This story is part of a special series that explores the global water crisis. For more, visit National Geographic's Freshwater website.

Pakistan’s extreme floods, which have displaced 20 million people and swamped a fifth of the country, have been made far worse by decades of river mismanagement, experts say.

In Pakistan’s wide plains where the bulk of the population lives, the rivers swelled by monsoons have been confined by levees, dams, and canals, in much the same way the Mississippi River has in the United States.

On Pakistan’s glacial-fed Indus River, the British started to build a system of canals and small dams for diverting water onto fields, when Pakistan was part of their Indian colony.

Since Pakistani independence in 1947, river managers have expanded the canal system. Now, instead of the natural flow from the Himalaya in the north to the Arabian Sea in the south, the Indus is diverted, piecemeal, east or west, wherever it is needed to support farming. Such river diversion is a common sight around the world as populations and food production boom.

These contrived river boundaries and tributaries in essence prevent the Indus River Basin from holding as much water as it once did during heavy and prolonged rains.

Farmland a Blessing and a Curse

The Indus and its canals are "the largest irrigation system in the world," says Tahir Qureshi, a forestry expert with the International Union for the Conservation of Nature (IUCN) and a former government forest officer and game warden.

Pakistan's irrigation system has turned this arid country into an agricultural powerhouse, but it has had its downside as well, experts say.

"The major river engineering is basically a Faustian bargain," says Daanish Mustafa of King's College London, recalling the fable in which a man sells his soul to the devil in exchange for a life of luxury. Mustafa is a geographer who has studied the history of Pakistan's river management.

Until a few decades ago, there were typically mild floods each summer—the time when the monsoon rainfall hits, and the melt from the snowpack in the Himalaya and Karakoram Mountains is at its peak.

But now, because humans have sculpted the river and the surrounding natural floodplain and wetlands for farming and other needs, there are fewer floods, but when they hit, they are far worse, said Mustafa.

"There's not very much space [in the river channel] to absorb all the rainfall," says Asad Sarwar Qureshi, a water resources expert at the International Water Management Institute (IWMI) branch in Lahore, Pakistan. "We need to get it back into shape, so that it can carry its original capacity."

Wetlands along the river’s course used to take up some floodwaters, and the government also used to divert excess water into "no man's land" during the monsoon season, he says. But those areas have been converted to farmland, he says.

"There was absolutely a mad rush to settle in these floodplains," says Mustafa.

Another part of the problem is that the Indus River and its tributaries carry some of the highest levels of silt of any river system. More silt equals less room for water as monsoons and snowmelt inundate the now-confined riverbed and canals.

"Most of our rivers and canals are already silted up," says IWMI’s Qureshi.

The Solution

Allowing the river to flood more regularly, and naturally, could help temper the floods and make them more tolerable, say Mustafa and other experts.

"They need to give the rivers room to expand," Mustafa says. "Not along the whole way, but they should restore some of the wetlands along the way."

At the same time, many of the levees should be kept in place, but maintained better, Tahir Qureshi says.

One way of doing this, he says, is to plant trees along the riverbanks.

"When I was in the forestry department in the 1970s and ’80s," Tahir Qureshi says, "we used to broadcast seeds of Acacia nilotica," a native tree species.

"They are soil binders, and a physical barrier to the flood flow. They are the flood guards, a biological means of protection."

In the past couple of decades, however, many of the embankment forests and trees have died or been chopped down, Tahir Qureshi says.

Managing Pakistan's floods is a delicate balance between giving the river more room, and building barriers to protect people and their land.