Optimal Desilting for Improving the Efficiency of Tanks in Semi Arid Regions

A research study has been carrted out to evaluate the economically viable depth of desiltation in old tanks to achieve a substantial increase in percolation and storage Two tanks -an old minor irrigation tank and a newly constructed percolation tank were selected in a granite terrain and infiltration studies were carried out with different thickness of silt removal Tritium tracer studies were coupled with the infiltration studies to follow the infiltrated water and evaluate the effectiveness of silt removal in percolation The study lndicated that in the case of irrigation tank, a steady state infiltration rate of 67 mm/h has increased to 350 mm/h with the removal of 65 cm silt showing a six-fold increase in infiltration rate Infiltration rate was found to be reducing by removal of 25 vm and 50 cm silt and the analysis of soil fraction indicated presence of clay at these depths The study at percolation tank indicated that the infiltration rate of 10-20 mm/h has increased to a maximum of 310 mm/h with removal of 40 cm silt The tritium tracer migration study supported a faster movement of percolated water at desilted sites by showing a greater dilution of tracer concentration and deeper penetration The research study strongly supports a necessity of carrying out infiltration studies at different places within the tank bed area with removal of varying thickness of silt to decide the optimal level of desiltation especially in old tanks before commencing revival of tank system.