We know that water exerts a pressure on the wall and this thrust is calculated by using the following formula

P = ½Y_{o} H^{2}

where H = height of water above bottom of wall, ft (m)

Y_{o}= unit weight of water.

Unit of water is 62.4 lb/ft^{3} 1001g/m for freshwater and 64 lb/ft^{3} or 1026.7 kg/m^{3} for saltwater.

The thrust applied by water is considered to be acting at a distance of H/3 from the bottom of the retaining wall. The pressure distribution is triangular and has the maximum pressure of 2P/H at the bottom of the wall.