HEC-22 Energy (Third Edition) - Entrance Loss

The first of three principle computational steps to computing energy losses through an access hole, according to the HEC-22 (Third Edition) procedure, is determining the Entrance Loss. Entrance Loss is the relative increase in energy grade line from the outflow pipe's upstream energy grade line ( ) up to the Initial Access Hole Energy Level () at the downstream boundary side of the structure.

In summary, Entrance Loss () is defined with the following equation:

= Initial Access Hole Energy Level.

= Outflow Pipe's EGL at the upstream End.

The Initial Access Hole Energy Level () is the maximum of three control conditions that parallel the governing flow regimes of culvert hydraulics:

= Estimated Energy Level under Outlet Control.

= Estimated energy level under Ssubmerged Inlet Control.

= Estimated Energy Level under Unsubmerged Inlet Control.

Estimated Energy Level Assuming Outlet Control

Under this condition the outflow pipe backs up the access hole, and this confines flow out of the structure. In this case the outflow pipe is flowing full or nearly full, and so the loss under outlet control () can be simply estimated with the outlet flow velocity:

= Energy Grade Line (ln) reported at the structure.

= Entrance Loss under Outlet Control.

= Outlet Pipe Velocity.

Estimated Energy Level Assuming Inlet Control

In this case the flow through the access hole is limited due to upstream conditions. Under inlet controlled conditions, a culvert analysis approach of computing an intermediate Discharge Intensity () term is used. Governing flow conditions under inlet control can be categorized as weir-like, transitional, or orifice-like. Therefore, within the inlet control case, the energy level considering entrance loss is the conservative selected as the larger of the calculated submerged () or unsubmerged () terms:

= Discharge Intensity

= Outlet pipe diameter (or Equivalent Diameter)

= Flow Area corresponding to the Depth (In) of the Outlet Pipe