Surface Water Hidrology - Chapter 2

KKKA 6923 Surface Water Hydrology

KKKA 6923Surface Water Hydrology

Muhammad bin RamlanP57600

KKKA 6923 Surface Water Hydrology

CONTENT

2.11 Frequency Of Point Rainfall 2.12 Maximum Intensity-Duration-Frequency

Relationship Maximum Intensity-Duration Relation Maximum Depth-Duration Relationship Maximum Intensity-Duration-Frequency Relationship

2.13 Probable Maximum Precipitation

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

WHAT In hydraulic –engineering applications (e.g flood), is to

determine the probability of occurrence of a particular rainfall The rainfall at a place is a random hydrologic process and a

sequence of rainfall data at a place; when arranged in chronological order constitute a time series. (Commonly used time series is annual rainfall)

This information is obtained by the frequency analysis of the point-rainfall data.

Purpose of frequency analysis: to obtain a relationship between the magnitude of the event and its probability of exceedence.

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

HOW The probability analysis can be made by:

Empirical method (e.g. Weibull etc) – Plotting Position

Analytical method (e.g. Gumbel Extreme Value Distribution & Log Pearson Type 3)

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

TERMINOLOGY The recurrence interval (aka return period) is defined

as T = 1/P ; where P is the probability of occurrence of an event.

Statement: The return period of rainfall of 20mm in 24h is 10years at a certain station A.› Means: an average rainfall magnitudes equal or greater

than 20cm in 24h occur once in 10 years. (however, it does not mean that every 10 years one such event is likely to happen)

› The probability is 1/T = 1/10 = 0.1

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

SAMPLE QUESTION

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

SAMPLE RESULT

KKKA 6923 Surface Water Hydrology

2.11 Frequency Of Point Rainfall

SAMPLE GRAPH

KKKA 6923 Surface Water Hydrology

CONTENT

2.11 Frequency Of Point Rainfall 2.12 Maximum Intensity-Duration-Frequency

Relationship Maximum Intensity-Duration Relation Maximum Depth-Duration Relationship Maximum Intensity-Duration-Frequency Relationship

2.13 Probable Maximum Precipitation

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

A. Maximum Intensity-Duration Relation B. Maximum Depth-Duration Relationship C. Maximum Intensity-Duration-Frequency

Relationship

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

A. MAXIMUM INTENSITY-DURATION RELATION

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

B. MAXIMUM DEPTH-DURATION RELATIONSHIP

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

C. MAXIMUM INTENSITY-DURATION-FREQUENCY RELATIONSHIP

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

SAMPLE QUESTION

>> Please Refer Example 2.9 Page 47

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

SAMPLE RESULT

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

SAMPLE RESULT

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

SAMPLE RESULT

KKKA 6923 Surface Water Hydrology

2.12 Maximum Intensity-Duration-Frequency Relationship

SAMPLE RESULT

KKKA 6923 Surface Water Hydrology

CONTENT

2.11 Frequency Of Point Rainfall 2.12 Maximum Intensity-Duration-Frequency

Relationship Maximum Intensity-Duration Relation Maximum Depth-Duration Relationship Maximum Intensity-Duration-Frequency Relationship

2.13 Probable Maximum Precipitation

KKKA 6923 Surface Water Hydrology

2.13 Probable Maximum Precipitation

WHAT The greatest or extreme rainfall for a given

duration that is physically possible over a station/basin.

E.g. from the operational point of view, PMP can be defined as rainfall over a basin which would produce a flood flow with virtually no risk of being exceeded.

Done by experienced hydrometeorologist.

KKKA 6923 Surface Water Hydrology

2.12 Probable Maximum Precipitation

HOW PMP can be determine using:

Meteorological method Statistical study of rainfall data; Pm = 42.16D0.475

KKKA 6923 Surface Water Hydrology

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