1

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

2

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

3

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 /

4

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

5

Rainfall (Precipitation) Measurement

Rain Gauges

Standard rain gauge

Pluviographs (recording rain gauges) Hellmann type Tipping bucket type Weighing type

Radars

6

Precipitation Measurement

Rain-Gauges

7

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

8

Rainfall and Runoff ParametersDependence on Time

Pluviograph

(Rain-gauge record)

h = f(t)

Hyetograph

q = f(t)

Hydrograph

Q = f(t)

9

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

10

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,

11

Rain-Gauge Records Reading

Pluviographs shapes

Pluviographs shapes impact

on the relevant hydrographs

Storms pluviographs shape

Rain-gauge records reading Method of maximum intensity

12

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

13

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