Time Travel and Time Detention are totally different fields in science .
I Have Already Written on Time Travel Check it out Here .
Now Back To Time Detention .
Detention time is a measure of how long a molecule of water remains in a pond before it is discharged. Techniques for evaluating detention time, as described below. These values are automatically calculated for all pond passages, and the results are displayed in the pond summary report.
Note: Calculating the detection time is not a routing process. They are a separate analysis that is performed after the passage of the actual hydrograph is completed by a specified routing process.
Center-of-Mass detention time
The center mass method is a basic procedure for calculating the time of detention. It works by calculating the time difference between the flow and the center-mass of the outflow hydrograph.
The time of mass detention of the center is automatically calculated by HydroCAD-7 and later, and the pond appears near the top of the summary:
Large-scale detention of the center. Time = 146.0 minutes (1132.9-986.9)
Values in parentheses are the large-time center for outflow and inflow hydrographs, and can be useful when verifying results.
Although the center-mass method has the appeal of an intuitive graphical solution, it does not fully account for the variation in the size of the inverted hydrograph, or for the effects of so-called "dead storage".
Plug-flow detention time
A better approach is the plug flow method, which can be used to determine the theoretical mean detention time within any pond. In short, this technique indicates the average length of time that a molecule of water resides within a pond.
This is a theoretical maximum value, in which it considers the first-before-outflow within the pond. This means that any pre-storm volume (such as "dead storage" that is pre-filled with water) will be discharged before any new arrivals, resulting in increased detention time. Depending on the layout of the pond and the location of the inflow relative to the outlet, there will be some mixing and short-cutting, resulting in a true detention time that is somewhat less than the theoretical maximum. (See this sample pond for a solution.)
Plug flow detention time is automatically calculated by HydroCAD-5 and later
versions. Plug flow report will be found in the center of each pond summary.
Image source Google
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