The national waterway project may put the turtles of Varanasi Ghats at stake, claims new study

Boats at Varanasi Ghats in Banaras, Uttar Pradesh, India
(Image credit: Jorge Royan/Wikimedia commons)

By Melbin Thomas

Large vessel movement through the Ganga River as part of the proposed National Waterway-1 system under Jal Marg Vikas Project (JMVP) will pose a major threat to the geomorphology of the river and endanger the habitat of soft shell turtles in Varanasi Turtle Sanctuary (VTS), claim researchers from IIT Kanpur and Wildlife Institute of India.

According to their study published in the Current Science journal, the geomorphology within the VTS has remained stable for the past 50 years, except for some minor changes. National Waterway-1 system under JMVP which proposes to connect Allahabad in Uttar Pradesh and Haldia in West Bengal, enabling the movement of large cargo vessels through VTS, may disturb this stability, says the study.

The large wavelength waves produced by large cargo ships on the water surface can exert lateral force on the banks. Such waves also have the tendency to travel far in comparison to waves with lesser wavelength. The waves would travel laterally and hit the banks and sometimes the channel bed; this may induce shear stress that can erode or re suspend sediments in the water column.

“Increase in ship traffic in the channel can increase bank erosion and sediment suspension of the Ganga River, and may hamper the existing suitable environmental conditions in VTA”, says the study.

To reduce pollution load in the Ganga River due to the large human population and associated effluents, soft shell turtle species were introduced in the Ganga River at Varanasi in 1989, under Phase-1 of the Ganga Action Plan 2. The soft shell turtle (Nilssonia gangetica) feeds on human carcasses that are released into the river as a part of religious ritual at the Manikarnika and Harishchandra Ghats in Varanasi. They help in disintegrating large decaying organic matter. To ensure protection of these turtle species from poaching and other accidental human encounters, their habitat at Varanasi, a 7 km long stretch from Ramnagar to Malviya Bridge was declared as the Varanasi Turtle Sanctuary (VTS) under the Wildlife (Protection) Act, 1972. VTS is the only such protected area for fresh water turtles in the country.

Apart from turtles, this stretch of the Ganga River is important for other conservation dependent species such as Gharials (Gavialis gangeticus), dolphins (Platanista gangetica) and several island nesting birds.

The study indicates that VTS has adequate depth throughout its reach to support turtle habitat even during the low flow period. A stable morphology and hydrodynamics of the river channel provide a suitable habitat for turtles and other faunal species. However, construction activities along the bank, movement of large vessels, sand mining in the sanctuary or dredging of the main channel may destabilize the river geomorphology that will negatively affect the integrity of the VTS as well as the Ghats at Varanasi.

As the Ganga is an alluvial river, it is susceptible to erosion. Any form of alteration in the existing physical habitat conditions, such as bank-side construction activities and large-scale river traffic may not only affect the channel stability but in turn will also cause irreparable damage to the Sanctuary as a habitat and also to the Varanasi Ghats. “We urge that it will disturb the morphological equilibrium that has been maintained in this region for long”, say the researchers.

The study adopted two different approaches -planform mapping and hydraulic assessment. In planform analysis, researchers studied and compared significant changes that have occurred in the different geomorphic units such as islands, bars, pools and riffles. For the assessment of hydraulic geometry (width, depth, velocity and discharge) of the river, we have used an Acoustic Doppler Current Profiler (ADCP) which works on the principle of Doppler Effect. It emits high-frequency acoustic pulses and receives a proportion of the emitted energy that is reflected back by the suspended particles or bubbles.

Gaurav Kailash Sonkar and Kumar Gaurav with the Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research, Bhopal, Niladri Dasgupt and Syed Ainul Hussain of Wildlife Institute of India and Rajiv Sinha of Department of Earth Sciences, Indian Institute of Technology, Kanpur conducted the study.