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19-9-2013
Challenge the future
Delft University of Technology
CT4491 Lecture. IDF and Design Storms for urban drainage systems design Marie-claire ten Veldhuis
2 CIE4491 Lecture. IDF curves and design storms
Use of rainfall data
in urban drainage system design
and analysis
Two approaches:
Stationary/steady state analysis:
constant rainfall intensity, stationary flow
Dynamic analysis:
variable rainfall intensity, non-stationary flow
3 CIE4491 Lecture. IDF curves and design storms
Rainfall data in urban drainage
system design and analysis
How to compose or choose a representative
rainfall intensity/event from rainfall time-series?
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4 CIE4491 Lecture. IDF curves and design storms
Rainfall data in urban drainage
system design and analysis
for Design:
How to choose rainfall characteristics, representative of
a pre-defined protection level, over a system’s lifetime?
5 CIE4491 Lecture. IDF curves and design storms
Rainfall data in urban drainage
system design and analysis
for Analysis:
How to find rainfall intensities characteristic of the
conditions we want to check performance for?
6 CIE 4491. Lecture IDF curves and design storms | xx
Stationary rainfall intensity for
stormwater design, IDF-curves
7 CIE 4491. Lecture IDF curves and design storms | xx
Storm water system design and
analysis
What method (stationary/dynamic) to apply when?
What rainfall intensity/intensities to use for analysis?
8 CIE 4491. Lecture IDF curves and design storms | xx
Storm water system design and
analysis
Examples of design/analysis situations:
Stationary .. Or..
.. Dynamic?
Design of small sewer system in Delft
Design of small sewer system in Jakarta
Analysis of small, existing sewer system
Analysis of large, complex existing sewer system
Design of large sewer system in Jakarta
9 CIE 4491. Lecture IDF curves and design storms | xx
Storm water system design and
analysis
Examples of design/analysis situations:
Stationary .. Or..
.. Dynamic?
NB:
Complexity of flow network
Comparison to real-life situation
Computer resources
Spatial rainfall variability
10 CIE 4491. Lecture IDF curves and design storms | xx
Storm water system design and
analysis
Design assignment, part 1: stationary conditions
Application of Rational Method
11 CIE4491 Lecture. IDF curves and design storms
Finding a representative IDF curve
Example of Intensity-Duration-Frequency curves
Horizontal axis: aggregation times
Vertical axis: corresponding rainfall intensities
Each curve: different return periods (T), derived from statistics
12 CIE 4491. Lecture IDF curves and design storms | xx
Finding a representative IDF-curve
Design assignment: 3 IDF-curves provided for 3 different climates: NW-Europe, Mediterranean, Tropics
13 CIE 4491. Lecture IDF curves and design storms | xx
Finding a representative IDF-curve
Design assignment: 3 IDF-curves provided for 3 different climates: NW-Europe, Mediterranean, Tropics
Make a motivated choice for 1 of the curves to use in your design:
Identify and report which curves stands for which climate
Choose and motivate use of 1 curve (think for instance of climate change)
14 CIE4491 Lecture. IDF curves and design storms
Spatial variation, annual rainfall
Average annual
rainfall depth
in the Netherlands
1971-2000
min: 700 mm/yr;
max: 950 mm/yr
Interpolated rain gauge data, period 1971-2000, Courtesy: KNMI
15 CIE4491 Lecture. IDF curves and design storms
Spatial variation daily rainfall
Return period T=20 years
Radar data, period 1998-2008
Daily rainfall depth in the
Netherlands for T=20 yrs
max: 100 mm/day
Yearly rainfall sums and
daily extremes - different
spatial pattern
16 CIE4491 Lecture. IDF curves and design storms
Rainfall curves used in the
Netherlands
Statistical curves: Braak (1933)
Rainfall data of different stations during 1899 t/m 1931: 33 years Van de Herik en Kooistra (1973)
Time series based on 5-minute rainfall data collected over 12 years: 1928, 1933 and 1951 – 1960
Buishand en Velds (1988) Time series of rainfall data collected over 1906 - 1977: 72 jaar
17 CIE4491 Lecture. IDF curves and design storms
Example: Buishand and Velds (KNMI report 1980) Curves are being updated for climate change effects (KNMI, 2004 a.o.)
18 CIE4491 Lecture. IDF curves and design storms
Rainfall data in storm water system
design and analysis
Stationary conditions: representative of real-life conditions?
Why use stationary conditions and IDF-curves?
Quickscan required dimensions new system
Quickscan capacity limits of existing system
Manual design: where there is no computer
NO
19 CIE4491 Lecture. IDF curves and design storms
Rainfall data in storm water system
design and analysis
Stationary conditions: representative of real-life conditions?
Why use stationary conditions and IDF-curves?
Manual design: where there is no computer
Some areas of the world
19th and 20th century, up to ±1990
NO
20 CIE4491 Lecture. IDF curves and design storms
Rainfall data in storm water system
design and analysis
Stationary conditions: representative of real-life conditions?
Why use stationary conditions and IDF-curves?
Manual design: where there is no computer
where there is a lack of data to build a proper model (many
areas worldwide, incl Europe!)
NO
21 CIE 4491. Lecture IDF curves and design storms | xx
Dynamic rainfall intensity for
stormwater design, design
storms
22 CIE4491 Lecture. IDF curves and design storms
Rainfall data in urban drainage
design and analysis
If dynamic calculation is reasonable: use dynamic rainfall
conditions
What rainfall characteristics to choose?
Maximum intensity of a rain event (mm/h)
Total volume of a rain event (mm)
Duration of a rain event (h)
Variation in intensities, high versus low
What is critical for the system we want to design/analyse?
23 CIE4491 Lecture. IDF curves and design storms
What is critical for the system we want to design/analyse?
Depends on characteristics of the catchment: dimensions,
imperviousness, slope
24 CIE4491 Lecture. IDF curves and design storms
Example synthetic standard design
storm T=2 years (NL: “Bui 08”) Rain
fall
inte
nsi
ty (
l/s/
ha)
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lag
[l/
s.h
a]
Max intensity, at end of event 110l/s/ha
(39.6mm/h), during 10 minutes
Total volume 19.8 mm
Duration 1 hour
25 CIE4491 Lecture. IDF curves and design storms
Synthetic storm T=2 jaar (e.g Belgium)
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T=2 years: Rainfall volume 48.09 mm Max rainfall intensity: 53 mm/h
26 CIE4491 Lecture. IDF curves and design storms
Can you explain why different design storms have been chosen
for BE and NL?
What do you expect to find when you apply the BE T=2yr design
storm to a system designed according to NL T=2yr storm ?
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Max intensity 39.6mm/h during 10 minutes
Total volume 19.8 mm
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T=2 years: Rainfall volume 48.09 mm Max rainfall intensity: 53 mm/h
27 CIE4491 Lecture. IDF curves and design storms
Use of rainfall data in urban
drainage design
Multiple event: Historical: rainfall measurements
e.g. in the Netherlands: time series of KNMI De Bilt, 15 minute time step: • 10 year series: 1955-1964 • 25 year series: 1955-1979
Mainly used for analysis of annual pollution from cso’s Because (why not for flooding analysis?):
Synthetic rainfall series
28 CIE4491 Lecture. IDF curves and design storms
Rainfall input for urban drainage
design
To summarise: Stationary design
- IDF curves, fixed design rainfall intensity
Dynamic design, single event: - Design storm
Multiple event/rainfall series
- Historical series e.g. in the Netherlands: time series of KNMI De Bilt, 10 or 25 yrs
- Synthetic rainfall series
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