How do you calculate unit hydrograph?
The concept of unit hydrograph is based on linear systems theory and follow the principles of superposition and proportionality. For example, if one inch of excess rainfall produces a direct runoff peak of 100 cfs then two inch of excess rainfall with produce a direct runoff of 2 x 100 = 200 cfs.
What is 2 hour unit hydrograph?
The ordinates, u of a 2-hour unit hydrograph (i.e. for 1 cm of effective rain), for a catchment are shown in the table.A 6-hour storm occurs over the catchment such that the effective rainfall intensity is 1 cm/hour for the first two hours, zero for the next two hours, and 0.5 cm/hour for the last two hours.
What is the application of unit hydrograph?
Unit hydrograph has various applications including; prediction of flood peak discharges and the determination of the direct runoff response to rainfall; estimation of design flood which is applied in the construction of dam, flood plain delineation and water evaluation; derivation of unit hydrograph desired duration …
What is the theoretical number of unit hydrographs?
infinite
Explanation: The number of unit hydrographs for a given basin is theoretically infinite. This is because there may be one unit hydrograph for possible duration of rainfall and every possible distribution pattern of rainfall in the basin.
What is a 3 hour unit hydrograph?
A 3 hour triangular unit hydrograph (UH) has a time base of 30 hours with peak discharge of 90m3/s. For the same catchment 9 hour unit hydrograph was derived using 3 hour UH.
What is 4 hour unit hydrograph?
Hence, a 4 – hour unit hydrograph means a 1 cm of rainfall excess over the entire watershed resulted from 4 hour of rainfall.
What is S curve in hydrology?
S curve represents the maximum rate at which an effective rainfall intensity of 1 cm/hr in D-hours duration can drain out from a catchment of area A km2 (SA).
How is CN number calculated?
The weighted CN is calculated by taking the sum of each CN value multiplied by its fraction of the total subcatchment area. The sum is (usually) rounded to the nearest whole number, as described below. The rounded result is used for all calculations and reports.
What are the limitations of unit hydrograph?
Limitations of the Unit Hydrograph The size of the catchment imposes an upper limit on the applicability of the unit hydrograph theory (because the centre of the storm can vary from storm to storm and each of these storms can give a different DRH under otherwise identical conditions in very large basins).