Runoff and the Outflow of the SWMM 5

I need a clarification about the SWMM5.0 ' Runoff ' and the ' Outflow' in the results Table.

When I do not have a ground water compartment, I observed that Runoff results time series and the Outflow results time series had nearly similar values. I think this ' Runoff ' results mean the surface runoff from the sub-catchments and the ' Outflow ' results mean the final output (after routing) at the outfall node, am I correct?

I did this because I didn't have the groundwater levels observations for the study area. I think, When there is no ground water contribution, SWMM5.0 generating only the surface runoff. I need to clarify this.

Then I modeled the catchment with groundwater compartment applying arbitrary values for the parameters of the groundwater flow editor.

Then the ' Runoff ' results similar to the previous approach and the ' Outflow ' results were changed. I think now the ' Outflow ' results mean the cumulative value of the surface runoff and the groundwater contribution after the routing process, am I correct?

Outflow is total of surface flooding and flow at the outfalls. It is normally a little less than the total inflow due to storage effects though you have a good understand of the importance of runoff, groundwater and storage on the outflow.

The overall continuity error at any time during the simulation is simply the total inflow minus the total outflow. The total inflow is the dry weather, wet weather, groundwater, I&I inflow, external inflow and the initial network storage. The total outflow is the amount of surface flooding, outfall flow, reacted flow and the final storage.

Continuity error = Total Inflow - Total Outflow

The continuity error can be variable over time as this graph of the total inflow, total outflow and continuity error over time shows for the classic extran example from SWMM 3 and SWMM 4. The continuity error can be negative or positive at each saved time step and it tends to balance out over time. As you can imagine depending on how long the simulation lasts the continuity error may be much greater than zero. If you can the simulation to dry weather flow is reached in the sanitary network or the stormwater network has drained the continuity error will be better. You can see that the CE increases at the beginning of the simulation, continues on and then goes to zero CE when the system drains.

If we look at a bubble chart of the continuity error over time (with the bubble size the continuity error) and the y axis the Total Inflow to the network you can see how continuity error increases and then decreases over time. The white bubbles are negative continuity error points.

Replies

susantha shameera June 25, 2013 at 6:54am

Thank you very much Bob, you have nicely explain everything.
Robert Dickinson June 25, 2013 at 6:35am

Outflow is total of surface flooding and flow at the outfalls. It is normally a little less than the total inflow due to storage effects though you have a good understand of the importance of runoff, groundwater and storage on the outflow.

The overall continuity error at any time during the simulation is simply the total inflow minus the total outflow. The total inflow is the dry weather, wet weather, groundwater, I&I inflow, external inflow and the initial network storage. The total outflow is the amount of surface flooding, outfall flow, reacted flow and the final storage.

Continuity error = Total Inflow - Total Outflow

The continuity error can be variable over time as this graph of the total inflow, total outflow and continuity error over time shows for the classic extran example from SWMM 3 and SWMM 4. The continuity error can be negative or positive at each saved time step and it tends to balance out over time. As you can imagine depending on how long the simulation lasts the continuity error may be much greater than zero. If you can the simulation to dry weather flow is reached in the sanitary network or the stormwater network has drained the continuity error will be better. You can see that the CE increases at the beginning of the simulation, continues on and then goes to zero CE when the system drains.

If we look at a bubble chart of the continuity error over time (with the bubble size the continuity error) and the y axis the Total Inflow to the network you can see how continuity error increases and then decreases over time. The white bubbles are negative continuity error points.

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