Floods do not have to end in tears

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The Independent Online

The weather is certainly making itself known at the moment in the United Kingdom. Floods and big winds; tales of rivers rising by 20 feet in a matter of hours.

The weather is certainly making itself known at the moment in the United Kingdom. Floods and big winds; tales of rivers rising by 20 feet in a matter of hours.

Torrential flooding can turn a gentle meandering stream into a monster that slaps to one side anything that gets in its path. It can be terrifying for those living near a river. But what of those living in it? Do the fish just adapt? Do they swim with it or against it?

Some tests (the fish are counted electronically) show that fish do indeed adapt and are found in the same numbers before and after flooding. They survive by finding places to shelter where the water doesn't flow as fast, and they stay there until the torrent dies down and they can return to the main channel.

But sometimes fish don't make it. The flooding is so fierce that they get swept along, and then when the waters recede they get beached. It's very sad.

But even if the adult fish survive, floods disturb the river bed. In mild cases this isn't bad at all as it churns everything up, exposing new hidey-holes, and literally breathing new life into a river. But when a flood is severe it can be devastating. Spawning grounds are destroyed as the young fish or eggs are just not strong enough to withstand the currents. Valuable food is swept away. It has has taken years to re-populate (re-piscinate?) some rivers.

But, as with all things to do with Mother Nature, everything happens for a reason. Rivers wouldn't flood every year if they weren't naturally (there's the catch) meant to in the great evolutionary way of things. Look at the Colorado river. It was dammed upstream of the Grand Canyon in 1963 when the Glen Canyon Dam was built. Within 20 years things were not looking good. The pike minnow, the river's largest fish, disappeared. The humpback chub, a fish indigenous to the river, had almost disappeared. In its place were non-native fish such as the brown trout and the rainbow.

In the days when the river was left to nature's instructions alone, the Colorado was murky in the canyon, thick with sediment from its surroundings (colorado means "red-coloured" in Spanish because the Colorado flowed through what used to be part of Mexico). When the dam was built, most of the sediment - 90 per cent - was stopped by it. This made for some lovely clear water. Lovely for trout - in fact, fishing for trout became big business. But it wasn't so very good for the little chubbies who couldn't hide - the cloudy sedimented river used to provide good camouflage for them - from predators.

The floods also used to blast through the canyon, clearing anything that had built up in the rapids. But now these became as choked as a fat man's arteries. This was further bad news for the chub because he likes his waters fast but constant. Instead what he got were very fast, narrow rapids with big calm pools in the middle, which the interloper trout loves.

In the spring of 1996 the Grand Canyon was artificially flooded in a rare act (especially for American politicians) of environmentalism over economics (it cost the electricity companies millions of dollars). It helped but it hasn't returned the canyon to the way things were meant to be.

The planned flood - 45,000 cubic feet per second over a period of eight days - was "a drop in the ocean" as one scientist at the time described it, compared "to what Mother Nature could do". Natural floods in the Grand Canyon, when they were allowed to happen, were a terrifying 200,000 to 300,000 cubic feet per second, for weeks at a time.

Now that's a flood. Ironic that the indigenous fish life there survived thousands of years of that, and yet within three decades of commercial intervention they are almost wiped out. It seems Mother Nature's hand, although it can be savage, is much more nurturing than man's.