BBC News - 'Back to nature' cuts flood risks

Reconnecting flood-plains to rivers will help reduce the risk of = future=20 flooding, suggest US scientists.

A study by US researchers said allowing these areas to be submerged = during=20 storms would reduce the risk of flood damage in nearby urban areas.=20

Pressure to build new homes has led to many flood-prone areas being=20 developed.=20

Writing in Science, they said the risks of flooding were likely to = increase=20 in the future as a result of climate change and shifts in land use.=20

"We are advocating very large-scale shifts in land use," said = co-author=20 Jeffrey Opperman, a member of The Nature Conservancy's Global Freshwater = Team.=20

"There is simply no way economically or politically that this could = be=20 accomplished by turning large areas of flood-plains into parks," he told = the=20 Science podcast.=20

"What we are proposing in this paper is a way that this strategy can = be=20 compatible, and even supportive, with vibrant agricultural economies and = private=20 land ownership."

For example, the authors explained, the flood season and growing = season in=20 California did not occur at the same time.=20

This meant that allowing the land to be submerged by floodwater would = not=20 result in a permanent loss of farmland or crops being destroyed.=20

In their paper, they said that man-made flood management systems, = such as=20 levees, also had an ecological impact.=20

"Control infrastructure prevents high flows from entering = flood-plains, thus=20 diminishing both natural flood storage capacity and the processes that = sustain=20 healthy riverside forests and wetlands," they observed.=20

"As a result, flood-plains are among the planet's most threatened=20 ecosystems."=20

'Ecosystem services'

The reconnection programmes would deliver three benefits, they added: =

=E2=80=A2 Reduce the risk of flooding=20

=E2=80=A2 Increase in flood-plain goods and services=20

=E2=80=A2 Greater resilience to potential climate change impacts=20

In other parts of the world, Dr Opperman said that there was a range = of=20 agricultural strategies for private landowners that would be compatible = with=20 allowing areas to be flooded.=20

"There are emerging markets for ecosystem services, such as carbon=20 sequestration and nutrient sequestration," he explained.=20

"These are services that flood-plains do provide, so with various = climate=20 policies there will be a price for carbon."=20

The researchers cited the Yolo By-pass, in California, US, in their = paper as=20 a successful demonstration of the idea they were advocating.=20

The scheme absorbed 80% of floodwater during heavy storms, they said, = protecting the nearby city of Sacramento.=20

"During a March 1986 flood, the by-pass conveyed [about] 12.5bn cubic = metres=20 of water, more than three times the total flood-control storage volume = in all=20 Sacramento basin reservoirs.=20

"Without the by-pass flood-plain, California would need to build = massive=20 additional flood-control infrastructure," they observed.=20

The Yolo by-pass was created back in the 1930s, when a 24,000 hectare = flood-plain was reconnected to the Sacramento River.=20

The scheme was introduced when it became apparent that a "levees = only"=20 approach would not offer the required flood protection.=20

"It's connected in an engineered way, which mean that when the river = reaches=20 a certain volume it flows over a weir and enters the flood-plain," Dr = Opperman=20 explained.=20

He added that the scheme also had numerous additional ecological = benefits:=20 "In recent decades, people began to notice that this area was a = phenomenal=20 habitat for birds.=20

"In the past 10 years, people recognised that native fish were moving = from=20 the river on to the flood-plain, and deriving all of the benefits that = fish get=20 from natural flood-plains.=20

"It was an excellent place for fish to spawn, and for juvenile fish = to be=20 reared."