Hydrology & Water Resources Engineering Subject Code:150602 Hytograph and Hydrograph Analysis 1) Hytograph: A hytograph can be defined as a plot of intensity of.
Download ReportTranscript Hydrology & Water Resources Engineering Subject Code:150602 Hytograph and Hydrograph Analysis 1) Hytograph: A hytograph can be defined as a plot of intensity of.
Slide 1
Hydrology & Water
Resources Engineering
Subject Code:150602
Slide 2
Hytograph and Hydrograph Analysis
1) Hytograph:
A hytograph can be defined as a plot of intensity of rainfall against
the time interval, represented as a bar chart.
2) Hydrograph:
A Hydrograph is a graphical plot of discharge of a natural stream or
River versus time.
Slide 3
1) Runoff:
Runoff is that portion of rainfall that is not evaporated or infiltrated
In ground
Unit
Discharge m3/s, cusecs, cumecs.
Slide 4
Classification of Runoff:
1) Surface runoff
2) Inter flow or subsurface flow
3) Ground water flow or base flow
Slide 5
Runoff
Runoff is that portion of rainfall that is not evaporated or intercepted.
Factor Affecting Runoff
1)Intensity of Rainfall
2) Soil Characteristics of Catchments
3) Topography of the Catchments
4) Shape and Size of Catchments
5) Cultivation and Vegetative Cover in Catchments
6) Geological Condition of Catchments
7) Weather Condition
Slide 6
i) Fan-shaped Watersheds
ii) Fern-Leaf shaped Watersheds
Slide 7
Drainage Basin Characteristics
Slide 8
Hydrograph:
A hydrograph is a graphical plot of discharge of a natural stream or
River versus time.
1) Effective Duration:
It is the time between which the rainfall rate is more than the
Infiltration rate.
Slide 9
2) Basin Lag (tp):
It is the time between centroid of the net rainfall (Pnet) and the
Peak (D) of the hydrograph.
3) Recession Time (tr):
It is the duration of direct runoff after the end of effective duration
of rainfall.
4) Time of concentration (tc):
It is the time in hours taken by rain water that falls at the farthest
Point to reach the outlet of a basin.
This time is equal to the time between point of inflection and of
Effective duration of rainfall.
Slide 10
Factors affecting the shape of hydrograph
1) Intensity and duration of rainfall
2) Size and shape of basin
3) Nature and slope of basin
4) Land use and Land cover
5) Drainage density
6) Type of soil and its infiltration rate
7) Lakes, depressions
8) Stream characteristics.
Slide 11
Separation of Base flow:
1) Direct run-off:
Direct run-off is that water which reaches the river shortly after it
Falls as rain.
Direct run-off is a overland flow (surface run-off)
2) Base Flow:
Base flow is the initial flow of the river before the rainfall comes.
Slide 12
Unit Hydrograph:
A unit hydrograph is hydrograph representing 1 cm of runoff
from a rainfall of some unit duration and specific areal
distribution.
Unit Hydrograph (UH) is defined as the hydrograph of surface
runoff of a catchment area resulting from unit depth (usually
1cm)
Slide 13
Propositions of the Unit Hydrograph:
1) Time invariance:
It means that the direct runoff hydrograph for a given effective
rainfall in a catchment is always the same irrespective of when
it occurs.
The direct runoff hydrograph does not depend upon the time
when the strom occurs.
2) Linearity of response:
It means that the relation between the direct runoff discharge
and the effective rainfall is linear.
This is the most important proposition of the unit-hydrograph.
3) Fixed base period:
The period during which the direct runoff occurs is called the
base period.
Slide 14
Assumptions of Unit Hydrograph Theory:
1) The effective rainfall is uniformly distributed within its duration
or specified period of time.
2) The effective rainfall is uniformly distributed over the entire
area of the drainage basin.
3) The base or time duration of the hydrograph of direct run-off due
to an effective rainfall of unit duration is constant.
4) The ordinates of all the direct runoff hydrographs of a common
base period are directly proportional to the total amount of
direct runoff represented by each hydrograph. This is known as
principle of linearity.
5) For a given drainage basin, the hydrograph of direct runoff
corresponding to a given period of rainfall reflects all the
physical characteristics of the basin.
Slide 15
Limitation of Unit Hydrograph Theory:
1) This theory is not applicable to large areas because uniformly
distributed effective rainfall can’t be expected in large area.
Hence UH theory is suited to catchment area under about 500
km2.
2) The unit hydrograph method can’t be applied when an
appreciable portion of the storm precipitation falls as snow.
3) In mountainous regions, subject to orographic rainfall, aerial
distribution is very uneven, but the patten tends to remain the
same from strom to strom, and unit hydrograph theory may not
be successfully applied.
4) The principle of linearity is not partically valid for smaller and
larger stroms.
5) The catchment having large storage like reservoir, lake, low area
etc. affect the linear relationship and hence theory cannot be
applied.
Slide 16
6) The principle of time invariance is valid only for specified time
and condition of drainage basin.
7) Practically no two stroms have the same nature in space and time
period. So, it is not possible to construct unit hydrograph
for each pattern.
Slide 17
Application of Unit Hydrograph Theory:
The unit hydrograph method is used for the estimation of the
maximum flood discharge of a stream.
1) Use of unit hydrograph for deriving a flood hydrograph resulting
from rainfall of unit duration.
2) Use of unit hydrograph for deriving a flood hydrograph resulting
from a series of rainfalls each of same unit duration.
3) Use of unit hydrograph for deriving a unit hydrograph of other
duration.
Slide 18
Ex.1 The ordinates of 3 hr unit hydrograph are given:
Time hr 0
3
6
9
12
15
18
21
24
27
30
Ordi
Cum.
10
25
20
16
12
9
7
5
3
0
0
Find the ordinate of a 6 hr unit hydrograph for the same basin
Analytically. Also sketch this unit hydrograph. What is the peak
Value of discharge in this unit hydrograph?
Slide 19
Time Hr.
1
1st 3 hr
2
2nd 3 hr
3
0
3
6
9
12
15
18
21
24
27
30
33
0
10
25
20
16
12
09
07
05
03
00
-
0
10
25
20
16
12
9
7
5
3
0
Ordi. 6 hr Ordi. 6hr
2cm
unit
4 =2+3
5 = 4/2
0
0
10
35
45
5
17.5
22.5
36
28
21
16
18
14
10.5
8
12
6
8
3
4
1.5
0
0
Slide 20
Graph….:
Slide 21
Ex.2 The ordinates of 8 hr unit hydrograph are given:
Time hr
Ord. 8 hr
Time hr
Ordi. 8 hr
0
0.0
44
79.0
4
5.5
48
57.0
8
13.5
52
42.0
12
26.5
56
31.0
16
45.0
60
22.0
20
82.0
64
14.0
24
162.0
68
9.5
28
240.0
72
6.6
32
231.0
76
4.0
36
165.0
80
2.0
40
112.0
84
1.0
Obtain a 24 hr unit hydrograph with graph
Slide 22
S- Hydrograph:
S- hydrograph is hydrograph of direct surface discharge that would
Result from successive storms each of which producing effective
Rainfall of 1 cm in unit duration.
S –hydrograph is therefore a continuously rising curve in the form
Of letter S, till a constant value of discharge is reached.
Slide 23
Ex.1 A 6-hr UH for a basin has the ordinates:
Time hr
0
6
12
18
24
30
36
42
48
54
60
66
Ordi. 6hr
(m3/s)
0
20
60
150
120
90
66
50
32
22
10
0
Determine the ordinates of 12-hr UH. Using S-curve method.
Slide 24
Time
hr
Ordi.
6hr.
Offset
S-curve S-curve
Diff.
Ordi.
Ordi.
Lagged
T1 =6hr
T2 =12 hr
Ordi.
12 hr.
UH.
1
2
3
4
5
4-5 =6
6 * t1/t2
0
0
-
0
-
0
0
6
20
0
20
-
20
10
12
60
20
80
0
80
40
18
150
80
230
20
210
105
24
120
230
350
80
270
135
30
90
350
440
230
210
105
36
66
440
506
350
156
78
42
50
506
556
440
116
58
48
32
556
588
506
82
41
54
22
588
610
556
54
27
60
10
610
620
588
32
16
66
0
620
620
610
10
05
Slide 25
Alternative Method:
Time hr
1st 6-hr
2nd 6-hr
Ordi. 12
hr
2 cm
Ordi. 12
hr.
UH
1
2
3
4 = 2+3
5 = 4/2
0
0
-
0
0
6
20
0
20
10
12
60
20
80
40
18
150
60
210
105
24
120
150
270
135
30
90
120
210
105
36
66
90
156
78
42
50
66
116
58
48
32
50
82
41
54
22
32
54
27
60
10
22
32
16
66
0
10
10
05
72
-
0
0
0
Slide 26
Ex.2 A 4-hr UH has the following ordinates:
Compute the ordinate of S-Curve .
Also compute 5 hr UH for basin.
Time hr
Ordi. UH
Time hr
Ordi. UH
0
0
11
41
1
6
12
34
2
36
13
27
3
66
14
23
4
91
15
17
5
106
16
13
6
93
17
9
7
79
18
6
8
68
19
3
9
58
20
1
10
49
21
0
Slide 27
Time hr
Ordi. UH
Offset
T1 = 4 hr
m3/s
SCurve
SCurve
T2 =5
hr
1
2
3
4
5
Diff.
Ordinates
5 hr UH
=6 x t1/t2
4-5=6
7
0
0
-
0
-
0
0
1
6
-
6
-
6
5
2
36
-
36
-
36
29
3
66
-
66
-
66
53
4
91
0
91
-
91
73
5
106
6
112
0
112
90
6
93
36
129
6
123
98
7
79
66
145
36
109
87
8
68
91
159
66
93
74
9
58
112
170
91
79
63
10
49
129
178
112
66
53
11
41
145
186
129
57
46
12
34
Slide 28
Prepared by,
Dr Dhruvesh Patel
www.drdhruveshpatel.com
Image Source: www.google.com
Hydrology & Water
Resources Engineering
Subject Code:150602
Slide 2
Hytograph and Hydrograph Analysis
1) Hytograph:
A hytograph can be defined as a plot of intensity of rainfall against
the time interval, represented as a bar chart.
2) Hydrograph:
A Hydrograph is a graphical plot of discharge of a natural stream or
River versus time.
Slide 3
1) Runoff:
Runoff is that portion of rainfall that is not evaporated or infiltrated
In ground
Unit
Discharge m3/s, cusecs, cumecs.
Slide 4
Classification of Runoff:
1) Surface runoff
2) Inter flow or subsurface flow
3) Ground water flow or base flow
Slide 5
Runoff
Runoff is that portion of rainfall that is not evaporated or intercepted.
Factor Affecting Runoff
1)Intensity of Rainfall
2) Soil Characteristics of Catchments
3) Topography of the Catchments
4) Shape and Size of Catchments
5) Cultivation and Vegetative Cover in Catchments
6) Geological Condition of Catchments
7) Weather Condition
Slide 6
i) Fan-shaped Watersheds
ii) Fern-Leaf shaped Watersheds
Slide 7
Drainage Basin Characteristics
Slide 8
Hydrograph:
A hydrograph is a graphical plot of discharge of a natural stream or
River versus time.
1) Effective Duration:
It is the time between which the rainfall rate is more than the
Infiltration rate.
Slide 9
2) Basin Lag (tp):
It is the time between centroid of the net rainfall (Pnet) and the
Peak (D) of the hydrograph.
3) Recession Time (tr):
It is the duration of direct runoff after the end of effective duration
of rainfall.
4) Time of concentration (tc):
It is the time in hours taken by rain water that falls at the farthest
Point to reach the outlet of a basin.
This time is equal to the time between point of inflection and of
Effective duration of rainfall.
Slide 10
Factors affecting the shape of hydrograph
1) Intensity and duration of rainfall
2) Size and shape of basin
3) Nature and slope of basin
4) Land use and Land cover
5) Drainage density
6) Type of soil and its infiltration rate
7) Lakes, depressions
8) Stream characteristics.
Slide 11
Separation of Base flow:
1) Direct run-off:
Direct run-off is that water which reaches the river shortly after it
Falls as rain.
Direct run-off is a overland flow (surface run-off)
2) Base Flow:
Base flow is the initial flow of the river before the rainfall comes.
Slide 12
Unit Hydrograph:
A unit hydrograph is hydrograph representing 1 cm of runoff
from a rainfall of some unit duration and specific areal
distribution.
Unit Hydrograph (UH) is defined as the hydrograph of surface
runoff of a catchment area resulting from unit depth (usually
1cm)
Slide 13
Propositions of the Unit Hydrograph:
1) Time invariance:
It means that the direct runoff hydrograph for a given effective
rainfall in a catchment is always the same irrespective of when
it occurs.
The direct runoff hydrograph does not depend upon the time
when the strom occurs.
2) Linearity of response:
It means that the relation between the direct runoff discharge
and the effective rainfall is linear.
This is the most important proposition of the unit-hydrograph.
3) Fixed base period:
The period during which the direct runoff occurs is called the
base period.
Slide 14
Assumptions of Unit Hydrograph Theory:
1) The effective rainfall is uniformly distributed within its duration
or specified period of time.
2) The effective rainfall is uniformly distributed over the entire
area of the drainage basin.
3) The base or time duration of the hydrograph of direct run-off due
to an effective rainfall of unit duration is constant.
4) The ordinates of all the direct runoff hydrographs of a common
base period are directly proportional to the total amount of
direct runoff represented by each hydrograph. This is known as
principle of linearity.
5) For a given drainage basin, the hydrograph of direct runoff
corresponding to a given period of rainfall reflects all the
physical characteristics of the basin.
Slide 15
Limitation of Unit Hydrograph Theory:
1) This theory is not applicable to large areas because uniformly
distributed effective rainfall can’t be expected in large area.
Hence UH theory is suited to catchment area under about 500
km2.
2) The unit hydrograph method can’t be applied when an
appreciable portion of the storm precipitation falls as snow.
3) In mountainous regions, subject to orographic rainfall, aerial
distribution is very uneven, but the patten tends to remain the
same from strom to strom, and unit hydrograph theory may not
be successfully applied.
4) The principle of linearity is not partically valid for smaller and
larger stroms.
5) The catchment having large storage like reservoir, lake, low area
etc. affect the linear relationship and hence theory cannot be
applied.
Slide 16
6) The principle of time invariance is valid only for specified time
and condition of drainage basin.
7) Practically no two stroms have the same nature in space and time
period. So, it is not possible to construct unit hydrograph
for each pattern.
Slide 17
Application of Unit Hydrograph Theory:
The unit hydrograph method is used for the estimation of the
maximum flood discharge of a stream.
1) Use of unit hydrograph for deriving a flood hydrograph resulting
from rainfall of unit duration.
2) Use of unit hydrograph for deriving a flood hydrograph resulting
from a series of rainfalls each of same unit duration.
3) Use of unit hydrograph for deriving a unit hydrograph of other
duration.
Slide 18
Ex.1 The ordinates of 3 hr unit hydrograph are given:
Time hr 0
3
6
9
12
15
18
21
24
27
30
Ordi
Cum.
10
25
20
16
12
9
7
5
3
0
0
Find the ordinate of a 6 hr unit hydrograph for the same basin
Analytically. Also sketch this unit hydrograph. What is the peak
Value of discharge in this unit hydrograph?
Slide 19
Time Hr.
1
1st 3 hr
2
2nd 3 hr
3
0
3
6
9
12
15
18
21
24
27
30
33
0
10
25
20
16
12
09
07
05
03
00
-
0
10
25
20
16
12
9
7
5
3
0
Ordi. 6 hr Ordi. 6hr
2cm
unit
4 =2+3
5 = 4/2
0
0
10
35
45
5
17.5
22.5
36
28
21
16
18
14
10.5
8
12
6
8
3
4
1.5
0
0
Slide 20
Graph….:
Slide 21
Ex.2 The ordinates of 8 hr unit hydrograph are given:
Time hr
Ord. 8 hr
Time hr
Ordi. 8 hr
0
0.0
44
79.0
4
5.5
48
57.0
8
13.5
52
42.0
12
26.5
56
31.0
16
45.0
60
22.0
20
82.0
64
14.0
24
162.0
68
9.5
28
240.0
72
6.6
32
231.0
76
4.0
36
165.0
80
2.0
40
112.0
84
1.0
Obtain a 24 hr unit hydrograph with graph
Slide 22
S- Hydrograph:
S- hydrograph is hydrograph of direct surface discharge that would
Result from successive storms each of which producing effective
Rainfall of 1 cm in unit duration.
S –hydrograph is therefore a continuously rising curve in the form
Of letter S, till a constant value of discharge is reached.
Slide 23
Ex.1 A 6-hr UH for a basin has the ordinates:
Time hr
0
6
12
18
24
30
36
42
48
54
60
66
Ordi. 6hr
(m3/s)
0
20
60
150
120
90
66
50
32
22
10
0
Determine the ordinates of 12-hr UH. Using S-curve method.
Slide 24
Time
hr
Ordi.
6hr.
Offset
S-curve S-curve
Diff.
Ordi.
Ordi.
Lagged
T1 =6hr
T2 =12 hr
Ordi.
12 hr.
UH.
1
2
3
4
5
4-5 =6
6 * t1/t2
0
0
-
0
-
0
0
6
20
0
20
-
20
10
12
60
20
80
0
80
40
18
150
80
230
20
210
105
24
120
230
350
80
270
135
30
90
350
440
230
210
105
36
66
440
506
350
156
78
42
50
506
556
440
116
58
48
32
556
588
506
82
41
54
22
588
610
556
54
27
60
10
610
620
588
32
16
66
0
620
620
610
10
05
Slide 25
Alternative Method:
Time hr
1st 6-hr
2nd 6-hr
Ordi. 12
hr
2 cm
Ordi. 12
hr.
UH
1
2
3
4 = 2+3
5 = 4/2
0
0
-
0
0
6
20
0
20
10
12
60
20
80
40
18
150
60
210
105
24
120
150
270
135
30
90
120
210
105
36
66
90
156
78
42
50
66
116
58
48
32
50
82
41
54
22
32
54
27
60
10
22
32
16
66
0
10
10
05
72
-
0
0
0
Slide 26
Ex.2 A 4-hr UH has the following ordinates:
Compute the ordinate of S-Curve .
Also compute 5 hr UH for basin.
Time hr
Ordi. UH
Time hr
Ordi. UH
0
0
11
41
1
6
12
34
2
36
13
27
3
66
14
23
4
91
15
17
5
106
16
13
6
93
17
9
7
79
18
6
8
68
19
3
9
58
20
1
10
49
21
0
Slide 27
Time hr
Ordi. UH
Offset
T1 = 4 hr
m3/s
SCurve
SCurve
T2 =5
hr
1
2
3
4
5
Diff.
Ordinates
5 hr UH
=6 x t1/t2
4-5=6
7
0
0
-
0
-
0
0
1
6
-
6
-
6
5
2
36
-
36
-
36
29
3
66
-
66
-
66
53
4
91
0
91
-
91
73
5
106
6
112
0
112
90
6
93
36
129
6
123
98
7
79
66
145
36
109
87
8
68
91
159
66
93
74
9
58
112
170
91
79
63
10
49
129
178
112
66
53
11
41
145
186
129
57
46
12
34
Slide 28
Prepared by,
Dr Dhruvesh Patel
www.drdhruveshpatel.com
Image Source: www.google.com