Video monitoring for coastal management and engineering
The use of the Argus video system offers 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, impact of 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 half an 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.
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 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 monitor long-term shoreline evolution in both erosive and accretional areas
- to assess the morphologic changes around coastal structures, like groins and harbour moles
- to assess dune erosion during heavy storm conditions
- to characterize bar dynamics
- to assess morphologic changes from patterns of breaking waves
- to evaluate the performance of a sub-aqueous beach nourishment
- to evaluate pre- and post-construction environmental impact
- to monitor hydrodynamics (longshore current velocity, wave period and direction)
- to monitor beach use on touristic beaches
- for dissemination purposes to the public
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 about 30 Argus stations worldwide, 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.