ANS:E - All of above.

The pressure rise due to water hammer primarily depends on all of the factors mentioned:

1. The velocity of flow of water in the pipe: Higher velocities of water flow result in more significant water hammer effects because they generate larger kinetic energy within the flowing water, which can be converted into pressure during abrupt changes in flow velocity.
2. The length of the pipe: Longer pipes provide more distance for the pressure wave caused by sudden changes in flow to propagate, potentially resulting in higher pressures at different points along the pipe.
3. Time taken to close the valve: The speed at which a valve is closed or an abrupt change in flow occurs affects the rate at which the pressure wave propagates through the pipe. Rapid closure of valves can create more intense water hammer effects.
4. The elasticity of the pipe material: The elasticity of the pipe material determines the ability of the pipe to deform and absorb the energy generated by water hammer, reducing the magnitude of pressure spikes. Pipes with less elasticity or made of rigid materials are more prone to water hammer effects.