Outlet
Device Options
HydroCAD provides a wide range of basic pond outlet devices,
including orifice flow, weirs, culverts, tubes, and siphons. These may be
used individually to model simple outlets,
or combined in various arrangements to model more complex outlets, such as a
riser structure or notched weir.
HydroCAD can also be used to model active outlet devices, such as
pumps, or time-varying outlets such as a
dam breach. Each pond can have an unlimited number of
outlet devices.
Many new outlet devices were added in HydroCAD-10,
including tubes, siphons, asymmetrical weirs, constant-flow devices (such as
floating weirs), and even a progressive dam breach.
Update details here.
For devices than cannot be modeled with one of the standard outlet devices
listed above, a special outlet can be used to
define a custom stage-discharge curve. HydroCAD also includes a library of
predefined rating curves for certain proprietary devices, allowing them to be
easily modeled with a special outlet. Details
here.
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 Routing
The flow from each outlet device is routed to a specific node outflow.
By default, most devices are routed to primary. This causes their
flow to be directed to the primary outflow arrow on the routing diagram.
If desired, individual devices can also be routed to secondary or
tertiary. This causes their flow to be calculated and reported
separately, and makes it available as a separate outflow on the routing diagram.
Any number of devices can be routed to each outflow. When several
devices are routed to the same outflow, their individual flows are combined and
routed together.
Flows that are not subject to further routing (such as exfiltration), are
usually routed to the discarded outflow. The device routing can
also be used to construct compound outlet structures, such as a
riser.
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 a different time for the primary and secondary discharge.
