The straightening of rivers is one form of river engineering(hydromodification). River engineering is “the process of planned human intervention in the course, characteristics or flow of a river with the intention of producing some defined benefit.” River engineering has been done since time immemorial. Straightening of a river,eliminates curves, bends and meandering of a river.
One reason why rivers have been straightened is to reduce erosion. For example, there is so much erosion on the Rio Grande that it has been difficult to know exactly where the border between the US and Mexico is.
Straightening of rivers also “facilitates the transportation of goods between ports.” Since the river is shortened by straightening, a shorter and easier route of transportation is created. The straightening also enables the water to be directed where it is needed. A stretch of the Kissimmee that was 103 miles long was shortened by straightening to a mere 56 miles! In the case of the Rioni River, “Soviet engineers turned the river lowlands along the Black Sea coast into prime subtropical agricultural land”.
Other reasons for straightening rivers are to avoid flooding, to make the management of the water resource in the river more manageable, and to hold water for recreation or power generation.
The dangers of tempering with the natural courses of rivers only began to be appreciated in the twentieth century, when the engineering marvels of straightening rivers began to be viewed as engineering failures because of the resulting environmental pollution and habitat loss.
In South Florida, the straightening of the Kissimmee resulted in the drying of 40,000 acres of floodplains. The number of birds and fish went down. The Duwamish ‘s pollution is so severe that parts of it have been declared “a Federal Superfund Site, a designation given to the most contaminated sites in the country”. Because the straightening of the rivers was to enable economic development along the river, there is a lot of pollution of the rivers by industries on the banks of the rivers. Heated water from the industries cooling systems is eventually discharged into the rivers, elevating the temperature of the water. The change of temperature adversely affects the native living organisms in the rivers.
Human populations along these rivers also pollute the rivers, especially with waste from sewage systems and fertilizers from agriculture. Fertilizers became food for algae which then thrives, and this causes a depletion of oxygen in the water. The result of this is that other living organisms in the water are choked because of lack of oxygen. Pollution creates undesirable conditions for nutrition and reproduction of life in the rivers, thus reducing populations of species. The population of species is also decreased by the reduction of space for nutrition and reproduction caused by the straightening of rivers.
The good thing is that the world finally realized that the straightening of rivers was causing destruction of ecosystems, and in many parts of the world the theme is now restoration of straightened rivers to their original courses.