Argus

Video monitoring for coastal management and engineering

The recent use of ARGUS video systems has offered enhanced opportunities for the monitoring of morphodynamics of the nearshore zone.

Covering space scales from less than a metre to several kilometres and time scales from seconds up to years, a wide range of coastal issues can be addressed, such as shoreline evolution, groins and beach nourishments. As data collection is automatically performed by unmanned video stations, operation is cost-efficient, enabling the technique to be competitive to the traditional survey methods of beach bathymetry and shoreline. Complementary to Deltares ' modelling tools like the Delft-3D system, the ARGUS video technique has been embedded as a monitoring tool in our consultancy practice.

Video data collected with an ARGUS station

Every daytime hour, snapshot images are collected and averaged over a period of 10 minutes, yielding time-exposure images. With the help of sophisticated routines, these oblique images can be projected on the ground plane, resulting in rectified images. These rectified images allow for the quantitative interpretation of image features. If multiple oblique images are rectified simultaneously, so-called merged images can be obtained, which give a plan view of the nearshore zone. The following figure shows an example of such a merged image of Noordwijk, The Netherland.

Information derived from ARGUS video images

The rectified video images show bright, longshore bands, clearly indicating the locations where waves preferably break. As the breaking of waves is caused by depth-limitation, the bright intensity patterns reflect underlying bottom topography. In addition, the location of the waterline can easily be identified. Taking into account the tidal level, this enables the intertidal beach bathymetry to be mapped using a sequence of hourly-sampled images. Finally, in the absence of breaking waves, local water depth could be estimated from the propagation speed of individual waves as observed from time series of image intensity at distinct locations. In this way, the morphologic changes of a coastal system can be monitored cost-effectively over long-term periods.

In practice, the ARGUS based monitoring system can be applied in the field of coastal zone management and coastal engineering, in a number of ways:

• to assess the morphologic changes around coastal structures, like groins and harbour moles, from patterns of breaking waves, in addition to their impact on neighbouring coastal areas
• to evaluate the performance of a sub-aqueous beach nourishment
• to monitor long-term shoreline evolution in both erosive and accretional areas from a so-called time stack images
• to assess dune erosion during heavy storm conditions
• to evaluate pre- and post-construction environmental impact
   

Summary

An ARGUS based monitoring system allows for enhanced opportunities for the monitoring of coastal systems, to serve consultancy over a wide range of coastal zone management related issues. Based on data from ten ARGUS stations worldwide (see the Oregon State University site), an extensive research group is continuously working on the development of tools for the quantitative interpretation of video data. Deltares has a license agreement with Oregon State University for the installation of ARGUS stations world-wide outside Northern America. Recently, the number of sites has been extended with two more ARGUS stations, one at Egmond, The Netherlands and one at the Gold Coast, Australia.