EVALUATION OF THE ADDAMS COMPUTER PROGRAM MODULES RELEVANT TO THE DISPOSAL OF MAINTENANCE DREDGING SPOIL FROM MARINAS AND SMALL BOAT HARBOURS

Transcription

1 EVALUATION OF THE ADDAMS COMPUTER PROGRAM MODULES RELEVANT TO THE DISPOSAL OF MAINTENANCE DREDGING SPOIL FROM MARINAS AND SMALL BOAT HARBOURS By Peter H. Morris RESEARCH REPORT

2 RESEARCH REPORT SERIES The primary aim of CRC Tourism s research report series is technology transfer. The reports are targeted toward both industry and government users and tourism researchers. The content of this technical report series primarily focuses on applications, but may also advance research methodology and tourism theory. The report series titles relate to CRC Tourism s research program areas. All research reports are peer reviewed by at least two external reviewers. For further information on the report series, access the CRC website [ EDITORS Prof Chris Cooper University of Queensland Editor-in-Chief Prof Terry De Lacy CRC for Sustainable Tourism Chief Executive Prof Leo Jago CRC for Sustainable Tourism Director of Research National Library of Australia Cataloguing in Publication Data Morris, P.H. (Peter H.). An evaluation of the ADDAMS computer program modules relevant to the disposal of maintenance dredging spoil from marinas and small boat harbours. Bibliography. ISBN Dredging spoil Queensland. 2. Sediment transport Queensland. 3. Waste disposal in the ocean Queensland. 4. Dredging spoil Computer programs. 5. Sediment transport Computer programs. 6. Waste disposal in the ocean Computer programs. I. Cooperative Research Centre for Sustainable Tourism. II. Title Copyright CRC for Sustainable Tourism Pty Ltd All rights reserved. No parts of this report may be reproduced, stored in a retrieval system or transmitted in any form or by means of electronic, mechanical, photocopying, recording or otherwise without the prior permission of the publisher. Any enquiries should be directed to Brad Cox, Director of Communications or Trish O Connor, Publications Manager to info@crctourism.com.au

3 ACKNOWLEDGEMENTS The author wishes to thank and acknowledge the following contributors whose combined efforts and willing cooperation made this research possible: WBM Oceanics Pty Ltd Mr Craig Witt and Mr Chris Nielsen Environmental Protection Agency (Queensland) Mr Chris Pattearson and Ms Katrina Wilkes Lawson and Treloar Pty Ltd Mr Ray Rice Mackay Port Authority Mr Ian Meech Port of Brisbane Corporation Ports Corporation of Queensland Mr Steve Hillman Queensland Government Hydraulics Laboratory Mr David Robinson and Mr Jim Waldron Queensland Transport, Hydrographic Services Mr Rod Ridley and Mr Bill Page Queensland Transport, Maritime Division Captain J Watkinson and Mr John Broadbent The University of Queensland Prof Colin Apelt and Mr Peter McMillan Townsville Port Authority Ms Caryn Anderson, Mr John Neal, and Mr Mick Fitzpatrick US Army Engineer Waterways Experiment Station, Vicksburg Dr Paul Schroeder WestHam Dredging Pty Limited Mr Kevin Green

4 EXECUTIVE SUMMARY This report summarises research conducted at The University of Queensland into the suitability of the ADDAMS suite of computer program modules for application to the preliminary assessment of the ocean disposal of sediments from marinas and small boat harbours under Australian conditions. The ADDAMS suite is under continuing development by the US Army Engineer Waterways Experiment Station, Vicksburg. The research comprised evaluations of the ability of relevant ADDAMS modules to model the short and long term fate of dredged sediments dumped at ocean disposal sites at the Ports of Weipa, Townsville, Hay Point, and Mackay in far north, north, and central Queensland. The ADDAMS modules of primary interest are STFATE, LTFATE, MDFATE. The module STFATE models the short-term fate of a single dump of contaminated dredged sediments from a hopper dredge or barge. LTFATE models the long-term fate of sediments on the seabed, but is limited to relatively simple bathymetry. MDFATE incorporates the capabilities of both STFATE, except that contaminants are not considered, and LTFATE, except for some graphical output options, and can also model multiple dumps and complicated bathymetry. All of the outputs of MDFATE and LTFATE are in US units, but the outputs of STFATE are a mixture of metric and US units. The ADDAMS module PSDDF is also of interest. It models the consolidation over time of dredge spoil freshly deposited on the seabed and of the underlying sediments. Any consistent set of engineering units can be used. For Weipa, the 1998 dredging campaign and the inter-campaign periods from 1994 to 1996 and from 1996 to 1998 were modelled. During these periods, two overlapping 4 km diameter offshore disposal sites, denoted the 1994 and 1998 sites, in Albatross Bay were used. Their average depths were about 9.7 m and 12.3 m MSL, respectively. Areas about 2.8 km 2 and about 4.0 km 2 respectively centred on the 1994 and 1998 sites were modelled. i

5 For Townsville, the period from June 1991 to January 1998 was modelled. This included dredging campaigns of varying magnitude in all years except During this period, two overlapping offshore disposal sites in Cleveland Bay with a total area of about 22 km 2 were used. Only the area common to both disposal sites, with an area of about 3.6 km 2 and an average depth of about 14.0 m MSL, was modelled. For Hay Point, the period from February 1981 to April 2000 was modelled. This included major capital and minor maintenance dredging campaigns that were undertaken in 1993 and 1995, respectively. Only the 1993 campaign was modelled in detail. All spoil from these campaigns was dumped at an offshore disposal site in Dalrymple Bay. The entire site, which had an area of about 1.3 km 2 and an average depth of about 15.3 m MSL, was modelled. For Mackay, the period from April 1998 to April 2000 was modelled. During this time continuous maintenance dredging by a small grab dredge, but no capital dredging, was undertaken. All spoil was dumped at the Mackay ocean disposal site, which has an area of about 1.3 km 2 and an average depth of about 14.9 m MSL. Unlike the other disposal sites modelled, this disposal site is very dispersive. The entire site was modelled. All four of the disposal sites modelled are located in low energy wave environments. In contrast, many US disposal sites, for which STFATE, LTFATE, and MDFATE were developed, are located in high energy wave environments. Thus the analyses summarised in this report evaluated STFATE, LTFATE, and MDFATE for relatively distinctive Australian conditions. The data available for the four disposal sites were unsuitable to evaluate STFATE and LTFATE independently of MDFATE. In the present analyses, LTFATE was used only to provide graphical output of tidal current and elevation input data, and STFATE was not used at all. However, MDFATE was used to model both the short and long term fate of sediments, and such evaluations of MDFATE s capabilities also constitute partial evaluations of STFATE and LTFATE. PSDDF was used only in the Townsville analyses to investigate whether the effect on ii

6 the bathymetry of the consolidation of freshly deposited spoil was significant. Extensive bathymetry data were available for all of the disposal sites modelled. However, the vertical control was greater than most of the (averaged) changes in bathymetry that were modelled. In addition, the Townsville and Hay Point data contained significant systematic errors. Consequently, most of the analyses summarised in this report constituted relatively weak tests of the ability of MDFATE, STFATE, and LTFATE to model the short and long term fate of dredged sediments. However, the analyses of the 1998 Weipa dredging campaign, during which comparatively large changes in the bathymetry occurred, constituted a relatively strong test of the ability of MDFATE and hence STFATE to model their short term fate. Extensive wave height and period data for the four disposal sites were provided by the Environmental Protection Agency (Queensland). No wave direction data were available, but the sediment behaviour at all four sites was shown to be insensitive to the wave direction. The spectrally significant wave height and the wave period at the peak spectral energy were used in the analyses. The wave recorder sites were located considerable distances from the disposal sites, but existing and new analyses showed that the recorder data could be applied to the disposal sites without change. Because the Waterways Experiment Station wave data pre-processing program HDPRE, which generates wave cross-correlation matrix input files for LTFATE and MDFATE, is not available to the public, average wave parameters were used in the analyses. Tidal harmonic constituent input files for MDFATE and LTFATE were compiled by combining tidal elevation constituent data sets with tidal current time series data or constituents from a number of sources. The tidal current time series data were processed into constituent sets comprising between 19 and 38 constituents using a program supplied by WBM Oceanics Pty Ltd. The largest elevation constituent set used comprised 36 constituents. Each of the input files was reduced to 20 constituents, the maximum that can be used in MDFATE, by culling either the smallest elevation constituents or the smallest current constituents. (More than 40 constituents may be used in LTFATE.) The resulting input files for each of the four sites differed considerably. iii

7 This had little effect on the results of the analyses for Weipa, Townsville, and Hay Point, but a significant effect on those for Mackay. The dredge dimensions and operating parameters that were required for MDFATE were supplied by the dredging contractors and the various Port Authorities. Data on the quantities of spoil dumped during the dredging campaigns were supplied by consultants with the consent of the Port Authorities, or by the Port Authorities themselves. In the absence of detailed data, simplified dumping sequences were adopted in all of the analyses. The dredged sediment geotechnical parameter values and the seawater density data required for MDFATE were estimated using data taken from consultants reports, representative data incorporated in MDFATE, and existing geotechnical correlations. Analyses showed that the Townsville, Hay Point, and Mackay disposal site sediment behaviour was relatively insensitive to most of these parameters. Representative geotechnical data incorporated in PSDDF were used in the analysis of the consolidation of the Townsville spoil. The dredged sediments dumped at the four disposal sites modelled contained a high proportion of silts and clays, but the cohesive sediment option in MDFATE is currently unavailable and the noncohesive sediment option was perforce used in all cases. While it was possible to input realistic sand and silt content and in-hopper solids fraction values for the Hay Point sediments, it was necessary to use unrealistically high values for both the Weipa and the Townsville sediments. Sensitivity analyses indicated that this had relatively little effect on the overall results obtained. It was also necessary to use an unrealistically high value for the median particle size of the Mackay dredge spoil. This led to the significant underestimation of the losses from that disposal site. The performance of MDFATE in analyses involving fine-grained, cohesive sediments may be expected to improve significantly when the cohesive sediment option becomes available. No attempt was made to optimize the results of the analyses by varying individual inputs arbitrarily. However, a range of input data was used in each case with little effect on the overall outcomes. iv

8 MDFATE matched poorly the changes in the detailed bathymetry of all four disposal sites modelled. This was at least partly attributable to the simplified dumping sequences used in the analyses. MDFATE matched well the overall short-term changes in the Weipa disposal site that occurred during the 1998 dredging campaign. However, the sediment losses that occurred during the descent from the dredge to the seabed were overestimated significantly. This may have been attributable to the unavailability of the cohesive sediment option. MDFATE matched poorly the volume of sediments retained on the Hay Point disposal site at the end of the 1995 dredging campaign. This was probably largely attributable to errors in the bathymetric data, but the results of the analyses suggested that MDFATE might have significantly overestimated the short-term losses from the Hay Point site. No data suitable for the investigation of the short-term fate of sediments were available for the Townsville or Mackay disposal sites. The discrepancies between the measured and calculated long term overall changes in the bathymetry at all four disposal sites modelled were relatively large, but readily accounted for by the uncertainties and errors in the input data and the poor vertical control. Analyses of the consolidation of freshly deposited Townsville spoil conducted using PSDDF showed that it could not account for the systematic error in the Townsville bathymetry data. Thus MDFATE matched the long term changes at the four sites reasonably well, in that the measured and calculated sediment movements were of comparable magnitude, but too small to measure accurately. Overall, within the limitations of the available data, MDFATE modelled the long-term behaviour of the dredged sediments at the essentially non-dispersive Weipa, Townsville, and Hay Point disposal sites and the very dispersive Mackay disposal site reasonably robustly and well. The MDFATE estimates matched the measured changes in the bathymetry at all four sites to a first approximation satisfactory for the preliminary assessment of ocean disposal sites. No conclusions could be drawn regarding the ability of MDFATE to model the short-term behaviour of the Townsville and Mackay sediments. However, the analyses of the short-term behaviour of the Weipa and Hay Point sediments suggested that MDFATE might overestimate significantly the losses from disposal sites that occur during spoil disposal. v

9 CONTENTS ABSTRACT INTRODUCTION THE ADDAMS SUITE ADDAMS program modules Scope of research ADDAMS modules relevant to ocean disposal of sediments from marinas and small boat harbours OCEAN DISPOSAL SITES MODELLED Weipa ocean disposal site Townsville ocean disposal site Hay Point ocean disposal site Mackay ocean disposal site Disposal site environments INPUT DATA USED IN ANALYSES Compatibility with ADDAMS modules Bathymetric data Wave data Tide data Dredged sediment and seawater data Dredge dimensions and operating constraints RESULTS OF ANALYSES Weipa ocean disposal site Townsville ocean disposal site Hay Point ocean disposal site Mackay ocean disposal site CONCLUSIONS...41 REFERENCES...44 APPENDICES 1: Input data requirements for STFATE v vi

10 2: Input data requirements for LTFATE v : Input data requirements for MDFATE v : Bathymetry input file for Cleveland Bay ocean disposal site.59 5: Tidal harmonic constituent input file for Mackay ocean disposal site : Input data requirements for PSDDF v AUTHOR...64 LIST OF TABLES 1. The ADDAMS suite...5 LIST OF FIGURES 1.1 Locations of disposal sites modelled Location of Albatross Bay ocean disposal sites Location of Cleveland Bay ocean disposal sites Location of Dalrymple Bay ocean disposal site Location of Mackay ocean disposal site Albatross Bay 1994 ocean disposal site bathymetry at September Cleveland Bay ocean disposal site bathymetry at June Dalrymple Bay ocean disposal site bathymetry at July Mackay ocean disposal site bathymetry at April Cleveland Bay tidal elevations based on Australian National Tide Tables elevation and WBM Oceanics current data emphasising currents Cleveland Bay north-south tidal velocity magnitudes corresponding to Figure Cleveland Bay east-west tidal velocity magnitudes corresponding to Figure Cleveland Bay tidal velocity directions corresponding to Figure Cleveland Bay tidal elevations based on Townsville Fairway Beacon (Queensland Transport) elevation and WBM Oceanics current data emphasising currents Cleveland Bay north-south tidal velocity magnitudes corresponding to Figure Cleveland Bay east-west tidal velocity magnitudes corresponding to Figure vii

11 4.12 Cleveland Bay tidal velocity directions corresponding to Figure Measured change in Albatross Bay ocean disposal site bathymetry between May and July Estimated change in Albatross Bay ocean disposal site bathymetry between May and July 1998 based on Australian National Tide Tables elevation and WBM Oceanics current data emphasising elevations Measured change in Cleveland Bay ocean disposal site bathymetry between June 1991 and June Estimated change in Cleveland Bay ocean disposal site bathymetry between June 1991 and June 1993 based on Australian National Tide Tables elevation and WBM Oceanics current data emphasising elevations Measured change in Dalrymple Bay ocean disposal site bathymetry between July and November Estimated change in Dalrymple Bay ocean disposal site bathymetry between July and November 1993 based on Australian National Tide Tables elevation and WBM Oceanics current data emphasising currents Measured change in Mackay ocean disposal site bathymetry between September 1998 and April Estimated change in Mackay ocean disposal site bathymetry between September 1998 and April 2000 based on Australian National Tide Tables elevation and Lawson and Treloar current data emphasising currents...40 viii

12

13 ABSTRACT The potential for the application the ADDAMS suite of computer program modules to the preliminary assessment of the ocean disposal of sediments from marinas and small boat harbours under Australian conditions has been investigated at The University of Queensland. The ADDAMS suite is under continuing development by the US Army Engineer Waterways Experiment Station, Vicksburg. Data from offshore disposal sites at Weipa, Townsville, Hay Point, and Mackay have been used to assess the three ADDAMS modules that model the short and long term fate of dredged sediments. A fourth ADDAMS module that models the consolidation of sediments was used in a minor way in the analyses of the Townsville disposal site. The performance of the first three ADDAMS modules was reasonably robust and generally satisfactory for the preliminary assessment of disposal sites. However, because of limitations of the data for all four of the sites modelled, all but one of the analyses were relatively weak tests of their capabilities. 1

14 1. INTRODUCTION Research is being undertaken at The University of Queensland for the CRC for Sustainable Tourism Pty Ltd on the land and ocean disposal of sediments dredged from marinas and small boat harbours. This report summarises the work on the application of the ADDAMS (Automated Dredging and Disposal Alternatives Management System) suite of computer program modules to the preliminary assessment of the ocean disposal of such sediments under Australian conditions. The ADDAMS suite, which is under development by the US Army Engineer Waterways Experiment Station, Vicksburg, the relevant modules, and their applications are described in Chapter 2 of the report. The remainder of the report summarises analyses of the short and long term behaviour of dredged sediments dumped at the offshore ocean disposal sites at the Ports of Weipa, Townsville, Hay Point, and Mackay in far north, north, and central Queensland (Fig. 1.1). More detailed descriptions of the analyses for the individual disposal sites are presented in Morris (2001a-d). Figure 1.1 Locations of ocean disposal sites modelled 2

15 The ocean disposal sites and the periods modelled are described in Chapter 3 of the report. The input data required for the ADDAMS modules are described in Chapter 4 and the Appendices, and the results of the analyses are described in Chapter 5. The conclusions reached regarding the ability of the ADDAMS modules to model the short and long term behaviour of dredged sediments are presented in Chapter 6. The references cited throughout the report and the Appendices follow Chapter 6. 3

16 2. THE ADDAMS SUITE 2.1 ADDAMS Program Modules The US Army Engineer Waterways Experiment Station, Vicksburg, has developed the ADDAMS suite of computer modules as a continually evolving personal computer based system that provides a comprehensive set of tools for modelling the land and ocean disposal of dredged sediments. Each module comprises computer programs designed to assist in the evaluation of a single aspect of a dredging project. The ADDAMS modules are relatively simple and lend themselves to relatively inexpensive, preliminary investigations of the viability of the ocean and land disposal of dredged sediments. They thus have the potential to provide valuable guidance for the more detailed and hence more expensive investigations required for final approval for dredged sediment disposal. The ADDAMS dredged material management modules currently available are listed in Table 1. (Water quality modules are not listed). Most are DOS based, but some are now available in Windows versions (Table 1). Both the ADDAMS modules and the associated user s manuals may be down-loaded, free of charge, from the US Army Engineer Waterways Experimental Station Internet site at However, source coding is available only for the HELP3 module. 4

17 Table 1: The ADDAMS suite MODULE APPLICATIONS CURRENT VERSION SETTLE Combined disposal facilities (CDFs) design 3.0 DYECON Hydraulic retention and efficiency of CDFs 3.0 EFFLUENT Combined effluent pathway evaluation (EFQUAL + LAT-E) 1.0 (Windows) EFQUAL Modified elutriate test analysis (effluent quality) 3.0 LAT-E Laboratory analysis of toxicity CDF effluent 1.0 RUNQUAL Runoff water quality and dilution needs analysis 1.0 LAT-R Laboratory analysis of toxicity CDF runoff 1.0 RUNOFF Combined runoff pathway evaluation (RUNQUAL + LAT-R) 1.0 (Windows) HELPQ Leachate quality and production prediction 2.1 PUP Freshwater plant uptake prediction 1.0 PSDDF Consolidation and desiccation of dredged fill 2.1 D2M2 Dredged material disposal management SPN CDFATE Fate of continuous discharge mixing zone 1.0 STFATE Short term fate of disposal in open water 5.01 LTFATE Long term fate of disposal in open water 1.0 MDFATE Fate of multiple discharges in open water 1.1 RECOVERY Contaminant release from bottom sediments 3.0 DREDGE Resuspension and contaminant release by dredge 1.1 DEMO Demonstration of ADDAMS modules 2.0 HELP3 Hydrologic evaluation of landfill performance Scope Of Research The algorithms incorporated in all ADDAMS modules have been extensively researched and verified experimentally and analytically by US Army Engineer Waterways Experiment Station personnel for North American conditions. The research summarised in this report did not seek to duplicate this work, but was restricted to verifying the suitability of the relevant ADDAMS modules (Section 2.3) for the preliminary assessment of the disposal of sediments from marinas and small boat harbours under Australian conditions. 5

18 The ADDAMS modules of primary interest (Section 2.3) are intended to be used with tide, wave, and storm data files prepared by the Waterways Experiment Station Wave Information Study for sites within the United States. No comparable pre-packaged data files are available for Australian sites, but the ADDAMS modules permit alternative methods of inputting equivalent data (Section 2.3). The consequences of this for the application of ADDAMS modules in Australia were explored in the research summarised here. 2.3 ADDAMS Modules Relevant To Ocean Disposal Of Sediments From Marinas And Small Boat Harbours The ADDAMS modules relevant to the ocean disposal of relatively small quantities of dredged sediments are STFATE, LTFATE, MDFATE, and, to a lesser extent, PSDDF (Table 1). The corresponding user s manuals are E. P. A. Office of Water and Office of Science and Technology and US Army Corps of Engineers (1995), Scheffner et al. (1995), Moritz (1994), and Stark (1996). A mixture of metric and US units are used for the input data for STFATE, LTFATE, and MDFATE, and for the output data from STFATE, but the outputs of LTFATE and MDFATE are in US units only. Any consistent system of units can be used with PSDDF. For compatibility with the outputs of the other modules, US units were used in the PSDDF analyses summarised here. However, preference is given to metric units in this report. Input and output data for the ADDAMS modules are accordingly expressed in metric units followed, where appropriate, by equivalent data in US units in brackets. Nevertheless, US units are retained in the figures incorporated in this report that were generated using LTFATE and MDFATE. STFATE models the Short Term FATE of sediments containing contaminants disposed of in a single dump from a dredge or barge. LTFATE models the Long Term FATE of sediments on the seabed. MDFATE (Multiple Dump FATE) models the long-term fate of sediments disposed of by multiple (or single) dumps. In STFATE, disposal is assumed to occur from a split-hull barge or a hopper dredge. The behaviour of the dredged material is separated into three phases: convective descent, dynamic collapse, and passive 6

19 transport-dispersion. In convective descent, the disposal cloud falls under the influence of gravity. Dynamic collapse occurs when the descending cloud either impacts the seabed or arrives at a level of neutral buoyancy, where descent is retarded and horizontal spreading dominates. Passive transport-dispersion commences when material transport is determined more by ambient currents and turbulence than by the dynamics of the disposal operation. LTFATE uses coupled hydrodynamic, sediment transport, and bathymetry change models to compute the stability over time of dredged sediments placed in a mound on the seabed as a function of local waves, tides, currents, bathymetry, and sediment size. Mound avalanching is modelled and the effects of storms may be simulated. The seabed sediments may be fixed or moveable. Thus, LTFATE will provide an estimate of the temporal and spatial fate of the dredged sediments and, if applicable, the seabed sediments. However, only relatively simple mound and seabed geometry can be modelled. MDFATE models the same phenomena as both STFATE and LTFATE, except that contaminants are not considered. Almost identical programming is used in both cases. The short-term phenomena modelled by STFATE and wave, tidal, and residual current effects can be neglected if desired. (If tidal effects are neglected, non-zero default inputs are used.) Sediments can be placed in any number of dumps over any length of time and any pattern of dumping can be specified. Complicated mound or seabed geometry can be modelled. The input data requirements for STFATE, LTFATE, and MDFATE and the associated pre and post processing programs are described in Appendices 1 to 3, respectively. Notably, the wave data pre-processing program HDPRE (Appendices 2 and 3), which is used by the US Army Engineer Waterways Experiment Station to produce wave crosscorrelation matrix input files for United States sites for LTFATE and MDFATE, is currently unavailable to the public. The cross-correlation matrix input files are used to generate time series data files within LTFATE or MDFATE. Consequently, it is not possible to generate such data files for Australian sites. Thus, the alternatives of user-supplied time series (available for LTFATE only) or average wave parameters (available for both LTFATE and MDFATE) must be used, or the effects of waves neglected (available for MTFATE only). 7

20 There are numerous minor discrepancies between the STFATE, LTFATE, and MDFATE modules and the corresponding user s manuals, but the modules generally perform in accordance with the documentation. However, some options are inoperative, some outputs are unavailable, and there are some minor programming errors. The user s manuals also contain minor errors. These shortcomings are discussed in detail in Morris (2002). The consequences for the analyses of the ocean disposal sites modelled of these and other limitations of the ADDAMS programs are discussed in Chapters 4 and 5. PSDDF models the primary consolidation, secondary consolidation, and desiccation processes (if any) in fine-grained soils such as dredge spoil using the one-dimensional finite strain theory of Gibson et al. (1967), the secondary compression theory of Mesri and Godlewski (1977), and the empirical desiccation model of Cargill (1985). It can be applied to both land and sea disposal. PSDDF calculates the total settlement of multi-layered fills based on the consolidation characteristics of each layer and the foundation material, the surface water management techniques used, and local climatological data. Additional layers of fill can be added at any time. The input data required by PSDDF are described in Appendix 6. No inoperative options, unavailable outputs, or significant programming errors were found in PSDDF, and there are only a small number of minor errors in the PSDDF user s manual. 8

21 3. OCEAN DISPOSAL SITES MODELLED 3.1 Weipa Ocean Disposal Site The Port of Weipa is located on Albatross Bay on the western side of Cape York Peninsular (Figs 1.1 and 3.1). Maintenance dredging at Weipa is normally undertaken at intervals of approximately two years (Morris 2001a), and most of the dredge spoil is dumped at the Albatross Bay ocean disposal site (Fig. 3.1). From 1961 onwards, this site has been moved gradually seaward into progressively deeper water. The analyses of the Albatross Bay ocean disposal site summarised in this report covered the period from May 1994 to July 1998 (Morris 2001a). This was determined by the availability of suitable bathymetric data (Section 4.2). During that time, all dredge spoil was dumped at disposal site locations that were first used in 1994 and The 1994 and 1998 disposal sites are both 4 km (13,100 ft) in diameter and are respectively centred about 20 km and 23 km east of Weipa (Fig. 3.1). Their average depths are about 7.9 m (25.9 ft) and 10.5 m (34.4 ft) LAT, equivalent to 9.7 m (31.8 ft) and 12.3 m (40.4 ft) MSL, respectively. The tidal range is about 3.1 m (10.1 ft). During the period modelled, there were dredging campaigns only in 1996 and Insufficient dredge spoil data were available to enable the 1996 dredging campaign to be modelled, but both the two inter-dredge periods, and , and the 1998 dredging campaign were modelled. The two inter-dredge periods were respectively 750 days and 630 days in duration. Due to limitations in the bathymetric data, it was possible to model only a 2750 m (9000ft) square area centred on the 1994 disposal site in the analyses of these periods. The 1998 dredging campaign was 56 days in duration. During that time, approximately 1,260,000 m 3 (1,650,000 cu.yd) of spoil were dumped on the 1998 disposal site. An area 3960 m (13,000 ft) square centred on that site was modelled in the analysis of this period. 9

22 Figure 3.1 Location of Albatross Bay ocean disposal sites 3.2 Townsville Ocean Disposal Site The Port of Townsville is located on Cleveland Bay (Figs 1.1 and 3.2). Maintenance dredging of the Port is normally carried out every year, and major capital dredging was last undertaken in 1993 (Morris 2001b). Since 1990, all dredge spoil has been deposited at two offshore disposal sites in Cleveland Bay (Fig. 3.2). The analyses of the Cleveland Bay disposal sites summarised in this report covered the period from June 1991 to January 1998, a total of about 2395 days, encompassing ten dredging campaigns with a total duration of 252 days (Morris 2001b). This period was subdivided in the analyses into periods of 724 days, 1257 days, and 414 days, which encompassed three, five, and two dredging campaigns, respectively. All of these periods were determined by the availability of suitable bathymetric data (Section 4.2). 10

23 Because only limited dredge spoil placement data were available, it was possible to model only the area common to the two offshore disposal sites (Fig. 3.2). This is approximately 2 km by 1.8 km (6600 ft by 5900 ft) in extent, equivalent to about one-third of the each of the two sites. The area modelled has an average depth of about 12.1m (39.7 ft) LAT, equivalent to about 14.0 m (46.0 ft) MSL, and a tidal range of about 4.0 m (13.1 ft). It was estimated that about 303,000 m 3 (397,000 cu.yd) of spoil were dumped on this area over the period modelled. Figure 3.2 Location of Cleveland Bay ocean disposal sites 11

24 3.3 Hay Point Ocean Disposal Site The Port of Hay Point is situated approximately 18 km south-east of the City of Mackay (Figs 1.1 and 3.3). Capital dredging of about 225,000 m 3 (in situ volume prior to dredging) was undertaken at the Port in 1993, but maintenance dredging has always been minimal. None was carried between 1981 and 2000, except for a small campaign in 1995 that removed about 14,400 m 3 (in situ volume) of spoil (Morris 2001c). Both the capital and the maintenance dredging spoil were dumped at a single disposal site located in Dalrymple Bay, about 3 km north-north-west of the northern most berth at Hay Point (Fig. 3.3). The average depth of the natural seabed at the disposal site is about 12.0 m (39.4 ft) LAT, equivalent to about 15.3 m (50.2 ft) MSL, and the tidal range is about 7.1 m (23.4 ft). The analyses of the Dalrymple Bay disposal site summarised in this report covered the period from February 1981 to April 2000 (Morris 2001c), a total of about 8080 days. This was subdivided into periods of 4522 days, 120 days, and 2358 days, which were determined by the availability of suitable bathymetric data (Section 4.2). The 1993 capital dredging campaign was modelled explicitly, but the 1995 maintenance dredging was accounted for only indirectly in the analyses of the changes in the volume of spoil on the seabed. The entire disposal site, which is 1.5 km by 0.85 km (4900 ft by 2800 ft) in extent, was modelled in the analyses. 12

25 Figure 3.3 Location of Dalrymple Bay ocean disposal site 3.4 Mackay Ocean Disposal Site Mackay Outer Harbour is an artificial harbour situated about 7 km north-east of the City of Mackay (Figs 1.1 and 3.4). Almost continuous maintenance dredging and occasional capital dredging is undertaken within the Harbour (Morris 2001d). All dredge spoil is dumped at a single disposal site located about 4 km east-north-east of the Harbour (Fig. 3.4). The average depth of the seabed at the disposal site is about 12.0 m (39.4 ft) LAT, equivalent to about 14.9 m (49.0 ft) MSL, and the tidal range is about 6.4 m (21.0 ft). In contrast to the Weipa, Townsville, and Hay Point disposal sites (Sections 3.1 to 3.3), the Mackay disposal site is very dispersive. 13

26 The analyses of the Mackay ocean disposal site summarised in this report covered the period from September 1998 to April 2000 (Morris 2001d), a total of about 581 days. This period was determined by the availability of suitable bathymetric data (Section 4.2). Approximately 66,500 m 3 (87,000 cu.yd) of maintenance dredging spoil (in-hopper volume) from Mackay Outer Harbour was deposited at the disposal site during that time, but there was no capital dredging. The entire disposal site, which is 1.3 km by 1.0 km (4300 ft by 3300 ft) in extent, was modelled in the analyses. Figure 3.4 Location of Mackay ocean disposal site 14

27 3.5 Disposal Site Environments The average depths of the Albatross Bay, Cleveland Bay, Dalrymple Bay, and Mackay disposal sites modelled (Sections 3.1 to 3.4) are comparable to those of many Australian and United States (Hands and DeLoach, 1984; Hands and Allison, 1991; Scheffner, 1991) ocean disposal sites, although some United States sites are considerably deeper (Demars et al., 1984). However, the disposal sites modelled are all located in low wave energy environments, whereas many United Sates sites are located in comparatively high wave energy environments. Thus the analyses summarised in this report evaluated STFATE, LTFATE, and MDFATE for relatively distinctive Australian conditions. 15

28 4. INPUT DATA USED IN ANALYSES 4.1 Compatibility With ADDAMS Modules Few data related to the short term phenomena associated with the dumping of sediments from dredges were available for any of the ocean disposal sites modelled. Consequently, STFATE could not be evaluated independently for these sites. Since none of the disposal sites modelled had simple topography, they were unsuited to modelling using LTFATE, and all were modelled using MDFATE. LTFATE was used only to provide graphical output of tidal elevation and current data that is not available from MDFATE (Section 4.4). However, MDFATE incorporates most of STFATE and LTFATE (Section 2.3). Hence evaluations of MDFATE in which short term processes are considered are also partial evaluations of STFATE, and evaluations of MDFATE for long term processes are also evaluations of LTFATE. 4.2 Bathymetric Data Extensive bathymetric data were available for the four disposal sites modelled. However, the vertical control was estimated to be about plus or minus 0.3 m (1ft) for the Weipa disposal site, and about plus or minus 0.1m (0.3 ft) to 0.2 m (0.7 ft) for the Townsville, Hay Point, and Mackay sites. Since the magnitudes of these errors were greater than many of the long term changes in bathymetry (averaged over the disposal site) that were modelled (Chapter 5), they constituted major constraints on the interpretation of the results of the analyses. There were also significant systematic errors in the Townsville and Hay Point bathymetric data. All bathymetric data were converted into ASCII files (Appendix 4) in US units for input into MDFATE. The eastings and northings were truncated to six significant figures to suit the limitations of the MDFATE graphical output program. (The MDFATE grid creation program cannot accept more than seven digits.) Contour plots of the Weipa (Albatross Bay), Townsville (Cleveland Bay), Hay Point (Dalrymple Bay), and Mackay ocean disposal sites 16

29 generated using MDFATE are shown in Figures 4.1 to 4.4. These figures were colour-coded prior to reproduction in this report. All dimensions in them are expressed in ft. Figure 4.1 Albatross Bay 1994 ocean disposal site bathymetry at September

30 Figure 4.2 Cleveland Bay ocean disposal site bathymetry at June 1991 Figure 4.3 Dalrymple Bay ocean disposal site bathymetry at July

31 Figure 4.4 Mackay ocean disposal site bathymetry at April Wave Data The wave heights and periods used in LTFATE and MDFATE are not defined in the user s manuals (Scheffner et al., 1995; Moritz, 1994). However, data are available from the US Army Engineer Waterways Experiment Station Wave Information Study Internet site that are intended for use with these programs. These indicate that Hm0, the spectrally significant wave height, and either Tsig, the average period of the highest one-third of zero up-crossing wave heights, or Tp, the period at the peak spectral energy, should be used. Digital data comprising time series of Hm0, Tsig, and Tp for the four disposal sites modelled were supplied for the analyses summarised in this report by the Environmental Protection Agency (Queensland). The period Tp was used in all of the analyses in preference to Tsig. No wave direction data were available for any of the sites modelled, and there were numerous large and small gaps in all of the data sets. 19

32 Because the Waterways Experiment Station wave data pre-processing program HDPRE is unavailable (Section 2.3, Appendices 2 and 3), it is possible in MDFATE only either to neglect the effect of waves, or to specify average wave parameters. When wave effects are neglected, MDFATE uses default values that represent a low energy wave environment comparable to that of the Townsville, Hay Point, and Mackay disposal sites, but a significantly higher energy environment than that of the Weipa disposal site. Nevertheless, the option to neglect wave effects was not used in for any of these sites. The average Hm0 and Tp for the Weipa, Townsville, and Hay Point disposal sites ranged from 0.30 m (1.0 ft) to 0.37 m (1.2 ft) and from 3.3 s to 3.9 s, from 0.55 m (1.8 ft) to 0.85 m (2.8 ft) and from 4.6 s to 5.3 s, and from 0.60 m (2.0 ft) to 0.69 m (2.3 ft) and from 4.4 s to 5.1 s, respectively. Those at the Mackay disposal site were 0.72 m (2.4 ft) and 5.3 s, respectively. The Environmental Protection Agency wave recorders were located between about 1 km and about 20 km from the four disposal sites, and the depths of water at the wave recorders differed somewhat from those at the disposal sites. However, an existing consultant s report indicated that the data from the Weipa recorder site could be adopted unchanged for the Weipa disposal site. Analyses showed that the behaviour of the sediments at the Townsville, Hay Point, and Mackay disposal sites was insensitive to variations in both the wave height and wave period, and the data from the associated recorder sites were also adopted unchanged for these disposal sites. Wave direction data are not used in LTFATE (Scheffner et al., 1995), but are used in MDFATE. In the absence of wave direction data, sensitivity analyses were conducted that showed that the effect of wave direction on sediment behaviour at all of the disposal sites modelled was small, and arbitrary wave directions were adopted in the analyses. 4.4 Tide Data In MDFATE, tidal effects may either be ignored or accounted for by means of the input file TIDAL.DAT (Appendices 2, 3, and 5). The latter option was adopted in all of the analyses summarised in this report. TIDAL.DAT files comprise tidal amplitude and Greenwich epoch 20

33 harmonic constituents for both the elevations and the currents at the location to be studied. Identical files are used in LTFATE. Both MDFATE and LTATE are intended to be used with the TIDAL.DAT files that are available from the US Army Engineer Waterways Experiment Station Wave Information Study Internet site. These files represent sites located at intervals of about 32 km (20 miles) around the US coast (Scheffner, 1994). They are derived from deep-water hindcasting studies and hence typically comprise only the eight primary harmonic constituents, K1, O1, P1, Q1, M2, S2, N2, and K2, for both elevation and currents (US Army Engineer Waterways Experiment Station, 1994). However, MDFATE allows up to 20 constituents in TIDAL.DAT files, and LTFATE allows more than 40. The tidal elevation harmonic constituents published in the Australian National Tide Tables (Department of Defence, Navy Office, 1999, 2000) are suitable for use in both LTFATE and MDFATE, and were used for all four disposal sites modelled. Tidal elevation constituents supplied by Queensland Transport were also used for the Weipa and Townsville sites. The various constituent sets used comprised between 18 and 36 constituents. The recording periods for all sites were comparatively long, and all of the elevation constituents used are consequently of good accuracy. The recorder sites were located within about 4.5 km or less of the associated disposal sites, and all of the elevation constituents were used unchanged in the MDFATE analyses. The tidal ranges at Weipa, Townsville, Hay Point, and Mackay were about 3.1 m (10.1 ft), 4.0 m (13.1 ft), 7.1 m (23.4 ft), and 6.4 m (21.0 ft), respectively. Current meter time series data were supplied by WBM Oceanics Pty Ltd and the Environmental Protection Agency (Queensland) for sites located within about 4 km or less of the four disposal sites modelled. Sets of 22 and 37 current constituents were also supplied by Queensland Transport and Lawson and Treloar Pty Ltd for sites within 1 km of the Hay Point and Mackay disposal sites, respectively. The data supplied by the two consulting firms were the property of the various Port Authorities and were supplied with their consent. The peak currents at Weipa, Townsville, Hay Point, and Mackay were about 60 cm/s, 60 cm/s, 45 cm/s, and 87 cm/s, respectively. The recording periods for the Weipa, Townsville, and Hay Point time series 21

34 data were all less than a month, and the constituents based on them are consequently of relatively poor accuracy. The recording periods for the Mackay time series data and constituents were comparatively long, and the Mackay constituents are consequently of good accuracy. All of the recording sites were located in depths of water reasonably comparable to those at the corresponding disposal sites and all of the current constituents supplied or derived from time series data were used unchanged in the MDFATE analyses. The tidal current time series data were analysed using an executable file supplied by WBM Oceanics Pty Ltd that was based on programs from the Institute of Ocean Sciences, Patricia Bay, British Columbia (Foreman, 1978). These data were converted to the current velocity component amplitudes and epochs required by MDFATE and LTFATE (Appendix 5) using an Excel spreadsheet based on Foreman (1978) and Godin (1972). The final constituent sets each comprised from 19 to 38 constituents. TIDAL.DAT files for each disposal site were compiled by combining the associated elevation and current constituent sets. The combined sets were reduced to the MDFATE limit of 20 constituents by deleting either the elevation constituents or the current constituents with the smallest amplitudes. Extensive culling was necessary in most cases since the elevation and current constituent sets had relatively few constituents in common. The tidal elevation and velocity plots for the Townsville (Cleveland Bay) disposal site shown in Figures 4.5 to 4.12 were derived from the Townsville TIDAL.DAT files using LTFATE. Similar plots were obtained for the other disposal sites modelled. All data in Figures 4.5 to 4.12 are expressed in US units. The elevation and velocity magnitude plots, which represent a period of one year, show clear seasonal variation. The velocity direction plots are restricted to periods of 312 days, the maximum period permitted by LTFATE. There are considerable differences between the various TIDAL.DAT files for each of the disposal sites modelled. Nevertheless, the results of the analyses (Chapter 5) for the Weipa, Townsville, and Hay Point sites suggest that there was relatively little to choose between the TIDAL.DAT files for those sites (Morris 2001a,b,c). However, the 22

35 results obtained for the Mackay disposal site differed significantly. This was attributed to local effects at the two recorder sites used, and to the large numbers of constituents that were eliminated to reduce the sets to the MDFATE limit of 20 (Morris 2001d). The results of the analyses for Townsville and Mackay were sensitive to changes in the velocity of the tidal currents, but those for Hay Point were not. As well as the tidal current harmonic data in TIDAL.DAT files, both MDFATE and LTFATE require residual current input data. Since the TIDAL.DAT files used for all four disposal sites modelled incorporated the residual currents, residual current values of zero were used throughout the analyses. Fig. 4.5 Cleveland Bay tidal elevations based on Australian National Tide Tables elevation and WBM Oceanics current data emphasising currents 23

36 Fig. 4.6 Cleveland Bay north-south tidal velocity magnitudes corresponding to Figure 4.5 Fig. 4.7 Cleveland Bay east-west tidal velocity magnitudes corresponding to Figure

37 Fig. 4.8 Cleveland Bay tidal velocity directions corresponding to Figure 4.5 Fig. 4.9 Cleveland Bay tidal elevations based on Townsville Fairway Beacon (Queensland Transport) elevation and WBM Oceanics current data emphasising currents 25

38 Fig Cleveland Bay north-south tidal velocity magnitudes corresponding to Figure 4.9 Fig Cleveland Bay east-west tidal velocity magnitudes corresponding to Figure

39 Fig Cleveland Bay tidal velocity directions corresponding to Figure Dredged Sediment And Seawater Data The dredged sediment data that are required by MDFATE if only long term processes are modelled are the bulk void ratio of the sediments on the seabed; the respective percentages of sand, silt, and clay in the sediments; and the median particle size. If both short and long term or only short term processes are modelled, it is necessary to specify the total volume and the number (to a maximum of 4) of sediment types to be dumped. The specific gravity, the volume fraction of solids in the dredge hopper, the sediment particle size, the bulk void ratio of the sediments on the seabed, and the critical shear stress for avalanching are required for each sediment type. It is also necessary to specify whether each sediment type is cohesive or non-cohesive, whether it is stripped during descent, and whether the seabed sediments are fixed or moveable. The volumes of spoil dumped at Weipa and Hay Point during the periods modelled were taken from consultants reports, while those 27

40 dumped at Townsville and Mackay were supplied, in a variety of forms, by the respective Port Authorities. For all four of the disposal sites modelled, representative median particle sizes and percentages of sand, silt, and clay for the capital and maintenance dredge spoil and the seabed sediments were taken from or estimated using data from consultants reports and other published data (Morris, 2001a-d). The median particle sizes of the Weipa, Townsville, Hay Point, and Mackay maintenance dredging spoils were about 0.05 mm, 0.05 mm, 0.1 mm, and mm, respectively. Those of the Townsville, Hay Point, and Mackay capital dredging spoils were about 0.1 mm, 0.6 mm, and 0.14 mm, respectively. Because the cohesive sediment option is currently unavailable in MDFATE, the minimum median particle size permitted is mm. This is smaller than the representative median particle sizes used for the Weipa, Townsville, and Hay Point analyses, but significantly larger than that of the Mackay maintenance dredging sediments. The results of the Mackay analyses suggested that the losses of spoil from that disposal site were consequently underestimated significantly. It was also necessary, because of the unavailability of the cohesive sediment option, to use higher than appropriate sand and silt fractions for the Weipa, Townsville, and Hay Point sediments. The effect of this on the results of the analyses is uncertain. However, increasing the sand fraction had little effect on the results of the Hay Point analyses. The specific gravity of the Hay Point and Mackay dredged sediments were obtained from consultants reports. In the absence of relevant data, the specific gravity of both the Weipa and Townsville dredged sediments was assumed to be It was assumed that the Weipa, Townsville, and Hay Point seabed sediments were moveable in all cases. The relatively coarse Mackay seabed sediments were assumed to be fixed in most analyses, but the assumption that they were moveable gave similar overall results. The volume fraction of solids in the dredge hopper for the sediments for all four disposal sites modelled were estimated from data taken 28