high intensity rainfall analysis for nelson urban area › assets › envirolink › 463... · high...

High intensity rainfall analysis for Nelson urban area

NIWA Client Report: CHC2008-093 July 2008 NIWA Project: ELF09211

All rights reserved. This publication may not be reproduced or copied in any form without the permission of the client. Such permission is to be given only in accordance with the terms of the client's contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.

High intensity rainfall analysis for Nelson urban area Alistair McKerchar

Prepared for

Nelson City Council

NIWA Client Report: CHC2008-093 July 2008 NIWA Project: ELF09211 National Institute of Water & Atmospheric Research Ltd 10 Kyle Street, Riccarton, Christchurch P O Box 8602, Christchurch, New Zealand Phone +64-3-348 8987, Fax +64-3-348 5548 www.niwa.co.nz

Contents Executive Summary i

1. Introduction 1

2. Available rainfall records 2

3. Map of annual rainfall 2

4. Extraction of rainfall intensity data 3

5. Data integrity checks 4

6. Frequency analysis method 4

7. Results 4 7.1. EVAN results 4 7.2. HIRDS estimates for gauge sites 5 7.3. Recent severe storms 5 7.4. Currently used design storm intensities 6 7.5. Allowance for climate change 6 7.6. Frequency of floods 6

8. Discussion 7

9. Conclusion 9

10. References 9

Reviewed by: Approved for release by:

Charles Pearson Murray Hicks

High intensity rainfall analysis for Nelson urban area i

Executive Summary

Records of short duration rainfalls for the Nelson Aero meteorological site date from 1944 and daily-

read gauge records are considerably longer.

Annual maxima Nelson Aero data for a range of durations are analysed with standard extreme value

frequency analysis methods. The results are compared with estimates of intensities from the NIWA

High Intensity Rainfall Design System (HIRDS), and confirm that the package provides acceptable

results.

Rainfall increases inland from the coast, and comparison of recorded intensities for two inland gauges

with the equivalent HIRDS estimates gave mixed results. However in the context of Nelson City urban

drainage design, these results are of lesser importance.

Data from recent severe storms is studied and a storm on 23 May 2007 is shown to have had rainfall

totals well above 100 year return period estimates for durations of 15 minutes to two hours.

The present Nelson City design storm intensity chart is somewhat conservative: the 50 year return

period totals on this chart are close to the 100 year return period HIRDS estimates. However, a degree

of conservatism in the estimates is probably desirable, especially since intensities increase moving to

higher elevations inland from the coast.

The MfE Guidelines provide a pragmatic approach for allowing for expected increases in rainfall

extremes as a consequence of global warming.

Frequency analyses are presented of peak flood flows recorded for the Wakapuaka and Maitai Rivers.

High intensity rainfall analysis for Nelson urban area 1

1. Introduction

Extreme rainfall intensities with specified probabilities of exceedence are a

fundamental parameter for urban drainage design.

With this awareness, this report was requested by Mr Paul Sheldon, Environmental

Monitoring Coordinator for the Nelson City Council. The request was to provide a

review of extreme rainfall statistics used for urban drainage design in the greater

Nelson area and to publicise a package that provides estimates of the statistics.

Rainfall intensities across New Zealand have been reported in a number of studies,

notably that of Tomlinson (1980) who undertook extreme value frequency analysis of

a large sample of rainfall records for the country. The result of the study was a set of

maps with storm rainfall contours that enabled the estimation of a storm rainfall depth

for any specified duration and frequency. These analyses and maps have been updated

with more recent data and the results have been encapsulated into a High Intensity

Rainfall Design System (HIRDS) which is available as a computer package

(Thompson, 2002). The HIRDS package Version 2 released in 2002 uses the general

extreme value (GEV) distribution to fit data for individual sites and fits a spline

surface to provide an estimate of rainfall intensity at any location in the country. In

fitting the surface, there is some spatial smoothing so that an estimate at a given site is

partially weighted by results to nearby sites.

This study:

• uses HIRDS to provide estimates of storm rainfall design statistics for the

Nelson City and Richmond area;

• compares HIRDS results with rainfall records for automatic gauges where

more than 10 years of record are available;

• compares results with currently used design storm intensities;

• investigates and reports on records of short duration extreme rainfalls;

• discusses use of MfE guidelines for allowing for climate change;

• reports on flood frequency for streams in the area that have flow records

exceeding 10 years length.


2. Available rainfall records

Rainfall data for daily read and recording (automatic) gauges were assembled from

NIWA’s climate database, from the Tasman District Council (TDC) and Nelson City

sources.

The available data for the area for the period 1930-2008 are shown as timelines in

Figure 1. Locations of the gauges are shown in Figure 2.

Where the data are from manual gauges read at 0900 h NZ Daylight Time, the stations

are named “daily”. Otherwise, the data are for automatic gauges. There are three daily-

read gauges with records exceeding 10 years length that are suitable for frequency

analysis of daily and longer duration storms: Mapua, Appleby and Nelson Aero.

The gauges for which rainfall records are used in the extreme value frequency analysis

are listed in Table 1.

Table 1: Rainfall records used in extreme value analysis.

Number Location NZMS260 map ref

Yr start

Yr end Gauge type

132003 Mapua N27:174953 1967 2006 Manual

132101 Appleby N27:183906 1932 1993 Manual

132202 Nelson Aero N27:289899 1942 2007 Manual. No data 1994-97

132212 Nelson Aero N27:289899 1944 1992 Auto

132310 Williams/Smiths Ford/Forks O27:398910 1988 2004 Auto

133336 Third House O27:372867 1992 2007 Auto

3. Map of annual rainfall

Figure 3 presents a map of mean annual rainfall for the Nelson City-Marlbrough

region. (Unfortunately the Richmond area is disconnected from this map and appears

in the Tasman region map.) The feature to note with respect to Nelson City is the

progressive increase of rainfall when moving inland from the coast to Bryant Range

behind the city. Overall, similar increasing patterns are expected in rainfall intensities.


4. Extraction of rainfall intensity data

In undertaking analysis of rainfall intensities, it is necessary to take account of the

recording resolution for the gauge.

For the manual gauges, totals are recorded at 0900 h NZ Daylight Time, which are not

necessarily the maxima over any 24 hour interval. This is handled by applying an

adjustment factor to daily-read data to estimate 24, 48 and 72 hour maxima. These

factors as given in Tomlinson (1980) are listed in Table 2.

Table 2: Factors to estimate 24, 48 and 72 hour maxima from rainfall totals read at daily intervals (Tomlinson, 1980).

Analysis interval (h) Factor

24 1.14

48 1.07

72 1.04

Most of the automatic gauge records (Figure 1) are less than ten years in length and

are too short to use in individual frequency analyses. However the main long term

automatic record is for the Nelson Aero gauge where useful records commence in

April 1943 and terminate in 1993, when the gauge was replaced by an automatic

weather station (AWS). This record is referred to as “Nelson AWS” and the gauge is

also located at Nelson Airport.

The AWS stations are programmed to record hourly rainfall totals and the same time-

sampling issue encountered with daily-read gauge data applies when using hourly

AWS data, such as for the Nelson AWS to get maxima for any 60, 120 or 180 minute

interval. This contrasts with the earlier Nelson Aero automatic data. The latter, which

have been read manually from charts, give estimates of rainfalls over intervals as low

as 10 minutes.

On the advice of Tasman District Council, another automatic record covering 1985-

2004 was assembled by concatenating records for Williams, Smiths Ford and Forks

records. These gauges were located short distances downstream of the Maitai Dam.

For brevity, this record will be referred to as “Williams xtd”. These automatic gauges

have time resolutions ranging from six to 15 minutes, and should provide good

estimates of totals for one hour and more.


A third automatic gauge, at a site named Third House and located in the headwater of

The Brook catchment (Figure 2), has records for 1992-2007.

5. Data integrity checks

To check the integrity of data, a range of checks were applied to the longer series. An

example of these is in Figure 4 which compares cumulative rainfalls for five different

gauges. It shows that the totals for four of the gauges are very similar, and the

increments of rain occur from the same times. However, the data for the fifth gauge

(Nelson AWS) are not representative of the others and the data for Nelson AWS over

this period are not used.

6. Frequency analysis method

For four of the longer records (Nelson Aero, Mapua, Appleby, Williams xtd)

frequency analysis is undertaken by extracting annual maxima for a range of durations

and fitting an extreme value type 1 (Gumbel) distribution to the data. The distribution

is extrapolated to estimate quantiles for specified annual exceedence probabilities

(AEPs) values. These analyses are termed the “at-site” analyses. The results are then

compared with the HIRDS values for the same locations. The intention of this process

is to provide confirmation that the HIRDS estimates are consistent with locally

recorded data. The analysis method is encapsulated with an Event Analysis module

(EVAN) of the Tideda hydrological data archiving package that is used throughout

New Zealand. The HIRDS package Version 2 released in 2002 uses the general

extreme value (GEV) distribution to fit data for individual sites and fits a spline

surface to provide an estimate of rainfall intensity at any location in the country. In

fitting the surface, there is some spatial smoothing so that an estimate at a given site is

partially weighted by results for nearby sites.

The Gumbel distribution is a particular limiting case of the GEV distribution and

because the use of GEV in HIRDS, the HIRDS estimates in some cases will exceed

the at-site Gumbel estimates.

7. Results

7.1. EVAN results

EVAN (at-site) results are prepared for five gauges with records exceeding 10 years in

length. These gauges are Mapua, Appleby, Nelson Aero, Williams xtd and Third

House.


For the Nelson Aero records, Figures 5 presents the annual maxima for durations

between 10 minutes and 3 hours, together with the fitted Gumbel frequency curves.

Similarly, Figure 6 presents the frequency analysis for durations between 12 and 72 h.

For the Williams xtd and Third House automatic gauge records, Figures 7 & 8 present

the EVAN results.

Similar plots, not included, were prepared for the Mapua and Appleby manual gauge

records.

7.2. HIRDS estimates for gauge sites

HIRDS estimates were prepared for the five gauge locations. These are presented as

charts in Figures 9 - 13. Estimates from the EVAN at-site analyses with the data for

the site are also shown on these figures.

7.3. Recent severe storms

Mr Sheldon from Nelson City Council supplied files with recent rainfall data recorded

at Princess Drive and St Vincent Street in Nelson from August 2006 to July 2008.

There were 10 minute totals for both sites as well as a separate file of hourly totals for

Princess Street.

To compare these data with the other records, cumulative totals for the various records

are plotted in Figure 14. This figure shows that the 10 minute Princess Drive record

has lower totals than the other Nelson City records, and it is not considered further.

The two most severe storms identified in this period are in 22/23 May 2007 and 14-15

April 2008. Cumulative totals for these two events are plotted in Figures 15 and 16.

The short duration intensities are more severe for the 2007 event, as indicated by the

steepness of the cumulative curves in Figure 15. Selected maxima for a range of

durations for this event are listed in Table 3 together with the HIRDS 100 year

estimates for Nelson Aero (Table 5). The previous largest values recorded for short

duration storms recorded at the Nelson Aero gauge are included in this table for

comparison.


Table 3: Comparison of rainfall totals during 23 May 2007 with previous large values and HIRDS 100 yr estimates.

Duration

Gauge Storm date 15 min 30 min 45 min 1 h 2 h 6 h 12 h

Orphanage 23 May 2007 34* 52* 59* 65 87 99 108

Nelson AWS 1992-2007 23 May 2007 - - - 60* 71* 83 93

Nelson Aero 1944-1992 10 Jan 1985 15 28 36 43 63 119 134

29 Feb 1964 18 29 36 42 53 73 82

HIRDS 100 yr 30 41 53 58 73 104 130

* Recorded value adjusted using the factors in Table 1.

7.4. Currently used design storm intensities

The current Nelson City storm rainfall intensity-frequency-duration curves were

supplied as a chart (Plan 21/201). The 10 year and 50 year curves from this chart are

reproduced in Figure 17 together with the HIRDS estimates for Nelson Aero, as in

Table 5 below.

Maximum recorded rainfalls intensities (Table 3) are also plotted on in Figure 17. The

storm of May 2007 is the most notable event, and the Orphanage 15 min, 30 min, 1 h

& 2 h intensities all exceed the HIRDS 100 year estimates.

7.5. Allowance for climate change

Guidance issued by the Ministry for the Environment (MfE, 2008) on allowance for

climate change recommends increases of 8% for (50 & 100 year) extreme rainfalls for

each degree Celsius of temperature rise. Typical temperature rises for the Tasman

Nelson area indicated for the 2090s are +2oC. Thus extreme rainfalls should be

increased by about 16 % to allow for increasing temperatures.

7.6. Frequency of floods

Two catchments with flow records in the Nelson City area are the Maitai South

Branch and the Wakapuaka. Results from frequency analyses of their annual

maximum flows are presented in Table 4.


Table 4: Frequency analysis of annual maxima (m3/s) for the Maitai and Wakapuaka Rivers.

River Maitai South Branch Wakapuaka

Location Above Old Intake Hira

Site number 57807/57804 58101

Years used 1981-2005 1979-2005

Catchment area (km2) 17.8/16.7 41.9

Return period (yrs)

2 42 49

5 56 100

10 65 129

20 75 158

50 87 195

100 96 223

8. Discussion

The Nelson Aero record, with data for 1944-1992, is an excellent record of rainfall

intensity. Figures 4 & 14 show that this record is consistent with other records for the

Nelson city area and Mapua and Appleby.

On the basis of this consistency, the HIRDS estimates for the Nelson Aero site are

recommended for use in the lowland city area. They are shown in Figure 9, and the

Gumbel at-site quantile estimates from Figures 5 & 6 are overplotted. Overall the

HIRDS estimates are close to the results for the Gumbel analysis for the Nelson Aero

data (Figure 9) but are somewhat higher for the extreme short duration rainfalls – for

example the HIRDS estimate for the 1 hour 100 year rainfall is 58 mm, compared with

50 mm from the at-site analysis. However the standard errors of estimate for the two

values, (±5 mm and ±4 mm respectively) indicates that the differences could arise

through chance. In addition, the HIRDS analysis does not necessarily use the Gumbel

distribution in all cases. HIRDS values that are greater than the EVAN EV1 estimates

are expected where the data are better fitted by a GEV distribution. For convenience,

the HIRDS estimates for Nelson Aero, as displayed in Figure 9, are listed in Table 5.


Table 5: HIRDS rainfall intensity estimates for Nelson Aero.

Duration 10 min 20 min 30 min 1 h 2 h 6 h 12 h 24 h 48 h 72 h

Return period

2 yr 7 11 14 21 27 43 57 75 90 99

5 yr 10 14 18 27 35 53 69 90 108 120

10 yr 11 17 21 31 40 60 78 100 120 133

20 yr 14 20 25 37 47 70 89 115 137 151

50 yr 18 26 33 47 60 87 109 138 165 182

100 yr 23 33 41 58 73 104 130 162 192 213

Inland from the city, higher rainfalls occur (Figure 3). The Williams xtd and Third

House records are located in this area. The fit of Gumbel distributions is not wholly

satisfactory (Figures 7 & 8), and there is some variation between the Gumbel “at-site”

estimates and the HIRDS results (Figures 10 & 11). However, it is likely that these

locations are of less concern for urban stormwater drainage.

The estimated 15, 30, 60 and 120 min rainfall maxima for the Orphanage site on 23

May 2007 (Table 3) all exceed the 100 year HIRDS estimate (Figure 17), and the 30

minute total (56 mm, 136% of HIRDS 30 min 100 yr estimate) was the most severe.

This event yielded easily the largest one hour rainfall recorded for the Nelson

Aero/AWS site. The lower totals recorded for St Vincent St and Princess Drive gauges

(Figure 15), indicate that this storm was more intense on the south side of the city. Its

extent is uncertain as no rainfall data were identified for the Richmond area.

No particularly notable short duration events were evident in the Princess Drive and St

Vincent St records.

The present Nelson city rainfall intensity curves (as reproduced in Figure 16) appear

to be somewhat conservative – for example the 50 year curve is very close to the

HIRDS 100 year estimate. However, a degree of conservatism in the estimates is

probably desirable, especially as the intensities increase moving to higher elevations

inland from the coast.

The MfE Guidelines provide a pragmatic approach for allowing for expected increases

in rainfall extremes as a consequence of global warming.


9. Conclusion

The HIRDS package provides extreme rainfall intensity estimates for the lowland

Nelson City area that are consistent with extreme rainfalls recorded at the Nelson Aero

raingauges and also records for Mapua and Appleby.

The storm of 23 May 2007 yielded rainfall depths in excess of the HIRDS 100 year

return period estimates for durations between 15 minutes and 12 hours.

10. References

MfE, 2008: “Climate change effects and impacts assessment, a manual for local

government in New Zealand, 2nd edition”. Available from:

www.mfe.govt.nz/publications/climate/climate-change-effect-impacts-assessments-may08/

Thompson, C.S. 2002: “The High Intensity Rainfall Design System (HIRDS)” Paper

presented at International Conference on Flood Estimation”, Bern, Switzerland, 6-8

March, 2002.

Tomlinson A.I. 1980: “The frequency of high intensity rainfalls in New Zealand, Part

1”, Water & Soil Technical Publication No. 19, Ministry of Works and

Development, Christchurch.


Jan-1930 Jan-40 Jan-50 Jan-60 Jan-70 Jan-80 Jan-90 Jan-00

Mapua daily

Appleby daily

Nelson Aero daily

Hira auto

Nelson Aero auto ex CLIDB

Roding Caretakers

Nelson daily

Maitai Williams

Nelson Princess Drive 10 m in

Nelson Princess Drive hrly

Nelson St Vincent St

Teal Valley daily

Nelson AWS ex MetShr.mtd

Brook at Third House

Roding at Skid s ite

Roding Caretakers

Orphanage

Maitai at Smiths Ford

Maitai at Forks

Williams/Sm iths Ford/Forks

Wakapuaka at Hira

SCAN of NelsonRain.mtd

Figure 1: Timelines showing rainfall records available for the Nelson City and Richmond areas.


Figure 2: Locations of study raingauges.

Mapua daily

Appleby daily & AWS

Nelson Aero & AWS daily & auto

Orphanage Third House

Williams/Smiths Ford/Forks

Hira


Figure 3: Distribution of annual rainfall across the Nelson City-Marlborough region.


0

1000

2000

3000

4000

5000

6000

rain

mm

Jan-1983 Jan-84 Jan-85 Jan-86 Jan-87site 132003 Mapua daily rain mm (Total=5367)site 132101 Appleby daily rain mm (Total=5221)site 132202 Nelson Aero daily rain mm (Total=5263)site 132212 Nelson Aero auto ex CLIDB rain mm (Total=5089)site 133202 Nelson AWS ex MetShr.mtd rain mm (Total=2654)

Figure 4: Cumulative rainfalls for 1983-1987.

A

B

C

DE

FGH

I

JKL

MN

OPQRST

UVWXYZabcdefghijklmnopqrst

uv

w

Annual prob. greaterA-w site 132212 Nelson Aero auto ex CLIDB Dec-1943 thru Dec-1992 3 hrs m ax. rain mm m =12

0

20

40

60

80

100

rain

mm

0.010.020.050.10.20.51

ABCD

EFGH

IJKLMNO

PQRSTUVWXYZabcdefghijklmnopqrstuv

w

AB

CDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv

w

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv

w

ABC

DEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvw

Figure 5: Gumbel frequency analysis for the annual maxima Nelson Aero data for 1944-1992

for durations of 3 h, 1 h, 30 min, 20 min, 10 min.

3 h 1 h 30 min 20 min 10 min


A

B

C

DE

FGH

IJKLM

NOPQRSTUVWXY

Zabcdefghijklmnopqrstuvwxy

zABCDEFGHIJ

Annual prob. greaterA-J site 132202 Nelson Aero daily Jan-1942 thru Jan-2008 3 day max. rain mm m=12

0

50

100

150

200

250

rain

mm

0.0010.010.11

A

B

CD

EF

GHIJKLMNOPQR

STUVWXYZabcdefghijklmnopqrstuvwxyzABCDE

FGHIJ

AB

C

DEFGHIJ

KLMNOPQRS

TUVWXYZabcdefghijklmnopqrstuvwxyzABCDEFGHIJ

A

B

CDEF

GHI

JKL

MNOPQRSTUVWXYZabcdefghijklmnopqrstuvw

A

B

CDEF

GHI

JKL

MNOPQRSTUVWXYZabcdefghijklmnopqrstuvw

Figure 6: Gumbel frequency analysis for the annual maxima Nelson Aero data for 1944-1992

for the 12 h duration data, and 1942-2007 (excluding 1994-1997) for 24, 48 & 72 h.

A

B

C

DE

FGHIJK

LMN

OPQ

RST

Annual prob. greaterA-T site 157899 Williams/Smiths Ford/Forks Dec-1984 thru Dec-2004 3 day max. rain mm m=12

0

100

200

300

400

rain

mm

0.010.020.050.10.20.51

A

B

C

DEFGHIJK

LMNOPQ

RST

A

B

CDE

FGHIJ

KL

MNOP

QRST

A

BCD

EFGHIJKLMNO

P

QRST

A

BCDEFGHIJKLMNOPQ

RST

ABCDE

FGHIJKLMNOPQRST

Figure 7: Gumbel frequency analysis for the annual maxima Williams xtd data for 1985-2004

for durations of 1, 3 12, 24, 48 & 72 h.

72 h 48 h 24 h 12 h

72 h 48 h 24 h 12 h 3 h 1 h


A

B

C

D

EF

GHIJK

LM

NO

P

Annual prob. greaterA-P site 133336 Brook at Third House Dec-1991 thru Dec-2007 3 day max. rain mm m=12

0

100

200

300

400

500

rain

mm

0.010.020.050.10.20.51

A

B

C

D

E

FGH

IJKL

M

NOP

A

B

C

DE

FGHIJ

KLM

NO

P

AB

C

DEFG

HIJ

KLMNOP

A

BC

DEFGHI

JKLMNOP

AB

CDEFGHIJKLMNOP AB

CDEFGHIJKLMNOP

ABCDEFGHIJKLMNOP

Figure 8: Gumbel frequency analysis for the annual maxima Third House data for 1992-2007

for durations of 1, 3, 6, 12, 24, 48 & 72 h.

Nelson Aero rainfall frequency-duration

1

10

100

1000

0.1 1 10 100Duration (h)

Rai

nfa

ll (m

m)

2 yr

5 yr

10 yr

20 yr

50 yr

100 yr

Figure 9: Gumbel frequency results (diamonds) and HIRDS estimates (lines) compared for the Nelson Aero site. The diamonds are from the Gumbel frequency analysis of the record as shown in Figures 5 and 6.

72 h 48 h 24 h 12 h 6 h 3 h 1 h


Williams xtd rainfall frequency-duration

1

10

100

1000

0.1 1 10 100Duration (h)

Rai

nfa

ll (

mm

)

2 yr

10 yr

20 yr

50 yr

100 yr

Figure 10: Gumbel frequency results (diamonds) and HIRDS estimates (lines) compared for the

Williams xtd record.

Third House rainfall frequency-duration

1

10

100

1000

0.1 1 10 100Duration (h)

Rai

nfa

ll (

mm

)

2 yr

10 yr

20 yr

50 yr

100 yr


Third House record.


132101, Appleby rainfall frequency-duration

1

10

100

1000

0.1 1 10 100Duration (h)

Rai

nfa

ll (

mm

)

2 yr

10 yr

20 yr

50 yr

100 yr


Appleby record.

132003, Mapua rainfall frequency-duration

1

10

100

1000

0.1 1 10 100Duration (h)

Rai

nfa

ll (

mm

)

2 yr

10 yr

20 yr

50 yr

100 yr


Mapua record.


0

500

1000

1500

2000

2500

rain

mm

5-Aug-2006 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Feb-08 May-08s ite 132210 Hira auto (Total=2404)s ite 132312 Nelson Princess Drive hrly (Total=1388)s ite 132311 Nelson Princess Drive 10 min (Total=970)s ite 132321 Nelson St Vincent St (Total=1436)s ite 133005 Appleby EWS (Total=1272)s ite 133202 Nelson AWS ex MetShr.mtd (Total=1278)s ite 133336 Brook at Third House (Total=2358)s ite 157608 Orphanage (Total=1397)

Figure 14: Cumulative rainfalls recorded at gauges in the Nelson area from August 2006 to July 2008. The arrows identify dates of storms that are detailed in subsequent figures.

0

20

40

60

80

100

125

rain

mm

22-May-2007 22 06: 22 12: 22 18: 23 00: 23 06: 23 12: 23 18:s ite 132312 Nelson Princess Drive hrly (Total=54.8)s ite 132321 Nelson St Vincent St (Total=47)site 133005 Appleby EWS (Total=58.4)s ite 133202 Nelson AWS ex MetShr.mtd (Total=93.8)s ite 157608 Orphanage (Total=108.8)s ite 157808 Maitai at Forks (Total=94)

Figure 15: Cumulative rainfalls recorded at gauges in the Nelson area during a storm on 22-23 May 2007.


0

50

100

150

160ra

in m

m

14-Apr-2008 14 06: 14 12: 14 18: 15 00: 15 06: 15 12: 15 18:site 132210 Hira auto (Total=142)site 132312 Nelson Princess Drive hrly (Total=91)site 132321 Nelson St Vincent St (Total=95)site 133005 Appleby EWS (Total=100.8)site 133202 Nelson AWS ex MetShr.mtd (Total=111.8)site 157608 Orphanage (Total=101.6)

Figure 16: Cumulative rainfalls recorded at gauges in the Nelson area during a storm on 14-15 April 2008.

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

10 20 30 40 50 60 70 80 90 100 110 120Storm duration (mins)

Rai

nfa

ll in

ten

sity

(m

m/h

)

HIRDS 10 yr HIRDS 50 yr HIRDS 100 yrNCC 10 yr NCC 50 yr Nelson Aero max 44-92

Nelson AWS max, 23 May 2007 Orphanage 23 May 2007

Figure 17: Currently Nelson City storm rainfall frequency duration curves, HIRDS estimates and maxima recorded at Orphanage, Nelson Aero and AWS.

high intensity rainfall analysis for nelson urban area › assets › envirolink › 463... · high...

Documents