Hydrological Impact of a Tidal Regulator on Land and on Water in a Tropical Estuary of Kerala, India

An opportunity to study the effects of artificial structures like tidal regulators on the near-shore environment is provided by the manually operated tidal regulator constructed across a man-made canal in an estuarine environment in the tropical climatic setting of the southern coastal State of Kerala in India. The regulator was constructed across a man-made canal at Pozhikkara in 1957 to control the salt water intrusion into Paravoor Kayal (Kayal = back water or estuary) and to protect a natural estuary. This protection was originally being afforded by a feature locally known as 'Pozhi', which is in fact a natural sand bar occurring along the coast separating backwaters from the sea during the summer, but allowing the sea and the backwater to merge by its erosion during the monsoon. This natural sandbar, thus, protected the Paravoor estuary from sea water ingress from the Lakshadweep sea (of the Indian Ocean) during the summer season. When a situation, where the natural sandbar could not protect the estuary and the inland paddy crops from saline water ingress arose, the concept of an artificial tidal regulator was evolved by the farmers of the Ithikara Ela (Ela = paddy field). An artificial canal was constructed 500 m south of the sandbar by cutting the main land, thus, connecting the lake and the sea. Thereby, around 1 sq. km of land was separated from the main land to become an island with 87 houses and 300 inhabitants. During 1985 the performance of the regulator started deteriorating, finally leading to its collapse in 1990. The water levels in the wells, the EC, pH, TH, Ca, Mg, Na, K, CO₃, HCO₃, SO₄ and Cl were determined in this study. The hydrological impacts of this regulator were (i) the hydraulic continuity of the aquifer has been disturbed, (ii) the dug wells, which used to yield fresh water on the separated land mass, became dry within five years of commissioning of the regulator, as the canal became effluent in nature, (iii) the dug wells were consequently deepened and salt water intrusion began and at present more than 25 wells are saline due to salt water intrusion into the freshwater aquifer of the 1 sq km area, (iv) the Paravoor estuary is becoming more saline day-by-day due to the free flow of saline water through the canal, and (v) the Paravoor estuary is getting filled up with ocean sediments during high tides and sand terraces are being formed within the lake. All these are direct outcome of the badly maintained tidal regulator. As a remedial step the spillway shutters should be refitted immediately. This will help protect the deteriorating environment and ecosystem of Paravoor estuary and the adjoining land. Rainwater harvesting is recommended for the polluted wells. The artificial tidal regulator project was implemented without a proper environmental impact assessment. Detailed environmental impact assessment is essential before implementing such schemes in coastal areas at the interface of varied environments, especially like an estuarine one in the tropics.