Rivers are changing all the time, and it affects their capacity to contain floods

phys.org | 10/25/2019 | Staff
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The rainfall that has inundated the North of England is the latest in a long line of flood events that are becoming the country's new normal. Indeed, across the world, flooding is expected to become more frequent and more extreme as the planet heats up.

Building robust flood defenses and modeling vulnerable areas is crucial if we are to avoid loss of life and livelihoods from these devastating weather events. But our new research reveals that the capacity of rivers to keep water flowing within their banks can change quickly—and in failing to acknowledge this, some flood models and defenses may be under-equipped to deal with the consequences when they do.

Flooding - Rainfall - Part - Explanation - Floods

Many assume that flooding is due to heavy rainfall. This is true, but only part of the explanation. Floods also occur when the amount of water running off the land exceeds the capacity of rivers to carry that flow—as was the case when the River Don breached flood defenses in the Sheffield area recently. So, floods are partly caused by the amount of rain falling, partly by the moisture that is already in the ground, and partly by the capacity of rivers to contain water within their channels.

This means that if the capacities of river channels change, then two identical rainfall events falling on similarly wet ground can cause flooding of very different severity.

Rivers - Sediments - Water - Humans - World

Most rivers are forever changing. They are shaped by the sediments and water they carry. Humans have modified most of the world's rivers in some way. In some cases this is through direct influence, such as dam construction or river engineering. Other influences are indirect—building on nearby land reduces the capacity of ground to absorb water, agriculture draws water from rivers, and deforestation leaves more water to flow elsewhere.

Rivers respond to changes in climate as well. During drier...
(Excerpt) Read more at: phys.org
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