Geotextile bags in groyne formation

This project provides an account of the construction and placement of the geotextile bags, referred to throughout this report as “geobags”. In 2017 Canterbury City Council, on behalf of Dover District Council, through the East Kent Engineering Partnership, submitted a Business Case for a five year programme of beach management works, titled the “Oldstairs Bay to Sandwich Bay Estate Beach Management 2017-2021” and as part of this application an opportunity for research and development arose.  

Geobags have been used in both the UK and internationally; however their primary function has been to avoid breach or defence toe protection to prevent undermining, such as the geobag trial between the Environment Agency and Shoreham Port, Sussex UK.  In addition they have been used in East Anglia on a sandy beach to reduce wave attack on the base of the cliffs and more regularly used on Australia’s sand beaches as control structures.

The geobag trial on the Walmer, Deal frontage is using the geotextile bags in groyne formation to form two controlling structures on a coarse shingle beach which rests at a 1 in 5 slope. The trial doubles as a test for the position of the rock groynes and the effect of their placement on an open stretch of coast before permanent rock groynes are constructed. Furthermore, the trial aims to test the durability of the geotextile in groyne formation, durability to abrasion from coast shingle, permanent placement in salt water and the durability of the handles and placement techniques.

The southern groyne was completed in June and the northern groyne was completed a week later.  A topographic baseline survey was undertaken immediately after construction of the southern one; which included topographic elevation points on the beach and the geobags.  A laser scan survey was undertaken, the day after the northern groyne was completed which included beach levels and the groyne position. In addition the southern geobag groyne was also scanned.

The surveys were conducted at different times to collect the geobags and the beach at their baseline condition, as soon as placement and beach recycling had taken place.

Future surveys of both groynes and the beach will be conducted over a single spring low tide once per month to provide a comparison of the beach levels in response to the groynes and to monitor the degradation of the geotextile.