Paridaens, K.

Plancke, Y.

Schrijver, M.

Willems, P.

Open Marine Archive

Comparison of measurement techniques for monitoring sediment transport, 
under field conditions, in the Scheldt estuary 
Kobe Paridaens1, Yves Plancke2, Marco Schrijver3, Patrick Willems4 
1University of Antwerp, Dept. of Biology, Universiteitsplein 1, 2610, Antwerp, Belgium 
2Flanders Hydraulic Research, Berchemlei 115, 2140 Antwerp, Belgium 
3Rijkswaterstaat Zeeland, Poelendaelesingel 18, 4330 KA Middelburg, The Netherlands 
4Catholic University of Leuven, Department of Civil Engineering, Kasteelpark Arenberg 
40, 3001 Heverlee, Belgium 
Phone: +32-(0)-497-669749
E-mail: Kobe.Paridaens@ua.ac.be 
 
Introduction: In 2001, the Dutch and Flemish 
Governments agreed on a Long Term Vision for the 
Scheldt Estuary. This long term vision is based 
around three major themes: port accessibility, safety 
against flooding and protection of the natural system 
of the estuary. It forms the basis for policies and 
strategies regarding the Scheldt in both countries. A 
joint integrated monitoring program, MONEOS, was 
set up around the long term vision’s goals, as well as 
the Water Framework Directive and Bird and Habitat 
Directive. MONEOS will follow up on the 
development of physical and ecological system 
characteristics of the Scheldt estuary. An important 
part of the program focuses on the quantification of 
the sediment transport. Within the program, a wide 
variety of sediment transport measurement devices is 
available, both for near-bed and suspended sediment 
transport. However, for practical reasons, it is 
preferable to work with a limited set of equipment 
only. This study aims to (1) evaluate the performance 
of different sediment transport measurement devices 
available, under field conditions, and (2) determine 
an optimal equipment configuration for monitoring 
purposes in the Scheldt estuary.  
 
Methods: The standard measurement protocol for 
sediment transport currently used on the Western 
Scheldt by Rijkswaterstaat Zeeland consists of point 
measurements with an ASTM (Acoustic Sand 
Transport Meter) for measuring near-bed and 
suspended sand concentrations and velocities, and a 
MEX (optical sensor based on transmission) for silt 
concentrations. In combination with this, flow 
velocity profiles are recorded along a transect near 
the measurement point through a ship-mounted 
ADCP (Acoustic Doppler Current Profiler). 
In order to allow for different devices measuring 
sediment transport to be compared, Rijkswaterstaat 
Zeeland and Flanders Hydraulic Research organized 
a 13 hour measurement campaign (spanning a full 
tidal cycle) on the Western Scheldt on the 4th of June 
2008, during which the available equipment was 
deployed. Three measuring ships were mobilized, 
equipped with a total of 12 devices for measuring 
flow velocities, sediment concentration or sediment 
transport. Sediment concentration and transport 
measurements included mechanical methods (Delft 
Bottle), acoustic techniques based on transmission 
and scattering of sound (ADCP, ASTM) and optical 
methods based on transmission (MEX), backscatter 
(Aanderaa RCM-9, OBS) or diffraction (LISST25-X) 
of light. Pump samples were taken during the 
measurements and their silt and sand concentrations 
determined. Analysis of measurement data consisted 
of calibration of the continuous measurements with 
the results of the pump samples and comparison of 
the silt and sand transport rates obtained with the 
different methods. Calibration comprised statistical 
analysis of the relationship between measurements 
and pump samples: identifying outliers, comparison 
of goodness-of-fit (R²) for the different devices and 
determining confidence intervals on the resulting 
transport rates.  
 
Results: Interpretation of the measurements from 
individual instruments was complicated by the 
presence of both sand and silt, variation in particle 
size over time and the occurrence of flocs during 
most of the experiment. Preliminary results show 
similar trends in transport and concentration time 
series for nearly all instruments. However, large 
differences exist in absolute transport and 
concentration values, especially for peak-
concentrations. Optical methods such as the OBS, 
MEX and Aanderaa give good results for silt, but due 
to the amount of silt present, perform poorly when it 
comes to sand transport. The Delft Bottle seems to 
overestimate sand transport somewhat, but has the 
advantage of providing a sample for analysis. The 
LISST-25X measurements suffer from the 
presence/absence of flocs: separate sand and silt 
concentrations cannot be obtained and a single 
calibration to total sediment mass concentration for 
the entire experiment is not possible. However, the 
LISST-25X does provide useful information with 
regards to the density of the flocs and their 
distribution in time. AZTM measurements seem 
unaffected by flocs. Measured concentration values, 
based on a laboratory calibration with sand 
correspond very well to sand concentrations in pump 
samples. The effect of flocs and combination of sand 
and silt on the ADCP measurements is yet unclear. 


Comparison of measurement techniques for monitoring sediment transport, under field conditions, in the Scheldt estuary

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