Chemical parameter ratios for identifying seawater intrusion into well waters

摘要

Inadequate availability of good quality irrigation water is often a major constraint to crop production in arid and semi-arid regions along the sea coast. The rapidly growing population in a developing country of semi-arid tropics like India has tonecessarily depend largely on underground resources for its water requirements, and the alarming implications of this heavy dependency on ground water resources leads to continuous lowering of water-table and consequent sea water intrusion into well water. In the present study, an attempt was made to study the pattern of seawater intrusion into well waters of coastal belt of Radhapuram taluk, Tirunelveli District, Tamil Nadu based on various chemical ratios. The coastal belt of Radhapuram taluk covers an area of about 600 sq. km. Forty five locations were selected at random as bench-mark sites in different coastal villages. Based on the distance from sea coast and land use pattern, the villages of Radhapuram taluk were divided into four zones i.e., Zone I (< 1 km from sea shore, 15 wells), Zone II (1-2 km from sea shore, 6 wells), Zone III (2-3 km from sea shore, 14 wells) and Zone IV (> 3 km from sea shore, 10 wells). Water samples from all 45 wells were collected at monthly interval for two years (September 1992 to August 1994) and analysed for their chemical constituents by adopting standard procedures. The unaffected good quality well water of the study area was also taken as a base well in Zone I (shallow depth) and compared with rest of wells of four zones, employing various chemical ratios like Na/Cl, Ca/Mg, Mg/Ca, SO_4/Cl, Cl/SO_4, HCO_3/Cl, Cl/HCO_3, HCO_3/SO_4, SO_4/HCO_3, Mg/Na, Na/Mg, Ca/Na and Na/Ca to ascertain whether sea water intrusion has taken place or not.