HydroCAD^® Stormwater Modeling - Since 1986

Modeling a Delayed Outlet

HydroCAD-10.1 provides a new outlet option for modeling delayed outlet devices, such as an automated gate valve or rotary weir (illustrated at right).  A delayed outlet may be initiated at a specific water surface elevation and/or time delay.  Flow is determined by the weir and orifice equations, depending on head.  The device can operate immediately or gradually over a specified period of time.  In the case of a rotating weir, the orifice will transition from a horizontal to vertical orientation as the lip is lowered. 

A delayed outlet is commonly used in "batch detention" systems, designed to retain the entire runoff volume for a specified time period, and then gradually release it over an extended time.

Because the discharge vs. head varies over time, modeling a delayed outlet requires the use of a dynamic pond routing procedure. This also allows the outlet to respond to tailwater conditions created by a downstream reach or pond.

For details see "delayed outlet" in HydroCAD help.  Also see the "Outlet Examples" file that is preinstalled with HydroCAD.

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