Hydrodynamic parameters like Salinity intrusion, circulation and mixing properties, flushing characteristics, Total salt etc., along outlet channel of Kolleru Lake have been studied during May 2010 - April 2011. The observations reveal that the channel had lost 94.2% of Total Salt during May - November 2010 and regained upto 94.0% by April 2011. Flushing time has been varied from 1.81 to 5.61 tidal cycles. The Diffusion Coefficient (K_x) varied

randomly between 0.0032 x 10⁵ and 5.6 x 10⁵ m²/s during July - August 2010. The yearly mean K_x ranges between 0.0095 x 10⁵ and 2.1 x 10⁵ m²/s. The seasonal variation of depth mean salinity along the axis of the channel shows a wide range. During periods of very high discharge, salt wedge has been formed near the confluence and extended few kilometers upstream. For moderate discharge, the channel has become partially mixed with a high degree of stratification. For very less or negligible discharge, the channel exhibits well mixed nature. Topography of the channel and the discharge from Kolleru Lake are identified as key parameters causing significant changes in the channel. The wider extent of the channel and the identical behavior like an estuary confirms the channel as a natural estuarine system.

Key words: Circulation, Mixing, Salt wedge, Flushing time, Diffusion Coefficients, Upputeru channel, Kolleru Lake.