelines /2/ DHI (2010) Browse Environmental Modelling - Phase 3: Coastal Processes

in the James Price Point Region



A P P E N D I X A

Winter dilution plots



Figure A-1: Maximum predicted winter extent of process waste water dilution zone, Scenario 1, location 1.The precinct boundary is presented by the black line.

Figure A-2: Maximum predicted winter extent of process waste water dilution zone, Scenario 2,

location 1.The precinct boundary is presented by the black line.

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Figure A-5: Maximum predicted winter extent of process waste water dilution zone, Scenario

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Figure A-6: Maximum predicted winter extent of process waste water dilution zone,

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Figure A-7: Maximum predicted winter extent of brine water dilution zone, location 3, Scenario 1. The

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Figure A10: Maximum predicted winter extent of brine water dilution zone, location 3, Scenario 4. The precinct boundary is presented by the black line.

0 0 Kilometres


Winter Dilution

Legend

CONTOUR

150 - 200 - 250 - 300

James Price P'm·

•

17'

17'31

122'1'f

' ' woodside I





0 0 Kilometres


Winter Dilution

Legend

CONTOUR

150 - 200 - 250 - 300

122'1'f

' ' woodside I



A P P E N D I X B

MIKE 21 Calibration



B1 Selection and Set-up, CALIBRATION of 2D MIKE 21 HD model and the validation of the combined HD MODEL

B1.1 General

As a part of the MIKE by DHI software suite a number of hydrodynamic models including 2- and 3-dimensional models are available. The selection of the 2-dimensional model applied in the present study is described below.

B1.2 Overview of Two Dimensional Models

B1.2.1 DHI’s Two Dimensional Models DHI’s 2-dimensional hydrodynamic model is called MIKE 21 (FM). MIKE 21 is a generalised mathematical modelling system designed for a wide range of marine, estuaries and lake applications and can be applied to oceanographic studies, water pollution studies, environmental impact assessment studies and sedimentation studies. The system solves the 2D momentum equation and continuity equations simulating unsteady flow taking into account bathymetry and external forcing such as meteorology, tidal elevations, currents and other hydrographic conditions. MIKE 21 is a finite volume model with an unstructured horizontal grid. It can be run on a single grid or with dynamically nested grids. This version is described in detail in Appendix A. In the current study the model provides the hydrodynamic input into the one way coupled advection-dispersion (AD) model.

B1.2.2 Model setup

The 2D hydrodynamic solution is used to drive the AD module. For this purpose, a coastal unstructured grid domain has been setup and validated around the JPP region and extends to beyond the 30 m depth contour. The unstructured mesh for the model was generated using 40280 triangular and quadrangular elements applying Mike Zero Mesh Generator. In order to have a proper examination from salinity dispersion in the vicinity of the project site, mesh resolution of 25 m has been used around outfall locations.

The time integration of the equations is performed using an explicit scheme. A variable time step interval is used so that the CFL number is less than a critical CFL



number in all computational nodes. In the present module, the variable time step interval is between 1 and 60 sec, so that the maximum Courant number is 0.8.

The horizontal dispersion coefficients represent the mixing and diffusion caused by turbulence, both of which are subgrid scale processes in the scales of HD modelling. The dispersion coefficient can be specified through a constant eddy formulation or a Smagorinsky formulation in the solution of the flow equations. A Smagorinsky coefficient of 0.28 m2/s is used to control the exchange of wastewater in the horizontal direction.

The bed resistance controls water surface elevation and current speed for each point and can be introduced to model through both Chezy and Manning formula. Although, there are some laboratory based relationships for calculation of bed resistance considering the type of bed materials, they present only an approximation of this parameter and the best method to get an appropriate value for this parameter is model calibration using field measurement of current speeds and tidal elevations. For present modelling studies a value of 32 was used for bed resistance in the form of Manning number.

The format of the wind data is specified as varying in time and domain. The magnitude and direction varies during the simulation period and over the model area. The wind friction is specified as a constant value of 0.001255.

The contribution of the outfall location to the continuity equation is taken into account by specifying the magnitude of the source (in m3/s). The AD module sets up additional transport equations for temperature and salinity. The calculated temperature and salinity are feed-back to the hydrodynamic equations through buoyancy forcing induced by density gradients. The source flux is calculated as Qsource

.Csource where Qsource is the magnitude of the source and Csource is the temperature/salinity of the source. The time integration of the transport equation is performed using an explicit scheme. The time step interval for the transport equations is synchronized to match the overall time step for the shallow water equations

B1.2.3 Model calibration

Bed resistance factor and eddy viscosity coefficient are parameters which can be used in calibration process as variable parameters regarding to the basic equations of hydrodynamics model. Model calibration was performed by changing bed resistance (Manning coefficient) and horizontal dispersion coefficient within a recommended range and the model was executed for each of them. The values tested in model ranged from 20-50 m1/3 sec-1 for bed resistance and 0.25-1 for the horizontal eddy viscosity. The default values of 32 m1/3 sec-1 and 0.28 had good results



The top plot on Figure B1 shows a comparison between measured and simulated current magnitudes over a 14-day period. Computed velocity magnitudes correspond well with the measured data during most of the periods. The current peaks are reproduced to a high degree and phase errors are very low. In the neap tide period, the model slightly under predicts the current peak values, which is not unusual in models of this sort. As it is only a small difference within the total set of model computations this level of error was considered acceptable.

The lower plot shows on Figure B1 indicate excellent agreement between simulated and measured current directions for both neap and spring tides.

Figure B1: Time series comparison of sea surface height, depth-averaged current magnitude and direction



A P P E N D I X C

MIKE 21 Short Description

MIKE 21 & MIKE 3 FLOW MODEL FM

Hydrodynamic Module

Short Description


Hydrodynamic Module

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Agern Allé 5 Tel: +45 4516 9200

DK-2970 Hørsholm Support: +45 4516 9333

Denmark Fax: +45 4516 9292

E-mail: [email protected]

Web: www.dhigroup.com

Application Areas

MIKE 21 & MIKE 3 Flow Model FM

The Flow Model FM is a new comprehensive

modelling system for two- and three-dimensional

water modelling developed by DHI Water &

Environment. The new 2D and 3D models carry

the same names as the classic DHI model versions

MIKE 21 & MIKE 3 with an ‘FM’added that

refers to the type of model grid - Flexible Mesh.

The modelling system has been developed for

complex applications within oceanographic,

coastal and estuarine environments. However,

being a general modelling system for 2D and 3D

free-surface flows it may also be applied for

studies of inland surface waters, e.g. overland

flooding and lakes or reservoirs.

MIKE 21 & MIKE 3 Flow Model FM is a new general hydrodynamic flow modelling system based on a finite volume method on an unstructured mesh

DHI’s new Flexible Mesh (FM) series includes the

following:

Flow Model FM modules:

Hydrodynamic Module, HD

Transport Module, TR

Ecology and water quality Module, ECO Lab

Sand Transport Module, ST

Mud Transport Module, MT

Wave module:

Spectral Wave Module, SW

The FM Series meets the increasing demand for

realistic representations of nature, both with

regard to ‘look alike’ and to its capability to model

coupled processes, e.g. coupling between currents,

waves and sediments. Coupling of modules is

managed in the Coupled Model FM.

All modules are supported by new advanced user

interfaces including efficient and sophisticated

tools for mesh generation, data management,

2D/3D visualization, etc. In combination with

comprehensive documentation and support, the

new FM series forms a unique professional

software tool for consultancy services related to

design, operation and maintenance tasks within

the marine environment.

An unstructured grid provides an optimal degree

of flexibility in the representation of complex

geometries and enables smooth representations of

boundaries. Small elements may be used in areas

where more detail is desired, and larger elements

used where less detail is needed, optimising

information for a given amount of computational

time.

The spatial discretisation of the governing

equations is performed using a cell-centred finite

volume method. In the horizontal plane an

unstructured grid is used while a structured mesh

is used in the vertical domain (3D).

This document provides a short description of the

Hydrodynamic Module included in MIKE 21 &

MIKE 3 Flow Model FM.

Example of computational mesh for Tamar Estuary, UK

Short Description Page 1


MIKE 21 & MIKE 3 FLOW MODEL FM supports both Cartesian and spherical coordinates. Spherical coordinates are usually applied for regional and global sea circulation applications. The chart shows the computational mesh and bathymetry for the planet Earth generated by the MIKE Zero Mesh Generator

MIKE 21 & MIKE 3 Flow Model FM - Hydrodynamic Module

The Hydrodynamic Module provides the basis for

computations performed in many other modules,

but can also be used alone. It simulates the water

level variations and flows in response to a variety

of forcing functions on flood plains, in lakes,

estuaries and coastal areas.

Application Areas The Hydrodynamic Module included in MIKE 21

& MIKE 3 Flow Model FM simulates unsteady

flow taking into account density variations,

bathymetry and external forcings.

The choice between 2D and 3D model depends on

a number of factors. For example, in shallow

waters, wind and tidal current are often sufficient

to keep the water column well-mixed, i.e.

homogeneous in salinity and temperature. In such

cases a 2D model can be used. In water bodies

with stratification, either by density or by species

(ecology), a 3D model should be used. This is also

the case for enclosed or semi-enclosed waters

where wind-driven circulation occurs.

Typical application areas are

Assessment of hydrographic conditions for

design, construction and operation of

structures and plants in stratified and non-

stratified waters

Environmental impact assessment studies

Coastal and oceanographic circulation studies

Optimization of port and coastal protection

infrastructures

Lake and reservoir hydrodynamics

Cooling water, recirculation and desalination

Coastal flooding and storm surge

Inland flooding and overland flow modelling

Forecast and warning systems

Example of a global tide application of MIKE 21 Flow Model FM. Results from such a model can be used as boundary conditions for regional scale forecast or hindcast models

Page 2 Hydrodynamic Module

Application Areas

The MIKE 21 & MIKE 3 Flow Model FM also

support spherical coordinates, which makes both

models particularly applicable for global and

regional sea scale applications.

Example of a flow field in Tampa Bay, FL, simulated by MIKE 21 Flow Model FM

Study of thermal recirculation

Typical applications with the MIKE 21 & MIKE 3 Flow Model FM include cooling water recirculation and ecological impact assessment (eutrophication)

The Hydrodynamic Module is together with the

Transport Module (TR) used to simulate the

spreading and fate of dissolved and suspended

substances. This module combination is applied in

tracer simulations, flushing and simple water

quality studies.

Tracer simulation of single component from outlet in the Adriatic, simulated by MIKE 21 Flow Model FM HD+TR

Prediction of ecosystem behaviour using the MIKE 21 & MIKE 3 Flow Model FM together with ECO Lab



The Hydrodynamic Module can be coupled to the

Ecological Module (ECO Lab) to form the basis

for environmental water quality studies

comprising multiple components.

Furthermore, the Hydrodynamic Module can be

coupled to sediment models for the calculation of

sediment transport. The Sand Transport Module

and Mud Transport Module can be applied to

simulate transport of non-cohesive and cohesive

sediments, respectively.

In the coastal zone the transport is mainly

determined by wave conditions and associated

wave-induced currents. The wave-induced

currents are generated by the gradients in radiation

stresses that occur in the surf zone. The Spectral

Wave Module can be used to calculate the wave

conditions and associated radiation stresses.

Model bathymetry of Taravao Bay, Tahiti

Coastal application (morphology) with coupled MIKE 21 HD, SW and ST, Torsminde harbour Denmark

Example of Cross reef currents in Taravao Bay, Tahiti simulated with MIKE 3 Flow Model FM. The circulation and renewal of water inside the reef is dependent on the tides, the meteorological conditions and the cross reef currents, thus the circulationmodel includes the effects of wave induced cross reef currents


Computational Features

Computational Features The main features and effects included in

simulations with the MIKE 21 & MIKE 3 Flow

Model FM – Hydrodynamic Module are the

following:

Flooding and drying

Momentum dispersion

Bottom shear stress

Coriolis force

Wind shear stress

Barometric pressure gradients

Ice coverage

Tidal potential

Precipitation/evaporation

Wave radiation stresses

Sources and sinks

Model Equations The modelling system is based on the numerical

solution of the two/three-dimensional incompress-

ible Reynolds averaged Navier-Stokes equations

subject to the the assumptions of Boussinesq and

of hydrostatic pressure. Thus, the model consists

of continuity, momentum, temperature, salinity

and density equations and it is closed by a

turbulent closure scheme. The density does not

depend on the pressure, but only on the

temperature and the salinity.

For the 3D model, the free surface is taken into

account using a sigma-coordinate transformation

approach.

Below the governing equations are presented

using Cartesian coordinates.

The local continuity equation is written as

Sz

w

y

v

x

u

and the two horizontal momentum equations for

the x- and y-component, respectively

Suz

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Temperature and salinity

In the Hydrodynamic Module, calculations of the

transports of temperature, T, and salinity, s follow

the general transport-diffusion equations as

STHz

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Unstructured mesh technique gives the maximum degree of flexibility, for example: 1) Control of node distribution allows for optimal usage of nodes 2) Adoption of mesh resolution to the relevant physical scales 3) Depth-adaptive and boundary-fitted mesh. Below is shown an example from Ho Bay Denmark with the approach channel to the Port of Esbjerg



The horizontal diffusion terms are defined by

sTy

Dyx

Dx

FF hhsT ,,

The equations for two-dimensional flow are

obtained by integration of the equations over

depth.

Heat exchange with the atmosphere is also

included.


Symbol list

t time

x, y, z: Cartesian coordinates

u, v, w: flow velocity components

T, s: temperature and salinity

Dv : vertical turbulent (eddy) diffusion coefficient

H : source term due to heat exchange with atmosphere

S: magnitude of discharge due to point sources

Ts, ss : temperature and salinity of source

FT, Fs, Fc : horizontal diffusion terms

Dh : horizontal diffusion coefficient

h : depth

Solution Technique The spatial discretisation of the primitive

equations is performed using a cell-centred finite

volume method. The spatial domain is discretised

by subdivision of the continuum into non-

overlapping elements/cells.

Principle of 3D mesh

In the horizontal plane an unstructured mesh is

used while a structured mesh is used in the vertical

domain of the 3D model. In the 2D model the

elements can be triangles or quadrilateral

elements. In the 3D model the elements can be

prisms or bricks whose horizontal faces are

triangles and quadrilateral elements, respectively.

Model Input Input data can be divided into the following

groups:

Domain and time parameters:

computational mesh (the coordinate type is

defined in the computational mesh file)

and bathymetry

simulation length and overall time step

Calibration factors

bed resistance

momentum dispersion coefficients

wind friction factors

Initial conditions

water surface level

velocity components

Boundary conditions

closed

water level

discharge

Other driving forces

wind speed and direction

tide

source/sink discharge

wave radiation stresses

View button on all the GUIs in MIKE 21 & MIKE 3 FM HD for graphical view of input and output files

Model Input

The Mesh Generator is an efficient MIKE Zero tool for the generation and handling of unstructured meshes, including the definition and editing of boundaries

Providing MIKE 21 & MIKE 3 Flow Model FM

with a suitable mesh is essential for obtaining

reliable results from the models. Setting up the

mesh includes the appropriate selection of the area

to be modelled, adequate resolution of the

bathymetry, flow, wind and wave fields under

consideration and definition of codes for defining

boundaries.


2D visualization of a computational mesh (Odense Estuary)

Bathymetric values for the mesh generation can

e.g. be obtained from the DHI Software product

MIKE C-Map. MIKE C-Map is an efficient tool

for extracting depth data and predicted tidal

elevation from the world-wide Electronic Chart

Database CM-93 Edition 3.0 from C-Map

Norway.

3D visualization of a computational mesh

If wind data is not available from an atmospheric

meteorological model, the wind fields (e.g.

cyclones) can be determined by using the wind-

generating programs available in MIKE 21

Toolbox.

Global winds (pressure & wind data) can be

downloaded for immediate use in your simulation.

The sources of data are from GFS courtesy of

NCEP, NOAA. By specifying the location,

orientation and grid dimensions, the data is

returned to you in the correct format as a spatial

varying grid series or a time series. The link is:

www.dhisoftware.com/mikemarine/onlinedata

The chart shows a hindcast wind field in the North Sea and Baltic Sea as wind speed and wind direction


Model Output Computed output results at each mesh element and

for each time step consist of:

Basic variables

water depth and surface elevation

flux densities in main directions

velocities in main directions

densities, temperatures and salinities

Additional variables

Current speed and direction

Wind velocities

Air pressure

Drag coefficient

Precipitation/evaporation

Courant/CFL number

Eddy viscosity

The output results can be saved in defined points,

lines and areas. In the case of 3D calculations the

results are saved in a selection of layers.

Output from MIKE 21 & MIKE 3 Flow Model

FM is typically post-processed using the Data

Viewer available in the common MIKE Zero shell.

The Data Viewer is a tool for analysis and

visualization of unstructured data, e.g. to view

meshes, spectra, bathymetries, results files of

different format with graphical extraction of time

series and line series from plan view and import of

graphical overlays.

The Data Viewer in MIKE Zero – an efficient tool for analysis and visualization of unstructured data including processing of animations. Above screen dump shows surface elevations from a model setup covering Port of Copenhagen

Vector and contour plot of current speed at a vertical profile defined along a line in Data Viewer in MIKE Zero

ValidationBefore the first release of MIKE 21 & MIKE 3

Flow Model FM the model was successfully

applied to a number of rather basic idealized

situations for which the results can be compared

with analytical solutions or information from the

literature.

The domain is a channel with a parabola-shaped bump in the middle. The upstream (western) boundary is a constant flux and the downstream (eastern) boundary is a constant elevation. Below: the total depths for the stationary hydraulic jump at convergence. Red line: 2D setup, green line: 3D setup, black line: analytical solution


Validation

A dam-break flow in an L-shaped channel (a, b, c):

a) Outline of model setup showing the location of gauging points

b) Comparison between simulated and measured water levels at the six gauge locations. (Blue) coarse mesh (black) fine mesh and (red) measurements

The model has also been applied and tested in

more natural geophysical conditions; ocean scale,

inner shelves, estuaries, lakes and overland, which

are more realistic and complicated than academic

and laboratory tests.


c) Contour plots of the surface elevation at T = 1.6 s (top) and T = 4.8 s (bottom)

Example from Ho Bay, a tidal estuary (barrier island coast) in South-West Denmark with access channel to the Port of Esbjerg. Below: Comparison between measured and simulated water levels



The user interface of the MIKE 21 and MIKE 3 Flow Model FM (Hydrodynamic Module), including an example of the extensive Online Help system

Graphical User Interface The MIKE 21 & MIKE 3 Flow Model FM are

operated through a fully Windows integrated

graphical user interface (GUI). Support is

provided at each stage by an Online Help system.

The common MIKE Zero shell provides entries

for common data file editors, plotting facilities and

a toolbox for/utilities as the Mesh Generator and

Data Viewer.

Overview of the common MIKE Zero utilities

Hardware and Operating System Requirements

Hardware and Operating System RequirementsThe MIKE 21 and MIKE 3 Flow Model FM

Hydrodynamic Module supports Microsoft

Windows XP and Microsoft Windows Vista.

Microsoft Internet Explorer 5.0 (or higher) is

required for network license management as well

as for accessing the Online Help.

The recommended minimum hardware

requirements for executing MIKE 21 & MIKE 3

Flow Model FM are listed below:


Processor: 2 GHz PC (or higher)

Memory (RAM): 1 GB (or higher)

Hard disk: 40 GB (or higher)

Monitor: SVGA, resolution 1024x768

Graphic card: 32 MB RAM (or higher), 24 bit true colour

Media: CD-ROM/DVD drive, 20 x speed (or higher)

SupportNews about new features, applications, papers,

updates, patches, etc. are available here:

http://www.dhigroup.com/Software/Download/DocumentsAndTools.aspx

For further information on MIKE 21 and MIKE 3

Flow Model FM software, please contact your

local DHI agent or the Software Support Centre:

Software Support Centre

DHI

Agern Allé 5

DK-2970 Hørsholm

Denmark

Tel: +45 4516 9333

Fax: +45 4516 9292

http://dhigroup.com/Software.aspx

[email protected]

ReferencesThe MIKE 21 & MIKE 3 Flow Model FM are

provided with comprehensive user guides, online

help, scientific documentation, application

examples and step-by-step training examples.

The MIKE 21 & MIKE 3 Flow Model FM have

been, and are, extensively used in DHI

consultancy services (some 50 studies in 20

different countries) and in several research

projects.

Petersen, N.H., Rasch, P. “Modelling of the Asian

Tsunami off the Coast of Northern Sumatra”,

presented at the 3rd Asia-Pacific DHI Software

Conference in Kuala Lumpur, Malaysia, 21-22

February, 2005

French, B. and Kerper, D. Salinity Control as a

Mitigation Strategy for Habitat Improvement of

Impacted Estuaries. 7th Annual EPA Wetlands

Workshop, NJ, USA 2004.

DHI Note, “Flood Plain Modelling using

unstructured Finite Volume Technique” January

2004 – download from

http://www.dhisoftware.com/mike21/Download/P

apers_Docs/M21FM_Floodplain.pdf