Monitoring the Disposal of Maintenance Material in River Orwell

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1 ABP Ipswich Monitoring the Disposal of Maintenance Material in River Orwell 7 Monitoring period February 8

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3 Monitoring the Disposal of Maintenance Material in River Orwell 7 Monitoring period February 8

4 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Document Information Document History and Authorisation Title Monitoring the Disposal of Maintenance Material in River Orwell 7 Monitoring period Commissioned by ABP Ipswich Issue date February 8 Document ref R.85 Project no R/458/ Date Version Revision Details 3..8 Issue for client review 5..8 Issued for client use Prepared (PM) Approved (QM) Authorised (PD) Alain Le Vieux Peter Whitehead Heidi Roberts pp Suggested Citation ABPmer, (8). Monitoring the Disposal of Maintenance Material in River Orwell, 7 Monitoring period, ABPmer Report No. R.85. A report produced by ABPmer for ABP Ipswich, February 8. Notice ABP Marine Environmental Research Ltd ("ABPmer") has prepared this document in accordance with the client s instructions, for the client s sole purpose and use. No third party may rely upon this document without the prior and express written agreement of ABPmer. ABPmer does not accept liability to any person other than the client. If the client discloses this document to a third party, it shall make them aware that ABPmer shall not be liable to them in relation to this document. The client shall indemnify ABPmer in the event that ABPmer suffers any loss or damage as a result of the client s failure to comply with this requirement. Sections of this document may rely on information supplied by or drawn from third party sources. Unless otherwise expressly stated in this document, ABPmer has not independently checked or verified such information. ABPmer does not accept liability for any loss or damage suffered by any person, including the client, as a result of any error or inaccuracy in any third party information or for any conclusions drawn by ABPmer which are based on such information. All content in this document should be considered provisional and should not be relied upon until a final version marked issued for client use is issued. All images on front cover copyright ABPmer. ABPmer Quayside Suite, Medina Chambers, Town Quay, Southampton, Hampshire SO4 AQ T: +44 () W: ABPmer, February 8, R.85 i

5 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Summary ABP Ipswich undertook their annual dredging and bed levelling campaign between the 8-5 April 7, in which circa 35,6 tonnes of maintenance dredge material were deposited within the River Orwell between Woolverstone Marina and Collimer Point. To satisfy the conditions placed on their marine licence, ABP Ipswich undertook comprehensive monitoring for this dredge campaign (method agreed with Cefas and MMO) to attempt to record the fate of the deposited material within the river, particularly the intertidal, at and beyond the immediate area of disposal. This report provides a discussion of the results arising from the May 7 monitoring campaign and longer-term trends. Compared to previous years, there is less evidence that the finer sediments from dredge disposal pass over the intertidal areas once carried in suspension in the water column. The results are consistent with the longer-term trends which indicate erosion in the down estuary half of the monitoring area and stability up estuary. Despite the increased supply of sediment, the effects of the dredge disposal are small compared with the overall natural variability and the on-going natural change and it is difficult to identify the specific effects. The monitoring has shown the effects of the disposal to be negligible in affecting morphological change on the mudflats, to the extent that the actual effects is almost impossible to measure. The natural variability caused by the natural flow and wave conditions dominate the functioning of the River Orwell and minimise the effects of the dredge-disposal. It is considered that the monitoring has fulfilled the requirements for which it was originally required and further monitoring will only further record the natural long-term trends. It is therefore recommended that no further monitoring linked to maintenance dredging is required in the future. ABPmer, February 8, R.85 ii

6 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Contents Introduction... Methodology Booner Tubes Measuring stakes Results and Discussion Weather conditions Booner Tubes Measuring stakes... 4 Conclusions References Abbreviations/Acronyms... 9 Appendices A B C TSS Historical Analysis Particle Size Analysis Reports Measuring Stakes Tables Table. Tide levels for the River Orwell based on Harwich tide gauge... 5 Table. Booner Tube sampling dates... 5 Table 3. Wind conditions for the period between April and 4 May Table 4. Normalised (to days) TSS collected in the Booner Tubes... 8 Table 5. Summary of changes observed for TSS and PSA for the 7 campaign... Table 6. Monitoring programme... 3 Figures Figure. Ipswich 7 dredge-disposal monitoring Stake and Booner Tube locations... 3 Figure. Wind roses for the pre, during and post disposal periods... 7 Figure 3. Changes in particle size distribution within the Booner Tubes During disposal compared to pre-disposal on the River Orwell... Figure 4. Changes in particle size distribution within the Booner Tubes Post disposal compared to pre disposal on the River Orwell... Figure 5. Observed changes seen at the measuring stakes on the North bank over the monitoring programme... 5 Figure 6. Observed changes seen at the measuring stakes on the South bank over the monitoring programme... 6 ABPmer, February 8, R.85 iii

7 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Introduction ABP Ipswich has a marine licence allowing the port to deposit maintenance dredged material, originating from the channel and berths at Ipswich in the River Orwell, between Woolverstone Marina and Collimer Point (Figure ). This licence is granted subject to several conditions which are given within Section 3 of the licence. One of these licence conditions, and the driver for this study, is the requirement for ABP Ipswich to carry out monitoring work to assess the effect of the disposal operation within the River Orwell with respect to siltation and general sediment transport from the deposit site. This monitoring has been undertaken by ABP Ipswich since 4. Although the deposit ground has remained in the same location, the monitoring methodology was revised in 3 to attempt to better capture the sediment transport processes arising from the disposal activities. The outcomes of these monitoring campaigns have been previously assessed annually, whereby considerable differences with respect to accretion, erosion and sediment transport have been identified. The key outcomes identified from the previous monitoring and the subsequent assessments of the available information are as follows: Deposited material moves quickly through the monitoring area, predominantly in the main channel flows, i.e. the sediment is naturally transient; The different size characteristics of material deposited give rise to different patterns of sediment movement, with finer sediments present throughout the water column and coarser sediment predominantly found nearer to the bed; There is evidence of some sedimentation of finer material over high elevated mudflats, whilst coarser sediments are typically only observed to settle close to the channel on the lower mudflats. This however, is variable from year to year and long-term measurements of mud flats levels indicate that any lasting sedimentary effects of the dredge are negligible compared to the natural trends and variability; and In some years, during neap tides, there is evidence of some temporary accretion occurring in the middle of the original monitoring area towards the northern side of the river. However, this material was re-eroded as tidal ranges increased (i.e. towards and over springs) and the supply of material from the dredge/disposal ceases. In general, the monitoring carried out prior to 3 indicated that most of the deposited material is continually transient, predominantly moving in the main estuary flows. A proportion of this sediment is transported across the intertidal areas, where some deposition has been identified through sediment sorting (i.e. finer material being moved/deposited higher on the mudflat and the coarser fractions further down the profile). This deposition was typically seen to be temporary as the monitoring also identified natural erosion characteristics of the mudflats at times (even when disposal was occurring), especially during periods of higher wind and wave action. Overall, the monitoring showed the disposal strategy does supply additional material to/over the intertidal, but the amounts and variability were too small to be able to ascertain the absolute accretion/erosion effects. This indicates that disposal activity has negligible effects on the morphological changes occurring in the estuary. Continuation of the disposal within the estuary does however maintain the sediment budget of the estuary compared to depositing at an offshore location. ABPmer, February 8, R.85

8 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Whilst the monitoring prior to 3 was comprehensive in answering the question posed in the original licence condition, following further discussions with Cefas and the MMO in January 3, a revision to the monitoring programme was agreed. The aim of revision was to determine the actual accretion occurring from the disposal activity from ongoing morphological trend alongside the natural variability. The overall area of monitoring was increased in an attempt to record the presence of the deposited material within the river beyond both the immediate area of disposal and the existing monitoring area. To achieve this, the introduction of graduated measuring stakes within the river at appropriate locations was agreed with Cefas (pers. comm. Tammy Stamford, 5 February 3). Further details of the revised monitoring methodology are provided in ABPmer, 3. ABP Ipswich undertook their annual dredging and bed levelling campaign between the 8-5 April 7, in which circa 35,6 tonnes of maintenance dredge material were deposited within the River Orwell between Woolverstone Marina and Collimer Point (see Figure for deposition areas). Details of the methodology employed for this monitoring campaign are described within the subsequent sections. A difference from the 6 monitoring campaign was that no sediment grab samples were collected during the 7 campaign as per the January 3 revision to the overall methodology. ABPmer, February 8, R.85

9 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure. Ipswich 7 dredge-disposal monitoring Stake and Booner Tube locations ABPmer, February 8, R.85 3

10 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Methodology Two different methods for monitoring sediment transport were used, to identify the fate of the deposited dredge material: Booner Tubes measuring the proportion of sediment in the near bed water column analysed for: o Total Suspended Sediments (TSS); and o Particle Size Analysis (PSA); Measuring stakes indicating direct erosion and accretion changes on the mud flats. As noted above, bed sediments sampling and PSA analysis was not a requirement for the 7 monitoring campaign.. Booner Tubes Booner Tubes were deployed at eight positions throughout the River Orwell, shown in Figure (blue icons), to help identify sedimentary processes (i.e. accretion, erosion and general sediment transport). The deployment locations for the Booner Tubes were agreed with Cefas prior to the commencement of the monitored dredge disposal campaign of June 3. The positioning of two Booner Tubes at the original locations allows for the continuation of long-term analysis, with six newer locations spread further afield throughout the estuary. The Booner Tubes were placed Pre, During and Post disposal to investigate whether the sediment deposited can be seen within the tubes because of increased suspended sediment within the water column. The TSS were calculated by normalising the data over a -day period to allow for comparable results due to the different lengths of time for each tubes deployment. A -day period was chosen for ease of comparison through all the years of assessment. The eight tubes were recovered after each period and the sediment volume captured within the devices was measured and analysed for PSA in the ABPmer sediment laboratory which is a current participant in the NE Atlantic Marine Biological Analytical Quality Control Scheme (NMBAQC). For comparative purposes, samples taken from representative dredger locations (e.g. Orwell Bridge) were also subject to PSA testing. These samples were collected from the dredger hopper. The monitoring period over which the Booner Tubes collected samples (e.g. between individual deployment and recovery cycles) extended from April to 4 May 7, which was broken down into Pre, During and Post disposal periods. Table and Table show a summary of the mean tidal state and the tide conditions over the monitoring period along with the sampling dates. ABPmer, February 8, R.85 4

11 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Table. Tide levels for the River Orwell based on Harwich tide gauge Descriptors Highest Astronomical Tide Mean High Water Springs Mean High Water Neaps Mean Sea Level Mean Low Water Neaps Mean Low Water Springs Lowest Astronomical tide Level 4.4 mcd 4. mcd 3.4 mcd. mcd. mcd.4 mcd -. mcd Table. Booner Tube sampling dates Monitoring Period A Pre Disposal B During Disposal C Post Disposal Activities Date Min. Tide Max. Tide Booner Tubes deployed /4/7 Booner Tubes recovered 9/4/7 Booner Tubes deployed 9/4/7 Booner Tubes recovered 5/4/7 Booner Tubes deployed 5/4/7 Booner Tubes recovered 4/5/7 Tidal Cycle Range.4 mcd 4. mcd 3.6 m.7 mcd 3.6 mcd.9 m. mcd 4.3 mcd 4. m. Measuring stakes In 3, eighteen graduated measuring stakes were placed within the River Orwell with the aim of measuring potential rates of accretion/erosion across intertidal areas due to disposal activities (see Figure ). Photographs were taken during April and May 7 monitoring campaign to coincide with the Pre, During and Post disposal periods. Analysis of all the photographs taken throughout the various campaigns provide information on any natural trends and/or seasonal variability that may be occurring in the estuary. The assessment of changes was made by visual inspection of the photographs, recording temporal changes in the vertical elevation of the mud surrounding the stakes. The centimetric scale on the side of the stake allowed an estimation of localised seabed elevations to be made, wherever possible to the nearest mm with the aid of photographic analysis. New graduated measuring stakes were placed next to the old stakes and synchronised, as the old graduations have become damaged during a cleaning process in 6 as discussed in ABPmer (7). ABPmer, February 8, R.85 5

12 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich 3 Results and Discussion This section describes the results from the monitoring undertaken for the most recent April/May 7 dredging campaign. A discussion of accretion, erosion and sediment transport processes (where applicable) as indicated by the monitoring is provided. Wind conditions during the monitoring phases continue to be noted as past results have indicated that the movements of sediments through the estuary is influenced by the wind conditions, particularly causing additional displacement of sediment due to wave action on different sides of the river. 3. Weather conditions To assess the potential reasons for changes observed over the monitoring period, differences in the tidal and meteorological (wind) conditions within the River Orwell were also considered, along with the monitoring results. Table 3 provides a summary of the wind conditions experienced over the monitoring periods (illustrated as wind rose plots for the Pre, During and Post disposal monitoring periods in Figure. The tidal statistics (Table ) for the area show for the Pre- and Post- disposal periods the tides were larger than During the periods of disposal, with Post disposal elevations approaching highest astronomical tide levels. During the disposal operations, the maximum tidal level was around MHWN. This means that flows with the potential to transport sediment are available for collection in the Booner Tubes would have been greater Pre and Post disposal (especially the latter) than During the period of dredge disposal, particularly for locations at the higher elevations of the mudflat. This will need to be considered in the discussion of the results obtained. Table 3 specifies the average and maximum wind speeds and predominant directions over the monitoring periods. Average wind speeds for the three periods varied from 4.3 to 5.5 knots with the lowest average wind speeds occurring whilst the dredged material was being disposed. Maximum wind speeds were generally highest Pre and Post (3 knots) dredging and disposal. Table 3. Wind conditions for the period between April and 4 May 7 Monitoring Period A Pre Disposal B During Disposal C Post Disposal Date /4/7 9/4/7 9/4/7 5/4/7 5/4/7 Average Wind Speed (knots) 4/5/7 * Wind direction uses the Atmospheric convention (where winds come from). Max. Wind Speed (knots) Predominant Wind Direction* (degrees) WNW 4.3. NW SE/NW The wind roses provided in Figure shows the wind direction distribution was distinctly different during the three monitoring periods. During the Pre-disposal (Period A), the wind directions were predominantly from the west north west and westerly sectors, but the strongest winds occurred from the north north-easterly direction with winds in the order of 3 knots. During the disposal (Period B) the wind was predominantly from the west at generally lower speeds than the Pre and Post periods with the maximum from the north westerly direction sector with wind speeds of. knots. Following the disposal (Period C) the winds were quite variable, blowing approximately equally in the arc from north west to south east (through north) with the maximum from circa the north east. ABPmer, February 8, R.85 6

13 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Pre-disposal /4/7 to 9/4/7 During disposal 9/4/7 to 5/4/7 Post disposal 5/5/7 to 4/5/7 Figure. Wind roses for the pre, during and post disposal periods ABPmer, February 8, R.85 7

14 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich The wind roses tend to indicate that winds were more likely to affect sediments and create more disturbance in a down estuary direction and towards the eastern banks, particularly Pre and During disposal. Post disposal the more variable winds were likely to disturb material on both banks of the estuary, depending on when winds were greatest at the higher water levels. This potential weather forcing also need considering when interpreting the Booner Tube results. 3. Booner Tubes As detailed previously in Section., three deployments of Booner Tubes were positioned at the eight monitoring stations (see Figure ), giving a total of 4 samples. The Pre-disposal (Period A) deployment of the Booner Tubes lasted for 7 days, the During disposal (Period B) deployment lasted for 7 days, and the Post disposal (Period C) deployment of the Booner Tubes were in place for days. 3.. Total suspended solids The volume of material collected in each Booner Tube for the Pre (A), During (B) and Post (C) monitoring periods are provided in Table 4. The volumes collected have been normalised to a period of days (rounded to the nearest ml) to account for the different time intervals of Booner Tube deployment. The particle size distribution of the material collected in the Booner Tubes was also analysed; these results are discussed in Section 3... Table 4 also shows a comparison of TSS between Periods A and B (Pre and During disposal), and A and C (Pre and Post disposal), as a percentage (%) difference. Table 4. Normalised (to days) TSS collected in the Booner Tubes Position Period A TSS (ml) Period B TSS (ml) Period C TSS (ml) % Difference A from B % Difference A from C The comparison between Pre-disposal (Period A) and During disposal (Period B) identified a significant decrease in TSS up to 8 % down estuary, at all locations except beyond the extent of deposit area at Position 7 on the west bank of the estuary. The 7 data therefore shows that, less sediment was transported over the intertidal area in the water column during the period of disposal than before the disposal operations took place. This was not the case during the majority of previous monitoring periods. This can be explained by both the tidal variation between the two monitoring periods and the difference in weather conditions. Both would have naturally reduced the sediment supply during the disposal period. Although sediment was disposed the tide and wind conditions did not allow this to be transported to the Booner Tubes or the magnitude of the natural variability considerably outweighed the effects of the disposal. A comparison between Pre-disposal (Period A) and Post-disposal (Period C) showed an increase in TSS at most sites, with the most significant occurring in Position (7 %) up estuary outside the licenced disposal site. Adjacent to the licence disposal area Position 5 (situated on the north bank) increased by 6 %, which is assumed to be the location closest to the likely location of maximum disposal on the ABPmer, February 8, R.85 8

15 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich north bank. The overall percentage difference was positive for 7 Post disposal period, this indicates that more sediment was being transported in the water column Post disposal and most sediment was found at the up-estuary sites. The lower tides During the disposal period would have not allowed, or reduced the time that sediments, would have been carried in suspension and transported over the higher inter-tidal areas. This would have confined the dredge disposal to the main channel until the larger tides of the Postdisposal period where the larger tides may have reactivated the dredge disposal sediment and transported them over the intertidal areas resulting in the higher readings during the Post disposal period. As noted in Section 3. the tidal range was greater during the Post dredging period, hence greater time for collection of sediment in the Booner Tubes. It therefore cannot be clearly ascertained whether the increase was a result of the dredging disposal. The sediment was however in the system, so may have contributed to the increase. The overall analysis, however, suggests that this contribution was likely to have been small compared to the weather and tide induced variability. Time series comparisons of the standardised Booner Tube at each of the current measurements locations for the corresponding Pre, During and Post disposal phases are provided in Appendix A to see if any trends are evident. These plots show that no longer term trends are visible through the dynamic natural variability. As with previous monitoring years, natural variability with the wind and tides during the different periods has had a significant influence on whether the sediment is transported over the intertidal areas or to the north or south bank. 3.. Particle size analysis The material collected in the Booner Tubes over the monitoring programme was also analysed for particle size distribution and the resulting analyses are presented in Appendix B. These results provide a graphical representation of gravel, sand, silt and clay contained within each sample, thus indicating the size distribution of the sediment carried within the water column at each location for the monitoring periods. For comparative purposes, samples taken from the dredger whilst dredging at locations near the No. 9 Buoy, Cliff Quay and Orwell Bridge were also subject to PSA testing. These results are also shown in Appendix B. This indicated that PSA of the material being deposited in the estuary. Comparison of the PSA statistics, show that the material dredged and deposited was marginally finer than collected in all three phases of Booner Tube analysis. This tends to indicate that during 7 the disposal of dredged material provided less material over the intertidal areas than had been the case in previous years and the change seen was more due to natural variability from the weather and variance in tidal conditions rather than the dredge disposal activity. Changes in the sediment size fraction (percentages) over the monitoring period are also provided spatially, in a comparison between Periods A and B (Figure 3) and between Periods A and C (Figure 4) for each Booner Tube position. The PSA results show a maximum sediment size fraction change of 9 % at Position 8 (Bird Reserve) between the Pre and During disposal. Figure 3 shows that in general terms that slightly more mud (silt/clay) collected in the Booner Tubes during the periods of dredge disposal up the estuary of Collimer Point and less down estuary. However, as noted above this change is more likely a variance in the tidal conditions as opposed to the effects of the dredge. The Post dredge change compared to the Pre-dredge situation is shown in Figure 4. This shows that less mud was transported over the intertidal areas Post dredge in the upper half of the monitoring area and more to the downstream section. This change however, cannot be directly associated with the dredge disposal. Analysis of the particle size statistics suggests that during the monitoring period there was a possible transfer of a small amount of sediment from the north and south bank, particularly between Pre and During disposal periods. ABPmer, February 8, R.85 9

16 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure 3. Changes in particle size distribution within the Booner Tubes During disposal compared to pre-disposal on the River Orwell ABPmer, February 8, R.85

17 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure 4. Changes in particle size distribution within the Booner Tubes Post disposal compared to pre disposal on the River Orwell ABPmer, February 8, R.85

18 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich 3..3 Conclusion of Booner Tube analysis Given the results presented in Section 3.. and 3.., the correlation between TSS and PSA is discussed here. To provide a better understanding of the variations observed, Table 5 shows a summary of changes for both parameters according to the location of the Booner Tubes. Table 5. Summary of changes observed for TSS and PSA for the 7 campaign Position Summary of Changes Observed Changes in TSS Changes in PSA Higher Post NO CHANGE 4 Higher Post Post (more sand) 5 Higher Post Post (more sand) 9 Higher Post NO CHANGE Lower Post NO CHANGE 3 Higher Post Post (more silt) 7 Higher Post NO CHANGE 8 Higher post NO CHANGE As described in Section 3.., the greatest difference (a net decrease) in TSS was observed During disposal whereas Post disposal there was an increase in TSS throughout the estuary. This suggests that, sediment was not transported in the water column during the period of disposal which coincided with the lowest tides during the tidal cycle. Post disposal showed an increase at higher water levels in TSS levels. This increase is considered to have resulted from the higher tides driving stronger tidal currents that are able to rework the sediments through the estuary. Secondly the lower TSS During disposal are likely to be a result of lower tides which are unable to transport the sediments to the Booner Tubes as a result of the lower water levels over the intertidal mud areas. Tides and winds influence the remobilisation of sediments within the estuary already deposited on the intertidal mud flats, thus increasing the TSS results during periods of increased wind as a results of surface wind stress to tidal flows and wave disturbance. The differences in sediment supply, are therefore a function of the relative difference in tidal levels, weather conditions and the increased sediment added to the water column at the time of disposal. Overall, as in previous years monitoring the contribution of sediment from the dredge disposal was small (negligible) when considered against the natural variability occurring on the mud flats as a result of natural processes. 3.3 Measuring stakes The dates of the stake monitoring programme is shown in Table 6. The inter survey analysis of erosion and accretion for each stake is shown in Appendix C. As per the recommendation from the ABPmer (7) report, the stake measurements were regrouped to better represent the spatial extent of the long-term changes. The stakes are now grouped into either the north bank or south bank and in order from north to south along the estuary. The measured change in bed elevation (shown in mm) are provided for each position over the complete monitoring period in Figure 5 and Figure 6 for the north and south banks respectively. ABPmer, February 8, R.85

19 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Table 6. Monitoring programme Year Monitoring Period Dates Spring Between 6-7 March 3 (stake deployment) and - May 3 (spring) Pre-disposal Between - May 3 (Spring) and 8-9 May 3 (pre-disposal) 3 During disposal Between 8-9 May 3 (pre-disposal) and 3-4 June 3 (during disposal) Post disposal Between 3-4 June 3 (during disposal) and - June 3 (post disposal) Summer/ Autumn Between - June 3 (post disposal) and 4-6 October 3 (Autumn) Autumn to Spring Between 4-6 October 3 (Autumn) and 6-7 April 4 (Spring) Pre-disposal Between 6-7 April 4 (spring) and 4-5 April 4 (pre-disposal) 4 During disposal Between 4-5 April 4 (pre-disposal) and - May 4 (during disposal) Post disposal Between - May 4 (during disposal) and 7-8 May 4 (post disposal) Summer/ Autumn Between 7-8 May 4 (post disposal) and 9-3 October 4 (Autumn) Pre-disposal Between 9-3 October 4 (Autumn) and 8-9 April (pre-disposal) 5 During disposal Between 8-9 April 5 (pre-disposal) and 8 May 5 (during disposal) Post disposal Between 8 May 5 (during disposal) and -3 May 5 (post disposal) Summer/ Autumn Between -3 May 5 (post disposal) and 5-6 November 5 (Autumn) Winter / Spring Between 5-6 November 5 (Winter) and - April 6 (Spring) Pre-disposal Between - April 6 and 8-9 April 6 (pre-disposal) 6 During disposal Between 8-9 April 6 (pre-disposal) and 3 May 6 (during disposal) Post disposal Between 3 May 6 (during disposal) and May 6 (post disposal) Summer / Autumn Between May 6 (post disposal) and - November 6 Winter / Spring Between - November 6 (Winter) and -3 April 7 Pre-disposal Between -3 April 7 (spring) and 8-9 April (Pre-disposal) 7 During disposal Between 8-9 April (Pre-disposal) and 4-5 April (During disposal) Post disposal Between 4-5 April (During disposal) and 3-4 May (Post disposal) Summer / Autumn Between 3-4 May (Post disposal) and 5-6 November 7 (Autumn). ABPmer, February 8, R.85 3

20 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich The previous monitoring of intertidal sedimentation undertaken in 3, 4, 5 and 6 (ABPmer, 3; 4, 5; 6 and 7) had not highlighted any significant patterns of accretion or erosion at the locations of measured stakes directly relating to the dredge disposal, and therefore sedimentation could not be attributed to the disposal activities. Some locations, however, were starting to reveal longer term trends, primarily due to the natural on-going processes rather than as a result of the dredge disposal. During the period of dredge disposal in May 7, Figure 5 and Figure 6 show that direct effects that could possibly have resulted from the disposal operations were generally small. On the north bank, there may be some evidence of accretion alongside the disposal area up estuary of the bend at Collimer Point, however this is not consistent. Erosion was generally seen to occur on the wide intertidal on the outside on the bend, with the maximum accretion occurring at Position 8 (Bird Reserve) at the furthest down estuary location. On the south side, a similar general pattern was evident with small amounts of accretion evident up estuary of Collimer Point and erosion immediately down estuary or high on the intertidal. The accretional change was for the most part less than mm. The fact that areas of erosion are also evident suggests the natural forcing processes are variable between locations, hence additional sediment supply does not always result in short term accretion. As noted above the monitoring is identifying longer term trends and the order of variability about these trends for the different locations. The results clearly show that long term erosion is prevalent on both sides of the estuary (particularly the south) around Collimer Point. Up estuary of this point the current trend is for relative long-term stability on the north side and stability/minor accretion on the south side. During the last year the most significant change has been substantial accretion (over cm) at Location 8 (Long Reach), which had previously been eroding. This change has occurred on the lower intertidal and does not appear to be connected to the disposal activity. Also during the last year there seems to have been a change from a generally stable/accretional trend to an erosional trend in the area up estuary of the disposal area, particularly on the south bank as illustrated by Location off the Stoke Sailing Club. Accretion has remained prominent at Location 8, the Bird Reserve, however it is suggested this is more a result of the effects of Harwich Berth developments and is little influenced by dredging disposal activities. Overall the stake monitoring during the last year shows a small correlation with the disposal activity at some locations, but not all. This correlation, however, was not picked up by the Booner Tube volume or PSA analysis. The reason for this might be the fact that the sediment primarily deposited out on neap tides locally and was less distributed over the mud flats higher in the water column, where it would be collected in the Booner Tubes, due to the differences in tidal range. Most of the sediment disturbance and settling occurred near to the bed, hence not recorded in the Booner Tubes. The results also continue to suggest that natural process changes are considerably greater than any effects of the dredge disposal. At this stage, therefore, it cannot be concluded that the dredgedisposal campaigns are having a beneficial improvement of the environment of the River Orwell that facilitates sedimentation over the intertidal areas. The natural variability of the system seems to account for more rapid and sudden changes on the intertidal areas, which tends to mask the effects of the dredge-disposal, despite an indication that a proportion of the deposited sediment passes over the intertidal areas at certain locations. ABPmer, February 8, R.85 4

21 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure 5. Observed changes seen at the measuring stakes on the North bank over the monitoring programme ABPmer, February 8, R.85 5

22 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure 6. Observed changes seen at the measuring stakes on the South bank over the monitoring programme ABPmer, February 8, R.85 6

23 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich 4 Conclusions Based upon the findings of the monitoring programme for the 7 dredging campaign, which includes the monitoring of measuring stakes during 7 between April and November along with previous trends in the data, the following key conclusions can be made: Winds and waves varied in strength and direction between the different monitoring phases. Wind (related to tidal state at the time) have been seen in past years to have an important influence on intertidal erosion/sediment disturbance at more exposed areas of the estuary. Wind induced waves over the intertidal zones could aid the removal of fine sediment. During the 7 campaign the wind was from a north westerly sector except for the Disposal period itself when winds from the westerly sectors dominated; Periods of larger tidal ranges will result in the greatest sediment transport. During this 7 campaign it would appear the plume of disposed sediments is likely to have been transient within the channel of the River Orwell, being transported in the estuarine channels by the neap tidal current with very little sediments moving over the higher mud flats. It should be noted that natural variations within the River Orwell may have also contributed to this observed pattern. For example, the near astronomical high tide experienced Post disposal would have increased the tidal currents and aided the maintenance of the fine sediments in suspension, thus aiding the observed increase in the TSS over this monitoring period. Whereas During the disposal the tidal range was at its lowest during this campaign, thus restricting the transport of TSS over the higher intertidal mudflats; The same conclusion as the 6 campaign (ABPmer, 7) can be made regarding the results from the stake monitoring which identifies that changes (circa cm) in intertidal elevation can occur within the River Orwell over relatively short periods of time. Stake measurements in past years were inconclusive in providing sufficient evidence of intertidal sedimentation due to the dredge-disposal campaigns. During 7 the stake measurements did indicate some potential correlation with the disposal period, but only to a small magnitude at some locations. This evidence, however, was not (in general) corroborated by Booner Tube analysis. The stake measurements continue to monitor the long term natural changes which are only marginally modified by the annual disposal operations. These changes are at most small and often negligible with respect to the natural variation. The long-term trends suggest erosion is prevalent and continuing on both sides of the estuary at Collimer Point with relative stability and occasional accretion at the up-estuary locations. The largest changes in elevation were recorded over autumn 3 to spring 4 period when significant extreme storm events occurred including one of the highest tides on record. Irregular patterns of change in intertidal elevations over the Post disposal period, which cannot be associated with the dredging activity, tend to suggest that these events are driven by the natural variability in tidal and meteorological conditions observed within the River Orwell over the monitoring period; With respect to the dredge disposal campaign, the Booner Tube volumes and PSA of collected sediment, in general over the survey programme, indicate an increase in sediment supply across the mudflats post the dredge which quickly dissipates. This, however, was less evident in 7 due the low tidal range and thus decreased tidal currents. The stake monitoring tends to indicate predominantly trends due to the natural processes (tide and weather formed) in the estuary with no changes to sedimentation patterns that can be specifically related to the dredge disposal; ABPmer, February 8, R.85 7

24 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich All previous monitoring has indicated that the natural variations occurring are considerably greater than is evident from the dredging at the monitoring locations. Continuation of the current dredge disposal operations maintains the sediment in the system, compared to disposal offshore, but has little direct influence on the local intertidal areas that can be detected outside the natural variation. The overall results from 7 are similar to previous campaigns with most variation resulting from natural processes. Sediments from the dredge disposal have been identified as passing over the intertidal areas and may deposit for a short period before being re-eroded during times of higher tidal currents and/or wind and wave activity. The effects of the disposal continue to be shown to be negligible compared to the change from natural processes. The monitoring has shown the effects of the disposal to be negligible in affecting morphological change on the mudflats, to the extent that the actual effects is almost impossible to measure. The natural variability caused by the natural flow and wave conditions dominate the functioning of the River Orwell and minimise the effects of the dredgedisposal. It is considered that the monitoring has fulfilled the requirements for which it was originally required and further monitoring will only further record the natural long-term trends. It is therefore recommended that no further monitoring linked to maintenance dredging is required in the future. ABPmer, February 8, R.85 8

25 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich 5 References ABPmer, 7. Monitoring of Disposal of Maintenance Material in River Orwell March 6. ABPmer, Report No. R.77, February 7. ABPmer, 6. Monitoring of Disposal of Maintenance Material in River Orwell March 6. ABP Marine Environmental Research Ltd, Report No. R.57, March 6. ABPmer, 5. Monitoring of Disposal of Maintenance Material in River Orwell April 4. ABP Marine Environmental Research Ltd, Report No. R.9, January 5. ABPmer, 4. Ensuring Flood Resilience: An overview of 5/6 December 3 UK storm surge. ABP Marine Environmental Research, 4/3. ABPmer, 3. Monitoring of Disposal of Maintenance Material in River Orwell June 3. ABP Marine Environmental Research Ltd, Report No. R., December 3. NE Atlantic Marine Biological Analytical Quality Control Scheme - Current Participants - PSA 7-8: 6 Abbreviations/Acronyms ABP CD Cefas MHWN MMO NMBAQC PSA SC SYH TSS Associated British Ports Chart Datum Centre for Environment Fisheries and Aquaculture Science Mean High Water Neaps Marine Management Organisation NE Atlantic Marine Biological Analytical Quality Control Scheme Particle Size Analysis Sailing club Suffolk Yacht Harbour Total Suspended Sediments Cardinal points/directions are used unless otherwise stated. SI units are used unless otherwise stated. ABPmer, February 8, R.85 9

26 Appendices

27 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich A TSS Historical Analysis Figure A. TSS in Booner Tube Stoke SC normalised to days (South bank) Figure A. TSS in Booner Tube 4 Pin Mill normalised to days (South bank) ABPmer, February 8, R.85 A

28 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure A3. TSS in Booner Tube 5 Nacton Point normalised to days (North bank) Figure A4. TSS in Booner Tube 9 Hares Creek outer normalised to days (South bank) ABPmer, February 8, R.85 A

29 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure A5. TSS in Booner Tube Levington Creek normalised to days (North bank) Figure A6. TSS in Booner Tube 3 Jill s Hole normalised to days (South bank) ABPmer, February 8, R.85 A3

30 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich Figure A7. TSS in Booner Tube 8 Bird Reserve normalised to days (North bank) ABPmer, February 8, R.85 A4

31 Monitoring the Disposal of Maintenance Material in River Orwell ABP Ipswich B Particle Size Analysis Reports ABPmer, February 8, R.85 B

32 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: No. 9 Buoy - Average Measured by: Afulford on 5 July 7 Sample Source: UKD Orca Obscuration:.53 % Sample Collected: /4/7 Weighted Residual:.668 % d(.): 3.3 µm d(.5):. µm d(.9): 68.4 µm Cumulative Frequency Plot No. 9 Buoy - Average, 5 July 7 :8: Clay Silt Sand 3 % 7 % 4 % 7 % 8 % 3 % % Frequency Curve No. 9 Buoy - Average, 5 July 7 :8: Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 6

33 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: Cliff Quay - Average Measured by: Afulford on 5 July 7 Sample Source: UKD Orca Obscuration:.89 % Sample Collected: /4/7 Weighted Residual:.6 % d(.): 3.37 µm d(.5):.747 µm d(.9): µm Cumulative Frequency Plot Cliff Quay - Average, 5 July 7 :4:43 Clay Silt Sand % 5 % 45 % 9 % 7 % % % Frequency Curve Cliff Quay - Average, 5 July 7 :4:43 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 66

34 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: Orwell Bridge - Average Measured by: Afulford on 5 July 7 Sample Source: UKD Orca Obscuration: 3. % Sample Collected: /4/7 Weighted Residual:.588 % d(.): 3.3 µm d(.5):.38 µm d(.9): µm Cumulative Frequency Plot Orwell Bridge - Average, 5 July 7 :3: Clay Silt Sand % 6 % 47 % 9 % 5 % % % Frequency Curve Orwell Bridge - Average, 5 July 7 :3: Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 7

35 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: A - Average Measured by: AFulford on 8 August 7 Sample Source: River Orwell Obscuration:.7 % Sample Collected: 9/4/7 Weighted Residual:.949 % d(.): 3.7 µm d(.5):.39 µm d(.9): µm Cumulative Frequency Plot A - Average, 8 August 7 :36: Clay Silt Sand % % 48 % 8 % 6 % 5 % % Frequency Curve A - Average, 8 August 7 :36: Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 56

36 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: B - Average Measured by: Afulford on July 7 Sample Source: River Orwell Obscuration:.67 % Sample Collected: 5/4/7 Weighted Residual:.769 % d(.): 4.9 µm d(.5):.497 µm d(.9): µm Cumulative Frequency Plot B - Average, July 7 :5:5 Clay Silt Sand % % 5 % 9 % 6 % % % Frequency Curve B - Average, July 7 :5:5 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 8

37 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: C - Average Measured by: Afulford on 5 July 7 Sample Source: River Orwell Obscuration:.57 % Sample Collected: 4/5/7 Weighted Residual:.795 % d(.): 3.73 µm d(.5):.66 µm d(.9): 73.5 µm Cumulative Frequency Plot C - Average, 5 July 7 ::38 Clay Silt Sand % % 46 % 9 % 8 % 3 % % Frequency Curve C - Average, 5 July 7 ::38 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 54

38 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: 4A - Average Measured by: Afulford on July 7 Sample Source: River Orwell Obscuration:.6 % Sample Collected: 9/4/7 Weighted Residual:.837 % d(.): 3.79 µm d(.5):.68 µm d(.9): µm Cumulative Frequency Plot A - Average, July 7 :6:3 Clay Silt Sand % 3 % 48 % 9 % 7 % % % Frequency Curve A - Average, July 7 :6:3 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 6

39 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: 4B - Average Measured by: Afulford on July 7 Sample Source: River Orwell Obscuration:.33 % Sample Collected: 5/4/7 Weighted Residual:.77 % d(.): 3.89 µm d(.5): µm d(.9): 4.87 µm Cumulative Frequency Plot B - Average, July 7 :37:44 Clay Silt Sand % 8 % 48 % 5 % 6 % % % Frequency Curve B - Average, July 7 :37:44 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 96

40 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: 4C - Average Measured by: Afulford on 4 July 7 Sample Source: River Orwell Obscuration: 3.87 % Sample Collected: 4/5/7 Weighted Residual:.8 % d(.): µm d(.5):.947 µm d(.9): 76.6 µm Cumulative Frequency Plot C - Average, 4 July 7 5:46:3 Clay Silt Sand % % 43 % % % 3 % % Frequency Curve C - Average, 4 July 7 5:46:3 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 3

41 Particle Size Analysis Report ABPmer Quayside Suite, Medina Chambers Town Quay, Southampton, SO4 AQ Sample Name: 5A - Average Measured by: Afulford on July 7 Sample Source: River Orwell Obscuration:.9 % Sample Collected: 8/4/7 Weighted Residual:.79 % d(.): 3.33 µm d(.5):.69 µm d(.9): 7.97 µm Cumulative Frequency Plot A - Average, July 7 :3:6 Clay Silt Sand % 5 % 44 % 7 % 9 % 3 % % Frequency Curve A - Average, July 7 :3:6 Malvern Instruments Ltd. Malvern, UK Mastersizer Ver. 5. Serial Number : File name: Ipswich_4Jul7.mea Record Number: 38