Outlet
Device Options
HydroCAD provides a wide range of pond outlet devices. These may be used individually to model simple outlets (such the weirs shown at the right), or combined in various arrangements to model more complex outlets, such as a riser structure.
Outlet Calculations
Complete details of the hydraulics calculations are provided in the HydroCAD Owner's Manual, as well as the built-in Help system. Just click the help button on the outlet selection screen, or on a specific outlet device.
Outlet Device Reporting
The summary report for each pond includes a graphical representation of the outlet devices, plus an analysis of the maximum flow through each device.
1) Each discharge (primary, secondary, discarded) is labeled
with the following information:
Maximum flow rate
(non-interpolated)
Time of maximum flow
Headwater elevation at time of
maximum flow
Tailwater elevation at time of
maximum flow
Tailwater settings
The maximum flow is calculated directly from the discharge equations at the listed HW and TW elevations. This value may be slightly less than the interpolated peak flow that appears a the top of the summary. This difference can often be reduced by using a smaller time step, but some difference is expected due to the different calculation procedure. If desired, the devices flows may be removed from the report by using the summary report context menu. (Requires HydroCAD-8.5 or later.)
2) Each device (culvert, weir, etc.) includes one of the following messages describing its role in determining the maximum flow through its designated discharge point:
Controls x.xx cfs @ x.x fps
- The device is acting as a control point, and is restricting the discharge to
the specified flow. This does not necessarily mean that the device is flowing
full, but that under the current conditions, its flow is more restrictive than
other devices to which it may be connected. The message also indicates the
approximate discharge velocity corresponding to this flow, and the governing
discharge equation.
Passes xx.xx cfs of xx.xx cfs
potential flow - The device is passing a specified flow that is less than
its potential flow for the headwater/tailwater conditions at that time. The
device is not a control point. The maximum flow is being controlled by other
device(s).
Passes < xx.xx cfs potential
flow - The device is passing a flow that is less than its potential flow,
but the flow could not be determined, since it is apportioned between two or
more devices. The device is not a control point. The maximum flow is being
controlled by another device to which this device contributes a portion of the
total flow.
Since the flows (and control points) are recalculated at each time step, these values can be expected to vary throughout the routing. The flow analysis shows only the conditions at the time of maximum discharge. Furthermore, when using a dynamic tailwater procedure, the maximum flow may occur at different time for the primary and secondary discharge.