The specific energy depth, also known as the critical depth, refers to the depth of flow in an open-channel system at which the total energy per unit weight of the fluid is minimized for a given discharge. This depth corresponds to a specific condition of flow where the kinetic energy and the potential energy of the fluid are balanced, resulting in the lowest total energy per unit weight. Mathematically, the specific energy depth (ye​) can be calculated using the specific energy equation,

Where:

• $E$ is the specific energy per unit weight of fluid,
• $V$ is the velocity of the fluid,
• $g$ is the acceleration due to gravity, 
• $y$ is the depth of flow.