T&A Survey performed a large-scale UXO waterbottom survey for the construction of a new sealock in IJmuiden, The Netherlands.

Detection in shallow water is often done using a survey boat equipped with several probes on a rack. In deeper waters a so called Fish is used, pulled by a survey boat.The disadvantage of this technology is it’s imprecise positioning and depth measurement. In the seaport of IJmuiden

T&A used an AUV (Autonomous Underwater Vehicle) for detection of UXO. The AUV follows the water bottom and is equipped with a magnetometer probe and Side Scan Sonar. Objects that were suspect according to magnetometer results could be excluded based on Side Scan Sonar results.

For this project T&A Survey  has mapped the bottom of the North Sea in order to detect possible obstacles for sand mining. These obtacles could be either of archaeological value, like old shipwrecks which by law are required to be handled wih care, or explosives from World War II. T&A has used three different geophysical techniques, which together created a detailed map of the bottom of the ocean: multibeam echo sounder, sidescan sonar and magnetometer.

The survey resulted in a list of objects and their GIS coordinates, distinguishing between object of archaeological value and potential explosives. With these results the client was able to determine whether further safety measures or archaeological research were necessary before starting the sand mining acitivities.



T&A Survey to conduct a geophysical water bottom survey for the RuwBouw Group to gain insight into the soil structure and thicknesses of the sludge layer for a sand mining project in Hoogersmilde (Drente). On the project location sand extraction had already taken place in the past. The aim of this field study was to determine the thickness of the sludge layer present in the research area.

Subbottom profiler

T&A chose to use a subbottom profiler for this survey, an acoustic survey technique that, mounted on a survey boat, maps the sediment by dragging a probe over the water surface or water bottom. Depending on the desired accuracy, water bottoms can be mapped from a few meters to many tens of meters in depth and obstacles can be detected on or under the water bottom.

Measurement results

A soil profile was made of each navigated measuring line. The transition from the sludge to the hard sandy bottom is marked in red. The sludge layer can be recognized by the horizontal layers in the  profile, visible in the figure below.



Client
Project goal
RijkswaterstaatCombineerd offshore sediment survey, North Sea
OpenIJWaterbottom UXO detection sealock IJmuiden
Klerk WaterbouwUXO detection and approach IJmuiden and Schellingwoude
RijkswaterstaatUXO detecion and approach Ruimte voor de Lek
Hoogheemraadschap Hollands NoorderkwartierUXO detection North Sea
Bouwcombinatie Stadsbrug NijmegenUXO detection and approach construcion new bridge over Waal river
OceAnco - Alblasserdam Yachtbuilding B.V.UXO detection and approach
Provincie Noord-HollandUXO detection and approach Ringvaart and Haarlemmermeerpolder
Dosco BaggerwerkenUXO detectie and approach Aarkanaal, Gouwe and Oude Rijn waterways
Ballast Nedam - De KlerkUXO detection and approach Amsterdam-Rijnkanaal