Brussels, February 2016 Steffen Grünler Christian Maushake Turbidity measurement issues in the Weser estuary Best practice in generating long-term and large-scale observational data sets of suspended particulate matter concentration - Workshop -

| Content 1.Motivation 2.Weser estuary monitoring network 3.In situ turbidity sensor calibration 4.SPMC estimation at monitoring stations 5.Conclusions Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 2

|  Federal Waterways and Shipping Administration (WSV) is operating an extensive monitoring network  need for monitoring due to Weser estuary deepening  Federal Waterways Engineering and Research Institute (BAW) is operating numerical models  results of long-term observations (WSV) and special measurements (BAW) foster numerical model calibration, validation, and development  The aim is to generate stable turbidity calibration functions to estimate suspended particle matter concentration (SPMC) at the long-term turbidity monitoring stations in the Weser estuary. Motivation Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 3

|  SPM characteristics: -ebb dominated hydrodynamic regime -Estuarine Turbidity Maximum (length 15–20 km) -SPMCs vary between 0.1 – 2 g/l -large mud-flocs can occur  mud layers (median grain size <63 μm) in south of Bremerhaven to center of ETM Weser estuary monitoring network water levels, salinity, current velocity, turbidity, freshwater flow continuously monitored Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 4 ETM Grain size distribution measured by LISST 100X

| Long-term turbidity time series Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 5 Image Sources: ETM Maintenance procedure: each 1-2 weeks sensor cleaning (high-pressure cleaner, metal scrapers) Image sources: GoogleEarth

| Long-term turbidity time series Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 6 ETM Image Source: GoogleEarth Sensor calibration:  once per year  sensor matching (milk-water solution, same reference sensor is used)

| In situ sensor calibration experiment Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 7 Slack water Flood Ebb 04. August November January 2011 Rechtenfleth RE Slack water 08. November November 2010 Brake BRA Ebb Flood 05. August November 2010 Elsfleth ELS Flood Ebb 08. March August 2010 Strohhauser Plate SP Flood Slack water 01. March May March 2011 Nordenham NH 03. March April April January March 2011 Robbensuedsteert RS Ebb Flood TideDateLocation Dwarsgat DG 19. April June 2010 Flood Ebb Flood Bremerhaven BHV 18. May May January March 2011 Flood Ebb Flood Ebb Blexen BLX 18. May June January March 2011 Ebb Flood Ebb  calibration of turbidity sensors, with focus on the long-term monitoring station (sensor type Aanderaa 3712, RCM9)  27 calibration measurements at 9 locations spanning different tidal phases and seasons

| Calibration unit Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 8 Aanderaa Seaguard 346 (Seapoint OBS) Campbell OBS 3A (D&A OBS) Aanderaa 3712 (Aanderaa OBS) LISST 100X (grain size, transmission) Valeport MIDAS & water sampler (Seapoint OBS) Water sampling rosette Reference system

| Calibration results Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 9 Aanderaa Seaguard 346 (Seapoint OBS) Campbell OBS 3A (D&A OBS) Aanderaa 3712 (Aanderaa OBS) LISST 100X Valeport MIDAS & water sampler (Seapoint OBS) Water sampling rosette 1.5 ± ± 0.07 = 2.7 ± 0.07 (station) 1.6 ± 0.05 NTU * c = SPMC [mg/l] (averaged factors)  in situ sensor calibration necessary  individual calibration of sensor type and serial number essential

|  ship-based ADCP SPMC (WorkHorse Monitor, 300 & 600 kHz) cross-section profile measurement spanning a full tidal cycle (~13h)  OBS (Valeport, type MIDAS CTD + Seapoint OBS), LISST 100X measurements, and water samples (European standard NEN-EN 872:2005) profiles, each ~ min  overall 10 campaigns (May-June 2009 – 2011), about 500 OBS profiles with water samples Calibration data from measurement campaigns Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 10 Rechtenfleth Nordenham Blexer Bogen

|  conversion factor suitable < 500 NTU (97% of all measurement values)  low differences between tidal phases Calibration factors Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 11 ClassRFLNUFBLX StationAll values1.47 ± ± ± 0.07 < 500 NTU1.47 ± ± ± 0.04 Tidal phases All values (flood period) ± ± 0.01 < 500 NTU (flood period) 1.43 ± ± ± 0.06 All values (ebb period) 1.51 ± ± ± 0.08 < 500 NTU (ebb period) 1.51 ± ± ± 0.05 Jensen et al. (2015), Internal report of BAW. University of Siegen (fwu). Valeport MIDAS = 1.56 ± 0.05 (Seapoint)c * NTU = SPMC [mg/l]

| SPMC at monitoring station Rechtenfleth Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 12

| SPMC at monitoring station Nordenham Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 13

| SPMC at monitoring station Blexer Bogen Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 14

|  SPMC > 200 mg/l, markedly uncertainties in lab analysis  higher differences, because only a partial quantity is analyzed (very fine grain sizes unfiltered) Duplicates of water samples Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 15 BAW LabBHV LabDifference Mean % < 200 mg/l % > 200 mg/l % (different lab analysis procedures)

| Summary Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 16  turbidity time series of 9 different monitoring stations spanning a time frame of partly more than 10 years in the Weser estuary  concept of multi-sensor calibration successfully tested  turbidity calibration factors (< 500 NTU) are generated for SPMC estimation at monitoring stations in the Weser estuary  spatially separated direct and indirect SPMC measurements show a good agreement

| Conclusions Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 17  Main critical points:  Operation: Ship surveys: hardly to get enough near bottom samples; Poles: single values each 5min (RCM9), sluggish sensor  Post-operation: rarly estimations of floc sizes  Uncertainty estimations  Random errors: human activities (dreding, disposal), ship traffic  statistics based on calibration data  Recommendations for good practice:  in situ sensor calibration is recommended; Pay attention to sensor s/n!  duplicate water samples are recommended for high SPMC

| Conclusions Turbidity measurement issues Weser estuary | Steffen Grünler & Christian Maushake Page 18 Thank you for your attention. Federal Waterways Engineering and Research Institute (BAW) Hamburg, Germany  Main critical points:  Operation, Ship surveys: hardly to get enough near bottom samples; Poles: single values each 5min (RCM9), sluggish sensor  Post-operation: rarly estimations of floc sizes  Uncertainty estimations  Random errors: human activities (dreding, disposal), ship traffic  statistics based on calibration data  Recommendations for good practice:  in situ sensor calibration is recommended; Pay attention to sensor s/n!  duplicate water samples are recommended for high SPMC