The river known as the "Shok" of Bihar is the Kosi River. The Kosi River is often referred to as the "River of Sorrow" or "Sorrow of Bihar" due to its long history of causing devastating floods in the state of Bihar, India.

Reasons for the Nickname:

1. Frequent Flooding: The Kosi River is notorious for its frequent and destructive floods. These floods result from a combination of factors, including heavy monsoon rainfall in the catchment area in Nepal, glacial meltwater from the Himalayas, and the river's tendency to change course.

2. Dynamic River Course: The Kosi River is known for its ever-shifting course, which is caused by the large amount of silt and sediment it carries from the mountains. The river often breaches its embankments, causing widespread flooding and displacement of people.

3. Historical Impact: Over the centuries, the Kosi River's floods have had a profound impact on the landscape and people of Bihar. Villages, farmlands, and infrastructure have been repeatedly inundated and damaged, leading to significant economic and human losses.

4. Human Tragedy: The floods caused by the Kosi River have resulted in tragic loss of life and displacement of communities. It is estimated that millions of people have been affected by these floods over the years.

Efforts to Manage the Kosi River:

Efforts have been made to manage and control the Kosi River's devastating floods. The Kosi Barrage, also known as the Bhimnagar Barrage, was constructed to regulate the river's flow and mitigate the impact of floods. Additionally, embankments and levees have been built along the river's course to contain its waters.

Despite these measures, the Kosi River remains a challenging and unpredictable watercourse, and flood management in the region remains a continuous endeavor. The river's reputation as the "River of Sorrow" serves as a reminder of the persistent challenges posed by natural forces in the region and the need for ongoing efforts to protect and support the communities along its banks.