The salinity distributions of estuaries exhibit unique characteristics due to the effects of various external forces including freshwater discharges and topographic effects. To identify the salinity distribution of Periyar River Estuary, Kerala the surface salinity of Aluva Head works area was observed from 2008 to 2010. Variations in the salinity were clearly correlated in month wise with all other fluctuations. Furthermore, the salinity strongly decreased when additional freshwater was discharged relative to the dry period. The characteristics of the salinity distribution in the Periyar River were studied using data from the Water Resources Department and Central Water Commission, and the length of the salinity intrusion relative to the amount of freshwater discharge, and topographic effects were expressed using an empirical equation. A correlation between the saltwater intrusion limit at the Periyar River the freshwater discharge rate was also expressed using an empirical equation. Based on this simple analytical approach, it can believe that the structural characteristics of the salinity distribution in estuarian rivers vary not only due to freshwater discharge but also due to topographic effects.