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Strategic tree planting in floodplains could reduce the height of floods in downstream cities by up to 20 percent.
According to a study published in the journal "Earth Surface Processes and Landforms," researchers from the universities of Birmingham and Southampton studied an entire basin in the New Forest, England, in an area of 100 square kilometers, upstream from the town of Brockenhurst. These experts wanted to understand how tree planting, river restoration, and levees could affect the "peak height" of a flood in a downstream urban area.
The research was funded by the UK Environment Agency which is interested in the potential of river restoration techniques for incorporation into broader flood risk management programs. Using a digital landscape terrain model and a hydrological simulation model, the scientists found that planting trees in the floodplain and increasing the number of blockages, over 10-15 percent of the total length of the river, it could reduce the peak height of a flood in the city by 6 percent once the trees have grown for 25 years.
They also found that more extensive forest planting and river restoration restoration, for example between 20 and 25 percent of the total river length, resulted in a reduction in peak flood height of up to 20 percent. hundred. As the age of trees and forests increases up to 100 years after planting, there are greater reductions in peak flood height.
"As our research shows, targeted tree planting and restoration can contribute to flood risk reduction. We believe tree planting can do much to reduce flood risk and should be part of a flood management approach. broader flood risk, including conventional flood defenses.
The planting of trees would represent an extra element that would help to slow down the arrival of rainwater to vulnerable places, "says Dr. Simon Dixon, from the Institute of Forestry Research at the University of Birmingham.
The research team also studied engineered artificial blockages, such as levees, which have numerous ecological benefits and have been shown to reduce the local speed of river flow. The scientists found that although levees slow flow, this does not always translate into a basin-scale reduction in flood risk.
Although these blockages reduced downstream flood risk in some places and had no effect, or even increased flood risk, in others, the researchers recommend detailed site surveys to identify the best places to install them to mitigate flooding.