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Total Precipitation Interception Infiltration Precipitation ChannelPrecipitation Depression Storage

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Title: Total Precipitation Interception Infiltration Precipitation ChannelPrecipitation Depression Storage


1
  • MINISTRY OF SCIENCE AND TECHNOLOGY
  • DEPARTMENT
  • OF
  • TECHNICAL AND VOCATIONAL EDUCATION
  • Department of Civil Engineering
  • CE 4026
  • Engineering Hydrology
  • (Sample Lecture)?
  • INFILTRATION
  • Daw Cho Cho
  • Associate Professor
  • Department of Civil Engineering
  • Yangon Technological University

2
(No Transcript)
3
Infiltration
  • Infiltration is the process by which enters the
    soil from the ground surface
  • Infiltration first replenishes the soil moisture
    deficiency
  • Infiltration is responsible for subsurface and
    ground water flow
  • The supply to ground water reservoir also depends
    upon infiltration
  • The infiltration rate is used for the computation
    of the water loss due to infiltration for the
    determination of the surface runoff

4
Infiltration Capacity
f0
ftfc(f0-fc)e -kt
f infiltration
fc
time t
when i f
faf
ilt f
fai
where, faactual infiltration rate f
infiltration capacity i intensity of
rainfall infiltration capacity at time t after
the beginning of the storm ftfc(f0-fc)e
kt where, fo initial infiltration capacity
fc limiting constant value of the
infiltration The values of fc, fo and k depends
upon the type and condition of soil
5
Factors affecting infiltration rates
  • soil moisture
  • type of soil medium
  • permeability
  • vegetal cover
  • surface fines
  • compaction of soil
  • available storage in soil stratum
  • depth of surface detention
  • temperature of water
  • other factors

6
Measurement of infiltration capacityThe
following two types of infiltrometer are commonly
used in practice1. Flooding type infiltrometer
2. Rainfall simulator-type infiltrometer
7
Infiltration indices
  • An average constant value of infiltration is
    called infiltration index.
  • Two types of infiltration indices are commonly
    used.-index
  • 1. ? -index
  • 2. w index
  • There are extremely used for the analysis of
    major floods when the soil is wet and the
    infiltration rate becomes constant

8
?-index
  • The value of f-index can be derived from the
    rainfall hyetograph and the resulting surface
    runoff volume by trial and error.
  • The unshaded area below the horizontal line is
    assumed that all losses are due to infiltration
    only.
  • For determination of ?- index, a horizontal line
    is drawn on the hyetograph such that the shaded
    area above that line is equal to the volume of
    surface runoff.
  • If the shaded area is not equal to the volume of
    measured surface runoff, the horizontal line is
    shifted upwards or downwards till this condition
    is satisfied.

9
W-index
  • w-index(P-R-S)/tf
  • where Ptotal storm precipitation (cm)
  • Rtotal surface runoff (cm)?
  • Sdepression and interception
    losses (cm)?
  • tftime period (in hours)?
  • The w-index is more accurate than the ?-index
    because it excludes the interception and
    depression

10
Example
  • For a storm of 3-hr duration, the rainfall rates
    are as follows
  • If the surface runoff is 3.4 cm, determine the
    ?-index and w-index.
  • Solution
  • Assume that f-index is more than 1.4 cm/hr.
    Therefore, surface runoff
  • R(3.4-?)(4.8-?)(3.2-?)(2.0-?)30/60
  • 3.406.7-2?
  • ?1.65 cm/hr
  • As the computed value of f-index is greater than
    1.4 cm/hr, the assumption was correct.
  • total precipitation P(1.43.44.83.22.01.2)30/
    60
  • 8 cm
  • W-index(P-R-S)/tf, assume S 0
  • (8.0-3.4)/3.0 1.53 cm/hr

11
  • Thank You
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