The morphodynamics of intertidal beaches are still not entirely understood. It appears that the equations used to predict sand transport in deeper water are not sufficient to explain morphological change in shallow waters (~<3 meter depth). Yet it is important to understand these dynamics for the design and management of future projects regarding coastal safety. With the data we collect at the Sand Motor we try to gain more insight on these processes. This post will give an overview of all the topics which are addressed during the Sand Motor field campaign, in later posts each research topic will be explained separately.
The past weeks we already introduced some of our instruments which were deployed at the beach. To give you a full overview, there is one cross-shore array with 4 rigs, several pressure transducers and groundwater pipes and there is an array with 10 pressure transducers along the shoreline of the Sand Motor. All of our instruments are in the intertidal zone, so during low tide we are able to change their height above the bed if necessary and during high tide the instruments are submerged and measuring.
The past weeks we already introduced some of our instruments which were deployed at the beach. To give you a full overview, there is one cross-shore array with 4 rigs, several pressure transducers and groundwater pipes and there is an array with 10 pressure transducers along the shoreline of the Sand Motor. All of our instruments are in the intertidal zone, so during low tide we are able to change their height above the bed if necessary and during high tide the instruments are submerged and measuring.
With the cross-shore array we try to understand all processes which are important for sand transport in the intertidal zone. When waves enter shallower water, waves become steep and asymmetric until they break. One of the four rigs is especially designed to study turbulence and sand transport beneath breaking waves. The turbulence generated by breaking waves can enhance the amount of sand which is suspended in the water and can determine the direction of sand transport. This rig also contains a 3D sonar to scan the bed for small bed forms to include the influence of ripples on sediment transport. The remaining three rigs are used to study the cross-shore variability of sand transport, they measure pressure, i.e. water height and thus waves, flow velocities and sand concentrations in the water. These measurements are mainly used to study the importance of 20-200s long waves for sand transport. Around the cross-shore array, the beach morphology is monitored with RTK-GPS daily, to be able to relate sand transport to beach morphology.
The intertidal zone is also an important source for sand which can be transported by the wind. Wind blown sand is important for beach and dune recovery after storms. For this reason, groundwater pipes are added to the cross-shore array to investigate how fast the groundwater drops after a high tide. The beach humidity determines whether sand is available to be transported by the wind towards the dunes. During a storm we will even extend our array with instruments on the dry beach and count sand grains transported by the wind.
Last but not least, 10 pressure transducers are deployed along the shore of the Sand Motor. These measurements will show the wave energy distribution around the Sand Motor, with which we test our hypotheses of why the Sand Motor is evolving as it is.
Questions or suggestions about the field campaign? Send an e-mail to: uusandmotor [at] gmail.com