03 – Site Orientation Map (SOM) and Design Rainfall Estimation
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Hydrology & Coastal Section Fasil Gebre BSc MEngSc PhD MIEI Introductory Lectures on the FSU Methodologies November/December 2014 03 – Site Orientation Map (SOM) and Design Rainfall Estimation
Transcript of 03 – Site Orientation Map (SOM) and Design Rainfall Estimation
Hydrology & Coastal Section
Fasil Gebre BSc MEngSc PhD MIEI
Introductory Lectures on the FSU MethodologiesNovember/December 2014
03 – Site Orientation Map (SOM) and Design Rainfall Estimation
Hydrology & Coastal Section
• The Site Orientation Map (SOM)
• Rainfall Depth Duration Frequency (DDF) Model
• Deriving the Rainfall DDF Model
• Design Rainfall Estimation in the DDF Module
• Calculation of Design Rainfall Depths (DRD)
Presentation Structure
Hydrology & Coastal Section
The Site Orientation Map (SOM)
Hydrology & Coastal Section
Rainfall Depth Duration Frequency (DDF) Model
What is the Rainfall Depth Duration Frequency (DDF) model?
• It is a gridded dataset (map) of rainfall depths for different durations and return periods
• Range of durations: 15 mins. – 600 hours
• Range of return periods: 2 – 500 years
Hydrology & Coastal Section
Deriving the Rainfall DDF Model for Ireland
Start Point - Gauged rainfall information
• Sub-daily rainfall data at 47 stations
• Daily rainfall data at 577 stations
Hydrology & Coastal Section
Deriving the Rainfall DDF Model for Ireland
Rainfall Depth-Duration-Frequency (DDF) Analysis
• Obtained Amax rainfall depths for range of storm
durations from each gauge
• Estimated index (median) rainfall depth
• Through kriging and interpolation, 2x2km grid index rainfall depth and duration was created …
Hydrology & Coastal Section
Deriving the Rainfall DDF Model for Ireland
Rainfall Depth-Duration-Frequency (DDF) Analysis
• Used this data to derive return period growth factors for a range of combinations of rainfall depth and duration
• Produced a gridded dataset relating rainfall depth and duration to return periods
Hydrology & Coastal Section
Deriving the Rainfall DDF Model for Ireland
Map of the 5-year return period rainfall of 2-day duration
Gridded Rainfall DDF Model (2km grid)
Output: Rainfall DDF Model
Range of durations: 15 mins. – 600 hours
Range of return periods: 2 – 500 years
Hydrology & Coastal Section
Design Rainfall Estimation in the DDF Module
Location Type
• Choose a Grid Point or a Catchment
Hydrology & Coastal Section
Design Rainfall Estimation in the DDF Module
Design Rainfall Depth (DRD)
• Choose a Grid Point or a Catchment,
• Input Rainfall Duration and Return Period
Design Rainfall Frequency (DRF)
• Choose a Grid Point or a Catchment
• Input Rainfall Depth and Duration Depth Frequency
Duration
Hydrology & Coastal Section
Design Rainfall Estimation in the DDF Module
DRF - Fixed Vs Sliding duration
• Fixed
• Sliding
Day1
09:00
Day 2
09:00
Day 3
09:00
Day1
09:00
Day 2
09:00
Day 3
09:00
Rainfall from 09:00 to 09:00
Rainfall from 13:00 to 13:00
Hydrology & Coastal Section
Calculation of Design Rainfall Depths
Design Rainfall Depth (DRD) for a Catchment
• Select the relevant
river node
corresponding to
the catchment of
interest
• The catchment
outline and the DDF
grid is displayed
Hydrology & Coastal Section
Calculation of Design Rainfall Depths
Design Rainfall Depth (DRD) for a Catchment
• Enter the return
period and duration
in the right hand
window
• The Portal will
automatically apply
an Areal Reduction
Factor (ARF)
• The DRD for the
catchment is
displayed
Hydrology & Coastal Section
Calculation of Design Rainfall Depths
• Takes catchment area into account when accounting for variability of rainfall across a catchment
• ARF = 1-bD-a
• a, b are functions of Area
• D is the Duration
• Average Point Rainfall x ARF = Design Catchment rainfall
Areal Reduction Factor (ARF)
