Role of Geobags and Gabions in Flood Protection

A flood can turn a calm river into a destructive current within hours, taking lives and destroying homes, farmland and public infrastructure. Many rivers now flood more often and more severely as rainfall patterns change.

Coasts face the same pressure from the sea. According to the UN, about 40% of the world’s population lives within 100 km of the coastline, and the IPCC’s 2019 Special Report on the Ocean and Cryosphere projects global mean sea level rise of roughly 0.43 to 0.84 m by 2100 (relative to 1986–2005), depending on emissions.

Protecting people, property and infrastructure from rising seas and heavier river floods is one of the main engineering problems of the 21st century.

Geosynthetics have been used in shoreline and river protection for decades, and depending on the site they are often cheaper and quicker to build than rock or concrete. Two of the most widely used for flood work are geobags and gabions, which protect riverbanks, embankments and coastlines against erosion and scour.

Use of Geobags and Gabions in Flood Protection:

Geosynthetics are used in flood defence to stop erosion, strengthen riverbanks and coastlines, and raise or protect embankments. Geobags, also called Geotextile Sand Containers, are sand-filled geotextile bags used mainly for riverbank and shoreline protection.

Geobags are made of heavy-duty woven or non-woven geotextile in polypropylene, polyester or polyethylene. They are laid as revetments on the bank slope and as launching aprons at the toe, where they settle into scour holes and armour the bed. On large rivers they are also packed inside steel wire or PP rope gabions to make heavier, more stable units for scour protection.

Geobags are filled with sand on or near site, which saves hauling rock, and stacked in layers for coastal protection, dams, levees and inland waterways. Their seams are sewn to survive rough handling and dumping, and the fabric retains the sand under abrasion and wave or current action.

Gabions suit taller structures. Stacked as gravity retaining walls along a bank or embankment, they make permanent flood protection structures, and are usually cheaper than concrete walls.

Gabion baskets filled with local stone form a heavy, permeable and flexible structure that can settle without cracking, which suits flood-prone waterways. Heavily galvanised wire, often with an extra PVC coating for polluted or saline water, gives a long design life. River works mostly use double-twisted hexagonal mesh, which stays intact if a wire breaks; welded mesh gabions joined with spiral binders are used where a rigid, neat face is wanted. Both resist current and debris impact once filled.

Choosing Between Geobags and Gabions

Use geobags where sand is at hand, rock is scarce, and the job is revetment or toe protection on a sandy bank, as on many reaches of the Ganga and Brahmaputra. Use gabions where a taller wall is needed or stone is available locally. Both are assembled on site, need little maintenance, and use less cement than concrete alternatives. Ocean’s Chhapra, Bihar geobag project shows geobags used on a flood-prone riverbank.

Ocean Geosynthetics supplies both gabions and geobags for flood protection.

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