Bihar received 27 per cent below-normal rainfall between June 1 and the first week of September. Even then, large parts of the state are under water. The Ganga, Gandak, Kosi, Budhi Gandak, Punpun and Ghaghra have all risen above danger levels in different stretches. A combination of high upstream river flows and erratic weather — spells of heavy, localised rainfall amid an overall rainfall deficit — has contributed to the rivers spilling over their banks. The unusually high level of the Ganga also created a “backwater effect” in the Gandak and Punpun. Since these rivers drain into the Ganga, its high water level made it difficult for them to discharge their water. As a result, water backed up in the tributaries, adding to the flooding.

Since colonial times, flood-prone Bihar has tried to contain its rivers within defined channels through embankments. But embankments separate rivers from their floodplains, while continuous silt deposition raises riverbeds and reduces channel capacity. When an embankment breaches, the artificially contained water can rush into homes and fields. Bihar, therefore, needs to revisit the idea that higher or stronger embankments will ipso facto contain floods. Embankment maintenance must be accompanied by the restoration of drainage channels, protection of floodplains, better land-use planning, restoration of wetlands, and deployment of early-warning systems. The Ganga Basin River Management Plan, implemented for more than a decade, acknowledges these imperatives. But the persistent monsoon floods in Bihar underline that much needs to be done to give the river space to spread safely during periods of high discharge. Addressing Bihar’s concerns will require greater coordination between the riverine states on reservoir releases.

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Bihar has long argued that the Farakka barrage and the India-Bangladesh Ganga Water Sharing Treaty have compounded the state’s river-management challenges. It contends that the barrage has altered the Ganga’s flow regime, affecting the movement and deposition of sediment load. The extent to which this contributes to floods in Bihar remains contested. Even so, renegotiation of the 1996 treaty, which expires in December, should take into account Bihar’s concerns over silt accumulation and the state’s river-management needs. The new arrangement needs to be informed by updated data on river flows and climate-change projections. In an era of erratic weather, states and countries sharing river basins should strengthen coordination to manage water flows and mitigate flood-related distress.