SWMM 5 and Energy Losses

SWMM 5 and Energy Losses

SWMM 5 does account for energy losses in its calculations, but it has specific ways of handling them:¹

• Friction Losses: SWMM 5 primarily focuses on friction losses within conduits (pipes and channels). These losses are calculated using Manning's equation, which considers the roughness of the conduit material and the flow velocity.
• Minor Losses: SWMM 5 also includes options for modeling minor losses, which are typically associated with changes in flow direction or velocity.² These can be represented using loss coefficients (K values) applied at the entrance, exit, or midpoint of a conduit.
  

Invert Changes and Energy Losses

Now, here's the nuance regarding invert changes:

• Direct Calculation: SWMM 5 doesn't explicitly calculate energy losses solely due to the difference in invert elevations across a node. It doesn't have a specific loss coefficient for that situation.
• Indirect Consideration: However, the change in invert elevation influences the water surface elevation at the node, which in turn affects the hydraulic gradient and flow conditions. This indirectly accounts for some of the energy losses associated with the invert change.
• Minor Loss Approximation: If you want to explicitly account for additional losses due to the invert change, you could potentially approximate it by applying a minor loss coefficient to the downstream conduit. The value of this coefficient would depend on the specific geometry of the invert change.

Key Points

• SWMM 5's primary focus is on friction losses and user-defined minor losses.
• Invert changes indirectly influence energy losses by affecting water surface elevations and flow patterns.
• You can approximate additional losses due to invert changes using minor loss coefficients, but this requires careful consideration and potentially some engineering judgment.

In summary: While SWMM 5 doesn't directly calculate energy losses solely based on invert changes, its hydraulic calculations incorporate the effects of those changes on flow and water levels, indirectly accounting for some of the associated energy losses. If more precise modeling of these losses is needed, you can use minor loss coefficients to refine the simulation.