The Time of Concentration is defined as the time for a storm of uniform area and temporal distribution to contribute to the runoff from the catchment. Provision is made for overland flow and/or flow along a watercourse. The following data can be entered.
Option
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Description |
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Longest Length |
The length of the catchment area in kilometres. |
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Average Slope |
The slope of the catchment area expressed in vertical metres/horizontal metres. |
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Overland Flow (Kerby Equation) |
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Percentage of Drainage Path |
The percentage of the drainage path that has no defined watercourse. |
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Roughness Coefficient |
The roughness coefficient defines the surface roughness which determines the flow speed. The options are as follows.
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Overland Flow Length |
The calculated overland flow length in km. |
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Overland Flow Slope |
The slope of the overland flow portion of the catchment area, expressed in vertical metres/horizontal metres. |
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Time of Concentration |
The calculated ToC of the overland flow. |
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Defined Watercourse (US Soil Conservation Services Equation) |
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Percentage of Drainage Path |
The percentage of the drainage path that has a defined watercourse. |
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Defined Watercourse Length |
The calculated watercourse flow length in km. |
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Defined Watercourse Slope |
The slope of the watercourse expressed in vertical metres/horizontal metres. |
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Time of Concentration |
The calculated ToC of the watercourse. |
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Combined Time of Concentration |
The calculated value is updated as you change the values and settings of the above items. |
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Click OK to accept and transfer the calculated value into the time of concentration control in the rational runoff page.
See Also Rational Runoff Data