Development of Intensity Duration Frequency(IDF) Curves for Bahir Dar City from Daily Rainfall Data by Using Simple Scaling Method, Bahir Dar, Ethiopia.
No Thumbnail Available
Date
2016-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa
Abstract
This research mainly dealt the development of intensity duration frequency curves for Bahir
Dar city from annual maximum daily rainfall data by using simple scaling method. Regarding
the rainfall data, 41 years of daily rainfall data and 4 years sub hourly and hourly rainfall data
were collected from National Meteorological Agency (NMA) in Addis Ababa, Ethiopia.
Hydrological data checking was conducted which were mainly testing for independence,
stationary, homogeneity and outliers of the rainfall data. And the data were found
independent, stationary, homogenous and with no outliers. There were missing data for 12
months in 1991, 2005 and 2014 and in-filling of the data were done using simple average
method.
By using easy fit software, it was possible to know that the annual maximum daily rainfall
data to Bahir Dar city followed the general extreme value(GEV) distribution function and the
three parameters of the distribution function were also determined. The annual maximum
daily rainfall were found to be time scale invariant which helped to develop the intensity
duration frequency relationships and curves using simple scaling method. The scale
exponents of the scale factor was found constant in two ranges of durations
and . Because of the distinction of the linearity of the slopes for these two
durations, it was possible to detect the slopes difference at one hour duration.
The automatically 15 minutes intervals recorded for 4 years (2012-2015) rainfall data were
the back bone of the successful development of the curves for Bahir Dar city. The
determination of the design daily rainfall for 2 years, 5 years, 10 years, 25 years, 50 years,
and 100 years return periods was done. The comparison of the regional IDF curves and
simple scaling method generated IDF curves showed that the intensity of the simple scaling
method generated curves were higher value than the intensities generated using the regional
IDF curves. Moreover, the 24 hour rainfall values calculated from simple scaling model fall
above the design rainfall values calculated from observed rainfall data for different selected
return periods using frequency factor method. In addition, the comparison of the regional IDF
curves, observed IDF curves, and simple scaling IDF curves were also analyzed in order to
understand and check the performance of simple scaling modeling with regards to the
observed rainfall data. Based on this analysis, it was learnt that the intensities or rainfall
values from simple scaling model fall above the values of the observed rainfall or intensity
values. In contrary, the values from regional IDF curves fall below both observed rainfall and
design rainfalls calculated values. This proved that simple scaling model performs better than
the regional IDF curves. From the study, it was also possible to learn that the intensities at
shorter rainfall durations are higher than the intensities at longer rainfall durations.
Description
Keywords
Development of intensity duration frequency