Protecting Foreshores and Coastlines with Purposedly-designed Geotextiles

The Project

The Warilla Seawall, extending over 930 meters, was established as an emergency response to storm events in 1966 that jeopardised private real estate and sewerage facilities. Over the years, subsequent reinforcements were executed following significant storm events After significant damage in 2016, periodic repairs became necessary. While traditionally termed a seawall, the structure at Warilla beach is technically a revetment. To maintain community recognition, the rejuvenation project is aptly titled a 'seawall renewal'.

The Challenge

Coastal erosion (or shoreline retreat) is the loss of coastal lands due to the net removal of sediments or bedrock from the shoreline, driven by the action of waves and currents, but can also result from mass wasting processes on slopes, and land subsidence. In addition, heavy rainfall can enhance the saturation of soils, with high saturation leading to a reduction in the soil's shear strength, and a corresponding increase in the chance of slope failure (landslides).

Shellharbour Council has been successful in securing a State Government grant via the Coastal and Estuary Grants Program for the reconstruction of the ailing seawall, which was first built in the 1960s. The 930 metre wall is eroded and unstable, and as a result will be rebuilt to modern engineering standards to address coastal erosion and public safety concerns.

Our Solution

A properly designed revetment will provide robust protection to foreshore assets and require minimal commitment to future maintenance.

The new wall will be constructed from 3 different size ranges of rocks. The primary layer will be smaller rocks 25mm to 300mm in diameter. The secondary layer will be rocks 100kg to 650kg. The outer or armour, visible, layer will be rocks 2t to 4t. The type of rock used will be selected to ensure it does not breakdown nor decompose in the marine environment.

Protection layers, typically heavy mass non-woven geotextiles, such as Profab® Ultra are used in geosynthetic engineering to reduce the occurrence of local stresses and thus to control potential puncture of the liner by the material installed directly above, typically an aggregate drainage layer.

The Result

Coastwide Civil have been engaged by Shellharbour City Council to construct the Rock Revetment to the Northern and Southern Sections of Warilla Beach approximately 800 meters, in Warilla, NSW. Coastwide Civil were selected for their extensive experience and on the back of being one of the most renowned and experienced marine contractors on the East Coast of Australia.

Global Synthetics AS1200X Profab Ultra, is a specifically designed non-woven geotextile was placed below the rock layer.  The geotextile layer then acts a protection layer, protecting the underlying soil from the rock, whilst providing vital filtration to prevent future erosion from tidal activity.

The hydraulic and filtration properties of 1200X geotextiles makes it highly effective in replacing traditional filter layers. Typically, a single layer of geotextile can replace a succession of stone filter layers. A single bedding layer of stone is laid on the geotextile and this is followed by the rock armour.

For unparalleled expertise and tailored solutions for your upcoming projects, look no further than Global Synthetics. Our team is ready to guide and support you every step of the way.