1. HYDROGRAPH ANALYSIS Topic 4 NATURAL HYDROGRAPH
Base flow separation technique, Qb:
a. Empirical formula
b. Master depletion curve
c. Simple straight lines
Topic 4
HYDROGRAPH
ANALYSIS
EXPLAIN
CONCEPT OF UNIT HYDROGRAPH
CONSTRUCT
UNIT HYDROGRAPH
CALCULATE
Volume Of Direct Runoff From Direct Runoff Hydrograph.
DETERMINE
The Change Of Unit Hydrograph Duration Using:
a. S-curve
b. Superposition Concept.

2. HYDROGRAPH
A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).

3. DEFINITION OF NATURAL HYDROGRAPH
A natural hydrograph is one recorded at a stream gauging site and is a finger-print of the upstream drainage area’s response to rainfall

4. CONCEPT OF UNIT HYDROGRAPH
A Hydrograph is a graph showing changes in the discharge of river over a period of time.
It can also refer to a graph showing the volume of water reaching particular outfall or location in a sewerage network, graph are commonly used in the design of sewerage,more specillcally, the design of surface water sewegare systems and combination system.

5. A hydrograph consists of:
a) A rising limb or
concentration curve
b) A peak or crest segment
c) Falling limb or recession curve

6. The properties or characteristics of a unit hydrograph are
a) the volume under a unit hydrograph is equal
to 1 unit (1cm or 1in) rainfall excess
b) If the duration of two rainfall excess events is equal,
without regard to their respective rainfall intensities,
they must result in the same hydrograph time base.
c) The unit hydrograph results in a linear system
whereby the direct runoff for a storm of a specified
duration is directly proportional to the rainfall excess
amount or volume
d) Rainfall distribution for all equal duration storms is
identical in space and time.

10. Calculate direct runoff from stream flow & base flow data
Direct runoff = stream flow – base flow

11. Schedule below shows observation data from stream flow with base flow depth in catchment's area 250 km2. from that data , get direct runoff magnitude.
Time (hour)
Stream flow, Q (m3/s)
Base Flow, (m3/s) 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
1.37
1.25
1.12
5.00
12.00
15.60
17.15
14.40
8.80
6.80
5.50
4.10
2.75
2.00
1.20
0.65
0.15
0.32
0.62
1.28
1.35
1.42
1.65
1.82
1.88
2.05
2.55
1.91
1.53
1.15
0.28
example

12. Calculate Direct Runoff Depth Base On Volume DRO And Cathment Area.
DRO Depth,rd = Vd A
DIMANA;
Vd = RUNOFF VOLUME =  Qn Δt
A = CATCHMENT WIDE
Qn = HYDROGRAPH ORDINATE
Δt = HYDROGRAPH TIME INTERVAL

13. Calculate runoff volume and excess rain depth to a 7 acres catchment's area. Schedule below show a direct runoff data resultant from one precipitation
Time (minute)
Flow, Q (cfs) 2 4 6 8 10 9 21 17 13
EXAMPLE

14. Convert the duration of unit hydrograph from short to long (superposition)

15. Convert The Duration Of Unit Hydrograph From Short To Long (Superposition Method)- graphic
The following are the ordinates of a 4-hour unit hydrograph. Derive the ordinates of a 12 - hour unit hydrograph
Time
(Hour)
4hr-UH
(m3/s) 4 3 8 33 12 96 16 63 20 35 24 25 28 32 6 36
Lagged
4hr-UH
Combined
12hr-UH
4hr-UH

16. Convert The Duration Of Unit Hydrograph From Short To Long (Superposition Method)- table
Time
4j-UH
Lagged
(+) 4j-UH
12j-UH
(Hour)
(m3/s) 4 3 1 8 33 36 12 96
132 44 16 63
192 64 20 35
194
64.67 24 25
123 41 28 72 32 6 43
14.33 21 7 40 9

17. Example :
The following are the ordinates of a 3-hour unit hydrograph. Derive the ordinates of a 6-hour unit hydrograph and plot the graph.

18. Solution

19. Time
4j-UH
Lagged
(+) 4j-UH
12j-UH
(Hour)
(m3/s) 3
1.5 2
0.75 6
4.5
3.00 9
8.6 13
6.55 12
12.0 21
10.30 15
9.4
10.70 18
4.6 14
7.00
2.3 7
3.45 24
0.8
1.55 27 1
0.40 30

21. Question 1:
Determine the 4hr-UH from the 2hr-UH given in the table using the superposition principle method

22. Changing a Short Duration Unit Hydrograph to Long Duration using S-Curved method

23. Example
The ordinates of a 4-hour unit hydrograph for a particular basin are given below. Determine the ordinates of the S-curve hydrograph and there from the ordinates of the 6-hour unit hydrograph

24. Solution Time (Hour) 4hr-UH S- Curve Addition S- Curve Ordinates
Lagged S- Curve
S- Curve difference
6hr - UH 2 25 4
100 6
160 8
190 10
170 12
110 14 70 16 30 18 20 22
1.5 24

25. Time
4hr-UH
S- Curve Addition
S- Curve Ordinates
Lagged S- Curve
S- Curve difference
6hr - UH
(Hour)
0.00 2 25
16.67 4
100
66.67 6
160
185
123.33 8
190
290
265
176.67 10
170
355
255
170.00 12
110
400
215
143.33 14 70
425
135
90.00 16 30
430 75
50.00 18 20
445 45
30.00
436 11
7.33 22
1.5
446.5
16.5
11.00 24 -9
-6.00 26
10.5
7.00 28
-10.5
-7.00

26. Question 1
Determine the 3hr-UH from the 1hr-UH given in the table using the S-curve method.

27. Time
3hr-UH
S- Curve Addition
S- Curve Ordinates
Lagged S- Curve
S- Curve difference
1hr - UH
(Hour) 1 66
198 2
134 68
204 3
266
132
396 4
534
600
334
1002 5
466 6
400
666 7
934
268
804 8
866
-68
-204 9
200 10
1068
202
606 11
932
-136
-408 12
-66
-198 13 14
Changing a Long Duration Unit Hydrograph to Short Duration using S-Curved method

28. Question
The following are the ordinates of a 4hr – UH. Derive the ordinates of a 3hr-UH

29. Derive the S-curve for 4hr-UH

30. Hydrograph Unit from Stream Discharge Data

31. Example
Table below show runoff from hydrograph data, for a 50km2 catchment . Calculate the unit hydrograph (UH)10mm. Assume that the basic flow is 5.0m3/s

32. Solution

33. Mendapatkan Hidrograf Jumlah
Penggunaan UH10 bagi kawasan tadahan yang sama dengan contoh 1.
Diberikan ribut yang lain dengan tempoh yang sama bagi kawasan tadahan yang sama iaitu 50km2. Anggapkan aliran dasar 7 m3/s

34. Latihan
Cerapan kadaralir bagi satu kejadian hujan berkesan 12 jam bagi kawasan seluas 1150km2 adalah seperti yang ditunjukkan. Dapatkan hidrograf unit (UH)10mm untuk kawasan ini.

35. Diberi UH 4jam dan dapatkan UH -12jam dengan menggubakan kaeadah tindihan

36. REFERENCES