Question regarding Catchment Time of Concentration
Question regarding Catchment Time of Concentration
(OP)
I want to challenge a statement made elsewhere as follows;
Statement: In general the SWMHYMO model shows that the run off from Highway row discharges downstream before the peak flow from the external areas reaches the highway culverts.
Challenge: How this statement can be made, when most Tc values are less than the rainfall duration i.e.12 Hours? Therefore at the time of Time of concentration, for most of the catchments, rainfall would still be going on, and all the areas, including those from the pavement would be still contributing to the peak flows.
Do you see that the challenge could be wrong in any ways?
Thanks in advance....KH
Statement: In general the SWMHYMO model shows that the run off from Highway row discharges downstream before the peak flow from the external areas reaches the highway culverts.
Challenge: How this statement can be made, when most Tc values are less than the rainfall duration i.e.12 Hours? Therefore at the time of Time of concentration, for most of the catchments, rainfall would still be going on, and all the areas, including those from the pavement would be still contributing to the peak flows.
Do you see that the challenge could be wrong in any ways?
Thanks in advance....KH





RE: Question regarding Catchment Time of Concentration
RE: Question regarding Catchment Time of Concentration
All catchment areas have Time of concentration less than 12 hours, that is why i thought that i could challenge the statement. Do you still think that my challenge is not justified?
RE: Question regarding Catchment Time of Concentration
If you think about the fact that the maximum precipitation will occur at the same time on the roadway as it does on the entire 1,000 Hectare watershed, the runoff from that precip will need to travel a kilometer or more until it reaches the culvert. However, the flow from the roadway may only need to travel a few hundred meters. It will arrive first and not combine with the peak from the offsite watershed.
RE: Question regarding Catchment Time of Concentration
RE: Question regarding Catchment Time of Concentration
In case Tc is longer than the storm duration, what do you recommend as a next step in modeling? should the modeling be repeated for longer storm duration or do something else?
RE: Question regarding Catchment Time of Concentration
RE: Question regarding Catchment Time of Concentration
You could use an event model for small to medium size basins (say up to 100 acres or so) but should route the flow, as cvg said, so that the attentuation in open channels and travel time lags can be assessed. I usually start with the WaterWorks software package (because it is easy to use and not too buggy) although I'm sure that different design programs could be used. Waterworks has several reach routing algorithms such as Muskingum, kinematic, etc.
RE: Question regarding Catchment Time of Concentration