What are the assumptions of the laplace equations ?

Some of the assumptions of the laplace theory are as follows:-

1. He assumes that Water seeping through the dam is incompressible. 
2. The soil is incompressible and porous. That means the size of the pore space does not change with time regardless of water pressure. 
3. The quantity of water entering the soil in any given time is the same as the quantity flowing out of the soil. 
4. Darcy's law is valid for the given soils(I.e, Velocity is directly proportional the the hydraulic gradient ). 
5. The hydraulic boundary conditions at the entry and exit are known.