The use of a low cost, time-lapse camera for high frequency monitoring of intertidal beach morphology

Coastal monitoring of sandy beach areas requires data gathering at regular time scales to capture daily to weekly geomorphological changes that are modified through tidal and wave action. Regular GPS profiling surveys carried out at medium (weekly) to long-term (month/annual) frequency can lead to misinterpretation of beach changes as they are not able to pick up subtle gross changes and instead usually only capture net changes that have occurred. Recently, a new suite of monitoring devices such as Terrestrial Laser Scanners, airborne LiDAR or the use of Unnamed Aerial Vehicles have become more readily available and have in many cases replaced traditional monitoring methods (e.g. the use of Emery method and GPS) as they can capture contemporary morphological impacts faster and more conveniently. Monitoring coastal systems using video cameras is also an increasingly common monitoring method as it allows a continuous monitoring method through the image capture at different time-scales.

Here, we present the use of high-frequency imagery generated from a low-cost, fixed, time-lapse camera system as an effective method for quantifying intertidal bar migration patterns on a daily to annual time scale. The time-lapse camera system was deployed over-looking a beach-dune complex at Five Finger strand, NW Ireland. It was located on high ground (around 80 m) obliquely overlooking the study site, with a field of view of 59° and set to acquire images every 30 min. Images captured were calibrated using multiple ground truth Ground Control Points (GCPs), positioned at regular geo-located intervals along intertidal profile lengths. Further, average distance of each pixel on the ground was converted into real-world distance using a pre-calculated scaling factor.

The method successfully tracked the leading edge of an onshore migrating intertidal bar using a set of chronological captured images over a shoreward distance of 31.23 m in a 3-month period. The technique can also be used in the monitoring of wave run-up and dune toe encroachment events by waves during high energy events. The use of the camera over long time periods provided a rich dataset for examining both long-term intertidal beach dynamics of sites to help fully compare forcing and response phenomena in between forcing events. We believe that this easy-to-use and low-cost technique will enhance future monitoring of highly dynamic coastal systems enabling a more detailed spatial and temporal analysis of intertidal sandy beach areas.