Unit Hydrograph - University of Asia Pacific · 2011. 5. 14. · Unit hydrograph of Different...
Transcript of Unit Hydrograph - University of Asia Pacific · 2011. 5. 14. · Unit hydrograph of Different...
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Unit Hydrograph A unit hydrograph is defined as the hydrograph of direct runoff resulting
from one unit depth (1cm) of rainfall excess occurring uniformly over the basin and at a uniform rate for a specified duration (D hours).
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Two basic assumptions of unit hydrograph
(i) the time invariance
(ii) the linear response
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Application of unit hydrograph using the basic principles of the unit hydrograph, one can easily calculate
the DRH in a catchment due to a given storm if an appropriate unit hydrograph was available
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Derivation of Unit Hydrograph
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Unit hydrograph of Different Durations
Two methods are available for this purpose
(i) Method of superposition, and
(ii) the S – curve
(i) Method of Superposition
If a D – h unit hydrograph is available, and it is desired to
develop a unit hydrograph of nD h, where n is an integer.
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(ii) The S – Curve
If it is desired to develop a unit hydrograph of duration mD, where m
is a fraction, the method of superposition cannot be used.
Ordinates (SA – SB) = T h DRH of (1/D x T) cm ER
UH – T h = (ordinates of DRH)/ (1/D x T)
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Example 6.10 – Solve example 6.9 by the S – curve method.
Solution:
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Solution:
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