Babai

The Babai is a river of the western Terai region of Nepal, rising at the eastern end of the Dang Valley in Dang Deukhuri District at an elevation of about 672 metres. The Dang Valley is an oval inner-Terai (Bhitri Madhesh) basin set between the higher Mahabharat (Lesser Himalaya) ranges to the north and the lower Siwalik (Churia) hills to the south, and the headwaters of the Babai drain much of this valley before the river breaks out toward the west.

From Dang the Babai flows into Salyan District, threading between sub-ranges of the Siwalik hills along a generally west-north-west axis. After receiving the Sharada Khola from the right, the river continues further before crossing into Bardiya District, where it enters Bardiya National Park and runs through the park's core as the Babai Valley. The river is frequently cited as having a total length on the order of 400 kilometres.

Unlike many Himalayan rivers, the Babai is a Siwalik- and inner-Terai-fed river rather than a snow-fed Himalayan one, so its flow is strongly seasonal and rainfall-driven. After leaving Nepal it crosses into Uttar Pradesh, India, and ultimately joins the much larger Ghaghara (Karnali/Ghaghara system) from the left in the plains west-north-west of Bahraich, rather than meeting the Karnali while still inside Nepal.

The Babai drains a catchment of roughly 3,500 square kilometres in Nepal, with an additional 200 square kilometres or so in India. Its long-term average discharge is on the order of 71 cubic metres per second, but flow varies enormously with the monsoon: dry-season lows can fall to around 4 cubic metres per second in April, while peak monsoon flows in July can rise to several hundred cubic metres per second.

The principal named tributary on the Nepalese reach is the Sharada Khola, which joins the Babai from the right after draining a large share of Salyan's middle-hill country. Numerous smaller seasonal streams (kholas) descending from the Siwalik hills feed the river along its course through Dang, Salyan and Bardiya, swelling it rapidly during heavy rain and contributing to its highly variable, flashy regime.

Because much of its basin lies in the geologically young and easily eroded Siwalik zone, the Babai carries a heavy sediment and bedload during high flows, building the broad gravel and sand floodplain that characterises the Babai Valley within Bardiya National Park.

The Babai is the receiving river of the Bheri Babai Diversion Multipurpose Project (BBDMP), Nepal's first inter-basin water-transfer scheme. The project diverts water from the neighbouring Bheri River into the Babai through a long headrace tunnel, with the aim of providing year-round irrigation to roughly 51,000 hectares of farmland in the Banke and Bardiya districts of the western Terai, a region that has historically suffered from seasonal water shortages.

The diversion is designed to transfer about 40 cubic metres of water per second from the Bheri into the Babai, taken behind a barrage of roughly 13 metres in height in Surkhet District. The transfer tunnel, about 12.2 kilometres long, was notably the first in Nepal to be excavated with a tunnel-boring machine (TBM), an engineering milestone reported when the breakthrough was achieved in 2019.

Exploiting the head between the Bheri intake and the lower Babai, the project also incorporates a hydropower component with an installed capacity of roughly 46.7 MW. Conceived as a national-pride project, construction began in the mid-2010s but has faced repeated delays and cost revisions, with completion and full water diversion pushed back well beyond the original early-2020s targets.

The upper Babai basin in the Dang-Deukhuri area is one of the culturally rich pockets of western Nepal, long associated with the indigenous Tharu people and, historically, with the principality of Tulsipur. The valley is dotted with temples and shrines linked in popular tradition to Shaivism, Shaktism and the Gorakhnath (Nath) tradition, and to legends drawn from the Mahabharata.

Among the prominent sites near the river is the Dharapani temple, situated in the Dang area, which local tradition associates with the Pandavas of the Mahabharata and which has become a notable pilgrimage and tourist destination. Other revered temples in the surrounding district, such as Ambikeshwari (a Shakti shrine) and Dhorbarahi, reinforce the area's standing as an important religious landscape of the mid-western Terai.

As with many Nepalese rivers, the Babai's waters and its riverbank sites carry ritual significance for nearby communities, and the river's valley supports a blend of mainstream Hindu observance and distinctive Tharu cultural practices.

Within Bardiya National Park, the Babai is the second great river system of the park alongside the Karnali, and the Babai Valley is regarded as some of the most pristine wildlife habitat in the Nepalese Terai. After the people who once farmed the valley were resettled outside the park, cultivation ceased and the naturally regenerating grasslands and forest became prime habitat for tigers, the greater one-horned rhinoceros, deer and other species.

The protected stretch of the Babai is one of the most important refuges in Nepal for the critically endangered gharial (Gavialis gangeticus), a fish-eating crocodilian known from only a handful of locations across Nepal and India. A 2017 survey along about 46 kilometres of the Babai counted 77 crocodilians, comprising 46 gharials and 31 mugger crocodiles, and successful gharial nesting and hatchlings have since been documented in the Karnali-Babai system, signs of a tentative recovery.

Conservationists value the Babai partly because its reach inside the park has remained largely free-flowing, an increasingly rare condition for South Asian rivers. The Bheri-Babai diversion, by altering downstream flows and sediment, has raised concern about impacts on gharial habitat and aquatic ecology. The river also poses natural hazards: its steep, sediment-laden Siwalik catchment makes it prone to flash flooding and channel shifting during the monsoon, affecting floodplain communities and infrastructure in Dang and Bardiya.