Pagladiya River: The Assam’s Shifting River

Pagladiya River

The Pagladiya river is a north bank tributary of the Brahmaputra River in Assam, India. Originating in the Bhutan Himalayas, the river traverses the floodplains of Baksa and Nalbari districts before joining the Brahmaputra River in the village Lawpara in Nalbari district

Pagaldiya is marked by a perennial yet shallow channel prone to heavy erosion and dramatic lateral shifts. As a rainfed river in an earthquake-prone zone, the Pagladiya tends to heavily erode its banks and drastically change course across the Brahmaputra Valley. Its channels also shift laterally during storms.

As fertile farmlands gets flooded from the pagladiya floods, dam building has been planned since the 1960s to control its floods and waters.

The construction of the Pagladiya Dam project was cleared by the Government of India in January 2001. However, Indigenous families in villages along the Pagladiya oppose such large dams. They refuse to lose their riverside ancestral grounds to dam reservoirs or get displaced under rehabilitation plans. Due to both natural geological shifts and social concerns about local cultures, proposed major dams over the Pagladiya have long stalled.

Where is the Pagladiya River located?

The Pagladiya River originates in the foothills of Bhutan and flows through the Baksa and Nalbari districts of Assam, India before joining the Brahmaputra River as a tributary.

What are the key characteristics of the Pagladiya River?

The Pagladiya river is characterised as a perennial river, having very shallow water depth, and is prone to flash floods and high discharge rates due to its characteristic of changing course.

What indigenous water systems exist on the Pagladia River?

The indigenous Bodo tribes of Assam have built traditional “dongs” to tap the Pagladia’s flows for their villages. These dong systems divert river water into earthen canals via small dams made locally using tree branches, stones and boulders.

The diverted Pagladia water gets stored in village ponds called pukhuris or used directly to irrigate fields. Convex dams help regulate water levels in the canals tapping the strong currents of the mountain river as it descends onto Assam’s plains.

Further, branches and sub-canals sprout off the main canals to distribute water widely across the villages. Managed by local committees, this network aims to provide water equitably to the entire community on fixed twice-daily schedules.

Pagladia Dam

A minor dam was first planned on the Pagladia in 1968 to control floods, budgeted at Rs. 126 million. But in 1984, the Brahmaputra Board took over the project and hugely increased its scale and goals to include irrigation and power generation too, rocketing costs to Rs. 5.4 billion.

However, this ambitious mega dam has not begun construction even after 35 years of planning. This is because the frequent, wide shifts in Pagladia’s river course makes building permanent dams difficult. More importantly, generations of indigenous families who stand to lose their riverside farms and homes strongly oppose the dam. They reject the rehabilitation offered for their displaced communities as inadequate.

With feasibility and people’s consent yet to be secured, the Pagladiya Dam proposal remains stalled despite decades of pursuit.

What was the original plan for the Pagladiya River?

The dam was originally planned in 1968 as a minor flood prevention project, at an estimated cost of Rs 126 million.

How was the project scope expanded over time?

In 1984-85 the project was taken over by the Brahmaputra Board and redesigned as a multipurpose project with irrigation and hydropower generation added to its objectives. Further additions raised its cost to Rs 5.4 billion by 1999.

How is the water quality of the Pagladiya River monitored?

Water quality is monitored under India’s National Water Quality Monitoring Programme (NWMP) at one location along the Pagladiya River stretch.

It is found to mostly meet the prescribed standards, except for high BOD levels recorded in around 19 of 47 tests during floods from 2016-19, when embankments breach.

What species are found in the Pagladiya River?

Pagladia River nourishes abundant fish and mollusks. Carp-like cyprinids comprise the biggest group among at least 10 identified fish families living here. Other key varieties include catfish, perch and eels. The river also harbors a diverse mollusk population – 6 species across 2 classes and 4 families spotted so far.

While cyprinids dominate, the Pagladia supports many species suited to its constantly shifting nature. These include fish that migrate within the river system as well as mollusks rooted in its unstable banks.