1 topic ii. 5. rain measurement: parameters, pluviographs, hyetographs and hydrographs. selection of...
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Topic II. 5. Rain Measurement: Parameters,Pluviographs, Hyetographs and Hydrographs.
Selection of Design Rain
Rain Parameters
Rain duration - t, min
Rain depth - h, mm
Rain intensity Physical intensity - i, mm/min Technical intensity - q, l/s.ha
Rain frequency - m, year-1
Return period - P, years
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Rain Parameters
Rain Intensities Relationship
Kinds of Rain Intensity
Mean intensity Partial intensity Momentum intensity
Return Period and Rain
Frequency Relationship
mP /1
iiq .7,166.60
10000
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Rain Parameters
Rain Frequency and
Rain Probability
Rain frequency - m, y-1
q1, q2, q3,…qi……qn-1, qn
q1 > q2 > q3 > … > qi > …… > qn-1 > qn
where qi position in the row is N0 = i
Rain probability - p
q1, q2, q3,…qi……qn-1, qn totally n number for the period of observation - T
q1 > q2 > q3 > … > qi > …… > qn-1 > qn
, when n )/lim( nNop
TNom /
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Rain Parameters
Rain Parameters Relationships
Example:
Given: T = 20 years; n = 1000; No = 4
Then, ,y-1
,y
2,020/4 m
%4,0004,01000/4 p
52,0/1/1 mP
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Rainfall (Precipitation) Measurement
Rain Gauges
Standard rain gauge
Pluviographs (recording rain gauges) Hellmann type Tipping bucket type Weighing type
Radars
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Precipitation Measurement
Rain-Gauges
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Precipitation Measurement
Radar for Precipitation Measuring
Radar beam parameters wave length - 3 - 10 cm wave frequency - 500 - 1000 Hz
Reflecting beam power - Pr
Formula of Marshal - Palmer
2/'. rzCPr
iAz .' 36 /' mmmz 'lg.10 zz dBzz
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Rainfall and Runoff ParametersDependence on Time
Pluviograph
(Rain-gauge record)
h = f(t)
Hyetograph
q = f(t)
Hydrograph
Q = f(t)
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Rain Duration - Intensity - Frequency (DIF) Relationships
I. Formulas Implicit in Respect
to the Return Period
Formula of Talbot (1891)
Formula of Belov (1922)-Montana
nt
Aq
tB
Aq
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Rain Duration - Intensity - Frequency (DIF) Relationships
II. Formulas Explicit in Respect
to the Return Period
Formula of Belov (1932)
Formulas of Dimovski (1987)
n
n
t
m
Pq
q
)lg
lg1.(.20 20
PtPtq I Pt lg.)]5lg(542,3288,11[)lg1.()]5lg(136,3477,9[ 33,
PtPtq IIPt lg.)]5lg(3974,38270,10[)lg1.()]5lg(0077,38899,9[ 33,
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Rain-Gauge Records Reading
Pluviographs shapes
Pluviographs shapes impact
on the relevant hydrographs
Storms pluviographs shape
Rain-gauge records reading Method of maximum intensity
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Return Period Impacton the Design Rain Selection
Factors Influencing the
Return Period Selection
Kind of the sewer system
Level of the settlement development
Terrain topography
Streets width
Underground infrastructure density
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Selection of Design Rain
Based on historical rain-gauge records (graphically)
;
Based on prescribed return period values Separate sewer system - P = 1 - 5 years Combined sewer system - P = 1 - 10 years, as follows: Settlements of I and II functional type - P = 3 - 10 years Settlements of III and IV functional type - P = 2 - 5 years Settlements of V, VI and VII functional type - P = 1 - 2 years
nt
Aq tnAq lg.lglg