The ordinates of a hydrograph at a section of a stream having a drainage area of...

The ordinates of a hydrograph at a section of a stream having a drainage area of 81 km² are given below. Find the unit hydrograph assuming the base flow equal 18 m³/s.

Time hr	Discharge m3/s
0	18
1	42
2	193
3	338
4	383
5	328
6	248
7	183
8	123
9	78
10	48
11	28
12	18

Solutions

Expert Solution

Lets say you want a 'Y' hour unit hydrograph then,

Area of catchment=81 Km2

= 81x10002 =81000000 m2

Area under DRH=1794 x (Y hour) x 60x60=6458400Y m3

DRH depth =

Rainfall excess = (6458400xY)/(81x1000x1000)

= 7.97333 x (Y) (centimetre )

Therefore, the ordinate of UH are obtained by dividing the ordinate of surface runoff hydrograph by rainfall excess 7.9733(Y) to get ordinates of UH.

Example- Obtaining unit hydrograph of 6Hr from this DRH

Y=6

Rainfall excess=7.97333x6=47.84

Data table-

6hr UH

similarily you can construct any hr duration UH

Ally Wells answered 5 months ago

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