Proposed Bleached Kraft Pulp Mill in Northern Tasmania December 2005

Transcription

1 GUNNS LTD Proposed Bleached Kraft Pulp Mill in Northern Tasmania Hydrodynamic Modelling Associated With A Proposed Wharf Facility in Bell Bay Report December 2005

2 Contents Executive Summary 5 1. Background Project Description Scope 7 2. Methodology 9 3. Project Data Proposed Wharf Facility Details Water Level Data Bathymetric Data River Discharge Data Wind Data Sediment Data Salinity Hydrodynamic Modelling Background Model Establishment Boundary Conditions Simulation Period Model Verification Hydrodynamic Model Results Conclusions References 35 Table Index Table 1: Diurnal tidal planes for the Port of George Town 14 Table 2 Navigational Charts 15 Table 3: Table 4 Major Findings With Respect to Sediment Size Distribution and Settling Rates 17 Components of the Modelling System Adopted for the Assessment of the Impact of the Outfall in the Five Mile Bluff Region 21

3 Table 5 Table 6 Table 7 Table 8 Summary Statistics of Predicted Existing (Preconstruction) Current Magnitudes (m/s) at Key Locations 26 Summary Statistics of Predicted Post-construction Current Magnitudes (m/s) at Key Locations 27 Summary Statistics of Predicted Existing (Preconstruction) Bed Shear Stress Magnitudes (N/m 2 ) at Key Locations 28 Summary of Predicted Post-construction Bed Shear Stress Magnitudes (N/m 2 ) at Key Locations 29 Figure Index Figure 1-1: Figure 2-1: Figure 2-2: Figure 2-3: Figure 2-4: Location map showing the Tamar River estuary and the proposed wharf facility in Long Reach. 8 A synoptic view of the Tamar River hydrodynamic model T1 and the parent regional model C providing the tidal signal to force T1. 10 The Tamar River hydrodynamic model T1 overlain on bathymetry. 11 The high resolution local hydrodynamic model N1 adopted for the assessment of fine scale hydrodynamics in the vicinity of the proposed wharf facility. 12 Detail showing the river bed represented on the high resolution hydrodynamic model N1. The proposed wharf facility is symbolically denoted in the figure by a star marker. 13 Figure 3-1: Sediment sampling sites (Aquenal Pty Ltd) 18 Figure 4-1: Figure 4-2: Summary of predicted, observed and modelled water levels at Low Head (July 01-15, 2004) 23 Map showing the location of numerical monitoring stations along the Tamar River used in the comparative assessment of currents and bed-shear stress 25 Appendices A Flow Module B Project Data C Model Verification D Hydrodynamic Results

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5 Executive Summary GUNNS proposes to develop and operate a bleached Kraft pulp mill in Northern Tasmania and have selected Long Reach, on the Tamar River near George Town, as the preferred site for the mill. In conjunction with the development of this mill, new wharf facilities are also proposed to cater for the exportation of the final product. The location of the proposed facility is on the stretch of river known as Long Reach. The wharf will be sited on the eastern side of the river, just downstream from Dirty Bay, approximately 18 km upstream from the entrance to the Tamar River (Figure 1-1). Data for the project was obtained from various sources including: GUNNS, Department of Primary Industries, Water and Environment (Tasmania), The Australian Bureau of Meteorology (BOM), The National Tidal Facility (NTF), Port of Launceston, Aquenal Pty Ltd, etc. A field data campaign was organised which provided data on particle size distribution and sediment settling rates. A hydrodynamic assessment has been undertaken in:» Response to the project requirement for a sound understanding of the impacts of the proposed wharf facility on the hydrodynamics of the Tamar River; and» Recognition of the fact that an accurate assessment of hydrodynamics can provide a stronger understanding of the interaction of the facility with the water body, and hence can ensure greater levels of confidence in the predictions of the impacts of the new structure on the environment. Two high-resolution regional models were developed. These provided detailed coverage of the Tamar River with emphasis on the fine scale representation of hydrodynamics within the river. A verification of the models against predicted tidal elevations yielded good results. Operational runs were performed for the period July 01 st, 2004 to July 15 th, 2004 during which period river discharges in the North Esk and South Esk Rivers reached a peak of 3,000 ML/day and 8,200 ML/day, respectively. The main findings from the current study include:» The most significant impact from the proposed wharf facility on local scale hydrodynamics is identified in the upstream direction from the facility. The impact is associated with the proposed land reclamation which is part of the facility and is relatively limited in extent.» Predictions are that the effect of the land reclamation will translate into a local obstruction of the currents along the eastern bank of the river and a reduction of post-construction peak current magnitude down to 14 cm/s from 37 cm/s. Mean current magnitude corresponding to existing conditions (16.1 cm/s) will be reduced down to 2.5 cm/s. The findings indicate that a stagnation point will form at this location. This may warrant further investigations of the area from a water quality point of view. Other conclusions from the study can be summarised as follows:» The majority of the structure for the proposed facility will be constructed on pylons, with a small amount of land reclamation. The installation method of the pylons, expected to be piling, and construction of the reclamation area is expected to cause little suspension of sediments and therefore associated turbidity plumes should be localised and short term. 5

6 » With the exception of the area located upstream from the land reclamation associated with the proposed wharf facility, the facility is predicted to cause little effect on the hydrodynamics of the river. The impacts from the proposed facility on current magnitude and direction are perceptible but can be qualified as low to negligible. 6

7 1. Background 1.1 Project Description GUNNS proposes to develop and operate a bleached Kraft pulp mill in Northern Tasmania and have selected Long Reach, on the Tamar River (near George Town), as the preferred site for the mill. In conjunction with the development of this mill, new wharf facilities are also proposed to cater for the exportation of the final product. A hydrodynamic assessment has been undertaken in response to the project requirement for a sound understanding of the impacts of the proposed wharf facility on the hydrodynamics of the Tamar River. The modelling work associated with the wharf facility takes advantage of some of the models already developed by GHD for the assessment of the ocean outfall, details of which can be found in GUNNS Pulp Mill EIS, Hydrodynamic Report, (GHD 2006). The location of the proposed facility is on the stretch of river known as Long Reach. The wharf will be sited on the eastern side of the river, just south of Dirty Bay, approximately 18 km upstream from the entrance to the Tamar River (Figure 1-1). The majority of the structure for the proposed facility will be on pylons, with a small amount of land reclamation. The installation method of the pylons, expected to be piling, and construction of the reclamation area is expected to cause little suspension of sediments and therefore associated turbidity plumes should be localised and short term. 1.2 Scope Given the nature of the proposed facility, only hydrodynamic (i.e., no water quality) modelling has been undertaken for the assessment of the impacts of the proposed wharf facility. The aim of the modelling is to determine whether the proposed structure will lead to any change in tidal behaviour (mainly localised currents), and to comment on what the implications of these changes might be. 7

8 Figure 1-1: Location map showing the Tamar River estuary and the proposed wharf facility in Long Reach. 8

9 2. Methodology The methodology adopted for the modelling of the proposed wharf facility and the assessment of the impacts on river hydrodynamics resulting from its construction included the following steps:» Acquisition of data, including: continuous records (time series) of wind magnitude and direction collected at Low Head - a meteorological station in the vicinity of the study site, hydrographs of flow discharges at the upstream boundary of the model; tidal records at the downstream boundary of the model; and bathymetry for the Tamar River, i.e., update of existing bathymetric records; acquisition of sediment data by Aquenal Pty Ltd for GHD Pty Ltd and Gunns Ltd;» Literature review and analysis of the obtained data, including selection of the simulation period;» Development of a large-scale model (C), shown in Figure 1-1, designed to provide adequate tidal forcing to the detailed models described next;» Update of the existing Tamar River hydrodynamic model (T1) shown in Figure 2-2;» Creation of wind and discharge time series for the simulation period;» Creation of a high resolution local hydrodynamic model - N1 (Figure 2-3) for assessment of fine scale hydrodynamics associated with the proposed wharf facility;» Nesting 1 of the T1 model in regional coastal model C and nesting of N1 into T1;» Preparation of model files including the establishment of a network of numerical monitoring stations for the quantitative assessment of impacts on the hydrodynamics;» Operation of the models to assess the existing hydrodynamic conditions;» Update the models to reflect changes associated with the proposed wharf facility (Figure 2-4);» Rerun models to obtain an estimate of the hydrodynamics associated with post-construction conditions; and» Analysis of the impacts. 1 Nesting refers to the generation of time-series of tidal elevation suitable for the forcing of high-resolution, local models on the basis of predictions of water elevation and currents obtained from large-scale parent grid(s) with extended coverage. 9

10 Figure 2-1: A synoptic view of the Tamar River hydrodynamic model T1 and the parent regional model C providing the tidal signal to force T1. 10

11 Figure 2-2: The Tamar River hydrodynamic model T1 overlain on bathymetry. 11

12 Figure 2-3: The high resolution local hydrodynamic model N1 adopted for the assessment of fine scale hydrodynamics in the vicinity of the proposed wharf facility. 12

13 Figure 2-4: Detail showing the river bed represented on the high resolution hydrodynamic model N1. The proposed wharf facility is symbolically denoted in the figure by a star marker. 13

14 3. Project Data 3.1 Proposed Wharf Facility Details For the purpose of hydrodynamic modelling, the proposed wharf facility has been represented on the basis of drawing #16B dated 21/10/2005. As proposed, the wharf facility is to be supported on pylons with a relatively small headland area (land reclamation). 3.2 Water Level Data Model Boundaries This section describes the water level data which is required as input to force the models. In general, the specification of water elevation for tidal forcing at the open boundaries of the models could be undertaken using a series of measured elevations or predicted values using tidal constituents. No measured time series of water elevations could be obtained to provide boundary conditions for the high resolution hydrodynamic models of the Tamar River - T1 (Figure 2-2) and N1 (Figure 2-3). Therefore, tidal elevations were obtained by nesting T1 and N1 into the regional model of the northern Tasmanian coastline (model C, refer Figure 2-1), which was developed as part of the modelling exercise for assessment of the impacts of the ocean outfall. The nesting of T1 and N1 into regional coastal model C provided varying water elevations around the ocean boundary of the models, which ensured an accurate representation of the hydrodynamic conditions and oceanic exchanges at the mouth of the river. The adopted method has a clear advantage over the traditional technique of applying a time series measured at a discrete point over the entire seaward boundary of the models. The signal at the boundaries of the regional coastal model C was generated using a set of eight tidal constituents (M2, S2, K1, O1, Q1, P1, N2, K2). A description of the model including details on the treatment of the boundary conditions can be found in Gunns Pulp Mill EIS, Hydrodynamic Modelling Preliminary Report, December Tidal planes for George Town on the Tamar River are presented for reference in Table 1. Table 1: Diurnal tidal planes for the Port of George Town HAT 3.5 MHWS 3.2 MHWN 3.0 MSL 2.0 AHD 2.0 MLWN 1.0 MLWS 0.8 Source: Australian Tide Tables, AHS All heights are in meters above Lowest Astronomical Tide. 14

15 3.2.2 Verification Data For the purpose of model verification, measured tidal elevation data was obtained from the NTF (National Tidal Facility) at two sites in the vicinity of the study area Low Head (Northing and Easting in UTM projection) and Bell Bay (Northing and Easting in UTM projection) over a period of approximately three years ending December 31, In addition to measurements, two predictions of tidal elevation at George Town were obtained. The first prediction was sourced from the Seafarer 2 while the second prediction was obtained using the so-called Canadian or IOS method (Foreman, M.G.G., 1996). 3.3 Bathymetric Data The bathymetry (geometry of the sea bed) in the modelled region is based primarily on navigational charts (refer Table 2): The charts have been digitised, adjusted to mean seal level as necessary (chart datum was 1.9 m near George Town) and exported as scattered data (Figure B-1, Appendix B) into a raster based GIS package from which the bathymetry of the models has been obtained by averaging. Averaging consisted in setting around each node a search cell half the size of a computational cell and averaging all data pertaining to the search cell. Depths for any remaining cells without data were calculated by linear interpolation. Table 2 Navigational Bathymetry Charts Item Reference Name Scale 1 Aus 487 Bass Strait 1:500,000 2 Aus 790 Stokes Point to Rocky Cape 1:150,000 3 Aus 798 Eddystone Point to Stony Head 1:150,000 4 Aus 799 Stony Head to Rocky Cape 1:150,000 5 Aus 167 Port Dalrymple 1:25,000 6 Aus 168 River Tamar, Long Reach to Launceston 1:25, River Discharge Data The major tributaries that have been included in the present modelling framework are the North Esk and South Esk rivers, which discharge into the Tamar Estuary in the City of Launceston. Daily streamflow data (January 01, 2003 May 01, 2005) for both tributaries was obtained from the Department of Primary Industries, Water and Environment (DPIWE). For the North Esk River with a catchment area of about 1,065 km 2 DPIWE provided data from the streamflow monitoring station located at Ballroom - station 76 of the DPIWE State-wide monitoring network. The station has been in operation since Seafarer tides is an official product, containing tabulated predictions for high and low water each day of the year for over 80 standard ports in Australia, PNG, Solomon Islands and East Timor. 15

16 Data for the much larger South Esk River with a catchment area covering approximately 3,350 km 2 was provided at Perth streamflow monitoring station 181 of the DPIWE State-wide monitoring network. Since municipal and industrial discharges are expected to have insignificant hydrological loading compared to the North and South Esk, they are not considered. In addition, the regime of operation of the Trevallyn Power Station on South Esk River operates as a typical run-of-the-river storage and therefore has been assumed to have no significant impact on the river regime (Hydro Tasmania, August 2003) and the assessment of wharf impacts. A review of the data from both monitoring stations indicates that a significant seasonal difference in freshwater inflows exist with the lowest rates of inflow occurring in spring and autumn (October, March and April). The peak historical average monthly discharge for the South Esk at Perth is estimated at approximately 135,000 ML. The peak historical average monthly discharge for the North Esk is estimated at approximately 32,000 ML. Both peaks have been estimated for the month of August. 3.5 Wind Data Wind data was obtained from the Bureau of Meteorology for the observational station at Low Head, which was the closest site to the proposed wharf facility. Wind speed and wind direction data for Low Head was collected for the period 08 Jan 1998 to 15 July Sediment Data Particle size distributions and sediment settling rates were obtained from a report prepared by Aquenal Pty Ltd for GHD Pty Ltd and Gunns Ltd (May 2005). Major findings from the report are reproduced in Table 1. 16

17 Table 3: Source Major Findings With Respect to Sediment Size Distribution and Settling Rates Major Findings Marine Biological and Sediment Survey at the Proposed Wharf Site, Long Reach, Tamar Estuary, Report prepared by Aquenal Pty Ltd for GHD Pty Ltd and Gunns Ltd Particle size distribution: Particle size analyses were performed for three samples of each of the sites sampled using a grab apparatus for the top 10 cm of sediment and a coring device for deeper samples (0-50 cm and >50 cm). Grab samples for all sites (refer Figure 3-1) were consistent in their particle size distributions, with all sites dominated by well-sorted sediments consisting of medium sands, silts/clays and, to a lesser extent, fine sands. Results for the deeper core samples (0-50 cm depth) were similar to those found in the shallow grab sample for each site, except for two of the deeper locations, sites L5 and L6. The core sample for site L5 was characterised by having a 20% proportion of coarse material in the form of dead shells and shell grit. Site L6 had a larger proportion of silts/clays than the other sample sites, 73% compared to 32-42%. Sediment settling rates: Sediments were collected using the same method as that for the particle size distribution. Fine sediments settling rates varied from 39.7 to 69.2 cm/hr with an average of 56.4 cm/hr for the grab sample (top 10 cm) sediments. For bottom sediments taken with the core sampler, settling rates varied from 25.8 to 47.1 cm/hr with an average of 37.4 cm/hr. It should be noted that these will be minimum settling rates as the experiments are performed under still laboratory conditions, in which there are no water movements which will extend the suspension period of particles. In addition to the above findings, Aquenal reported that sub-tidal soft sediments at the proposed wharf site are dominated by well-sorted medium sands to fine silts/clays, reflecting fairly constant, moderate levels of water movement. Sediments were surveyed up to 90 cm depth, with particle size distributions in deeper sediments resembling those of surface sediments in most cases. There were some exceptions however, with increased coarse material in deeper sediments at a number of sites, as well as a large increase in silts/clays with depth at one site. The increase in coarse material is the result of dead shells from native oysters and other bivalve species, suggesting that these species were once more common at the wharf site than they are now. Alternatively, or additionally, the accumulation of shell debris in deeper sediments may be the result of historically different deposition patterns, with deposition since altered as a result of channel modification works and other disturbances in the estuary. 17

18 Figure 3-1: Sediment sampling sites (Aquenal Pty Ltd) Photographs of the proposed wharf site (refer Aquenal Pty Ltd (May 2005)) show that the shoreline in the intertidal region of the proposed wharf facility is predominantly rocky. For the purpose of assessing the erosion potential of the currents in the immediate vicinity of the proposed wharf facility, a median grain diameter D 50 (mm) had to be determined for the surface sediment layer at the site. Appendix 6 Particle Size Data at the Six Survey Sites of the above report was reviewed with the D 50 determined as falling within the mm range at all but one site (LR6, refer Figure 3-1) 3.7 Salinity Time- and space-varying fields of salinity in the Tamar River were obtained as a result of the nesting process, i.e., salinity was the product of mixing of freshwater discharges from the North and South Esk Rivers (i.e., salinity concentration at 0 ppt) and a constant value of 35.0 ppt assigned at the offshore boundaries of model C. 18

19 4. Hydrodynamic Modelling This chapter documents the model development process, with emphasis on hydrodynamics of the Tamar River at the project site as forced by the tide, river flow and local winds. An accurate assessment of hydrodynamics will provide a stronger understanding of the interaction of the facility with the water body, and hence can ensure (1) greater levels of confidence in the predictions of the impacts of the new structure on the environment and (2) confirmation from an operational perspective that changed currents would be unlikely to adversely impact on shipping. The purpose of the model is to provide a means to quantify:» the existing currents at the proposed wharf site;» the changes that these currents may incur in response to construction of the proposed facility; and» the erosion potential of the currents for the simulated period in terms of threshold current speed. 4.1 Background Background information has been largely drawn from the Marine Farming Development Plan of the Tamar Estuary (DPIWE, July 2000) and is supported by a series of investigations undertaken as part of the Bell Bay Industrial Zone environmental baseline program. The program included drogue work to determine tidal velocities, direction and maximum tidal excursions, depth profiling for salinity and temperature at different locations along the estuary and estimates of volume of water in the estuary and the total tidal discharge. Only findings related to the hydrodynamics are reported here. The information is summarized as follows: 1. The estuary is tidal to the First Basin and predominantly semi-diurnal (two tides per day of similar magnitude) with the mean tidal range varying from 2.34 m at George Town to 3.25 m at Launceston. The South Esk River and North Esk River are the main sources of freshwater into the estuary with input from a number of smaller local creek systems that also drain into the estuary. The water gradually becomes less saline with distance upstream of the estuary. 2. The volume of the water in the estuary at low tide during the month of June 1991 was about 125,700,000 m 3 with a tidal change of about 21,000,000 m 3 (the tidal change accounted for about 14.4% of the total water volume); 3. Tidal excursions are in the order of about 9-10 km on both sides of the flood and ebb tides, however complete flushing of the estuary from the Long Reach area may be slow and probably in the order of days; 4. From Wilmores Bluff to off Point Rapid on a rising tide the drogue at 10 m depth took 80 minutes to travel 3 km up the estuary; and 5. From Wilmores Bluff to off Point Rapid on a flood tide the drogue at 1 m depth took 2 hours 10 minutes, the drogue at 5 m depth took 1 hour 40 minutes and the drogue at 10 m depth took 1 hour 10 minutes (which indicates a velocity range of 0.38 to 0.70 m/sec over the 10 m depth). 6. At different points along the river it is possible to notice up-welling of the river, whirlpools and backcurrents which are caused by the tidal flows, river topography and the bathometry of the estuary. 19

20 The report concludes that: 1. There is considerable contrast in water conditions between the upper and lower reaches of the Tamar Estuary with the Long Reach area experiencing strong tidal flows in the order of 2-4 knots; and 2. The water column in the Long Reach area is well mixed and that there is little evidence of stratification between fresh and salt waters. 4.2 Model Establishment All simulations have been carried out using the Delft3D modelling system developed by Delft Hydraulics (The Netherlands). This is a state-of-the-art, fully interactive coastal area modelling framework, with a long history of successful applications to coastal and estuarine waters and a proven capability of modelling hydrodynamics, transport and water quality processes in complex coastal areas. The simulation of the hydrodynamics of the Tamar River made use of several nested models of Bass Strait and the northern Tasmanian coastline incorporating the mouth of the Tamar River and Five-Mile Bluff region. These models have been developed by GHD for the assessment of the impacts of the outfall discharge associated with the proposed mill. Details of these models and associated results can be found in the Gunns Pulp Mill EIS, Hydrodynamic Modelling Preliminary Report, December In order to make an assessment of the impacts of the proposed wharf facility, two high-resolution regional models were developed to provide detailed coverage of the Tamar River with emphasis on the fine scale representation of hydrodynamics within the river. Both models used quasi-orthogonal, boundary fitted curvilinear grids in the horizontal. They allow a wide range of spatial scales while preserving key boundaries and maintaining the traditional advantages of gridded representations. Other benefits of the use of orthogonal grid systems is the economy of computational and storage resources. Grid nesting, in addition to the adoption of curvilinear grids, was particularly useful in this application since it enabled high resolution to be specified in the vicinity of the proposed wharf and larger grid sizes to be adopted elsewhere. The models were based on the FLOW module (refer Appendix A) of Delft3D and are referred to as C, T1 and N1. T1 and N1 are the high resolution models covering the Tamar River, with T1 reaching upstream to the confluence of the North and South Esk Rivers. N1 was nested inside T1 to provide fine scale representation of the hydrodynamics in the location of the proposed wharf facility. The extent of the computational model grids covering the Tamar River and northern Tasmanian coastline are shown in Figures 2-1 to 2-4. All models were operated in two-dimensional, depth-integrated mode. All models were forced by the tide, constant river discharge and time varying wind fields applied at the free surface of the water body. The adopted three levels of nesting enabled a large coverage of the northern Tasmanian coastal area (140 x150 km) in order to generate time-series of tidal elevations suitable for the forcing of the high-resolution models of the Tamar River (T1 and N1). As seen from Table 4, the resolution varied from 250 m grid spacing offshore for the outer model C to 25 m near the wharf facility in the high-resolution model N1. The extent of each model has been determined based on fitness to purpose considerations as follows:» Regional model C has a relatively large spatial extent - over 140 km in the offshore direction and 150 km along the Tasmanian Coast. In the absence of recorded tidal elevations, this model provides 20

21 time series of elevations for the two high-resolution hydrodynamic models boundaries which are situated 6.5 km offshore from the entrance to the Tamar River;» High resolution model T1 extends the whole length of the Tamar River until the confluence of the North and South Esk Rivers. This allows for the introduction of inflows from these watercourses, and any impacts that they may have on the hydrodynamics of the river to be introduced into the model.» High resolution Model N1 has the same offshore boundary as T1, however it has a smaller grid size and its reach upstream is limited to Batman Bridge to allow representation of the fine scale hydrodynamics within the river and in the vicinity the proposed wharf facility. Table 4 Components of the Modelling System Adopted for the Assessment of the Impact of the Outfall in the Five Mile Bluff Region C T1 N1 Extent 140 x150 km 74x1.5 km 36x1.5 km Mode of Operation 2D, depth-averaged 2D, depth-averaged 2D, depth-averaged Horizontal Resolution 250 m ~ m ~ m Assumptions The hydrodynamic modelling has been undertaken under the following assumptions:» Models C, T1 and N1 are two-dimensional, depth-averaged models intended for applications in which vertical accelerations are negligible and velocity vectors generally point in the same direction over the entire depth of the water column at any instant of time;» The spatially constant, time varying winds provided by the Australian Bureau of Meteorology (BOM) from observations obtained at Low Head apply to the project site for the period of simulation;» Salinity is constant at 20 ppt at the proposed wharf facility site. Variations in salinity have minimal effect on the hydrodynamic simulations; and» The selected simulation period (July 01 st, 2004 to July 15 th, 2004) provides a good representation of the physical behaviour of the modelled system in terms of tidal elevations, currents and river inflows Datum Depths and tidal elevations in the model are referenced to the Australian Height Datum (AHD). All topographical features are in the MGA Zone 55 (GDA 94) projection. 4.3 Boundary Conditions Boundary conditions were obtained by means of nesting which ensured that errors due to reflection from solid boundaries, which tend to contaminate the signal at the open-sea boundaries were minimized. The high resolution, numerical model of the Tamar River N1 obtains its water elevation time-series from the larger C and T1 models, which provide the ocean and the upstream boundaries respectively. 21

22 4.4 Simulation Period Historically, Tamar River flows peak in July. Hence, operational runs were performed for the period July 01 st, 2004 to July 15 th, 2004 during which period river discharges in the North Esk and South Esk Rivers reached a peak of 3,000 ML/day and 8,200 ML/day, respectively. 4.5 Model Verification For the purpose of model verification, a comparative assessment was undertaken between measured, predicted and modelled tidal elevations for the simulation period. Measured tidal elevation data for the verification process was obtained from the NTF (National Tidal Facility) at two sites in the vicinity of the study area Low Head and Bell Bay over a period of approximately three years ending December 31, In addition to measurements, two predictions of tidal elevation at George Town were obtained. The first prediction was sourced from the Seafarer and consisted of high and low water levels for each day. The second prediction was generated by applying the so-called Canadian or IOS method (Foreman, M.G.G., 1996) using a time step of one hour. Seafarer predictions are usually generated using as many tidal (harmonic) constituents as could possibly be derived from the existing records of tidal elevation for a particular location. In case of George Town, the Seafarer lists 22 tidal constituents. For the purpose of modelling, however, care should be taken to preserve consistency in the analysis, i.e., comparison of predicted and simulated tidal elevations should be conducted using the same number (set) of constituents. Accordingly, the IOS prediction was generated for a set of eight tidal constituents (M2, S2, K1, O1, Q1, P1, N2, K2) and si referred to as Gtown_8c in all plots discussed in this section. The set of tidal constituents selected for the prediction is identical to the one adopted for the numerical simulations. 22

23 Figure 4-1: Summary of predicted, observed and modelled water levels at Low Head (July 01-15, 2004) The results from the verification of the model are discussed below and presented in Appendix C. Low Head: The comparison of the results is qualitative with focus on the two solid lines the simulated (black) and predicted IOS (red) tide (Figure 4-1). As seen from the figure, a spring to neap tidal cycle corresponding to the upper limit of the observed tidal range has been captured in the simulation. Model results (refer Figures C-1 to C-5 in Appendix C) extracted from numerical monitoring station #1 (refer Figure 4-2) show very good agreement with the IOS predictions during the entire simulation period. The results compare favourably, but to a lesser degree, to the Seafarer prediction (broken line). This finding is despite the much larger number of constituents used for the generation of the Seafarer prediction compared to the number of constituents used in the simulations. When assessing the quality of the agreement, it should also be recalled that all predictions have been generated for George Town a few kilometres upstream from the location of numerical monitoring station #1 and Low Head. As expected, the agreement of simulations and predictions with observations (square markers) is degraded for both phase and amplitude. Based on anecdotal evidence (CSIRO (1996, 1997)), the observed differences may be attributed to non-tidal effects such as low frequency motions, which are generated outside of the study area. Such physical processes are not part of the current analysis. Bell Bay: Model results (refer Figures C-6 to C-10 in Appendix C) for the analysis were extracted from numerical monitoring station #12 (Figure 4-2). Due to the significance distance separating numerical 23

24 monitoring station #12 and George Town, the focus of the comparison at Bell Bay is on the numerical results and the observations. The tidal predictions for George Town have been plotted only for reference. Impacts from meteorological (low frequency) forcing that have resulted in a set-up of the water surface are evident in the plots of observation data throughout the entire simulation period (in particular, the 2 nd, 4 th, 5 th and 7 th of July). The latter discrepancy between observations and simulation results is not expected to affect the conclusions from the current study which is based on a relative assessment of impacts. The comparison has been is documented to preserve the transparent character of the study. 4.6 Hydrodynamic Model Results Selection of Monitoring Sites Distributions of currents and bed shear stress were predicted at hourly intervals for the first half of July 2004 and time series extracted from these distributions at 52 locations along the Tamar River (Figure 4-2). A representative cross-section of 12 locations (refer inset in Figure D-1) was then selected and the time-series corresponding to these locations (Figures D-2 to D-7, Appendix D) were used to generate:» frequency histograms of magnitude and direction for currents and bed shear stress (Figures D-8 to D- 15); and» tidal orbits and summary statistics (Tables 5 to 8). The visualisation of the results allowed a detail comparison to be drawn between existing (preconstruction) and post-construction hydrodynamic conditions in the vicinity of the proposed wharf. The 12 monitoring locations were established as follows:» monitoring stations A, B, C and D were positioned across the river;» monitoring stations E, F, G and H were positioned along the east bank of the river; and» monitoring stations I, J, K and L were positioned along the shipping berth of the wharf. With respect to the distance separating the various stations, it is further noted that:» monitoring station D is located on the shoreline behind the southern end of the proposed wharf;» monitoring station G is positioned at a distance of approximately 330 m upstream from the south corner of the proposed facility (approximate location of monitoring station C); monitoring station H is established at an additional 220 m further upstream from monitoring station G or 550 m upstream from the south corner of the proposed facility.» monitoring stations I, J, K and L, aligned with the main berth of the wharf facility, are 50 m apart. Station F is at a distance of approximately 60 m in the downstream direction from station I. Station E is positioned at a distance of approximately 250 m in the downstream direction from station F or at a distance of approximately 310 m in the downstream direction from station I. The reader is referred to the inset in Figure D-1 for more detail. The analysis of the simulation results at the monitored sites is summarised in the following sections. It is noted that the nautical convention has been used when discussing current and bed shear stress directions. 24

25 Figure 4-2: Map showing the location of numerical monitoring stations along the Tamar River used in the comparative assessment of currents and bed-shear stress Discussion of Results This section presents a summary of the main findings from the impact assessment of the proposed wharf facility. A detailed description of the predicted changes in terms of magnitude and direction for both currents and bed shear stress at each numerical monitoring station is presented in Appendix D. The following comments are made: Current Magnitude For the purpose of frequency analysis, current magnitude has been subdivided into 25.0 cm/s groups (bins), i.e., 0 to 12.5 cm/s bin, 12.5 to 37.5 cm/s bin, 37.5 to 62.5 cm/s bin, etc. The most significant impact on current magnitude is observed at monitoring station D. Owing to the reclamation of land associated with the proposed wharf facility, the results from the analysis indicate that current magnitude at monitoring station D has been significantly reduced in comparison with the current 25

26 magnitude corresponding to existing conditions, i.e., the 12.5 to 37.5 cm/s range of current magnitude is nil. Post-construction peak current magnitude is reduced down to 14 cm/s from 37 cm/s; mean current magnitude corresponding to existing conditions (16.1 cm/s) is reduced down to 2.5 cm/s. The findings indicate that a stagnation point will form at this location. This may warrant further investigations of the area from a water quality point of view. At all other monitoring stations, the predicted changes are observed to be low to negligible, i.e., of the order of few percent. Accurate estimates of these can be found in Appendix D. Peak current velocities for existing conditions are predicted at station B and reach 0.74 m/s during spring tides (Table 5); according to the predictions, no change in peak current velocities is expected at station B during post-construction conditions (Table 6). Predicted post-construction peak current velocities along the shipping berth are in the 0.45 to 0.55 m/s range, unchanged from existing conditions. Table 5 Summary Statistics of Predicted Existing (Pre-construction) Current Magnitudes (m/s) at Key Locations Station ID Mean Maximum 5 th percentile Median 95 th percentile Standard Deviation A B C D E F G H I J K L

27 Table 6 Summary Statistics of Predicted Post-construction Current Magnitudes (m/s) at Key Locations Station ID Mean Maximum 5 th percentile Median 95 th percentile Standard Deviation A B C D E F G H I J K L Current Direction For the purpose of frequency analysis, current direction has been subdivided in 30.0 degree bins with their respective axis set at 0 degree, 30 degree, 60 degree, 90 degree, 120 degree, etc. As in the case of current magnitude, the most significant impact on current magnitude is observed at monitoring station D. The impact from the proposed facility in terms of current direction translates into a shift from the degree bins into the degree bins on the ebb tide for more than 50% of the time and a shift from the 150 degree bin into the 30 degree bin on the flood tide for more than 55% of the time. The shift in direction is best illustrated by the comparison of tidal orbits presented in the bottom right panel of Figure D-16; At all other monitoring stations, the predicted changes are observed to be low to negligible, i.e., of the order of few percent. Accurate estimates of these can be found in Appendix D. Bed Shear Stress Magnitude Bed shear stress (BSS) provides an estimate of the erosion potential of the river bed and is closely correlated to currents. For the purpose of this analysis, the predicted values of BSS have been subdivided into 0.25 N/m 2 bins. The most significant impact from the proposed wharf facility is predicted at monitoring station D. BSS have been significantly reduced by the presence of the wharf (refer Figures D-12 to D-15 in Appendix D); the BSS pertaining to the to N/m 2 bin and the to N/m 2 bin under existing conditions, are no longer detected in post-construction conditions; 27

28 At all other numerical monitoring stations without exception, the impacts from the proposed wharf facility are observed to be low to negligible (maximum 3%). Accurate estimates of these can be found in Appendix D. A maximum in post-construction bed shear stress magnitude is predicted at monitoring station B 1.35 N/m 2, down from 1.39 N/m 2 at pre-construction stage. Table 7 Summary Statistics of Predicted Existing (Pre-construction) Bed Shear Stress Magnitudes (N/m 2 ) at Key Locations Station ID Mean Maximum 5 th percentile Median 95 th percentile Standard Deviation A B C D E F G H I J K L

29 Table 8 Summary of Predicted Post-construction Bed Shear Stress Magnitudes (N/m 2 ) at Key Locations Station ID Mean Maximum 5 th percentile Median 95 th percentile Standard Deviation A B C D E F G H I J K L Bed Shear Stress Direction For the purpose of frequency analysis, bed shear stress (BSS) direction has been subdivided in 30.0 degree bins with their respective axis set at 0 degree, 30 degree, 60 degree, 90 degree, 120 degree, etc., and the results plotted in Figures D-12 to D-15 in Appendix D. Comparison of the plots for existing and post-construction conditions lead logically to the same conclusions as those obtained from the analysis of current direction (refer Current Direction above) Erosion Potential Erosion potential of the river bed in the immediate vicinity of the proposed wharf facility has been assessed based on the following methodology:» Determine the median grain diameter D 50 (mm) which is considered as representative for the surface sediment layer at the site (refer Appendix 6 Particle Size Data at the Six Survey Sites, Aquenal Pty Ltd, May 2005); and» Evaluate the threshold current speed for motion of sediment by steady currents presented in Figure D-19 of Appendix D. As explained earlier (refer section 3.6), for the purpose of this analysis, D 50 has been determined as pertaining to the mm range. Assuming that water depths are in the 2 m to 10 m range, the threshold current speed for motion of sediment by steady currents has been determined from Figure D- 19 to fall in the 0.35 m/s to 0.45 m/s range. 29

30 For the assessment of the mobility of the material at the bed of the river, the threshold current speeds corresponding to 2 m of depth (the bottom curve in Figure D-19) have been used. This is a conservative estimate which is considered practical and reasonable for this type of assessments. Table 9 lists the results from the analysis under the form of the percentage of time during which the threshold current speed for motion of sediment by steady currents is predicted to be exceeded at each of the 12 numerical monitoring stations that have been established. Table 9 Station Percentage of time during which the threshold current speed for motion of sediment by steady currents is exceeded Depth of 2 m A 0 B 60 C 15 D 0 E 10 F 5 G 20 H 40 I 5 J 5 K 5 L 10 As seen from the table, station B has the maximum erosion potential, i.e., the representative bed material is predicted to be mobilised approximately 60% of the time. Station H ranks in second with bed material predicted to be mobilised approximately 40% of the time. At all other stations mobility of the bed material is predicted to occur in less than 20% of the time. At station D, where the changes in current magnitude (decrease) and direction due to the proposed wharf facility were predicted to be most significant, erosion potential is predicted to be nil. Note that, irrespective of the significantly high values listed in Table 9, the above results do not necessarily imply a significant rate of erosion of river bed material. The real rate of erosion will be subject to availability of the material at the surface layer of the bed and may be significantly reduced by armouring effects. 30

31 5. Conclusions GUNNS proposes to develop and operate a bleached Kraft pulp mill in Northern Tasmania and have selected Long Reach, on the Tamar River near George Town, as the preferred site for the mill. In conjunction with the development of this mill, new wharf facilities are also proposed to cater for the exportation of the final product. A hydrodynamic assessment has been undertaken in:» response to the project requirement for a sound understanding of the impacts of the proposed wharf facility on the hydrodynamics of the Tamar River; and» recognition of the fact that an accurate assessment of hydrodynamics can provide a stronger understanding of the interaction of the facility with the water body, and hence can ensure greater levels of confidence in the predictions of the impacts of the new structure on the environment. To achieve the above objectives, two high-resolution regional models were developed to provide detailed coverage of the Tamar River with emphasis on the fine scale representation of hydrodynamics within the river. Both models used quasi-orthogonal, boundary fitted curvilinear grids in the horizontal and were nested in a large scale model which covered the Tamar River and northern Tasmanian coastline. All models were operated in two-dimensional, depth-integrated mode and were forced by the tide, constant river discharge and time varying wind fields applied at the free surface of the water body. The hydrodynamic models were operated for the period July 01 st, 2004 to July 15 th, a spring to neap tidal cycle corresponding to the upper limit of the observed tidal range. During the simulation period, river discharges in the North Esk and South Esk Rivers reached a peak of 3,000 ML/day and 8,200 ML/day, respectively. The models provided predictions of water levels, currents and bed shear stress and a means to quantify:» the existing currents at the proposed wharf site;» the changes that these currents may incur in response to construction of the proposed facility; and» the erosion potential of the currents for the simulated period in terms of threshold current speed. For the purpose of model verification, a comparative assessment was undertaken at Low Head and Bell Bay between measured, predicted (by Seafarer and IOS method) and modelled tidal elevation for the simulation period. Model results for Low Head yielded very good agreement with the IOS predictions during the entire simulation period. The results compared favourably, but to a lesser degree, to the Seafarer prediction due to the larger number of constituents used for the generation of the Seafarer prediction. All predictions used in the verification process were obtained for George Town. Because of the distance separating Bell Bay from George Town, the verification for Bell Bay was only indicative, i.e., based on the comparison of observation data and simulation results. No attempts were made to adjust the model to observation data which was significantly impacted by non-tidal effects such as low frequency motions, which are generated outside of the study area. 31

32 However, it is noted that any discrepancies observed between observations and simulation results during the process of verification of the model are not expected to affect the conclusions from the current study which is based on a relative assessment of impacts. Three different visualisation techniques have been implemented to assess the results of the simulation. The techniques - frequency histograms, tidal orbits and the conventional time-series, substantially complement each other. As demonstrated by this study, each presentation format has advantages over the remaining two. For instance, it has been possible to quantify even minor changes in current magnitude and direction owing to the adoption of frequency analysis. Alternatively, the correlation between changes in current magnitude and corresponding shifts in current direction is best preserved, hence identifiable and quantifiable, in the form of tidal orbits and time-series. The results from the modelling exercise have been visualised at a representative cross-section of 12 locations established in the immediate vicinity of the proposed wharf facility as follows (refer inset in Figure D-1):» monitoring stations A, B, C and D were positioned across the river;» monitoring stations E, F, G and H were positioned along the east bank of the river; and» monitoring stations I, J, K and L were positioned along the shipping berth of the wharf. The following conclusions have been reached: Impacts from the proposed wharf facility on local scale hydrodynamics in the vicinity of the proposed wharf facility are detectable but minimal - generally of the order of 2-3 %, reaching on one occasion 5-7%. More significant impacts, however, in terms of current and BSS magnitude and direction, are observed in the area upstream of the land reclamation associated with the proposed facility. These are described in detail below: With respect to current magnitude: The most significant impact on current magnitude is observed at monitoring station D. Owing to the reclamation of land associated with the proposed wharf facility, the results from the analysis indicate that current magnitude at monitoring station D has been significantly reduced in comparison with the current magnitude corresponding to existing conditions, i.e., the 12.5 to 37.5 cm/s range of current magnitude is nil. Post-construction peak current magnitude is reduced down to 14 cm/s from 37 cm/s; mean current magnitude corresponding to existing conditions (16.1 cm/s) is reduced down to 2.5 cm/s. The findings indicate that a stagnation point will form at this location. This may warrant further investigations of the area from a water quality point of view and the need for assessment of sediment deposition. At all other monitoring stations, the predicted changes are observed to be low to negligible, i.e., of the order of few percent. Accurate estimates of these can be found in Appendix D. Peak current velocities for existing conditions are predicted at station B and reach 0.74 m/s during spring tides (Table 5); according to the predictions, no change in peak current velocities is expected at station B during post-construction conditions (Table 6). Predicted post-construction peak current velocities along the shipping berth are in the 0.45 to 0.55 m/s range, unchanged from existing conditions. 32

33 With respect to current direction: As in the case of current magnitude, the most significant impact on current magnitude is observed at monitoring station D. The impact from the proposed facility in terms of current direction translates into a shift from the degree bins into the degree bins on the ebb tide for more than 50% of the time and a shift from the 150 degree bin into the 30 degree bin on the flood tide for more than 55% of the time. The shift in direction is best illustrated by the comparison of tidal orbits presented in the bottom right panel of Figure D-16; At all other monitoring stations, the predicted changes in current direction are observed to be low to negligible, i.e., of the order of few percent. Accurate estimates of these can be found in Appendix D. With respect to bed shear stress magnitude The most significant impact from the proposed wharf facility is predicted at monitoring station D. BSS have been significantly reduced by the presence of the wharf (refer Figures D-12 to D-15 in Appendix D); the BSS pertaining to the to N/m 2 bin and the to N/m 2 bin under existing conditions, are no longer detected in post-construction conditions; At all other numerical monitoring stations without exception, the impacts from the proposed wharf facility are observed to be low to negligible (maximum 3%). Accurate estimates of these can be found in Appendix D. A maximum in post-construction bed shear stress magnitude is predicted at monitoring station B 1.35 N/m 2, down from 1.39 N/m 2 at pre-construction stage. With respect to bed shear stress direction For the purpose of frequency analysis, bed shear stress (BSS) direction has been subdivided in 30.0 degree bins with their respective axis set at 0 degree, 30 degree, 60 degree, 90 degree, 120 degree, etc., and the results plotted in Figures D-12 to D-15 in Appendix D. Comparison of the plots for existing and post-construction conditions lead logically to the same conclusions as those obtained from the analysis of current direction (refer Current Direction above). With respect to erosion potential: Erosion potential of the river bed in the immediate vicinity of the proposed wharf facility has been assessed based on a correlation between the median grain diameter D 50 (mm) which is considered as representative for the surface sediment layer at the site and the threshold current speed for motion of sediment by steady currents. Based on field data collected by Aquenal Pty Ltd, D 50 has been determined as pertaining to the mm range for this study. Assuming that water depths are in the 2 m to 10 m range, the threshold current speed for motion of sediment by steady currents has been determined from Figure D-19 to fall in the 0.35 m/s to 0.45 m/s range. The results indicate that station B has the maximum erosion potential, i.e., the representative bed material is predicted to be mobilised approximately 60% of the time. Station H ranks in second with bed material predicted to be mobilised approximately 40% of the time. At all other stations mobility of the bed 33

34 material is predicted to occur in less than 20% of the time. At station D, the erosion potential is predicted to be nil. Note that:» the above results do not necessarily imply a significant rate of erosion of river bed material. The real rate of erosion will be subject to availability of the material at the surface layer of the bed and may be significantly reduced by armouring effects.» no transport and water quality processes were included in the agreed scope, hence sediment processes were not included in the model. However, photographs of the proposed wharf site taken in the report prepared by Aquenal Pty Ltd show that the shoreline in the region of the proposed wharf facility is predominantly rocky intertidal habitat, therefore the wharf is not expected to interrupt any littoral transport processes which will then cause erosion on either side of the facility. 34

35 6. References 1. Australain National Tidal Tables, Australian Hydrographic Service, Boags Rocks Environmental Impact Assessment Program, CSIRO Division of Marine Research, Report No. OMR-101/107, December Foreman, M.G.G. (1996), Manual for Tidal Heights Analysis and Prediction, Pacific Marine Science Report 77-10, Department of Fisheries and Oceans, Institute of Ocean Sciences, Patricia Bay, Victoria, B.C. 4. Gunns Pulp Mill EIS, Hydrodynamic Modelling Preliminary Report, December Marine Farming Development Plan, Tamar Estuary, DPIWE, July Marine Biological and Sediment Survey at the Proposed Wharf Site, Long Reach, Tamar Estuary, Report prepared by Aquenal Pty Ltd for GHD Pty Ltd and Gunns Ltd. 7. Modelling Effluent Dispersion in Australian Coastal Waters, Technical Report No.16, CSIRO Division of Oceanography, March South Esk Great Lake Water Management Review, Scientific Report on Tamar Siltation prepared by Hydro Tasmania, August

36 Appendix A Flow Module Theoretical Background of the Hydrodynamic Models

37 Appendix A Flow Module Delft-3D FLOW the hydrodynamic module of Delft-3D developed by Delft Hydraulics in the Netherlands, is a multi-dimensional hydrodynamic simulation program that calculates non-steady flows and transport phenomena resulting from tidal and meteorological forcing in two (depth-averaged) or three dimensions on a curvilinear, orthogonal boundary fitted grid or in spherical coordinates. In threedimensions, the flow module applies the sigma coordinate transformation in the vertical, which results in a smooth representation of the bottom topography. Delft-3D FLOW solves the Navier-Stokes equations for incompressible fluid, under the shallow water and the Boussinesq assumption. In the vertical momentum equation the vertical accelerations are neglected, which leads to the hydrostatic pressure equation. In three-dimensional models the vertical velocities are computed from the continuity equation. The set of partial differential equations in combination with an appropriate set of initial and boundary conditions is solved on a finite difference grid resulting in a highly accurate, unconditionally stable solution procedure. The flow is forced by tide at the open boundaries, wind stress at the free surface, pressure gradients due to free surface gradients (barotropic) or density gradients (baroclinic). Source and sink terms are included in the equations to model the discharge and withdrawal of water. If the fluid is vertically homogeneous, a depth-averaged approach is appropriate. In such cases, the hydrodynamic module is able to run in two-dimensional mode using only one computational layer the equivalent of solving the depth averaged shallow water equations. Examples in which the twodimensional, depth averaged flow equations can be applied are tidal waves, storm surges, tsunamis, harbour oscillations (seiches) and transport of pollutants in vertically well-mixed flow regimes. Three-dimensional hydrodynamic modelling is of particular interest in transport problems where the horizontal flow filed shows significant variations in the vertical direction. This variation may be generated by wind forcing, bed stress, Coriolis force, bed topography or density differences. Examples are dispersion of waste or cooling water in lakes and coastal areas, upwelling and downwelling of nutrients, salt intrusion in estuaries, fresh water river discharges in bays and thermal stratification in lakes and seas. A.1 Physical Processes The Delft-3D FLOW model includes mathematical formulations that take into account the following physical phenomena:» Free surface gradients (barotropic effects)» The effect of Earth s rotation (Coriolis force)» Water with variable density (equation of state)» Horizontal density gradients in the pressure (baroclinic effects)» Turbulence induced mass and momentum fluxes (turbulence closure models)» Transport of salt, heat and other conservative constituents» Tidal forcing at the open boundaries» Space and time varying wind shear stress at the water surface» Space varying shear stress at the bottom 1

38 » Space and time varying atmospheric pressure on the water surface» Time varying sources and sinks (e.g. river discharges)» Drying and flooding of tidal flats» Heat exchange through the free surface» Evaporation and precipitation» Effect of secondary flow on depth averaged momentum equations» Lateral shear-stress at lateral walls» Vertical exchange of momentum due to internal waves» Influence of waves on the bed-shear stress (2D and 3D)» Wave induced stresses (radiation stress) and mass fluxes» Flow through hydraulic structures A.2 Assumptions Delft-3D FLOW solves the 2D (depth-averaged) or 3D non-linear shallow water equations derived from the three-dimensional Navier-Stokes equations for incompressible free-surface flow. The following assumptions and approximations are applied:» The depth is assumed to be much smaller than the horizontal length scale. For such small aspect ratios, the shallow water assumption is valid, which means that the vertical momentum equation is reduced to the hydrostatic pressure relation. The vertical accelerations are assumed to be small compared to the gravitational acceleration and are therefore not taken into account» The effect of variable density is only taken into account in the pressure term (Boussinesq approximation)» The immediate effect of buoyancy on the vertical flow in not considered. Vertical density differences are taken into account in the horizontal pressure gradients and in the vertical turbulent exchange coefficients. Applications of Delft-3D FLOW are restricted to mid-field and far-field dispersion simulations of discharged water» A dynamic online coupling between morphological changes and flow is possible» In a Cartesian frame of reference the effect of the Earth s curvature is not taken into account» In a Cartesian frame of reference the Coriolis parameter is assumed to be uniform. Optionally, a space varying Coriolis force can be specified. In spherical coordinates, the inertial frequency depends on the latitude» A slip boundary condition is assumed at the bottom and a quadratic bottom stress formulation is applied» The formulation for the enhanced bed shear stress due to the combination of waves and currents is based on a 2D flow field, generated from the velocity field near the bed using a logarithmic approximation» The equations of Delft-3D FLOW are capable of resolving the turbulent scales (large eddy simulation), but usually the hydrodynamic grids are too coarse to resolve the fluctuations. Therefore, 2

39 the basic equations are Reynolds-averaged introducing the so-called Reynolds stresses. These stresses are related to the Reynolds-averaged flow quantities by a turbulence closure model» The 3D turbulent eddies are bound by the water depth. Their contribution to the vertical exchange of horizontal momentum and mass is modelled through a vertical eddy viscosity and eddy diffusivity coefficient (eddy viscosity concept). The coefficients are assumed proportional to a velocity scale and a length scale. The coefficients may be specified (constant) or computed by means of an algebraic, k- L or k-ε turbulence model, where K is the turbulent energy, L is the mixing length and ε is the dissipation rate of turbulent kinetic energy» In agreement with the aspect ratio of shallow water flow, the production of turbulence is based on the vertical gradients of the horizontal flow. In case of small scale flow (partial slip along closed boundaries) the horizontal gradients are included in the production term» The boundary conditions for the turbulent kinetic energy and energy dissipation at the free surface and bottom assume a logarithmic law of the wall» The eddy viscosity is an-isotropic. The horizontal eddy viscosity and diffusivity coefficients should combine both the effect of 3D turbulent eddies and the horizontal motions that cannot be resolved by the horizontal grid. The horizontal eddy viscosity is generally much larger the vertical eddy viscosity» For large-scale flow simulations the tangential shear stress at lateral closed boundaries can be neglected (free slip). In case of small-scale flow partial slip is applied along closed boundaries» For large-scale flow simulations the horizontal viscosity terms are reduced to a bi-harmonic operator along coordinate lines. In case of small-scale flow the complete Reynold s stress tensor is computed. The shear stress at the sidewalls is calculated using a logarithmic law of the wall.» Delft-3D FLOW solves the long wave equation. The pressure is hydrostatic and the model is not capable of resolving the scales of short waves. Therefore, the basic equations are averaged in analogy with turbulence introducing the so-called radiation stresses. These stresses are related to the wave quantities of Delft-3D WAVE by a closure model» It is assumed that a velocity point is set dry when the actual water depth is below half of a userspecified threshold. If the point is set dry, then the velocity at that point is set to zero. The velocity point is set wet again when the local water depth is above the threshold. The hysteresis (time lag) between drying and flooding is introduced to prevent drying and flooding in two consecutive time steps. The drying and flooding procedure leads to a discontinuous movement of the closed boundaries at tidal flats» A continuity cell is set dry when the four surrounding velocity points at the sides of the cell are dry or when the actual water depth at the cell centre is zero» The flux of matter through a closed wall and through the bed is zero» Without specification of a temperature model, the heat exchange through the free surface is zero. The heat loss through the bottom is always zero» If the total heat flux through the water surface is computed using a temperature excess model, the exchange coefficient is a function of temperature and wind speed. The natural background temperature is assumed to be constant in space and may vary in time. In the other heat flux formulations the fluxes due to solar radiation, atmospheric and back radiation, convection and heat loss due to evaporation are modelled separately 3

40 » The effect of precipitation on the water temperature is accounted for A.3 Governing Equations In the vertical direction a σ coordinate system is used, which is defines as: z ζ z ζ σ = =, (A.1) d + ζ H where z the vertical coordinate in physical space ζ the free surface elevation above the reference plane (at z = 0 ) d the water depth below the reference plane H the total water depth, given by H = d + ζ At the bottom σ = 1 and at the free surface σ = 0. The σ coordinate is boundary fitted both to the bottom and to the moving free surface. The partial derivatives in the original Cartesian coordinate system are expressed in σ coordinates by the chain rule introducing additional terms. The flow domain of a 3D shallow water model is limited in the horizontal plane by sea and land boundaries and consists in the vertical direction of a number of layers. The number of layers is the same at every location in the horizontal plane, i.e., the layer interfaces are chosen following planes of constant σ. For each layer a set of coupled conservation equations is solved. The equations are formulated in orthogonal curvilinear coordinates. the velocity scale is in physical space, but the components are perpendicular to the cell faces of the curvilinear grid. The grid transformation introduces curvature terms in the equations of motion. The depth-averaged continuity equation is given by: ζ + t G ξξ 1 G ηη [( d + ζ ) U G ] ( d + ζ ) ξ ηη + G ξξ 1 G ηη [ V G ] η ξξ = Q (A.2) with Q representing the contributions per unit area due to the discharge or withdrawal of the water precipitation and evaporation. The momentum equations in ξ and η direction are given by: u + t G ξξ v u G 2 ξξ G u + ξ ηη G ξ v G ηη ηη u ω u + + η d + ζ σ fv = ρ 0 1 G ξξ ξ G ξξ ξ uv P + F + G ηη 1 ( d + ζ ) G η 2 ξξ + u ν σ σ V + M ξ (A.3) and 4

41 v + t G ξξ G u u 2 ξξ G v + ξ ηη G η v G ξξ ηη v ω v + + η d + ζ σ fu = ρ 0 1 G ηη η G ξξ uv P + F + η G ηη 1 ξ ( d + ζ ) G 2 ηη + v ν σ σ V + M η (A.4) Density variations are neglected, except in the pressure terms. gradients. The forces Reynold s stresses. Fξ and M ξ and P ξ and P η represent the pressure F η in the momentum equations represent the unbalance of horizontal M η represent the contributions due to external sources or sinks of momentum by hydraulic structures, discharge or withdrawal of water, wave stresses etc. The vertical velocity ω in the adapting σ coordinate system is computed from the continuity equation: ζ + t G ξξ 1 G ηη [( d + ζ ) u G ] ( d + ζ ) ξ ηη + G ξξ 1 G ηη [ v G ] η ξξ ω + = H σ ( ) q in q out At the surface the effect of precipitation and evaporation is taken into account. The vertical velocity ω is defined at the iso σ -surfaces, with ω being the vertical velocity relative to the moving σ -plane. It may be interpreted as the velocity associated with up- and down-welling motions. The physical vertical velocities w in the Cartesian coordinate system are not involved in the model equations. Computations of the physical vertical velocities is only required for post processing purposes and can be expressed in terms of the horizontal velocities, water depths and vertical ω velocity according to: w = ω + G ξξ 1 G ηη u G ηη H ζ σ + + v ξ ξ G ξξ H ζ H σ + + σ + η η t ζ t (A.5) (A.6) 5

42 Appendix B Project Data Sample of Scattered Data Used for Bathymetry Generation 6

43 Figure B-1 Sample Scattered Data Used for Bathymetry Generation 1

44 Appendix C Model Verification Time Series of Predicted, Observed and Modelled Water Elevation 1

45 Figure C-1 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Low Head (July 01-04, 2004)

46 Figure C-2 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Low Head (July 04-07, 2004)

47 Figure C-3 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Low Head (July 07-10, 2004)

48 Figure C-4 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Low Head (July 10-13, 2004)

49 Figure C-5 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Low Head (July 13-15, 2004)

50 Figure C-6 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Bell Bay (July 01-04, 2004)

51 Figure C-7 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Bell Bay (July 04-07, 2004)

52 Figure C-8 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Bell Bay (July 07-10, 2004)

53 Figure C-9 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Bell Bay (July 10-13, 2004)

54 Figure C-10 Verification of the hydrodynamic model: Comparison of predicted, observed and modelled water levels at Bell Bay (July 13-15, 2004)

55 Appendix D Hydrodynamic Results Discussion of Results Schematic Map Time Series Frequency Histograms of Current Magnitude and Direction Frequency Histograms Of Bed-Shear Stress Magnitude And Direction Tidal Orbits Threshold Current Speed for Motion 1

56 Figure D-1 Schematic map showing the location of numerical monitoring stations along the Tamar River 1

57 Figure D-2 Existing Conditions: Time history of bed shear stress at locations A,B and C

58 Figure D-3 Existing Conditions: Time history of bed shear stress at locations D,E and F

59 Figure D-4 Existing Conditions: Time history of bed shear stress at locations G and H

60 Figure D-5 Existing Conditions: Time history of current magnitude and direction at locations A, B and C

61 Figure D-6 Existing Conditions: Time history of current magnitude and direction at locations D, E and F

62 Figure D-7 Existing Conditions: Time history of current magnitude and direction at locations G and H

63 Current Direction (degrees T) Current Magnitude (m/s) Current Direction (degrees T) Current Magnitude (m/s) Figure D-8 Existing conditions: Frequency histograms of current magnitude and direction at monitoring stations A to F

64 Current Direction (degrees T) Current Magnitude (m/s) Current Direction (degrees T) Current Magnitude (m/s) Figure D-9 Existing conditions: Frequency histograms of current magnitude and direction at monitoring stations G to L

65 Current Direction (degrees T) Current Magnitude (m/s) Current Direction (degrees T) Current Magnitude (m/s) Figure D-10 Proposed wharf facility: Frequency histograms of current magnitude and direction at monitoring stations A to F

66 Current Direction (degrees T) Current Magnitude (m/s) Current Direction (degrees T) Current Magnitude (m/s) Figure D-11 Proposed wharf facility: Frequency histograms of current magnitude and direction at monitoring stations G to L

67 BSS Direction (degrees T) BSS Magnitude (N/m 2 ) BSS Direction (degrees T) BSS Magnitude (N/m 2 ) Figure D-12 Existing conditions: Frequency histograms of bed shear stress magnitude and direction at monitoring stations A to F

68 BSS Direction (degrees T) BSS Magnitude (N/m 2 ) BSS Direction (degrees T) BSS Magnitude (N/m 2 ) Figure D-13 Existing conditions: Frequency histograms of bed shear stress magnitude and direction at monitoring stations G to L

69 BSS Direction (degrees T) BSS Magnitude (N/m 2 ) BSS Direction (degrees T) BSS Magnitude (N/m 2 ) Figure D-14 Proposed wharf facility: Frequency histograms of bed shear stress magnitude and direction at monitoring stations A to F

70 BSS Direction (degrees T) BSS Magnitude (N/m 2 ) BSS Direction (degrees T) BSS Magnitude (N/m 2 ) Figure D-15 Proposed wharf facility: Frequency histograms of bed shear stress magnitude and direction at monitoring stations G to L

71 Figure D-16 Comparison of existing (red diamonds) versus post-construction (blue diamonds) tidal orbits: A, B, C and D

72 Figure D-17 Comparison of existing (red diamonds) versus post-construction (blue diamonds) tidal orbits: E, F, G and H

73 Figure D-18 Comparison of existing (red diamonds) versus post-construction (blue diamonds) tidal orbits: I, J, K and L