Flood Protection in Bihar – Case Study

Ocean Non Wovens supplied Ocean Geobags for flood protection in Bihar, one of India’s most flood-affected states. Filled with sand, the bags build walls and embankment protection that divert flood water and slow the river’s attack on its banks.

Product – Ocean Geobags

Quantity – 1.5 L (lakh) bags

Location – Bihar

Problem

Floods damage the infrastructure people depend on most: drinking water, telecommunications, hospitals and electricity. When factories flood, contaminants can reach nearby rivers and lakes and cause harm for years. Heavier and more intense rainfall linked to climate change, along with rising sea levels, is making flood protection a larger part of climate adaptation worldwide. According to the UN Office for Disaster Risk Reduction’s report The Human Cost of Weather-Related Disasters 1995–2015, 3,062 flood disasters in those 20 years affected 2.3 billion people and killed 157,000.

Bihar lies in the Ganga basin and is the most flood-prone state in India. About 73% of its land area is flood-affected, which is about 17.2% of India’s total flood-prone area. About 65% of the catchment of north Bihar’s rivers lies in Nepal and Tibet, and only 35% in Bihar, so much of the water that floods the state falls as rain beyond its borders. Bihar’s flat terrain, an average annual rainfall of about 1200 mm and heavy sediment loads in its rivers add to the risk.

The main flood-causing rivers are the Ghaghara, Gandak, Burhi Gandak, Bagmati, Kamla, Bhutahi Balan, Kosi and Mahananda, which overflow during the monsoon. The Kosi, which shifts its course and breaches embankments, is known as “Bihar’s sorrow”.

Recent floods show the scale of the problem:

• 2007: among the worst floods in Bihar’s recent history, affecting more than 10 million people with heavy property losses.
• 2017: floods affected more than 15 million people in Bihar.
• 2019: floods hit about 13 districts, affecting more than 8 million people and causing significant property losses.
• 2020: more than 8 million people were affected, on top of the hardship caused by COVID-19 and the lockdowns.

Solution

Conventional flood defences, such as earth embankments with stone pitching or concrete walls, are slow and expensive to build and need quarried stone that often has to be hauled long distances to the Gangetic plain. Geobags are a cheaper alternative. Ocean Geobags are filled with sand, usually dug on site, and placed to build walls that redirect flood water or slow the river. Sand-filled geobag walls are low-cost, quick to assemble, and do not damage existing structures and buildings.

A geobag is made of non woven geotextile, so it acts as a filter: water passes through the fabric, but the sand stays inside. Laid in overlapping layers, the bags form flexible revetments and launching aprons that follow the riverbed as it scours, instead of cracking like rigid protection. The same properties make geobags useful for harbours, dams and other water-related structures, and for protecting foundations in areas with strong currents, where the bags resist heavy water flow and keep water from eroding paths under and around the structure.

On a river bank, the slope behind the bags is usually covered with a geotextile filter layer so that fine soil cannot wash out between the bags. For larger volumes or longer embankments, sand-filled geotubes are another option.

See more river and flood protection projects in our case studies.