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MODULE-2
HYETOGRAPH AND HYDROGRAPH
ANALYSIS
PREPARED BY:-
Prof. ANKIT N PATEL
HYETOGRAPH
 A hyetograph is a graphical representation of the
relationship between the rainfall intensity and time.
 It is the plot of the rainfall intensity drawn on the
ordinate axis against time on the abscissa axis.
 The hyetograph is a bar diagram.
 The area under the hyetograph gives the total rainfall
occurred in that period.
 This chart is very useful in representing the
characteristics of storm, and is particularly important in
developing the design storm to predict extreme floods.
Bits Edu Campus Prof. Ankit Patel 2
Mass curve of rainfall
0
10
20
30
40
50
60
0 20 40 60 80 100 120
Time, hour
accumulatedprecipitation,mm
Mass Curve of Rainfall:
The total accumulated precipitation is plotted against time
Bits Edu CampusProf. Ankit Patel 3
Hyetograph of a storm
0
0.1
0.2
0.3
0.4
0.5
0 – 8 8 – 16 16 – 24 24 – 32 32 – 40 40 – 48
Time, hours
Intensity,cm/hr
Hyetograph
-A hyetograph is a graphical representation of the relationship
between the rainfall intensity and time
Bits Edu CampusProf. Ankit Patel 4
Bits Edu CampusProf. Ankit Patel 5
RUNOFF
 Runoff is that portion of rainfall that is not
evaporated.
 The runoff is defined as the portion of the rainfall
that makes its way towards river or ocean as
surface or subsurface flow.
 The discharge flowing in a river is the runoff from
the basin drained by that river.
 Runoff is usually expressed as volume per unit time,
the common unit being m3/s or cumec.
Bits Edu Campus Prof. Ankit Patel 6
Classification of Runoff
 Surface runoff:
Water flows over the land and is first to reach the
streams and rivers which ultimately discharge the
water to the sea.
 Inter flow or subsurface flow:
A portion of rainfall infiltrates into surface soil and
depending upon the geology of basins, runs as
subsurface runoff and reaches the streams and rivers.
 Ground water flow or base flow:
It is that portion of rainfall which after infiltration,
percolates down and joins the ground water reservoir
which is ultimately connected to the ocean.
Bits Edu Campus Prof. Ankit Patel 7
PROCESS OF RUNOFF
 When rainfall a part of it is intercepted by vegetation some of it is
stored as depressions on the ground surface and is known as
depression storage which later infiltrate or evaporates some of the
rain is absorbed by soil.
 If the rain continues further, the water starts infiltrating into the
surface soil and if rate of rainfall exceeds the infiltration rate then
this excess water start collecting on the surface as surface
detention and this water flows overland and joins the stream, river
oceans.
 The water which percolates without joining the water table and
flows below the ground surface and then joins the stream or river as
a sub surface flow and is considered as a part of surface runoff.
 The water that percolates to the ground water table and later after
long time joins the river or stream is known as ground water flow
or base flowBits Edu Campus Prof. Ankit Patel 8
PROCESS OF RUNOFF
Bits Edu Campus Prof. Ankit Patel 9
FACTORS AFFECTING
RUNOFF
1. Climatic Factors
 Type of precipitation
 Rain intensity
 Duration of rainfall
 Distribution of rainfall
 Direction of storm movement
 Soil moisture deficiency
 Other climatic conditions
2. The physiographic Factors
 Size of basin
 Shape of the basin
 Topography of the basin
 Soil characteristics of basin
 Cultivation and vegetative cover in basin area
Bits Edu Campus Prof. Ankit Patel 10
FACTORS AFFECTING
RUNOFF
Bits Edu Campus Prof. Ankit Patel 11
FACTORS AFFECTING
RUNOFF
Bits Edu Campus Prof. Ankit Patel 12
Bits Edu Campus Prof. Ankit Patel 13
Bits Edu Campus Prof. Ankit Patel 14
Characteristics of drainage basin
1. Divide Lines: The boundary line, along a topographic ridge
separating two adjacent drainage basins is called drainage
divide.
2. Concentration Point: The single point or location at which
all surface drainage form a basins comes together or
concentrates as outflow from the basin in the stream channel is
called concentration point
3. Time of concentration: the time of a concentration of a
drainage basin is the time required by the water to reach the
outlet from the most remote points of the drainage area.
Bits Edu Campus Prof. Ankit Patel 15
HYDROGRAPH
 A hydrograph is a graphical plot of discharge of a
natural stream or river versus time.
 It shows variations of discharge with time, at a
particular point of a stream.
 It also shows the time distribution of total runoff at
the point of measurement.
 Discharge is plotted on Y-axis and the corresponding
time is plotted on X-axis.
 Flood analysis and derivation of unit hydrograph a
single peaked hydrograph is required.
 Hydrograph analysis is the most widely used method
of analyzing surface runoff.
Bits Edu Campus Prof. Ankit Patel 16
Hydrograph
Record of River Discharge over a period of time
River Discharge
= cross sectional area
rivers mean
(average) velocity
X
(at a particular point in its course)
Storm Hydrographs
Show the change in discharge caused by a
period of rainfall
Why
Construct & Analyse
Hydrographs ?
To find out discharge patterns of
a particular drainage basin
Help predict flooding events,
therefore influence implementation
of flood prevention measures
Construction
Of
Storm (flood)
Hydrographs
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
Base flow
Through flow
Overland
flow
Basin lag time
mm
4
3
2
Peak flow
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
mm
4
3
2
Rainfall shown
in mm, as a
bar graph
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
mm
4
3
2
Discharge in
m3/s, as a
line graph
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
mm
4
3
2
The rising
flood water in
the river
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
mm
4
3
2
Peak flow
Peak flow
Maximum
discharge in
the river
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
mm
4
3
2
Peak flow
Falling flood
water in the
river
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/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
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
Base flow
Basin lag time
mm
4
3
2
Peak flow
Base flow
Normal
discharge of
the river
0 12 24 36 48 30 72
Hours from start of rain storm
3
2
1
Discharge(m3/s)
Base flow
Through flow
Overland
flow
Basin lag time
mm
4
3
2
Peak flow
Overland flow
Through flow
+
=
Storm Flow
Volume of
water reaching
the river from
surface run off
Overland flow Through flow
Volume of water
reaching the river
through the soil and
underlying rock
layers
COMPONENTS OF A HYDROGRAPH
• Rising limb: The rising limb of hydro graph, also known
as concentration curve, reflects a prolonged increase in
discharge from a catchment area, typically in response
to a rainfall event
• Recession (or falling) limb: The recession limb extends
from the peak flow rate onward. The end of storm flow
(direct runoff) and the return to groundwater-derived
flow (base flow) is often taken as the point of inflection
of the recession limb. The recession limb represents
the withdrawal of water from the storage built up in
the basin during the earlier phases of the hydrograph.
Bits Edu Campus Prof. Ankit Patel 31
• Peak discharge: the highest point on the
hydro graph when the rate of discharge is
greatest
• Lag time: the time interval from the center of
mass of rainfall excess to the peak of the
resulting hydrograph
• Time to peak: time interval from the start of
the resulting hydro graph
• Discharge: the rate of flow (volume per unit
time) passing a specific location in a river or
other channel
Bits Edu Campus Prof. Ankit Patel 32
SEPERATION OF BASE
FLOW
The total runoff comprises direct runoff and base flow
1. Direct runoff: it is that water which reaches the river shortly
after it falls as rain. It is a overland flow
2. Base Flow: It is the initial flow of the river before the rainfall
comes. It is sustained or dry weather flow of the river resulting
from the outflow of perennial or almost permanent ground water
contribution that reaches the river.
Bits Edu Campus Prof. Ankit Patel 33
Unit Hydrograph
Unit Hydrograph is defined as the
hydrograph of surface runoff of a
catchment area resulting from unit
depth of rainfall excess or net rainfall
occurring uniformly over the basin
and at uniform rate for a specified
duration.
Bits Edu Campus Prof. Ankit Patel 34
UNIT HYDROGRAPH
 The effective rainfall also called rainfall excess is that part of total
rainfall that enters the stream directly.
 The specified or unit duration is that period within which the
effective rainfall is considered to be uniformly distributed.
 A unit hydrograph is designed according to the unit duration
 Since the area under a hydrograph represents the total runoff, it is
evident from the definition of unit hydrograph that the area under
the unit hydrograph represents a direct runoff of 1 cm
Bits Edu Campus Prof. Ankit Patel 35
Text in
here
Text in
here
ASSUMPTIONS
 The effective rainfall is uniformly distributed within its duration or
specified period of time
 The effective rainfall is uniformly distributed over the entire area of
drainage basin.
 The base or time duration of the hydrograph of direct runoff due to
an effective rainfall of unit duration is constant.
 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.
Bits Edu Campus Prof. Ankit Patel 36
Text in
here
Text in
here
 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.
Bits Edu Campus Prof. Ankit Patel 37
LIMITATIONS OF UH
 This theory is not applicable to large areas because uniformly
distributed effective rainfall cannot be expected in large area.
 The UH method cannot be applied when an appreciable portion of
the storm precipitation falls as snow
 Practically no two storms have the same nature in space and time
period. So it is not possible to construct UH for each pattern.
Bits Edu Campus Prof. Ankit Patel 38
39
Derived Unit Hydrograph
0.0000
100.0000
200.0000
300.0000
400.0000
500.0000
600.0000
700.0000
0.0000 0.5000 1.0000 1.5000 2.0000 2.5000 3.0000 3.5000 4.0000
Total
Hydrograph
Surface
Response
Baseflow
Bits Edu Campus Prof. Ankit Patel
APPLICATION OF UH
 Use of UH for deriving a flood hydrograph resulting from rainfall
of unit duration
 Use of UH for deriving a flood hydrograph resulting from a series
of rainfalls each of same unit duration
 Use of UH for deriving a UH of other duration.
Bits Edu Campus Prof. Ankit Patel 40

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Module 2 ch-1 heytograph and hydrology analysis

  • 2. HYETOGRAPH  A hyetograph is a graphical representation of the relationship between the rainfall intensity and time.  It is the plot of the rainfall intensity drawn on the ordinate axis against time on the abscissa axis.  The hyetograph is a bar diagram.  The area under the hyetograph gives the total rainfall occurred in that period.  This chart is very useful in representing the characteristics of storm, and is particularly important in developing the design storm to predict extreme floods. Bits Edu Campus Prof. Ankit Patel 2
  • 3. Mass curve of rainfall 0 10 20 30 40 50 60 0 20 40 60 80 100 120 Time, hour accumulatedprecipitation,mm Mass Curve of Rainfall: The total accumulated precipitation is plotted against time Bits Edu CampusProf. Ankit Patel 3
  • 4. Hyetograph of a storm 0 0.1 0.2 0.3 0.4 0.5 0 – 8 8 – 16 16 – 24 24 – 32 32 – 40 40 – 48 Time, hours Intensity,cm/hr Hyetograph -A hyetograph is a graphical representation of the relationship between the rainfall intensity and time Bits Edu CampusProf. Ankit Patel 4
  • 5. Bits Edu CampusProf. Ankit Patel 5
  • 6. RUNOFF  Runoff is that portion of rainfall that is not evaporated.  The runoff is defined as the portion of the rainfall that makes its way towards river or ocean as surface or subsurface flow.  The discharge flowing in a river is the runoff from the basin drained by that river.  Runoff is usually expressed as volume per unit time, the common unit being m3/s or cumec. Bits Edu Campus Prof. Ankit Patel 6
  • 7. Classification of Runoff  Surface runoff: Water flows over the land and is first to reach the streams and rivers which ultimately discharge the water to the sea.  Inter flow or subsurface flow: A portion of rainfall infiltrates into surface soil and depending upon the geology of basins, runs as subsurface runoff and reaches the streams and rivers.  Ground water flow or base flow: It is that portion of rainfall which after infiltration, percolates down and joins the ground water reservoir which is ultimately connected to the ocean. Bits Edu Campus Prof. Ankit Patel 7
  • 8. PROCESS OF RUNOFF  When rainfall a part of it is intercepted by vegetation some of it is stored as depressions on the ground surface and is known as depression storage which later infiltrate or evaporates some of the rain is absorbed by soil.  If the rain continues further, the water starts infiltrating into the surface soil and if rate of rainfall exceeds the infiltration rate then this excess water start collecting on the surface as surface detention and this water flows overland and joins the stream, river oceans.  The water which percolates without joining the water table and flows below the ground surface and then joins the stream or river as a sub surface flow and is considered as a part of surface runoff.  The water that percolates to the ground water table and later after long time joins the river or stream is known as ground water flow or base flowBits Edu Campus Prof. Ankit Patel 8
  • 9. PROCESS OF RUNOFF Bits Edu Campus Prof. Ankit Patel 9
  • 10. FACTORS AFFECTING RUNOFF 1. Climatic Factors  Type of precipitation  Rain intensity  Duration of rainfall  Distribution of rainfall  Direction of storm movement  Soil moisture deficiency  Other climatic conditions 2. The physiographic Factors  Size of basin  Shape of the basin  Topography of the basin  Soil characteristics of basin  Cultivation and vegetative cover in basin area Bits Edu Campus Prof. Ankit Patel 10
  • 11. FACTORS AFFECTING RUNOFF Bits Edu Campus Prof. Ankit Patel 11
  • 12. FACTORS AFFECTING RUNOFF Bits Edu Campus Prof. Ankit Patel 12
  • 13. Bits Edu Campus Prof. Ankit Patel 13
  • 14. Bits Edu Campus Prof. Ankit Patel 14
  • 15. Characteristics of drainage basin 1. Divide Lines: The boundary line, along a topographic ridge separating two adjacent drainage basins is called drainage divide. 2. Concentration Point: The single point or location at which all surface drainage form a basins comes together or concentrates as outflow from the basin in the stream channel is called concentration point 3. Time of concentration: the time of a concentration of a drainage basin is the time required by the water to reach the outlet from the most remote points of the drainage area. Bits Edu Campus Prof. Ankit Patel 15
  • 16. HYDROGRAPH  A hydrograph is a graphical plot of discharge of a natural stream or river versus time.  It shows variations of discharge with time, at a particular point of a stream.  It also shows the time distribution of total runoff at the point of measurement.  Discharge is plotted on Y-axis and the corresponding time is plotted on X-axis.  Flood analysis and derivation of unit hydrograph a single peaked hydrograph is required.  Hydrograph analysis is the most widely used method of analyzing surface runoff. Bits Edu Campus Prof. Ankit Patel 16
  • 17. Hydrograph Record of River Discharge over a period of time River Discharge = cross sectional area rivers mean (average) velocity X (at a particular point in its course) Storm Hydrographs Show the change in discharge caused by a period of rainfall
  • 18. Why Construct & Analyse Hydrographs ? To find out discharge patterns of a particular drainage basin Help predict flooding events, therefore influence implementation of flood prevention measures
  • 20. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) Base flow Through flow Overland flow Basin lag time mm 4 3 2 Peak flow
  • 21. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s)
  • 22. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) mm 4 3 2 Rainfall shown in mm, as a bar graph
  • 23. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) mm 4 3 2 Discharge in m3/s, as a line graph
  • 24. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) mm 4 3 2 The rising flood water in the river
  • 25. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) mm 4 3 2 Peak flow Peak flow Maximum discharge in the river
  • 26. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) mm 4 3 2 Peak flow Falling flood water in the river
  • 27. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/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
  • 28. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) Base flow Basin lag time mm 4 3 2 Peak flow Base flow Normal discharge of the river
  • 29. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) Base flow Through flow Overland flow Basin lag time mm 4 3 2 Peak flow Overland flow Through flow + = Storm Flow
  • 30. Volume of water reaching the river from surface run off Overland flow Through flow Volume of water reaching the river through the soil and underlying rock layers
  • 31. COMPONENTS OF A HYDROGRAPH • Rising limb: The rising limb of hydro graph, also known as concentration curve, reflects a prolonged increase in discharge from a catchment area, typically in response to a rainfall event • Recession (or falling) limb: The recession limb extends from the peak flow rate onward. The end of storm flow (direct runoff) and the return to groundwater-derived flow (base flow) is often taken as the point of inflection of the recession limb. The recession limb represents the withdrawal of water from the storage built up in the basin during the earlier phases of the hydrograph. Bits Edu Campus Prof. Ankit Patel 31
  • 32. • Peak discharge: the highest point on the hydro graph when the rate of discharge is greatest • Lag time: the time interval from the center of mass of rainfall excess to the peak of the resulting hydrograph • Time to peak: time interval from the start of the resulting hydro graph • Discharge: the rate of flow (volume per unit time) passing a specific location in a river or other channel Bits Edu Campus Prof. Ankit Patel 32
  • 33. SEPERATION OF BASE FLOW The total runoff comprises direct runoff and base flow 1. Direct runoff: it is that water which reaches the river shortly after it falls as rain. It is a overland flow 2. Base Flow: It is the initial flow of the river before the rainfall comes. It is sustained or dry weather flow of the river resulting from the outflow of perennial or almost permanent ground water contribution that reaches the river. Bits Edu Campus Prof. Ankit Patel 33
  • 34. Unit Hydrograph Unit Hydrograph is defined as the hydrograph of surface runoff of a catchment area resulting from unit depth of rainfall excess or net rainfall occurring uniformly over the basin and at uniform rate for a specified duration. Bits Edu Campus Prof. Ankit Patel 34
  • 35. UNIT HYDROGRAPH  The effective rainfall also called rainfall excess is that part of total rainfall that enters the stream directly.  The specified or unit duration is that period within which the effective rainfall is considered to be uniformly distributed.  A unit hydrograph is designed according to the unit duration  Since the area under a hydrograph represents the total runoff, it is evident from the definition of unit hydrograph that the area under the unit hydrograph represents a direct runoff of 1 cm Bits Edu Campus Prof. Ankit Patel 35
  • 36. Text in here Text in here ASSUMPTIONS  The effective rainfall is uniformly distributed within its duration or specified period of time  The effective rainfall is uniformly distributed over the entire area of drainage basin.  The base or time duration of the hydrograph of direct runoff due to an effective rainfall of unit duration is constant.  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. Bits Edu Campus Prof. Ankit Patel 36
  • 37. Text in here Text in here  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. Bits Edu Campus Prof. Ankit Patel 37
  • 38. LIMITATIONS OF UH  This theory is not applicable to large areas because uniformly distributed effective rainfall cannot be expected in large area.  The UH method cannot be applied when an appreciable portion of the storm precipitation falls as snow  Practically no two storms have the same nature in space and time period. So it is not possible to construct UH for each pattern. Bits Edu Campus Prof. Ankit Patel 38
  • 39. 39 Derived Unit Hydrograph 0.0000 100.0000 200.0000 300.0000 400.0000 500.0000 600.0000 700.0000 0.0000 0.5000 1.0000 1.5000 2.0000 2.5000 3.0000 3.5000 4.0000 Total Hydrograph Surface Response Baseflow Bits Edu Campus Prof. Ankit Patel
  • 40. APPLICATION OF UH  Use of UH for deriving a flood hydrograph resulting from rainfall of unit duration  Use of UH for deriving a flood hydrograph resulting from a series of rainfalls each of same unit duration  Use of UH for deriving a UH of other duration. Bits Edu Campus Prof. Ankit Patel 40