Section 15(1)(b) in Tamil Nadu Urban Local Bodies (Regulation and Monitoring of Swimming Pools) Rules, 2015
(b)The wall shall be vertical for a distance of at least 1 m below the water level, below which the wall shall form a curve to the floor. The curve shall be tangent to the pool wall and shall have a radius of curvature at least equal to the vertical distance between the centre of curvature and the pool floor.