The dangers of 'flood prevention'

By Bob McNitt

Outdoors Writer

The soggy events of recent days is a liquid reminder that nature can, at any time, inundate us with such a surplus of precipitation that streams and rivers overflow and basements of structures can be transformed into indoor wading and swimming pools while lawns and fields become shallow lakes. We all know the negatives that flooding can bring, but are there any benefits to it? Of course there are. However, contemporary society tends to concentrate primarily on eliminating them, often unsuccessfully.

Natural flooding on our planet has been occurring ever since water vapors first rose to form clouds which then released it in the form of rain. Floods move and distribute large amounts of water and suspended sediment over surrounding areas which helps replenish valuable topsoil components and can keep the elevation of lands above sea level. The best example is the Mississippi delta - at least before massive manmade control measures were adopted all along the river's length to discourage flooding.

For thousands of years, the delta of the Mississippi River grew, each year forming a few square miles of new land in the Gulf of Mexico. But the trend began reversing about 1900; as manmade flood control projects were constructed all along the river. In recent years, Louisiana loses about 60 square miles of its wetlands each year, and in some areas the shoreline retreats 30 yards annually. Louisiana, which contains 40 percent of the wetlands in the US, suffers about 80 percent of this country's total wetlands loss.

Without the continued replenishment of sediment from river flooding, increasingly more of southern Louisiana continues to sink below sea level. Rather than allowing natural floods to occur, we've chosen instead to create a vast and complex system to keep Mississippi waters from reaching these lands. While these lands may remain dry, each year they subside more, making it ultimately more and more difficult to keep them that way. Remember Hurricane Katrina?

Closer to home, high water and natural flooding have historically renewed stream and river basins by moving sediment and debris from the bed channel, while increased current velocity scoured out new pools while filling in old ones and cutting straighter channels where bends had become too severe. Sediment left outside the normal channel when the water receded added to the soil nutrients while also increasing the land elevation there. Any moving natural waterway is dynamic by nature and, left to itself, will keep changing and rejuvenating its ecosystem and that around it.