Land use changes led to floods in Nethravathi: IIT-B

Rapid urbanisation that led to increased concretisation and loss of forest due to rise in farming are the two major contributors behind frequent floods in the Nethravathi basin in south Karnataka, researchers at IIT Bombay have demonstrated.

The conclusion was drawn on the basis of a sophisticated computer model-based study on the land use and land-use changes analysing the trend.

While the research was conducted for the Nethravathi basin, its conclusion hold water for other basins too.

“Flood is a consequence to unplanned growth in the river plain. What happened to Kerala and south Karnataka this time can also be blamed to unplanned urbanisation to a large extent. So much of unplanned development took place in the periphery of Perriyar river in Kerala damaging the flood plain,” T I Eldho, a professor of civil engineering at Indian Institute of Technology, Bombay told DH.

Earlier this year, Eldho and his colleague Rakesh Kumar Sinha showed heightened flood risk was an outcome of the change in basin characteristics seen along the Nethravathi.

Such land use changes increase draining of the rainwater and washing away of the soil downstream in the Netravathi basin, compounding the flood risk.

Studying the changes at five different time periods since 1972 and one projected scenario for 2030, the Indian Institute of Technology Bombay team reported that urbanisation enhanced the risk of floods, adversely impacted groundwater availability and caused loss of agricultural productivity due to erosion.

The Netravati originates in the Western Ghats, and is the primary source of drinking water for Mangalore and Bantwal in Dakshina Kannada district. “Approximately 1.2 million people live in the Netravati basin, and this number is expected to more than double by the year 2030.

The study – published recently in the journal Environmental Earth Sciences - reports a four-time increase in the urban area from about 60 sqkm in 1972 to 240 sqkm in 2012 and projects it could increase to a whopping 340 sqkm by 2030.

Increasing agriculture is the second major cause for the alterations in basin characteristics. Since 1972, the agricultural area has increased by around 15% until 2012 and is projected to increase by another 24% by 2030.

On the contrary, there has been a continuous decrease in the forest area resulting in 18% of deforestation during the same period. The study predicts a further decline of about 26% in the forest area by 2030.

“This kind of heavy rainfall seen in 2018 can be expected once in 50 or 100 years. But with proper water and basin management, the scale of damage could be curbed,” said Eldho.