Geobag for slope protection

Abstract: River bank erosion is getting worse in many places as human activity changes river channels. Eroding banks can be restored and protected with erosion control structures, and geotextiles are one of the main materials for them. A Geobag is a geotextile application: a large bag of geotextile fabric filled with sand or soil and placed against the bank. This post explains how geobags protect slopes and banks, using the Panchganga river in Kolhapur as an example of where bank erosion is a growing problem, and covers four common applications.

The Panchganga rises in the Western Ghats and flows through Kolhapur district in Maharashtra. It is formed in the steep western talukas of the district by the Kasari, Kumbhi, Tulsi and Bhogawati rivers (local tradition counts the Saraswati as a fifth). It flows east past Kolhapur city and joins the Krishna at Kurundwad, near Narsobawadi, before the Krishna enters Karnataka. Bank erosion along it is getting worse because of farming encroachment on the banks and frequent floods, and farmers in the basin are worried about losing land. River bank protection is needed there, along with a way of checking whether the erosion control works.

Industrial textiles grew out of the invention of man-made fibres in the twentieth century. A geotextile is any textile product used in or under the soil, and geosynthetic materials are now standard in geotechnical and civil engineering.

The three basic types of geotextile fabric are non-woven, woven and coir geotextiles. Each has properties that suit particular applications, and each comes in a range of weights and strengths. A non-woven geobag is made of technical fabric sewn tightly on three sides and left open on the fourth. It is filled with soil or sand and placed during the construction of marine and hydraulic works. Geobags are made of polyester or polypropylene geotextile, non-woven or woven, and protect hydraulic structures and river banks from erosion and scour.

Sand-filled geobags are used to protect riverbanks, shorelines and beaches, and to build flood defences. Below are four key applications and benefits of geobags.

Soil Erosion Prevention on Riverbanks

India has many large rivers, and bank erosion is a serious problem along them. Eroded soil silts up river channels, which makes flooding worse, and farmland and riverside habitat are lost with it. Geobags laid in layers against the bank (often over a geotextile filter) protect the slope from the current while letting water drain, and they follow the bank as it settles. Stopping erosion keeps the soil, and the farm land on it, in place. Ocean has supplied geobags for this kind of work, for example the 9,000 geobags used to protect flood-prone banks at Chhapra, Bihar.

Flood-Prevention Alternative That Isn’t Expensive

Conventional flood-control works such as concrete walls and stone revetments are expensive, which makes them hard to build everywhere they are needed. Geobags are a cheaper alternative. Filled with local sand, they can be stacked into barriers that divert flood water or slow it down. These walls cost less to build, and they can be placed next to existing structures and buildings without damaging them. The same low-cost walls can form small check dams for rainwater harvesting in drought-prone areas such as Maharashtra’s Marathwada.

Ports, Dams, and Harbours Construction

Geobags are used in building ports, dams, harbours and other water-front structures because a mass of filled bags resists strong currents and wave action. They protect the foundations of these structures from scour and help keep the water from eroding the land around them. Where the current is strong, geobags can add protection around dock and jetty foundations.

Groynes and Breakwaters Under Scour Protection

Groynes and breakwaters are built out into the sea to protect the coast from waves. Over time, waves and currents scour the seabed at their base, which undermines them and puts the coast behind at risk. Geobags placed as scour protection around the toe keep the sand at the base in place, which extends the life of the groyne or breakwater at lower cost than rock armour.