HYDROGRAPH AND HYDROLOGICAL ANALYSIS.ppt

Hydrograph & Hydrological
Analysis for floods
Prof. Payal V. Shah
Assistant Professor
Civil Engineering Department, GEC, Bharuch

OUTLINE
Hyetograph and Hydrograph Concept
Unit Hydrograph
S-Hydrograph
Design Flood
Flood Estimation
Frequency Analysis
Flood Routing 2

Hyetograph :
Defined as a plot of intensity of rainfall
against time interval, represented as a
bar chart.
Intensity of rain is expressed in cm/hr .
This time intensity curve is generally
assumed to be made up of straight lines
as shown in figure and is called
hyetograph .
3

Hyetograph :
▰Prepared either from the mass curve of rainfall, or directly
from the data obtained from automatic rain gauges .
▰The area under a hyetograph represents the total rainfall
received in that period .
▰Very useful in presenting the characteristics of a storm, and
is particularly important in developing the design to predict
extreme floods . 4

Construction of Hyetograph from
mass curve of rainfall :
 Mass curve of
rainfall is a plot
of accumulated
rainfall
(cumulative
rainfall) against
time .
5

Construction of Hyetograph from
mass curve of rainfall :
The hyetograph
is derived from
the mass curve
and is usually
represent as a
bar chart .
6

Hydrograph
Introduction
7
 A hydrograph is a graph showing variation of discharge (Q)
with time (t) , at a particular point of stream or river
 River discharge = Cross sectional area x river’s mean
velocity
 Discharge is usually expressed in cumecs or hectare meter
per day and time is expressed in hours or days.
 Since the hydrograph is generated from runoff due to
precipitation resulting from an isolated storm or a series of
consecutive storms, it is also known as a storm hydrograph.

“Why Construct & Analyze Hydrographs ?
 To find out discharge patterns of a
particular drainage basin
 Help predict flooding events, therefore
influence implementation of flood
prevention measures
8
8

Components of a single peaked hydrograph
D
B
C
A
Rising
limb recession
peak
Direct
runoff
Ground water
Flow due to
channel storage
E
Point of inflection
N DAYS
Discharge
time 9

 The rising limb is the ascending portion of the hydrograph
corresponding to increase of discharge due to gradual
accumulation of storage in the channels existing in the area.
 The peak segment includes the part of the hydrograph from
the inflection point on rising limb to an inflection point on
recession line.
 The recession limb extends from the inflection point to the
point which represents the recommencement of the natural base
flow or ground water flow. 10

0 12 24 36 48 30 72
t (hrs)
Hours from start of rain storm
___ Components of Stream flow
___ Elements of Hydrograph
3
2
1
Discharge
(m
3
/s)
Base flow
Inter flow
Overland
flow
Basin lag time
mm
4
3
2
Peak flow (crest)
11

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
12

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
mm
4
3
2
Rainfall shown in
mm, as a bar graph
13

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
mm
4
3
2
Discharge in m3/s,
as a line graph
14

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
mm
4
3
2
The rising flood water in the
river
15

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
mm
4
3
2
Peak flow
Peak flow
Maximum discharge in the
river
16

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
mm
4
3
2
Peak flow Falling flood water in the
river
17

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
Basin lag time
mm
4
3
2
Peak flow
Basin lag time
Time difference between the
peak of the rain storm and the
peak flow of the river
18

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
Base flow
Basin lag time
mm
4
3
2
Peak flow
Base flow
Normal discharge of the river
19

0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
Base flow
Inter flow
Overland
flow
Basin lag time
mm
4
3
2
Peak flow
Overland flow
Inter flow
+
GW (BF)
+
=
Stream Flow
Or
Total Runoff
20

Volume of water reaching the
river from surface run off
Overland flow Inter flow
Volume of water reaching the
river through the soil and
underlying rock layers
21

Interpretation of Storm Hydrographs
•Rainfall Intensity
•Rising Limb
•Recession Limb
•Lag time
•Peak flow compared to Base flow
•Recovery rate, back to Base flow
You need to refer to:
Basin lag time
0 12 24 36 48 30 72
3
2
1
Discharge
(m
3
/s)
Base flow
Through flow
Overland
flow
mm
4
3
2
Peak flow
22

Factors influencing
Storm Hydrographs
• Area
• Shape
• Slope
• Rock Type
• Soil
• Land Use
• Drainage Density
• Precipitation / Temp
• Tidal Conditions
23

Area
Large basins receive more precipitation than small
therefore have larger runoff
Larger size means longer lag time as water has a longer
distance to travel to reach the trunk river
Area Rock Type Drainage Density
Shape Soil Precipitation / Temp
Slope Land Use Tidal Conditions
24

Shape
Elongated basin will produce a lower peak flow and longer
lag time than a circular one of the same size
25

Slope
Channel flow can be faster down a steep slope therefore
steeper rising limb and shorter lag time
26

Rock Type
Permeable rocks mean rapid infiltration and little overland
flow therefore shallow rising limb
27

Soil
Infiltration is generally greater on thick soil, although less
porous soils eg. clay act as impermeable layers
The more infiltration occurs the longer the lag time and
shallower the rising limb
28

Land Use
Urbanization - concrete and tarmac form impermeable
surfaces, creating a steep rising limb and shortening the
time lag
Afforestation - intercepts the precipitation, creating a
shallow rising limb and lengthening the time lag
29

Drainage Density
A higher density will allow rapid overland flow
30

P & Temp
Short intense rainstorms can produce rapid overland flow and steep
rising limb
If there have been extreme temperatures, the ground can be hard
(either baked or frozen) causing rapid surface runoff
Snow on the ground can act as a store producing a long lag time and
shallow rising limb. Once a thaw sets in the rising limb will become
steep
31

Tidal Conditions
High spring tides can block the normal exit for the water,
therefore extending the length of time the river basin takes
to return to base flow
32

Hydrograph Analysis : Hydrograph : Q vs. t
34
Duration , t
Lag Time , tL
Time of Concentration , tc
Rising Limb
Recession Limb (falling limb)
Peak Flow ,Qp
Time to Peak (rise time),tp
Recession Curve
Base flow , BF
Separation of BF from Runoff

Hydrograph Components
Taken from Wanielista, M., R. Kersten, and R. Eaglin, Hydrology: Water Quantity and Quality Control, p. 184
35

36
Graphical Representation
Lag time
Time of
concentration
Duration of excess
precipitation.
Base flow

37
Separation of Baseflow
0.0000
100.0000
200.0000
300.0000
400.0000
500.0000
600.0000
700.0000
0
.
0
0
0
0
0
.
1
6
0
0
0
.
3
2
0
0
0
.
4
8
0
0
0
.
6
4
0
0
0
.
8
0
0
0
0
.
9
6
0
0
1
.
1
2
0
0
1
.
2
8
0
0
1
.
4
4
0
0
1
.
6
0
0
0
1
.
7
6
0
0
1
.
9
2
0
0
2
.
0
8
0
0
2
.
2
4
0
0
2
.
4
0
0
0
2
.
5
6
0
0
2
.
7
2
0
0
2
.
8
8
0
0
3
.
0
4
0
0
3
.
2
0
0
0
3
.
3
6
0
0
3
.
5
2
0
0
3
.
6
8
0
0
Baseflow
Surface
Response

38
Separation of base flow from direct runoff
1) Straight line method :
Figure shows the two
points A and C which mark
the beginning and end of
the direct run off.

39
Separation of base flow from direct runoff
2)Two tangent method:
 Most widely used method in which base flow
is separated from direct runoff by two lines.
 The first line AB is obtained by extending
the base flow curve existing prior to the
commencement of the surface runoff, till it
intersects a vertical line, drawn from the
peak.
 Point B and C are joined by straight line.
 Empirical equation to locate point C:
N = 0.83 A0.2 days
Where, N = time interval in days from peak
A = area of drainage basin

40
Unit Hydrograph(UH) Theory:
A unit hydrograph is a hydrograph representing 1 cm of runoff from a rainfall
of some unit duration.
ASSUMPTIONS :
1) The effective rainfall is uniformly distributed within its duration or specified
period of time.
2) The base or time duration of hydrograph of direct runoff due to effective
rainfall of unit duration is constant
3) The ordinates of all direct runoff hydrographs are proportional to the total
amount of direct runoff .
4) The effective rainfall is uniformly distributed over the entire area of drainage
basin.

41
Unit Hydrograph
The hydrograph (direct runoff)resulting from 1cm of
excess precipitation spread uniformly in space and
time over a watershed for a given duration.
The key points :
1cm of EXCESS precipitation
Spread uniformly over space - evenly over the watershed
Uniformly in time - the excess rate is constant over the
time interval
There is a given duration. t-UH (ex. 2hr-UH)

42
DERIVATION OF UNIT HYDROGRAPH
:
The unit hydrograph method is used for estimation of
the maximum flood discharge of stream as well as for
developing a flood hydrograph corresponding to
anticipated rainfall.
For the application of this method unit hydrograph of
suitable unit duration is derived from an observed
hydrograph of drainage basin.

43
DERIVATION OF UNIT HYDROGRAPH
:
In order to derive unit hydrograph from storm hydrograph of same unit duration following steps are
followed.
1) From the past records select hydrograph resulting from an isolated, intense, short duration
rainfall of uniform duration over the drainage basin.
2) Separate the base flow from direct runoff.
3) Subtracting the ordinates of base flow from total ordinates, find the ordinates of direct runoff.
4) Compute the depth of direct runoff .
5) Depth of direct runoff = =
where , = sum of direct runoff ordinates in cumecs.
= time interval in hours between successive ordinates.
A = area of drainage basin in square kilometers.
6) By dividing each of direct runoff by depth of direct runoff , the ordinates of unit hydrograph
are obtained.

44
Unit Hydrograph
LIMITATION :
1) The unit hydrograph theory can not be applied to catchment areas >500 km2.
2) The unit hydrograph theory cannot be applied to very small catchments with area < 2 km2.
3) This theory cannot be applied when the major portion of the storm is in form of snow.
4) This theory is not accurate.
USES:
1) Flood forecasting and flood warning based on the observed rainfall in the basin.
2) To determine runoff from a storm of unit duration.
3) To draw maximum flood hydrograph for the design of spillways.

0
2000
4000
6000
8000
10000
12000
0 5 10 15 20 25 30 35 40
Flow
Rate
(m
3
/s)
Time (hrs)
Plot of the Total Hydrograph
46

47
Final UH
0
5000
10000
15000
20000
25000
0
11
22
33
44
55
66
77
88
99
110
121
132
Flow
(cfs)
Time (hrs.)
Storm #1 hydrograph
Storm#1 direct runof f
hydrograph
Storm # 1 unit
hydrograph
Storm #1
basef low

48
SUMMATION HYDROGRAPH
(s –hydrograph)
 S- hydrograph is hydrograph that is produced by a
continuous effective rainfall at a constant rate for
indefinite period.
 It is continuous rising curve , in the form of letter s ,
till equilibrium is reached.

49
SUMMATION HYDROGRAPH
(s –hydrograph)

50
SYNTHETIC UNIT HYDROGRAPH
The unit hydrograph determined for the ungauged
catchment is known as synthetic unit hydrograph.
Several techniques are adopted for establishing
relationship between the basin characteristics and the
unit hydrograph characteristics for unit rainfall , but most
commonly method is Snyder's method.

51
INSTANTANEOUS UNITHYDROGRAPH
If duration of rainfall excess becomes infinitely small(T 0 )
the resulting unit hydrograph is called instantaneous unit
hydrograph.
This is only a theoretical concept , because 1 cm of rainfall
cannot occur in a zero time on any catchment , but it is useful
because , such a unit hydrograph represents watershed’s response
to a rainfall without reference t the duration of rainfall.
Comparatively easier method for developing an IUH has been
evolved by Clark and is known as Clark's method or time area
histogram method.

52
Determine Duration of UH
The duration of the derived unit hydrograph is found by
examining the precipitation for the event and determining that
precipitation which is in excess.
Generally accomplished by plotting the precipitation in
hyetograph form and drawing a horizontal line such that the
precipitation above this line is equal to the depth of excess
precipitation as previously determined. This horizontal line is
generally referred to as the F-index and is based on the
assumption of a constant or uniform infiltration rate.

53
Estimating Excess Precipitation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Time (hrs.)
Precipitation
(inches)
Uniform loss rate of
0.2 inches per hour.

56
Develop S-Curve
0.00
10000.00
20000.00
30000.00
40000.00
50000.00
60000.00
0
10
20
30
40
50
60
70
80
90
100
110
120
Flow
(cfs)
Time (hrs.)

57
Shortcut Method
•There does exist a shortcut method for changing the
duration of the unit hydrograph if the two durations are
multiples of one another.
•This is done by displacing the unit hydrograph.
•For example, if you had a two hour unit hydrograph and
you wanted to change it to a four hour unit hydrograph.

58
Shortcut Method Example
Time (hr) Q
0 0
1 2
2 4
3 6
4 10
5 6
6 4
7 3
8 2
9 1
10 0
• First, a two hour unit hydrograph is given and a four hour
unit hydrograph is needed.
• There are two possibilities, develop the S - curve or since
they are multiples use the shortcut method.

59
• The 2 hr-UH is then
displaced by 2 hours.
• This is done because the
2 hr-UH will be used to
represent a 4 hr-UH.
Time (hr) Q Displaced UHG
0 0
1 2
2 4 0
3 6 2
4 10 4
5 6 6
6 4 10
7 3 6
8 2 4
9 1 3
10 0 2
11 1
12 0

60
• These two hydrographs
are then summed.
Time (hr) Q Displaced UHG Sum
0 0 0
1 2 2
2 4 0 4
3 6 2 8
4 10 4 14
5 6 6 12
6 4 10 14
7 3 6 9
8 2 4 6
9 1 3 4
10 0 2 2
11 1 1
12 0 0

61
• Finally the summed
hydrograph is divided by
two.
• This is done because when
two unit hydrographs are
added, the area under the
curve is two units. This has
to be reduced back to one
unit of runoff.
Time (hr) Q Displaced UHG Sum 4 hour UHG
0 0 0 0
1 2 2 1
2 4 0 4 2
3 6 2 8 4
4 10 4 14 7
5 6 6 12 6
6 4 10 14 7
7 3 6 9 4.5
8 2 4 6 3
9 1 3 4 2
10 0 2 2 1
11 1 1 0.5
12 0 0 0

62
Average Several UH’s
• Recommend that several unit hydrographs be derived and
averaged.
• Unit hydrographs must be of the same duration in order to be
properly averaged.
• It is often not sufficient to simply average the ordinates of the unit
hydrographs in order to obtain the final unit hydrograph. A
numerical average of several unit hydrographs which are
different “shapes” may result in an “unrepresentative” unit
hydrograph.
• Recommended to plot the unit hydrographs that are to be
averaged. Then an average or representative unit hydrograph
should be sketched or fitted to the plotted unit hydrographs.
• Finally, the average unit hydrograph must have a volume of 1 cm
of runoff for the basin.

BIG CONCEPT
Bring the attention of your audience over a
key concept using icons or illustrations
63

White
Is the color of milk and fresh
snow, the color produced by the
combination of all the colors of
the visible spectrum.
YOU CAN ALSO SPLIT YOUR CONTENT
Black
Is the color of ebony and of
outer space. It has been the
symbolic color of elegance,
solemnity and authority.
64

IN TWO OR THREE COLUMNS
Yellow
Is the color of gold,
butter and ripe
lemons. In the
spectrum of visible
light, yellow is found
between green and
orange.
Blue
Is the colour of the
clear sky and the deep
sea. It is located
between violet and
green on the optical
spectrum.
Red
Is the color of blood,
and because of this it
has historically been
associated with
sacrifice, danger and
courage.
65

A PICTURE IS WORTH A THOUSAND WORDS
A complex idea can be
conveyed with just a single
still image, namely making it
possible to absorb large
amounts of data quickly.
66

Want big impact?
USE BIG IMAGE
67

USE CHARTS TO EXPLAIN YOUR IDEAS
68
Gray
White Black

AND TABLES TO COMPARE DATA
A B C
Yellow 10 20 7
Blue 30 15 10
Orange 5 24 16
69

89,526,124
Whoa! That’s a big number, aren’t you proud?
71

89,526,124$
That’s a lot of money
100%
Total success!
185,244 users
And a lot of users
72

OUR PROCESS IS EASY
73
first second last

LET’S REVIEW SOME CONCEPTS
Yellow
Is the color of gold, butter and ripe
lemons. In the spectrum of visible
light, yellow is found between
green and orange.
Blue
Is the colour of the clear sky and
the deep sea. It is located
between violet and green on the
optical spectrum.
Red
Is the color of blood, and because
of this it has historically been
associated with sacrifice, danger
and courage.
74
Yellow
Is the color of gold, butter and ripe
lemons. In the spectrum of visible
light, yellow is found between
green and orange.
Blue
Is the colour of the clear sky and
the deep sea. It is located
between violet and green on the
optical spectrum.
Red
Is the color of blood, and because
of this it has historically been
associated with sacrifice, danger
and courage.

You can insert graphs from Excel or Google Sheets 75
GRAPH TITLE
4000
3000
2000
1000
0

76
MOBILE PROJECT
Show and explain your
web, app or software
projects using these
gadget templates.

77
TABLET PROJECT
gadget templates.

78
DESKTOP PROJECT
gadget templates.

79
THANKS!
Any questions?
You can find me at
@username & user@mail.me

CREDITS
Special thanks to all the people who made and
released these awesome resources for free:
▰ Presentation template by SlidesCarnival
▰ Photographs by Startup Stock Photos
80

PRESENTATION DESIGN
This presentation uses the following typographies and colors:
▰ Titles: Roboto Condensed
▰ Body copy: Roboto Condensed
You can download the fonts on this page:
https://material.io/guidelines/resources/roboto-noto-fonts.html
Navy #3f5378 · Dark navy #263248 · Yellow #ff9800
You don’t need to keep this slide in your presentation. It’s only here to serve you as a design guide if you need to create
new slides or download the fonts to edit the presentation in PowerPoint®
81

EXTRA RESOURCES
For Business Plans, Marketing Plans,
Project Proposals, Lessons, etc
2
82

TIMELINE
83
DEC
NOV
OCT
SEP
AUG
JUL
JUN
MAY
APR
MAR
FEB
JAN
Blue is the colour of the
clear sky and the deep sea
Red is the colour of danger
and courage
Black is the color of ebony
and of outer space
Yellow is the color of gold,
butter and ripe lemons
White is the color of milk
and fresh snow
and fresh snow
and courage
and of outer space
Yellow is the color of
gold, butter and ripe
lemons

ROADMAP
84
1 3 5
6
4
2
and courage
and of outer space
and fresh snow

GANTT CHART
85
Week 1 Week 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Task 1
Task 2 ◆
Task 3
Task 4 ◆
Task 5 ◆
Task 6
Task 7
Task 8

SWOT ANALYSIS
86
STRENGTHS
Blue is the colour of the clear
sky and the deep sea
WEAKNESSES
Black is the color of ebony and
of outer space
OPPORTUNITIES
White is the color of milk and
fresh snow
THREATS

BUSINESS MODEL CANVAS
87
Key Activities
Insert your content
Key Resources
Insert your content
Value Propositions
Insert your content
Customer Relationships
Insert your content
Channels
Insert your content
Customer Segments
Insert your content
Key Partners
Insert your content
Cost Structure
Insert your content
Revenue Streams
Insert your content

FUNNEL
88
PURCHASE
LOYALTY
AWARENESS
EVALUATION
DISCOVERY
INTENT
Insert your content
Insert your content
Insert your content
Insert your content
Insert your content
Insert your content

TEAM PRESENTATION
89
Imani Jackson
JOB TITLE
Blue is the colour of the clear sky
and the deep sea
Marcos Galán
JOB TITLE
and the deep sea
Ixchel Valdía
JOB TITLE
and the deep sea
Nils Årud
JOB TITLE
and the deep sea

90
LOW
VALUE
1
HIGH
VALUE
1
LOW VALUE 2
HIGH VALUE 2
Our company
Competitor
Competitor
Competitor
Competitor
Competitor
Compet
itor
COMPETITOR MATRIX

WEEKLY PLANNER
91
SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY
9:00 - 9:45 Task Task Task Task Task Task Task
12:00 - 13:15 ✔ Free time ✔ Free time ✔ Free time ✔ Free time ✔ Free time ✔ Free time ✔ Free time

SlidesCarnival icons are editable shapes.
This means that you can:
● Resize them without losing quality.
● Change line color, width and style.
Isn’t that nice? :)
Examples:
92

You can also use any emoji as an icon!
And of course it resizes without losing quality.
How? Follow Google instructions
https://twitter.com/googledocs/status/730087240156643328
✋👆👉👍👤👦👧👨👩👪💃🏃💑❤😂
😉😋😒😭👶😸🐟🍒🍔💣📌📖🔨🎃🎈
🎨🏈🏰🌏🔌🔑 and many more...
94

HYDROGRAPH AND HYDROLOGICAL ANALYSIS.ppt

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to HYDROGRAPH AND HYDROLOGICAL ANALYSIS.ppt

Similar to HYDROGRAPH AND HYDROLOGICAL ANALYSIS.ppt (20)

Recently uploaded

Recently uploaded (20)

HYDROGRAPH AND HYDROLOGICAL ANALYSIS.ppt