Sediment and Flocculation dynamics in the area of Zeebrugge Marc Sas, Alexander Breugem and Andrew Manning

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 2 Overview Objectives Overview of the measurement campaign Global overview Long term measurements Through tide measurements Coastal zone Harbour of Zeebrugge Near bed measurements using HCBS frame INSSEV settling velocity measurements Flocculation Dynamics Conclusion

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 3 Introduction Within the scope of the optimization of dredging activities in the maritime access to the coastal harbours, it is important to determine the siltation of the access channels and the sediment dynamics of temporary soft mud layers. The layout of the outer harbour of Zeebrugge and corresponding current conditions lead to the entrance of muddy water into the harbour during flood, after which low current velocities in the harbour lead to sedimentation of material, after which relatively clean water flows back to the sea during ebb. This process amounts to a considerable siltation in the harbour.

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 4 Objectives The project : Langdurige monitoring van zout/zoet-verdeling in de haven van Zeebrugge en monitoring van zoutconcentratie, slibconcentratie en hooggeconcentreerde slibsuspensies in de Belgische kustzone Waterbouwkundig Laboratorium Maritieme Toegang

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 5 Objectives Objective of the complete project The first goal of the study and the survey is to detect the occurrence of near-bed high-concentration mud suspensions (referred to as high-concentration benthic suspensions - HCBS), their dynamic behaviour and the conditions and locations of their occurrence The second goal is to gain insight in density currents between harbour and sea, and their relationship to siltation in the harbour of Zeebrugge. Objective of the present presentation Give overview of the measurements and some details about the flocculation dynamics inside the harbour of Zeebrugge.

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 6 Global Overview Survey 1 : autumn-winter Survey 2 : summer 2007

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 7 Long term measurement locations Period: June 2006-Aug 2007 RCM9 at: MOW 1 Sterneneiland CTD at: LNG terminal Hermespier

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 8 Long term measurement setup RCM-9 Velocity Salinity SSC Pressure Temperature CTD Salinity Pressure Temperature

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 9 Through tide measurement locations Harbour entrance: One spring and one neap tide meas. ADCP and SiltProfiler Inside the harbour: One summer and one winter meas. SiltProfiler and CTD Coastal zone: Two transects in winter Three transects in summer SiltProfiler (summer and winter) ADCP (summer only)

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 10 Through tide measurement instruments : ADCP + CTD ADCP: Velocity profile Sediment concentration profile CTD: Salinity (multiple depths) Temperature

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 11 Through tide measurement instruments : ADCP + CTD Harbour entrance; Neap tide 2h before HW Harbour; Neap tide 3.30 h before HW

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 12 Through tide measurement instruments : SiltProfiler SiltProfiler: Sediment concentration profile Salinity profile Temperature profile Specifications  High Frequency (100 Hz)  Wireless Data Transfer via Bluetooth technology  Freefall Profiling  3 Silt sensors: o 1 Seapoint BS sensor (0-700 mg/l) o 2 Transmittance Extinction Sensors ( mg/l and 3500 – mg/l)  CTD sensor

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 13 Through tide measurement instruments : SiltProfiler Navigation channel; winter. Avg. tide; 5h after HW Harbour; summer. Avg. tide; 0.20h after HW

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 14 Near bed measurement locations Campaigns: 1 x Summer 1 x Winter Two different frames Deployment: 2-4 weeks

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 15 Near bed measurements (HCBS Frame) Valeport Midas and RCM-9: Velocity (0.3 m and 1.0 m above bed) Sediment concentration Argus: Sediment concentration profile Altus echo sounder: Bed level

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 16 Near bed measurements (HCBS Frame) : ARGUS MOW 1 during winter.

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 17 Near bed measurements (HCBS Frame) : Altus MOW 1; Winter

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 18 INSSEV Settling velocity measurements INSSEV floc camera surface electronics in laboratory on RV Lancaster survey vessel Example of floc images Hydrodynamic sensors on bed frame being deployed from RV Lancaster survey vessel 1.2 mm

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide INSSEV samples from Albert-II Dok Obtained 0.6m above the bed 8 th November 2006 HW +1hr 16m deep Water Temp ~ 12.8 o C Salinity = 32 U = 0.14 m/s SPM = mg/l TMZ (17:00hr – HW+2.5hr) SPM rose to 5 g/l U = 0.03 m/s INSSEV Settling velocity measurements

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 20 Shear stress range: HW+1 = 2 Pa TMZ = 0.4 Pa LW = 0.15 Pa D mean response: 130  m 375  m Ws mean response: 2 mm/s at HW+1 Four-fold rise in TMZ to 8.5 mm/s INSSEV Settling velocity measurements

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 21 HW+1:  = 2.1 Pa, SPM=333 mg/l 621 flocs,  m Microflocs dominate high shear env. D < 160  m (SBs 1-4) Ws MACRO = 1.4 mm s -1 only 29% of SPM Ws micro fell 0.8 mm s -1 FASTER 71% of SPM nf Micro : % of 643 mg.m -2 s -1 MSF (mass settling flux) INSSEV Settling velocity measurements

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 22 TMZ:  = 0.4 Pa, SPM = 5.5 g/l Floc population more bi-modal Macroflocs dominate TMZ D > 160  m (SBs 5-12) 2730 macroflocs, D max = 940  m Ws MACRO = 10.2 mm s -1 81% of total flocs 95% of SPM (1/3 in SB12) 85-95% porous, nf ~ % of 61 g.m -2 s -1 MSF Ws micro fell 9 mm s -1 SLOWER 5% of SPM INSSEV Settling velocity measurements

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 23 Sediment & Flocculation Dynamics A significant data set has been collected There is no evidence for a tick HCBS layer in the navigation channels in the vicinity of Zeebrugge Siltation of the harbour of Zeebrugge is strongly influenced by tidal filling and the eddy pattern in the harbour mouth. Siltation of the harbour of Zeebrugge shows a strong influence on the neap-spring tidal cycle. Density differences due to the fresh water discharge into the harbour have only a limited effect on the harbour siltation.

14-Sep-15 / Sediment and Flocculation dynamics in the area of Zeebrugge / slide 24 Conclusion A significant data set has been collected on fine cohesive sediment characteristics in the vicinity of Zeebrugge, calling for: A regular follow up: a series of fixed stations is highly recommended Efforts should be put in characterizing the physical conditions leading to the siltation rate in the access channels and the port Integration of wave/wind characteristics is necessary Integration of biological parameters is recommended