HEC-22 Junction Energy Loss Method

In an update from the junction energy loss method detailed in the Second Edition, the U.S. DOT - FHA has released a new procedure for computing this head loss in the Hydraulic Engineering Circular No. 22, (HEC-22), Third Edition manual is used in Bentley StormCAD .

In addition to the formula outlined in the HEC-22 manual, the following calculation details are notable:

Entrance Loss

In computing the entrance loss effects, the dimension of downstream pipe was chosen as equivalent diameter.

Plunging Loss

Plunging inflow effects are evaluated for an incoming piped flows as well as any surface inflow captured by the inlet opening of the structure. The referenced plunging elevations include the inverts of the incoming links, and if applicable, the rim elevation of the structure.

Exit Loss

During plunging inflow conditions, the exit loss of an incoming pipe is derived from the difference in energy level representative of the free outfall condition and the energy level at the upstream end of the structure after including entrance and additional structure losses. Exit loss is calculated with the velocity of the inflow pipe computed at its downstream end.

Flooding and Non-Bolted nodes:

For non-bolted manholes (or other gravity node) HGL (In) and (Out) results are equal to the rim elevation or less. The software assumes energy loss due to surface flooding. Special considerations include:

When Addition of Entrance Loss Results in Flooding: If the Entrance Loss raises hydraulic grade above the non-bolted rim elevation of the node, entrance loss is reported as the difference between the outflow pipe's HGL In and the node's rim elevation. The sum of total additional structure losses is reported as zero. The individual values for loss due to benching, plunging, and angled inflow are reported as N/A, because they cannot be reported accurately. All of the connected upstream pipes will report zero exit loss so that these incoming pipes can report their HGL (down) value as equal to the node's rim elevation.
When Addition of Additional Structure Losses Results in Flooding: If the addition of 'total additional structure losses' raises the node's hydraulic grade to above its non-bolted rim elevation, then the 'total additional structure losses' is reported as the difference of rim elevation - (outflow pipe's Upstream HGL + exit loss). The individual values for loss due to benching, plunging, and angled inflow remain unchanged, so the user can validate the sum of these results relative to rim elevation. All of the connected upstream pipes will report zero exit loss so that these incoming pipes can report their HGL (down) value as equal to node's rim elevation.
Addition of Exit Loss Results in Flooding: If the Exit Loss raises hydraulic grade above the non-bolted rim elevation of the node, exit loss is reported as the difference in the node’s rim elevation and the node’s HGL (In). Exit Loss is computed at the downstream of each incoming pipe into a HEC-22 3rd Edition node. The HGL (down) on an incoming pipe is computed as the sum of HGL (In) at the downstream node and Exit Loss.