CHENNAI: Chennai’s famed Marina Beach is a man-made beach — the result of an unfortunate decision to construct a harbour in a place where one ought not to be. The harbour gave birth to the Marina beach. But in doing that it killed several other beaches. This is the story of how modern-day engineers are generally good at answering the wrong questions.
Ideally, harbours are located in places where deep still waters are naturally found near the shoreline. Tamil Nadu’s high-energy coast does not have many such places. So harbour engineers construct artificial harbours by building breakwaters into the sea. The Chennai Harbour has a long southern breakwater, and a shorter northern breakwater with a shipping channel in between.
Breakwaters are a problem. The east coast witnesses heavy movement of sand that travels up and down the coast seasonally. For roughly nine months a year, sand brought in by rivers like the Kaveri is transported north by nearshore drifts. The flow reverses during the three months of the Northeast monsoon. Roughly and on average for the east coast, there is a net northerly movement of about 5 lakh cubic metres of sand
every year. Building a breakwater obstructs this northerly drift, causing the southern beach to grow, and the northern beach to shrink.
Eroding at an annual rate of 8 metres, Chennai’s northern shores have lost 875 acres since the port was built, according to a Ministry of Earth Sciences estimate. Between Kasimedu and Ennore, India’s map has been redrawn by the port’s breakwaters, and we have not called in the army.
Built by dumping huge boulders, groynes are essentially breakwaters. They induce erosion. But some engineers see this erosion-causing structure as a solution for erosion. Groyne-building is a growth industry and a great favourite of corrupt contractors and government officials. It is, after all, a renewable source of revenue.
Every groyne induces erosion and gives the government cause to build another groyne to the north of the first one. As the sea periodically swallows the boulders, new granite boulders quarried out of inland hillsides are transported to the coast killing the seashore and the inland.
There is an easier solution. Pumping the sand that accumulates to the south of the harbour to the north will allow waves to carry them and rebuild the beaches. But that is not as exciting as gouging hillsides and dumping boulders in water. Besides, why make the Chennai Port Trust pay, when Tamil Nadu taxpayers can be milked?
(Nityanand Jayaraman is a Chennai-based researcher, writer and activist)
