摘要：An opportunity to study the effects of artificial structures like tidal regulators on thenear-shore environment is provided by the manually operated tidal regulator constructedacross a man-made canal in an estuarine environment in the tropical climatic setting ofthe southern coastal State of Kerala in India. The regulator was constructed across aman-made canal at Pozhikkara in 1957 to control the salt water intrusion into ParavoorKayal (Kayal = back water or estuary) and to protect a natural estuary. This protectionwas originally being afforded by a feature locally known as ‘Pozhi’, which is in fact anatural sand bar occurring along the coast separating backwaters from the sea duringthe summer, but allowing the sea and the backwater to merge by its erosion during themonsoon. This natural sandbar, thus, protected the Paravoor estuary from sea wateringress 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 theinland paddy crops from saline water ingress arose, the concept of an artificial tidalregulator was evolved by the farmers of the Ithikara Ela (Ela = paddy field). An artificialcanal 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 fromthe main land to become an island with 87 houses and 300 inhabitants. During 1985the performance of the regulator started deteriorating, finally leading to its collapse in1990. The water levels in the wells, the EC, pH, TH, Ca, Mg, Na, K, CO 3 , HCO 3 , SO 4and 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, whichused to yield fresh water on the separated land mass, became dry within five years ofcommissioning of the regulator, as the canal became effluent in nature, (iii) the dugwells were consequently deepened and salt water intrusion began and at present morethan 25 wells are saline due to salt water intrusion into the freshwater aquifer of the 1sq km area, (iv) the Paravoor estuary is becoming more saline day-by-day due to thefree flow of saline water through the canal, and (v) the Paravoor estuary is getting filledup with ocean sediments during high tides and sand terraces are being formed withinthe lake. All these are direct outcome of the badly maintained tidal regulator. As aremedial step the spillway shutters should be refitted immediately. This will help protectthe deteriorating environment and ecosystem of Paravoor estuary and the adjoiningland. Rainwater harvesting is recommended for the polluted wells. The artificial tidalregulator project was implemented without a proper environmental impact assessment.Detailed environmental impact assessment is essential before implementing suchschemes in coastal areas at the interface of varied environments, especially like anestuarine one in the tropics.
