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 l Physical intensity - i, mm/min l 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

3 Rain Parameters Rain Frequency and Rain Probability §Rain frequency - m, y -1 q 1, q 2, q 3,…q i ……q n-1, q n q 1 > q 2 > q 3 > … > q i > …… > q n-1 > q n where q i position in the row is N 0 = i §Rain probability - p q 1, q 2, q 3,…q i ……q n-1, q n  totally n number for the period of observation - T q 1 > q 2 > q 3 > … > q i > …… > q n-1 > q n, when n  

4 Rain Parameters Rain Parameters Relationships Example: Given: T = 20 years; n = 1000 ; No = 4 Then,,y -1,y

5 Rainfall (Precipitation) Measurement Rain Gauges §Standard rain gauge §Pluviographs (recording rain gauges) l Hellmann type l Tipping bucket type l Weighing type §Radars

6 Precipitation Measurement Rain-Gauges

7 Precipitation Measurement Radar for Precipitation Measuring §Radar beam parameters l wave length cm l wave frequency Hz §Reflecting beam power - P r §Formula of Marshal - Palmer

8 Rainfall and Runoff Parameters Dependence 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

10 Rain Duration - Intensity - Frequency (DIF) Relationships II. Formulas Explicit in Respect to the Return Period §Formula of Belov (1932) §Formulas of Dimovski (1987)

11 Rain-Gauge Records Reading §Pluviographs shapes §Pluviographs shapes impact on the relevant hydrographs §Storms pluviographs shape §Rain-gauge records reading l Method of maximum intensity

12 Return Period Impact on 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 l Separate sewer system - P = years l Combined sewer system - P = years, as follows: l Settlements of I and II functional type - P = years l Settlements of III and IV functional type - P = years l Settlements of V, VI and VII functional type - P = years