HEC-RAS Culvert Normal Depth Computations

HEC-RAS Culvert Normal Depth Computations

For culvert computations, normal depth is the depth at which uniform flow will occur as free surface flow within the culvert. In other words, for a uniform channel of infinite length, carrying a constant flow rate, flow in the channel would be at a constant depth at all points along the channel, and this would be the normal depth.

Normal depth often represents a good approximation of the actual depth of flow within a channel segment. The program computes normal depth using an iterative approach to arrive at a value, which satisfies Manning’s equation:

Manning's equation (1)

Manning's equation formula

If the normal depth is greater than the culvert rise (from invert to top of the culvert), the program sets the normal depth equal to the culvert rise.

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