Availability of water is very important natural resource of a nation, which can be used for the development of the country. Dam is a type of hydraulic structure built across a river (or stream). At the back of this barrier; water gets collected, forming a pool of water. The side on which water gets collected is called the upstream side and the other side of the barrier is called the downstream side. The lake of water which is formed upstream is called reservoir. Thus a reservoir and a dam exist together. The present study area is on Nagarjunasagar Dam, the giant among the masonry dams across River Krishna in Telangana State. In the design of hydraulic structures, many problems of non uniform and unsteady flow, sediment motion, dispersion, density currents and cases with complicated geometry fully defy. Therefore experimental work on scale models is often the most efficient and sometimes indeed the only method for solving the problem. The experiment cannot be carried out on the full size hydraulic structures, which are proposed to be erected. It is then essential to construct a small scale replica of the structure and the tests are performed on it to obtain the desired information. An attempt has been made to find the solution to the problem encountered in Nagarjunasagar dam constructed across river Krishna in Nalgonda district, Telangana state by using the theory of physical model study. A hydraulic model study was conducted to evaluate the cavitation damage due to negative pressures in terms of their magnitudes and locations on the spillway of the dam due to the floods in 2009 using the model studies on it. The experiment was carried out for free flow and gated operations for various discharge conditions. The maximum negative pressures observed at pressure tube points in vent no 1 is 0.079 at P7 for 1/4th of maximum flood discharge for gated condition. The maximum negative pressures observed at pressure tube points in vent no 2 is 0.031 at P7 for 3/4th, half and 1/4th of maximum flood discharge for free flow condition. The maximum negative pressures observed at pressure tube points in vent no 3 is 0.031 at P2 for 3/4th of maximum flood discharge for both free flow and gated conditions and 1/2 and 1/4th of maximum flood discharge for gated condition.