Runoff Calculations
Runoff Calculations
Runoff Calculations
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Drainage
 Runoff Calculations |
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The Runoff Calculations command
will calculate the estimated runoff of water over a flat surface area,
the minimum pipe inside diameter and the minimum required grate open surface
area. The calculations will be displayed in the dialog box. The calculations
are based on the area, the soil type and vegetation in the form of the
Runoff Coefficient, and the worst case estimated rainfall in a one hour
period. There is no limit to the number of areas you may have per design.
To calculate the estimated runoff of a flat
surface:
Chose the area
selection method from the drop down menu under the Add/Delete/Rename
Selected Area header. Draw
Manual will allow you to set points to outline the area. From Selection will allow you to
select the entities that enclose the area. From
Point will allow you to set a point inside of a closed area.
Click on the Add
button or 
icon and follow the prompts
in the Status Bar. You can add,
delete or rename the area names.
A New Area
will be added to the list. You can Rename
the area as required.
Under the Area Properties
header, select a Coefficient of Runoff
from the drop down menu by clicking on the selection one time with
the left mouse button. The coefficient of runoff is based on
the soil texture and vegetation within the area.
Type in the maximum one hour rainfall amount expected
in 100 years in the Rainfall Intensity
text box. One or more rainfall maps are provided for assistance.
You may select a rainfall map from the drop down menu or enlarge
a map for better viewing by clicking on the map itself or on the Enlarge Map button.
Multiple areas may be combined into one area by clicking
on the 
Combine
Areas button. In the resulting dialog box, click on each
area to combine with the left mouse button until a checkmark
appears in the box. Click on the OK
button to combine the areas. The areas will take on the Runoff
Coefficient and Rainfall Intensity properties of the top most area
in the list. Multiple combined areas cannot have different settings
for the Runoff Coefficient and Rainfall Intensity.
Combined areas may be separated into individual areas
by clicking on the 
Break Areas button. All combined
areas will be displayed in the resulting dialog box. Click on
each area to break with the left mouse button until a checkmark appears
in the box. Click on the OK
button to break the areas into individual areas. Each area will
take on the name of the originating area followed by a number in sequential
order located inside of an open and closed parenthesis.
Click on the Insert
Data button to place the area runoff calculations information
on the design screen. Adjust any of the font settings as necessary
and click on the Place Text Table
button. Set one point on the design screen for the top left
corner of the table.
Click on the Close
button to exit the dialog box.
Note:
The Minimum Pipe Inside Diameter
does not display the actual pipe size. For example, if the Minimum
Pipe Inside Diameter displays a value of 3.4 inches, round the value
up to the next available size to determine the minimum required pipe
size. A value of 3.4 inches would round up to a 4" minimum
pipe size.
You may assign a color or pattern
to each runoff area by selecting the area and making use of the Fill command.
These calculations are not intended
to be used for sophisticated drainage designs. For critical drainage
designs, consult a landscape architect or engineer.
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