The Harappa civilization flourished on the banks of the river Indus and the Egyptian on the banks of the river Nile. Similarly the civilizations of China, Incas, Mayans and many more, all existed on the banks of the river or a large water body. Even in modern day we see that most of the big cities are located on the banks of rivers, lakes or sea. This tells the undisputable important role water plays in the life of man, necessary for sheer existence and required for socio economic life.
Since the dawn of civilization man has tried to modify the water sources to suit his needs, what started as digging small wells and canals for irrigation, today has grown to be a huge branch of engineering, called ‘River Engineering’. 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 encompasses many activities like building dams, straightening of the rivers, building canals, leaves and bunds, reversing the flow of rivers, altering the depth and width of the rivers etc. The most commonly seen product of river engineering are dams, and common though less heard river engineering feat is river straightening, the words are self explanatory, river straightening is a process of straightening the path of the river to reduce its curves and bends. The river does change its path, but over a period of time slowly and gradually flowing along the path of least resistance, and also allowing its associated ecosystem to evolve along with it.
To understand the how and why of river straightening, let’s study a hypothetical river ecosystem. The components of this ecosystem are the man living on the bank of the river, fish in the river, plants on the river bank, birds and other small animals living on the river bank. Let us get a snapshot of the ecosystem of the river before and after river straightening and then study them.
Before the river straightening:
The river meandered across plains and flowed to the sea, carrying sediments and debris and depositing them in its path. The debris like logs of trees, small boulders trapped more debris forming mini dams and extending the bank into the river, constantly adding to and eroding the river banks. The sediments deposited on the river bed and the moist rocks were a thriving home for algae, the main source of food for the fish. The river plains along the river bank being rich in sediments deposited by floods every year in the rainy season and easy irrigation were a thriving farmland and also housed lush fauna. A thriving school of fish and farms also enabled a habitation of many birds and small animals. This ecosystem was well balanced and thriving, when the human habitation was sparse and the river plains were cultivated only seasonally. But as human population increased, human habitation encroached the river plains and farm cultivation became an all year process. Every year in the rainy season, the river flooded the river plains damaging crops and property. The constant erosion of banks by the river caused the loss of farmlands. Due to the meandering of the river, and the debris in it, made navigation and transportation in the river cumbersome.
The ideal solution to all the above issues is to restrict the river and straighten it. So canals were built to shunt the river banks. Dikes, bunds and leaves built to restrict the width of the river.
After the river straightening:
Now the river was narrower and straighter, making the river flow faster which pushed all debris and sediments on the bank and river bed downstream, making river deeper. Since water was removed faster from a place, it greatly reduced flooding by water logging, and navigation became much viable. As an added bonus the land under the initial path of the river was also freed for human use.
Along with all these advantages came the side effects. With no flooding upstream, the annual depositing of sediments on the flood plains does not take place, slowly rendering the plains infertile. The ground water is depleted and small lakes and tributaries which would fill with flood water run dry. New land and increase in water transport has increased the human habitation on the river banks, polluting them greatly. All the debris picked up by the river make the river murkier and warmer retarding algae growth, and making it uninhabitable for the fishes, and this is propagated all the way up the food chain, till humans, in the form of decrease in fishery yields. The pollution and drying up of flood plains convert the farmlands into waste lands. Since the river is flowing faster it erodes its banks and bed at a rapid rate, devouring chunks of land causing destruction to structures on the bank and on the river like buildings and bridge, inorder to prevent this, large concrete walls are erected along the banks of the river. The once meandering river now almost looks like a straight man-made canal.
There can be many more effects of straightening based on the location of the river, according to some experts, changing the course of river can trigger earthquakes in earthquake prone zones. All the above, today have made engineers and experts to rethink the benefits of river straightening, and some rivers are restored to their original paths.
River straightening is a fine example of the myopic vision of mankind, and how man’s intervention with Mother Nature is taking him two steps back for every step he takes forward.