Reservoir routing is used to determine the peak flow attenuation that a hydrograph undergoes as it enters a reservoir. A reservoir is defined by a stage-storage curve and a stage-discharge curve, which can be entered or computed using commands in the Structure pull-down menu. A runoff hydrograph travels through the reservoir to an outlet. The outflow hydrograph is calculated by Storage Indication method, which is developed from the continuity equation:
ΔS/Δt = I - O
Where: ΔS = Change in storage (cubic ft
or cubic meter)
Δt = Routing time step (hours)
I = Inflow discharge (cfs or cms)
O = Outflow discharge (cfs or cms)
Please refer to the National Engineering Handbook Section 4 for
the detail of the Storage-Indication method.
Select Reservoir Routing from Watershed > Hydrograph Routing
menu. This command opens a dialog for hydrograph routing. First,
select the runoff hydrograph file that you want to do the reservoir
routing. Second, select the stage-storage and stage-discharge curve
files of a known reservoir. Then specify the initial water
elevation at the time when the routing starts and the routing
interval. When the routing interval is too large, negative outflows
can occur and the program would prompt a error message asking for a
smaller interval.
After entering all information, click Routed Hydrograph button to generate the routing hydrograph. A dialog is opened with the tabular and graphic hydrograph data, from there you can draw the hydrograph on screen and save it to a file.
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Routing Hydrograph - Reservoir Routing |
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| Routed Hydrograph Dialog |