Autodesk AUTOCAD 2008 - PREVIEW GUIDE Informações Técnicas descarregar pdf (Página 156)

146 | Chapter 10 Hydrology and Hydraulics

Before calculating runoff you should check with your local city or county for

their applicable requirements. For a general guide refer to the following table.

Key Concepts

You can use the commands from the Hydrology menu to determine

■ Applicable rainfall distribution type

■ Size of the drainage area (A)

■ Runoff curve number (RCN)

■ Runoff coefficient (C)

■ Adjustment factor, the time of concentration (T

)

■ Time of travel (T

)

■ Size of the pond and swamp area

■ Rainfall frequency

■ Rainfall intensity for each subarea

■ Slopes and elevations across a site can be extracted from a surface model.

You can also build a surface and model the watershed before calculating

runoff by using Terrain Model Explorer in AutoCAD Land Desktop.

■ Establish an intensity duration frequency (IDF) curve file (.idf extension)

for the project location.

If you want to …Then use …

size a storm pipe or culvert the Rational Method or TR-55 Methods.

calculate runoff from multiple subareas the Rational Method or TR-55 Tabular

Method.

create a hydrograph for a storm event

with a 24-hour duration

the TR-55 Tabular Method or the TR-20

Method.

create a hydrograph for a storm event

of different length than 24 hours

the TR-20 Method.

calculate runoff volume for designing

storage facilities using the storage

indication method (reservoir routing)

a hydrograph method, like the Tabular

method or the TR-20 method.

calculate runoff volume for designing

storage facilities

TR-55 methods.

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Autodesk AUTOCAD 2008 - PREVIEW GUIDE Informações Técnicas Página 156