SWMM "Time of Concentration"
SWMM "Time of Concentration"
(OP)
We have been committed to using SWMM to perform a flood study for a 2.26 square mile urban watershed. The watershed has been divided in to 26 subcatchments.
It appears SWMM assumes overland flow to determine a "time of concentration" for a subcatchment (from what I can gather, the equation used was developed from a kinematic wave analysis).
With that, I am not entirely comfortable with assuming overland flow in each subcatchment. Although some subcatchments are moderately developed with little drainage infrastructure, others are significantly developed with drainage infrastructure, curbing, et cetera. It is apparent (at least to me) that overland flow in certain subcatchments would be minimal.
I should mention that flow metering data is available for this watershed. Therefore, I do have the ability to adjust the length parameter in the time of concentration equation until a good fit exists between the observed and simulated hydrographs. However, flow metering is not available at the outlet of each subcatchment meaning I could not adjust the length parameter for each subcatchment.
As there are no other options available in SWMM to model a time of concentration, I am looking for some reasoning/verification/etc. behind SWMM's methodology for assuming overland flow.
Thanks in advance!!
It appears SWMM assumes overland flow to determine a "time of concentration" for a subcatchment (from what I can gather, the equation used was developed from a kinematic wave analysis).
With that, I am not entirely comfortable with assuming overland flow in each subcatchment. Although some subcatchments are moderately developed with little drainage infrastructure, others are significantly developed with drainage infrastructure, curbing, et cetera. It is apparent (at least to me) that overland flow in certain subcatchments would be minimal.
I should mention that flow metering data is available for this watershed. Therefore, I do have the ability to adjust the length parameter in the time of concentration equation until a good fit exists between the observed and simulated hydrographs. However, flow metering is not available at the outlet of each subcatchment meaning I could not adjust the length parameter for each subcatchment.
As there are no other options available in SWMM to model a time of concentration, I am looking for some reasoning/verification/etc. behind SWMM's methodology for assuming overland flow.
Thanks in advance!!





RE: SWMM "Time of Concentration"
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RE: SWMM "Time of Concentration"
RE: SWMM "Time of Concentration"
RE: SWMM "Time of Concentration"
I have completed further research on the topic, and it appears that SWMM does not calculate a time of concentration. The hydrograph is developed assuming each subcatchment is a non-linear reservior. Flow discharging from the "outlet" of the reservoir (if you will) represents the hydrograph of the subcatchment.