Measurement of Metocean & Other Parameters within Poole Harbour, Dorset, During Dredge Operations (09/11/05-22/02/06)

Transcription

1 A FINAL REPORT BY PARTRAC LIMITED: MAY 6 Measurement of Metocean & Other Parameters within Poole Harbour, Dorset, During Dredge Operations (9/11/5-22/2/6)

2 QUALITY CONTROL SHEET Publication title Client Ref: Version Measurement of Metocean & Other Parameters within Poole Harbour, Dorset, During Dredge Operations, (9/11/5-22/2/6) RNA/MD/ FINAL Report Date May 6 File Reference Prepared under the management of: Kevin Black Project Manager Reviewed and approved by: Peter Wilson Director Client Address: Engineering Department Harbour Office Poole Harbour Commissioners New Quay Road Hamworthy Poole Dorset BH15 4AF Dick Appleton (Harbour Engineer) Tel heng@phc.co.uk Contact Details: Ltd 141 ST James Road Glasgow G4 LT UK Kevin Black (Project Manager) Tel +44 () Fax +44 () kblack@partrac.com Web

3 EXECUTIVE SUMMARY Poole Harbour Commissioners (PHC) commissioned Ltd to acquire nearbed suspended sediment concentration (SSC), current speed and direction, bed elevation and significant wave height, at various sites within Poole Harbour, Dorset, during dredging operations (a period of 6 days). The locations of the monitoring sites together with their monitoring durations are summarised in Table 1, below. Table 1 Monitoring Site Details of the 4 marine monitoring locations and deployment periods Deployment Recovery Latitude Longitude BF3 9/11/5 12:15 16/12/5 7: BF4a 16/12/5 12:3 22/12/5 : BF4b 22/12/5 11:15 4/1/6 12: BF2 4/1/6 15: 9/2/6 9: BF3 9/2/6 12:3 22/2/6 12: A data recovery of 96% was achieved across the entire monitoring period. Individual data summaries for each of the discrete (monthly) monitoring periods have already been issued to PHC. Following cessation of monitoring activities PHC provided to a range of ancillary data (RoRo tide height, dredger activity including volume/mass dumped, cross-channel ferry activity, mean wind velocity and barometric pressure and water temperature). This report summarises this information and combines it with the hydro-sedimentological data obtained from the entire monitoring period, to provide a general overview of the metocean conditions and dredge activities during the dredge operations. The following conclusions from the metocean and dredging data have been derived: 1. The sediment transport within Poole Harbour is largely tidally driven. The majority of resuspension events can be clearly correlated to temporal variations in tidal current velocity. 2. The sediments that are recurrently resuspended, transported and deposited back onto the bed exist in the form of a mobile layer 5 to mm thick on the seabed. 3. Background (slack tide) concentrations of suspended sediment within Poole Harbour are 25 to 5 mgl -1 and there are no large or persistent departures from this concentration range over the monitoring period. Tidal currents alone can produce suspended sediment concentrations of up to ~4 mgl -1, notably towards the western extent of the monitoring area (site BF2). 1

4 4. There is bed resuspension on both Neap and Spring tides and this is indicated by cyclic changes in bed level. However, current velocities >~.4 ms -1 are necessary to suspend sediment to the turbidity measurement height (.5 m a.b.). 5. The influence of winds on sediment resuspension can be viewed on a frequency-magnitude basis. Persistent wind speeds (longer in duration than approximately 12 hours from a given direction) above ca. 6 to 7 ms -1 produce waves that can enhance sediment resuspension. A combination of persistent strong wind (speed > 6 to 7 ms -1 ) with Spring tides can give rise to suspended sediment concentrations of the order several hundred mgl -1, but the maximum observable suspended sediment concentration varies with location within the harbour. 6. Persistent wind activity generally gives rise to accretion at the seabed. This is likely due to the creation of a greater loading of suspended sediment by wave scouring and subsequent settling of this sediment mass to the bed. 7. The scour potential of waves depends on wind direction and this varies according to the monitoring location. 8. Waves induced by boat passage may give rise to intermittent but brief resuspension of bottom sediments. 9. Several instances of high siltation and accretion caused by forces/events other than normal oceanographic conditions were observed.. Surface buoys recording suspended sediment concentrations indicate generally lower surface values in comparison to bed frame measurements, although this view is a complex function of changing relative positions of the monitoring locations, as well as factors such as depth and sediment type. 11. Surface suspended sediment concentrations were observed to be consistently higher than nearbed concentrations during Weeks 7-8 ( ). This may be a function of dredge vessel activity and wind direction. 12. Water temperatures range from 2.73 C to C. Temperature fluctuates by up to ca. 2 C on an intra-tidal basis and these variations are most pronounced during Spring tides. No consistent correlation exists between mean daily temperatures and the Spring-Neap cycle. 2

5 CONTENTS EXECUTIVE SUMMARY 1 1. INTRODUCTION Background Field Sites and Equipment Deployment Summary 6 2. MARINE MONITORING DATA ACQUISITION Nortek Aquaprofiler Acoustic Profiler (flow velocity and significant wave height) Seapoint Optical Backscatter Sensor (suspended sediment concentration) NKE Altus Marine Altimeter (bed elevation) Aquatech Aqualogger (back-up suspended sediment concentration) Deployment Frame Sampling Interval Settings Data Units Calibrations QA 9 3. METEOROLOGICAL DATA ACQUISITION Meteorological Data Data Units FERRY ACTIVITY DATA Cross Channel Ferry Activity Dredge Vessel Activity RESULTS GENERAL SYNTHESIS Introduction Data Interpretation Considerations Data Synthesis CONCLUSIONS REFERENCES 26 3

6 APPENDICES Turbidity Sensor Calibration Graphs Weekly data summaries Time-Series Data for the total monitoring period Weekly Time-Series Data 44 4

7 1. INTRODUCTION 1.1 Background As part of their Environmental Impact Assessment of the Poole Harbour Approach Channel Deepening, Poole Harbour Commissioners (PHC) agreed a monitoring programme with relevant authorities and stakeholders. As part of this monitoring programme were contracted to provide and deploy a bed mounted frame to be sequentially located, for periods of approximately a month, at different locations within the Harbour. The frame, instrumented to measure suspended sediment concentration (SSC), (significant) wave height, current speed and direction and bed elevation, was deployed at 4 different locations between 9/11/6-22/2/6. Individual data summaries for each of these monitoring periods have already been issued to PHC. Following cessation of monitoring activities PHC provided to a range of ancillary data (RoRo tide height, dredger activity, cross-channel ferry activity, mean wind velocity and direction, barometric pressure and water temperature) with a view to integrating meteorological information to the marine monitoring data and then to relate these in a wider sense to commercial harbour activities, in particular to the activities of the dredging vessel[s]. This report summarises the metocean information from the entire monitoring period, combining it with the data provided on commercial and dredge vessel activities to provide an integrated view to PHC. 5

8 1.2 Field Sites and Equipment Deployment Summary Table 2 summarises the location of the marine monitoring sites and provides relevant information on the monitoring durations at each of these. An aerial view of the monitoring site locations is provided in Figure 1. Table 2 Details of the 4 marine monitoring locations and 5 deployment periods Monitoring Site Deployment Recovery Latitude Longitude BF3 9/11/5 12:15 16/12/5 7: BF4a 16/12/5 12:3 22/12/5 : BF4b 22/12/5 11:15 4/1/6 12: BF2 4/1/6 15: 9/2/6 9: BF3 9/2/6 12:3 22/2/6 12: SSC1 15/11/6 18: 24/2/6 : SSC2 15/11/6 18: 24/2/6 : Figure 1 Field site locations SSC1, SSC2, BF2, BF3, BF4a & BF4b, Poole Harbour, Dorset. 6

9 2. MARINE MONITORING DATA ACQUISITION 2.1 Nortek Aquaprofiler Acoustic Profiler (flow velocity, significant wave height & water temperature) The Aquadopp Acoustic Profiler measures the flow velocity profile in water using acoustic Doppler technology. It is designed for stationary applications and can be deployed on the seabed, on a mooring rig, on a buoy, or on any other fixed structure. It is an integrated instrument and includes all the parts required for a self contained deployment with data stored to an internal data logger. The wave spectrum is calculated using the PUV method (Nortek, 2) in which measured water pressure is used to estimate the wave height and the two horizontal velocity components U and V are used to calculate the wave direction. Significant wave height, H s, is approximately equal to the average of the highest one-third of the waves. Water Temperature is recorded on the internal logger via an accurate temperature sensor. 2.2 Seapoint Optical Backscatter Sensor (suspended sediment concentration) A Seapoint optical backscatter sensor (OBS) interfaced with the Aquaprofiler was used to record suspended sediment concentration at the same frequency as current data i.e. every 15 minutes. 2.3 NKE Altus Marine Altimeter (bed elevation) Altus is a high frequency, submersible recording acoustic altimeter. It is based on a 2 MHz transducer located centrally within the frame and at a fixed distance from the bed. A separate housing includes altimeter electronics, data logger, pressure sensor and power supply. 2.4 Aquatech Aqualogger (back-up suspended sediment concentration) An Aquatech Aqualogger suspended sediment sensor was included to provide a completely independent back-up turbidity sensor on the mooring frame. The AQUAlogger 2TY uses the industry-standard Seapoint optical sensor. The OBS has four switchable gain ranges and these can be pre-set by the user or automatically selected by the AQUAlogger software for maximum dynamic range encountered in field deployment conditions. 7

10 2.5 Deployment Frame The equipment was mounted on a bespoke stainless steel tripod seabed mooring frame, equipped with Kg of ballast, lifting shackles and a standard J- configuration mooring arrangement (Figure 2). The current velocity and optical suspended sediment sensors were mounted on horizontal cross-bars; an altimeter was fixed centrally within the frame in a rigid plastic housing at a fixed distance from the bed. A vertical sediment trap was attached to one of the frame legs to collect suspended sediment. Note the open area within the frame legs; this was a deliberate design feature that reduces flow turbulence and thereby facilitates collection of good quality bed level data. The various instruments mounted in the frame. Sediment Trap Altus Aqualogger Aquaprofiler 8

11 2.6 Sampling Interval Settings The Aquaprofiler was used to record current speed and direction, significant wave height and to log the SSC signal from the optical backscatter sensor (OBS, see Section 2.2). The Aquaprofiler was secured along one of the arms of the mooring frame (Figure 2) and programmed to take measurements at.5-.6m above the bed at 15 minute intervals for current data and SSC and for 17 minutes each hour for wave height. It was initially proposed to locate the Aquaprofiler at.25m above the bed, but prior field observations showed that this was too close as the frame tended to bed into the soft mud slightly on deployment. The Aqualogger backup suspended sediment concentration sensor was also programmed to acquire data every 15 minutes synchronously with the Aquaprofiler. The Altus was programmed to acquire bed elevation every 3 minutes and this interval was chosen in order to avoid acoustic interference between the instrument and the Aquaprofiler. The instruments were tested and functioning correctly prior to deployment. 2.7 Data Units All times are quoted in GMT (24hrs). All current directions are quoted in degrees relative to true north ( o T). The units of current flow speed are metres per second, suspended sediment concentrations are in milligrams per litre (mgl -1 ), significant wave height is in metres (m) and bed elevation is in millimetres from sensor (mm) or net vertical sediment deposition/erosion (mm). Water temperature is in degrees Celsius o C. 2.8 Calibrations The Aquaprofiler and the Altus were pre-calibrated by the manufacturer and checked by prior to deployment. The OBS was calibrated in the field by using five varying concentrations of native suspended sediment obtained from the sediment trap. The water samples were then filtered across. µm Nucleopore filter membranes to determine the dry mass concentration (units mgl -1 ) of suspended sediment. The calibration graphs for the OBS for each of the monthly deployment periods may be found in Appendix QA operate a Quality Management System which outlines methods of good practice, procedures for bottom and suspended sediment sampling, use of sediment traps, monitoring deployment methodologies and practical and logistical factors associated with field work that must be recognised. staff closely adhered to the guidance in this internal documentation through all field and laboratory monitoring, sampling, analysis and related work. 9

12 2.9.1 Data Loss Table 3 summarises the number of days during each monitoring period during which data was not acquired. The various reasons behind zero data return have been presented previously in the monthly reports. A data recovery of 94% was achieved. Table 3 Summary of the number of days of zero data return. Monitoring Site No. of days deployed Days of zero data return BF BF4a 6 BF4b 13 2* BF BF3 (#2) 13 Total (5.8%) * Altimeter data only

13 3. METEOROLOGICAL DATA ACQUISITION 3.1 Meteorological Data No meteorological data were collected directly by. PHC provided to (in electronic format) the following information: 1. Tide height at the RoRo ferry terminal. 2. speed in knots recorded at the PHC office. 3. direction in degrees true recorded at the PHC office. 3.2 Data Units All times are quoted in GMT (24hrs). speed has been transformed and is quoted in ms -1 (1 knot =.514 ms -1 ). direction is quoted as degrees relative to true north ( o T). Note marine current direction corresponds to the direction towards which the current is flowing, whereas in meteorology wind direction refers to the direction from which the wind is blowing. Tide height at the RoRo Ferry terminal is metres above Chart Datum. 11

14 4. FERRY ACTIVITY DATA 4.1 Cross Channel Ferry Activity The activities of cross channel ferries Barfleur (Length m and Draft 5.4m) and Coutances (Length m and Draft 4.51m) were recorded by the Poole Harbour Office and are reported by time entering the harbour and time exiting the harbour. 4.2 Dredge Vessel Activity The activities of dredge vessels Volvox Scaldia (Length 85.81m and Draft 3.94m), HAM311 (Length 94.54m and Draft 5.68m) and Waterway (Length 97.7m and Draft 6.58m) were recorded by the Poole Harbour Office and are reported by time entering the harbour and time exiting the harbour. This is an approximation of the active dredging period in the harbour. Extended periods in the harbour related to non-dredging periods have been removed from the data set. 12

15 5. RESULTS The results are presented in Appendices 1 to 4. Appendix 1 contains the calibration data for the optical backscatter turbidity sensors at each of the monitoring locations. Appendix 2 contains data in the form of weekly summary tables of all parameters measured, including dredge vessel and ferry activities. Appendix 3 presents time-series data for the entire monitoring period for current velocity, RoRo berth tide height, suspended sediment concentration, bed level, water temperature and wind speed and direction. Appendix 4 presents weekly time-series of all parameters measured, including dredge vessel and ferry activities. There are 16 panels in total. 13

16 6. GENERAL SYNTHESIS 6.1 Introduction Poole Harbour is the second largest natural harbour in the world. The harbour is an expansive shallow marine setting in which the natural sediment regime is a function of water depth, tidal phase and surface wind wave action. The water movements associated with the daily tides and wind-generated wave action can give rise to friction at the seabed which can suspend bottom sediments. Once in suspension in the water column, these sediments can be transported horizontally to other parts of the Harbour, where they can settle back to the seabed if the tidal currents slow and if the wave action is negligible. These processes collectively form the sediment cycle (Figure 3) and as the name suggests most shallow marine environments display natural, recurring cycling of sediment. The surficial layer of bottom sediments is the region principally involved in the sediment cycle. The layer of sediment which is recurrently resuspended, transported and deposited (and frequently undergoes consolidation) is commonly referred to as the active layer and can range in thickness from mm to cm, or (in the case of fluid muds) decimetres to metres (Eisma, 1992). Only severe storms are sufficiently powerful to erode the bed beneath the active layer. The thickness of the active layer is a function of sediment supply, sediment properties and the range or spectrum of nearbed flow velocities which the bed regularly experiences. Figure 2 The Sediment Cycle 14

17 The transport path[s] that the sediments take and the location of the areas where they may finally deposit and accumulate over the longer term, is dependent upon the location from which they derive, the particle physical properties (e.g. size, settling velocity) and the general and residual tidal circulation pattern (Eisma, 1992). Together the processes associated with the sediment cycle and the residual tidal circulation pattern govern the morphological form of the embayment (Pethick, 1996), which may or may not be in equilibrium over medium to longer timescales. In addition to the natural cycling of sediment, anthropogenic factors such as boat and ship activities, fishing, dredging, coastal engineering and aquaculture, can influence the sediment regime of a coastal environment. Generally, where these activities add to or increase the level of energy in the water column, or where they directly destabilise the seabed (as in the case of dredging), then the consequence can often be to introduce more sediment into the water column than would ordinarily be there due to natural processes alone. 6.2 Data Interpretation Considerations In this study, a monitoring programme was commissioned to observe and quantify both the natural sediment regime at specific nearshore coastal locations within Poole Harbour and any potential influences on the natural sediment regime of dredge activities associated with deepening of the main channel. A monitoring rig was specially constructed for this purpose (see Section 2) and measurements of tidal current strength and direction, water depth, water turbidity (clarity) and bed level were collected at.5m above the bed for a period of 6 days. A data return of 94% was achieved. The height above the bed of.5m was chosen because the instruments remain sufficiently far from the bed if the frame sinks slightly upon deployment and it is the optimum height from which to make bed level measurements. The data collected are considered to be of high quality. The Aquadopp instrument provides consistently good measures of tidal current speed and direction, but is limited in its ability to measure surface waves in such a shallow water column:- frequently low Spring tide water depths often only just covered the sensor and the appropriate data could not therefore be acquired. The optical turbidity sensors also performed reliably and calibrations conducted each month using sediments retained within the frame-mounted suspended sediment traps provided strong linear correlations (Appendix 1) for the range of suspended sediment loadings observed in the Harbour. Data from the altimeter (i.e. bed level data) requires careful analysis. Strictly, bed level measurements should be made from an immovable support (e.g. a harbour wall), wherein any changes in the distance-to-bed measurement can be attributed solely to sediment deposition or erosion. Of course, this is not possible in this study where offshore measurements are required. One must recognise that the frame can sink and that this may then create an illusion of sediment deposition (Bassoulett et al., 1992). Large (.25 m in diameter) plastic feet were fitted to the frame in order to limit sinkage of the frame. Use of ancillary data such as tilt and pitch/roll (which the Aquadopp instrument collects at a resolution of.1 every 15 minutes) is important in judging whether the frame has moved or whether the bed level data collected reflects real sedimentation events. Sudden, large movements 15

18 of the bed frame are readily seen in the altimeter data as step-adjustments in bed level and it is unlikely that these would be caused by natural oceanographic conditions. In addition, it is also possible to inspect the acoustic backscatter intensity of the altimeter. If the frame settles or moves, it is unlikely that this is equal across the tripod legs and thus the sensor is no longer perpendicular to the bed. This is analogous to mounting an echo-sounder oblique to the bed. Some reflected acoustic energy is lost since the optimal line-of-sight conditions are not present and this is evident in the backscatter intensity data. Data associated with low intensity values can be rejected. Our experience was that the frame did settle into the bed in Poole Harbour following deployment, but on the whole remained vertically stable thereafter. The frame was designed specifically to be of low drag and therefore not susceptible to mechanical disturbance by strong tidal currents. Further, in estuaries there is frequently, as described in Section 6.1, an active sediment layer which is recurrently resuspended and deposited on the tidal frame. Most usually the altimeter when logged at high frequency (e.g. every 3 minutes) provides data in the form of an envelope i.e. the difference between the bed level when devoid or semi-devoid of the active layer (when it becomes resuspended) and the bed level when the active layer rests on the bed proper. In view of the highly temporal variability in the active layer thickness it can be problematic defining net accretion with accuracy. The derived values in this report whilst internally consistent should therefore be treated with caution. Finally, the field monitoring was measured at a single point in space (the socalled Eulerian frame) and yet the daily running of the tide can transport sediments from elsewhere within the harbour to the fixed monitoring location (as well as remove sediments from the frame environ). It can thus sometimes be difficult to separate local sedimentation effects from far-field sedimentation effects. This must be borne in mind when evaluating the time-series data Van Oord Surface Suspended Sediment Concentration Data A 3 rd party (Van Oord) collected sea surface suspended sediment concentration data using 2 telemetric buoy systems. These were located at positions referred to only as SSC1 and SSC2 (no co-ordinates were provided). SSC1 was close to location BF2, whereas SSC2 was close to location BF3. were provided the time-series data from SSC1 and SSC2. A single calibration was applied to the raw data values using samples of suspended sediment collected using a hand-held water sampler. The equation used was: Suspended sediment concentration (mgl -1 ) = 1.1xFTU Where FTU are formazin turbidity units (the units of the sensor output) The data from these buoy deployments are presented and discussed here. Whilst we are in a position to comment upon any trends in sediment concentration, we cannot substantiate the absolute (numerical) values suspended sediment concentration and these are likely to be less than corresponding data measured.5 m above the bed on the monitoring frame. 16

19 6.3 Data Synthesis The following is a synthesis of the data by monitoring location in chronological order together with several notes addressing tide height measurements, the nature of the mobile layer, seawater temperature variability and the 3 rd party turbidity data. The syntheses are intended to provide a general, rather than highly specific, overview of the nature and variability of the hydro-sedimentological conditions and vessel data at each of the monitoring sites. Where reference is made to a summary panel (Appendix 1) we use the notation (Week 1), for example. speed is frequently denoted by u or u max (indicating the maximum recorded current speed) and the term turbidity is used in a colloquial fashion to refer to suspended sediment concentration measured in mgl -1. Waves are described generically in terms of height in metres, but this specifically relates to the highest one third of waves measured (H sig ; see Section 2.1). The abbreviation a.b. refers to above the bed. The term event is used to refer to instances where turbidity is seen to peak to a maximum over a short amount of time, or where winds become strong and are associated with the creation of waves. The phrase tidally dominated or tidally modulated generally refers to sediment movements (e.g. suspended sediment concentration or bed level) which are judged to be driven by tidal currents A Note on Tidal s and RoRo Tide Height Measurements In estuaries generally there are predictable relationships between current speed and direction measured at a point and the stage (height) of the tide. In this report we present data collected from the RoRo berth, which is naturally not the same measurement location as the instrument frame. Because of this, although the general correlation of measured current velocity and recorded tide is good, there are some notable differences and these are associated with lag effects and local effects at the measurement rig such as bathymetry and wind A Note of Bed Level Data and the Existence of a Benthic Mobile Sediment Layer There is consistent evidence throughout the monitoring period at all sites of a mobile sediment pool that exists ephemerally on the seabed (see Section 6.1) according to the oceanographic and meteorological conditions. This layer is between 5 to mm thick. The bed level varies regularly as a function of the tide phase with periods of short-lived accretion during slack tides followed by periods of erosion during the running tide. During Neap tides, when the maximum current speeds are generally less than about.4 ms -1, tidal modulation of the mobile layer is observed even though there may be no corresponding peaks in suspended sediment concentration measured.5 m a.b. Good examples may be found in Week 1 ( : to :; site BF3) and Week 11 ( to :; site BF2) In contrast, similar variability is observed in bed level for u>.4 ms -1, but in this case there are correlatable and synchronous variations in suspended sediment concentration (e.g. Weeks 9 and, site BF2). This simply reflects the reality that higher current speeds produce sufficient shear in the water column to mix this sediment upward to the level of the optical turbidity sensors (.5 m a.b.). During Neap tides this does not happen, even though there is some sediment transport at the bed. 17

20 6.3.3 Seawater Temperature Variability The range of water temperatures measured was 2.73 C to C (see Tables in Appendix 2). The temperature time-series for the entire monitoring period is shown in Appendix 2. Both long-term (Spring-Neap) and short term (intra-tidal) changes in water temperature are apparent. Generally water temperature falls as tide ebbs, although during Neap tides (e.g. Week ) this pattern of change is not as pronounced. In some cases e.g. Week 3 the observed change is ~2 C. The strong link to tide presumably reflects consistent differences in the temperature of the offshore waters and those within the harbour. Although intra-tidal variability in water temperature is linked to the Spring-Neap tide cycle, there appears to be no consistent relation between the absolute or average daily water temperature and the Spring-Neap cycle. This is most clear from the entire temperature time-series (Appendix 2). The detailed reasons behind the observed temperature changes are beyond the scope of this report rd Party (Van Oord) Surface Turbidity Data The data from Van Oord s surface monitoring buoy is presented with all other time-series data in the weekly summary panels (Appendix 4). A complete dataset was obtained from the SSC1 unit to ; the data record from SSC2 was corrupted on at 12:hrs and therefore no data are presented after this time. Generally it is to be expected (in natural systems) that any correlation with framemounted data should show similar peaks and troughs in turbidity and that surface measurements would be less that bottom measurements. However, in shallow, tidal embayments exposed to wave action such as Poole Harbour, the water column can become well-mixed (especially during Spring tides) and surface and bottom measures of turbidity can become very similar in magnitude. In addition, surface input, in this study from dredge vessel overflow, can distort any natural vertical sediment distribution patterns. In general terms the three time-series are in phase i.e. peaks and troughs of the surface and bed frame records are coincident (e.g. Week 3). This is especially obvious during Spring tides when there is strong tidally driven sediment transport, or during periods of strong winds (e.g. Week ). During periods of weaker or Neap tides (e.g. Week 3, Week 14) this phase similarity is not so pronounced. A limited quantitative interpretation can be provided on account of the 3 rd party nature of the data. Notwithstanding this, the values of suspended sediment concentration derived from the Van Oord calibration are of the same order as those recorded by the bed frame and therefore some confidence exists in the buoy datasets. Generally, the bed frame turbidities are usually higher than surface values, although this view is complicated by temporally changing relative positions of the monitoring location, as well as factors such as depth and sediment type. Of the two buoy monitoring stations, the recorded turbidities at SSC1 (west) are closer in numerical value to the bed frame positions and this may reflect the generally more dynamic nature of the tides at SSC1 and a greater sediment flux. 18

21 A distinctive reversal of the expected vertical suspended sediment concentration gradient occurs during Weeks 7-8 ( ); surface suspended sediment concentrations recorded by SSC2 (East) rise uncharacteristically above the values for both SSC1 (West) and the bed frame by 5 to mgl -1 through to Week 8 (3.12.5). This is the only period during which this top-bottom reversal in suspended sediment concentrations occurs and is persistent. This period is coincident with dredging activity at B2 and D3 and the turning basin. One of the principal means that surface turbidities can exceed bottom measured turbidities is through a surface input of sediment i.e. potentially from overflow from dredging activities. It is interesting to note that this period is also one of dominantly northwesterly and northeasterly winds, which may act to transport turbid surface waters south toward the SSC2 monitoring station Site BF3 (1 st Deployment) Site B3 was monitored during Week 1 Week 6. The general pattern of change during this monitoring period would appear to be related principally to natural processes and natural cycling of sediment. During the first week (Week 1) current speeds typically are lower (generally u max <.4 ms -1 ), which is a function of Neap tides and nearbed turbidity is generally <5 mgl -1 (Table 4). However a single event is notable on with suspended sediment concentrations rising to ca. 167 mgl -1 ; inspection of both the wind record and wave height time-series suggests that the cause of this event is likely due to an increase of wind speed from the southwest above about 7 ms -1 and generation of waves.5-. m in height. There is simultaneous scouring of the seabed of ca. mm. There were no dredge activities during this week and therefore this factor can be discounted here. Through Week 2 (as the tide moves onto Springs), a correlation begins to appear in the turbidity-current velocity data, with tidal cycles generating regular peaks in turbidity of mgl -1 or more over background (slack water) values of -4 mgl -1. Although dredge activities had commenced, background suspended sediment concentrations do not differ substantially from the first week. As the tide finishes the Spring cycle (Week 3) the correlation between current velocity and turbidity disappears. speeds typically are <7 ms -1, current speeds rarely reach.4 ms -1 and turbidity is low (<5 mgl -1 ) for a larger proportion of the time. It is interesting to note that wind speeds of 6 to 8 ms -1 were recorded on producing some small waves (height <. m); however, there was no observed bed resuspension event as there was during Week 1. The reason for this may relate to the fact that wind speeds were higher and persisted for a longer period during Week 1, indicative of a frequency-magnitude threshold for wind influence. Dredge activity remained reasonably constant throughout Weeks 2 and 3. In Week 4 several notable events occurred. From the wind speeds at first from the west then veering to south, picked up appreciably, rising to ms -1 on the These winds produce waves with significant wave heights approaching.6 m. Further, the maximum current velocity increased during the week from.44 to.68 ms -1 as a function of both increasing tide range and strong west-southwest winds. Peaks in turbidity approaching 4 mgl -1 were recorded and the temporal variability of these peaks correlates reasonably closely with the temporal pattern of wind speed. During this windy period the dredger switches from the Volvox Scaldia to the Ham 311, but the dredge volumes are generally 19

22 similar. It is interesting to note that bed level during this windy period reflects a general accretion of 12 mm rather than erosion unlike Week 1. This accretion is interpreted to be a function of the generally greater loading of sediment in the water column created by the wave action. Waves are powerful eroding agents and in Poole Harbour the broad and shallow embayment provides a significant opportunity for wave resuspension across a very large area; subsequently this sediment mass can be redistributed around the Harbour by the tidal circulation. At some stage this material will settle to the bed and a greater suspended sediment concentration can give rise to a thicker deposited layer. For the remainder of the record at this site, the correlation between tidal current velocity and turbidity persists with maximum values reaching 4 mgl -1 (Week 4) and 367 mgl -1 (Week 6). The average bed level remained around + mm (although regular tidal erosion-deposition is apparent), indicating that the storm deposit retained some integrity and was not washed out. speeds were generally low (<4 ms -1 ) and it is interesting to observe that increased winds (~6 to 8 ms -1 ) around produce negligible wave action and no difference to water column turbidity. This is likely owing to the fact that the wind speeds were on the cusp of those necessary to induce sediment resuspension and were not sufficiently persistent from a single direction (the wind swings from 1 to 355 over 24 hours). In fact, a closer inspection of the time-series of current velocity and turbidity shows that turbidity decreases throughout the morning of , most likely because u max drops below.4 ms -1. Throughout Week 5 dredge activity was increased, with consequential increased dredge volumes (Table 8), with both the Volvox Scaldia and Ham 311 operating continuously Site BF4a Site B4a was monitored during Week 6 Week 7. The monitoring frame was deployed on the margin of the navigation channel for a brief period only ( ). The seabed at this location consists of sands rather than fine-grained silts. Although BF4a was monitored for a short period only, it represents the closest physical measurement point to dredge activities and ferry passage in the entire monitoring period. Thus, if either of these anthropogenic influences gives rise to additional sediment loadings in the water column, then it should be observable in the data. Unfortunately, quality data on bed level was not collected and our conclusion following examination of ancillary data was that the frame had shifted (see Section 6.2). The tilt data indicated this to be the case directly and, further, the altimeter data indicated up to 1 mm of sediment accumulation with no concomitant increase in suspended sediment concentrations as one would expect. This data is not shown in the Week 6 panel. However, useful data on turbidity and current velocity was obtained. There appears a weak, tidally-forced resuspension signal in the turbidity time-series with peaks in suspended sediment concentration of 5 8 mgl -1 and occasional maxima of ca. 157 and 184 mgl -1.

23 The dredge and ferry activities were operational throughout this monitoring period, with the Ham 311 and Waterway vessels active and the cross-channel ferry Barfleur running. These larger turbidity peaks may be a function of vessel passage/dredge excavation if they sailed or operated especially close to the northern flank of the channel; however, these peaks are more likely a function of Spring tidal currents. Waves were recorded during this period (. to.19 m), but since there is no appreciable wind, these waves may, in fact, be caused by boat passage. It is difficult to separate these two influences, but regardless of the cause of these peaks, resuspension of the bed sediment is brief and turbidity rapidly decreases to background levels (ca. 4 to 5 mgl -1 ) Site BF4b Location BF4b was further inshore on a siltier site and to the north of site BF4a. The deployment began mid-week during Week 7, continued through Week 8 and into Week 9. The general pattern of change during this monitoring period was one of low currents (u max <.4 ms -1 ) and low turbidity (mean value ca. 5 mgl -1 ) for a period of about 9 days during Neap tides, followed by a period of 5 days in which both wind speeds and tidal currents were stronger (Springs) and turbidity was higher. There is a notable peak in suspended sediment concentration (maximum 336 mgl - 1 ) from 4: hrs on to 17:3 hrs on (Week 7) and a corresponding greater sediment deposition (6 mm) and yet a close inspection of all time-series records does not reveal any linkage to any hydro-sedimentological forcing. The dredge record indicates that this was a time of peak dredging activity (75,189 m 3 ; Table 12) and therefore it is possible that this signal in the turbidity and bed level records may be associated with dredge activity. A significant wind event occurred during Week 8. This started on was characterised by frequent and persistent southerly-south westerly winds in excess of 7 ms -1 with maximum speeds of ms -1 recorded on These stronger winds produced waves up to.22 m in height. The wind event coincided with Spring tides in which current speeds in excess of.5 to.6 ms -1 were recorded. Turbidity values were regularly above 15 mgl -1 and periodically rose to over 25 mgl -1 (maximum mgl -1 ). Over the period of higher winds, there was a gradual net accretion of the seabed of the order 5- mm. This pattern of net accretion following energetic wind events was also seen at site BF3. 21

24 6.3.8 Site BF2 Site BF2 is a shallow location in the western area of Poole Harbour. It is generally a site of naturally stronger tidal currents (u max.85 ms -1 ), slightly elevated background turbidity levels (6 to 7 mgl -1 ) in comparison to other sites but far greater maximum turbidity (values approach 3 to 4 mgl -1 under non-wind conditions). This may be a function of its proximity to the broad shallow basins farther west which can act as source areas for sediment. The record at BF2 extends from Weeks 9 to 14. The sediment transport at site BF2 is strongly tidally driven; except when the tide range measured at the RoRo berth is <~.6 to.8 m, there is a strong co-variation of tidal current velocity, suspended sediment concentration and bed level. There is considerably greater variability (data scatter) in the bed level record and this is thought to be a function of the greater tidal current velocities characteristic of this site, which are observed to be more temporally variable (less steady) than other sites. The dominant feature of the record at this site is a wind event in Week. There are 3 periods of windier conditions where wind directions are dominantly 16 to 2 and mean wind speeds exceeded 6 ms -1, reaching a maximum speed of 12.3 ms -1. In each case winds of this magnitude produced waves ranging.4 to.22 m high. However, these wind-wave conditions do not, in fact, appear to modulate the peak suspended sediment concentrations, which under non-windy conditions (e.g. Week 9) can approach 3 to 4 mgl -1 through tidal resuspension alone. The reason for this is not clear but may be related to the wind direction and the sheltering of the site afforded by headland to the south of the site. However, during this time there was a period of ~ 9 days accretion of ca. mm at the seabed. At the end of Week much of this layer of sediment is removed, possibly by wave scour, although then in Week 11 a gradual period of accretion begins once again to build the sediment layer on the seabed. This may be a function of a decreasing tide range and consequently reducing current velocities: weaker currents will remove less sediment. Although there is considerable variability (scatter) in the bed level data, a general period of limited bed erosion occurs in Week 12, probably related to the increasing tide range and current velocities. This is followed by a general accretion in Week 13. In each case, the amount of sediment eroded or deposited is of the order 5 to mm. These patterns of change reflect a strongly tidally driven, medium term sediment redistribution processes with the seabed acting at different times as both a source and sink for sediment. There are two instances in the bed-level record (in Week 11 and Week 13) where accretion rates appear rather higher than the general trend for about a day and yet there appears to be no clear metocean reason for this. In Week 11 this amounts to ca. 5 mm and in Week 13 this amounts to ca. mm of additional sediment. The dredge activity record shows that in Week 11 the Ham 311 ceases operation and in Week 13 the Ham 311 begins operations, but it is not clear how these may have influenced or dominated the observed sediment deposition. 22

25 6.3.9 Site BF3 (2 nd Deployment) Site BF3 was re-occupied on the suggestion of PHC from mid-week 14 through to the end of the monitoring period (Week 16). During the first 4 days, the site was very weakly tidal i.e. although values of u max reach.55 ms -1 there is only very limited, concomitant sediment resuspension with suspended sediment concentration values consistently < 5 mgl -1. There is a spike in turbidity of 132 mgl -1 on , which may be a function of a brief increase in wind velocity and change in wind direction from easterly to southwesterly. A wind event beginning on during which wind speeds reached ca. 16 ms - 1 and waves approached.25 m height, was observed to cause a peak in suspended sediment concentration of 172 mgl -1. Initiation of this resuspension event appears to have occurred when wind speeds reached 6 to 7 ms -1 which reflects generally the wind speed threshold for sediment resuspension found for other sites. Thereafter (during Week 15) the system became more strongly tidal, with obvious correlations of suspended sediment concentration with current velocity, principally due to the increasing tide range. Through Weeks 14 and 15 there was gradual net accretion at the seabed, both prior to and following the wind event described above. There is considerable tidally driven variability (approx. mm) and this sediment is regularly resuspended and deposited, but of the order mm of sediment had accumulated by (7 days). During this monitoring period the dredger Ham 311 was working continuously and both the cross-channel ferries were operating normally. 23

26 7. CONCLUSIONS The following conclusions from the metocean and dredging data have been derived: 1. The sediment transport within Poole Harbour is largely tidally driven. The majority of resuspension events can be clearly correlated to temporal variations in tidal current velocity. 2. The sediments that are recurrently resuspended, transported and deposited back onto the bed exist in the form of a mobile layer 5 to mm thick on the seabed. 3. Background (slack tide) concentrations of suspended sediment within Poole Harbour are 25 to 5 mgl -1 and there are no large or persistent departures from this concentration range over the monitoring period. Tidal currents alone can produce suspended sediment concentrations up to ~4 mgl -1, notably towards the western extent of the monitoring area (site BF2). 4. There is bed resuspension on both Neap and Spring tides and this is indicated by cyclic changes in bed level. However, current velocities >~.4 ms -1 are necessary to suspend sediment to the turbidity measurement height (.5 m a.b.). 5. The influence of winds on sediment resuspension can be viewed on a frequency-magnitude basis. Persistent wind speeds (longer than about 12 hours from a given direction) above ca. 6 to 7 ms -1 produce waves that can enhance sediment resuspension. A combination of persistent strong wind (speed > 6 to 7 ms -1 ) with Spring tides can give rise to suspended sediment concentrations of the order several hundred mgl -1, but the maximum observable suspended sediment concentration varies with location within the harbour. 6. Persistent wind activity generally gives rise to accretion at the seabed. This is likely due to the creation of a greater loading of suspended sediment by wave scouring and subsequent settling of this sediment mass to the bed. 7. The scour potential of waves depends on wind direction and this varies according to the monitoring location. 8. Waves induced by boat passage may give rise to intermittent but brief resuspension of bottom sediments. 9. Several instances of high siltation and accretion caused by forces/events other than normal oceanographic conditions were observed.. Surface buoys recording suspended sediment concentration indicate generally lower surface values in comparison to bed frame measurements, although this view is a complex function of changing relative positions of the monitoring locations, as well as factors such as depth and sediment type. 24

27 11. Surface suspended sediment concentrations were observed to be consistently higher than nearbed concentrations during Weeks 7-8 ( ). This may be a function of dredge vessel activity and wind direction. 12. Water temperatures range 2.73 C to C. Temperature fluctuates by up to ca. 2 C on an intra-tidal basis and these variations are most pronounced during Spring tides. No consistent correlation exists between mean daily temperatures and the Spring-Neap cycle. 25

28 8. REFERENCES Bassoulett, P., Le Hir, P., Goulean, D. and Robert, S., 2 Transport over an intertidal mudflat:field investigations and estimations of fluxes within the Baie de Marennes-Oleron (France). Continental Shelf Research, Eisma, D., 1992 Suspended Matter in the Aquatic Environment, Springer- Verlag, pp. Pethick, J., 1996 The geomorphology of mudflats. In Nordstrom, K. and Roman, C.T., (Eds.) Estuarine Shores: Evolution, Environments and Human Evolution, Wiley, pp Nortek 2, Wave Measurements using the PUV method, Technical Note 19, December 15, 2, Doc. No. N

29 APPENDICES 1. Turbidity Sensor Calibration Graphs 2. Weekly Data Summaries 3. Time Series Data for the Total Monitoring Period 4. Weekly Time-Series Data 27

30 1. TURBIDITY SENSOR CALIBRATION GRAPHS The OBS was calibrated in the field for each deployment by using five varying concentrations of native suspended sediment obtained from the sediment trap from each site. The water samples were then filtered across. µm Nucleopore filter membranes to determine the dry mass concentration (units mgl -1 ) of suspended sediment. The calibration graphs for each deployment of the OBS can be seen in Figures 4-8. Figure 3 OBS calibration graph including correlation coefficient (R 2 ) for site BF3 OBS Calibration Graph for Monitoring Site BF3 1 1 OBS Output Reading y = x R 2 = Suspended Sediment Concentration (mgl -1 ) Figure 4 OBS calibration graph including correlation coefficient (R 2 ) for site BF4a 275 OBS Calibration Graph for Monitoring Site BF4a OBS Output Reading y = 3.678x R 2 = Suspended Sediment Concentration (mgl -1 ) 28

31 Figure 5 OBS calibration graph including correlation coefficient (R 2 ) for site BF4b OBS Calibration Graph for Monitoring Site BF4b OBS Output Reading y = x R 2 = Suspended Sediment Concentration (mgl -1 ) Figure 6 OBS calibration graph including correlation coefficient (R 2 ) for site BF2 OBS Re-Calibration Graph for Monitoring Site BF2 1 1 OBS Output Reading y = 44.9x R 2 = Suspended Sediment Concentration (mgl -1 ) 29

32 Figure 7 OBS calibration graph including correlation coefficient (R 2 ) for site BF3 (2 nd Deployment) OBS Calibration Graph for Monitoring Site BF3 (2nd Deployment) OBS Output Reading y = x R 2 = Suspended Sediment Concentration (mg -1 ) 3

33 2. WEEKLY DATA SUMMARIES Table 4 Week 1 BF3 Data Summary Week 1 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 9.73 Net Erosion of SW to NW mm Max o to 27 o 2336 Table 5 Week 2 BF3 Data Summary Week 2 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 5.69 Net Accretion NW to NE. of 1.64 mm Max o to 27 o

34 Table 6 Week 3 BF3 Data Summary Week 3 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net NW to NE Min 5.24 Accretion to NW.2 of 4.8 mm Max o to 2 o Table 7 Week 4 BF3 Data Summary Week 4 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net Accretion NW to S to Min 5.24 of SW.2 mm Max o to 27 o

35 Table 8 Week 5 BF3 Data Summary Week 5 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net NW to SE Min 5.24 Accretion to NW.7 of 2.44 mm Max o to 25 o Table 9 Week 6 BF3 Data Summary Week 6 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 5.24 Net Accretion NW. of 2.86 mm Max o to 26 o

36 Table Week 6 BF4 Data Summary Week 6 BF4a Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min Net Accretion NW.7 of.81 mm Max o to 16 o Table 11 Week 7 BF4a Data Summary Week 7 BF4a Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 13.3 Poor Data Return SW.5 Max o to 3 o

37 Table 12 Week 7 BF4b Data Summary Week 7 BF4b Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 3.59 Net Erosion of SW mm Max o to 165 o Table 13 Week 8 BF4b Data Summary Week 8 BF4b Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 2.12 Net Accretion NW to NE.2 of 2. mm Max o

38 Table 14 Week 9 BF4b Data Summary Week 9 BF4b Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net WSW to Min 4.5 Accretion NE. of 1.64 mm Max o to o 8431 Table 15 Week 9 BF2 Data Summary Week 9 BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net WSW to Min 17. Erosion of NE. 4.9 mm Max o to 3 o

39 Table 16 Week BF2 Data Summary Week BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net Min 9. Accretion of SW / SE.2 Max mm o to o Table 17 Week 11 BF2 Data Summary Week 11 BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min Net Accretion SW / NW.2 of 1.23 mm Max o to o

40 Table 18 Week 12 BF2 Data Summary Week 12 BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net Min.27 Accretion of NE.2 Max 24.3 mm o to 3 o 815 Table 19 Week 13 BF2 Data Summary Week 13 BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 8.25 Net Accretion NE / NW. of.53 mm Max o to o

41 Table Week 14 BF2 Data Summary Week 14 BF2 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net WNW to Min 4.75 Erosion of SW mm Max o to 335 o 7657 Table 21 Week 14 BF3 Data Summary Week 14 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Net WNW to Min 2.7 Accretion SW. of 2. mm Max o to 26 o

42 Table 22 Week 15 BF3 Data Summary Week 15 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min 4.42 Net Accretion NW to ESE.8 of 7.35 mm Max o to 27 o Table 23 Week 16 BF3 Data Summary Week 16 BF3 Data Summaries Suspended Sediment (mgl -1 ) Relative Change in Bed Elevation Tide (m CD) Temp ( C) Wave Height (m) (Deg True) Dredge Disposal Volumes (m 3 ) Average Min Net Accretion E. of 4.9 mm Max o to 27 o 18 4

43 3. TIME-SERIES DATA FOR THE TOTAL MONITORING PERIOD 41

44 14 12 Water Temperature ( C) /2/6 /2/6 13/2/6 6/2/6 27/2/6 /2/6 13/2/6 6/2/6 27/2/6 /2/6 13/2/6 6/2/ PHC\SSC\ Monitoring Station Water Temperature ( C) & RoRo Tide Height (m above CD) 5/12/5 12/12/5 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 23/1/6 3/1/6 Tide Temperature Date at Poole Harbour Office 5/12/5 12/12/5 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 23/1/6 3/1/6 14/11/5 21/11/5 28/11/5 14/11/5 21/11/5 28/11/5 Tide Height (m CD) 7/11/ Date at Poole Harbour Office 5/12/5 12/12/5 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 23/1/6 3/1/6 14/11/5 21/11/5 28/11/5 (Degrees True) 7/11/ Date 7/11/5

45 6/2/6 13/2/6 /2/6 6/2/6 27/2/6 13/2/6 /2/6 6/2/6 27/2/6 13/2/6 /2/6 27/2/ PHC\SSC\9 43 3/1/6 3/1/6 3/1/6 23/1/6 23/1/6 23/1/6 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 Date Suspended Sediment Concentration 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 12/12/5 12/12/5 5/12/5 5/12/5 28/11/5 28/11/5 21/11/5 21/11/5 14/11/5 14/11/5 7/11/ Date Relative Change in Seabed Elevation (mm) 19/12/5 26/12/5 2/1/6 9/1/6 16/1/6 12/12/5 5/12/5 28/11/5 21/11/5 14/11/5 Suspended Sediment Concentration (mgl -1 ) 7/11/ Date Relative Changbe in Seabed Elevation (mm) 7/11/5

46 4. WEEKLY TIME-SERIES DATA 44