Estimation of flood peak magnitude and return period: Waipoua River at Mikimiki 20th October 1998.

The magnitude of the return period of the 1998 flood peak at the Waipoua River Mikimiki hydrological recording station is a critical factor in the assessment of potential flood plain inundation in Masterton. Using rating and slope-area information available at the Mikimiki site, and assuming subcritical flow and occurrence of bed scour, the peak discharge of the 1998 flood is calculated to be 400 ±40 m3/s. From historical flood information and rainfall intensity data, the 1998 flood is deemed to be the second largest peak since 1897 which implies that it has a return period of about 75 years. This estimate combined with flood frequency analyses of site annual maxima yields a return period of 70 ±7 years for the 1998 flood peak, a figure consistent with the results of regional flood frequency analysis. The largest flood since 1897 occurred in 1947 and has a return period of about 200 years. Both the 1947and the 1998 floods were safely passed by the existing Masterton Flood Protection Scheme. The following analytical output resulted from the data: (1) Plot of apparent bed level for flow of 400 L/s at Waipoua River at Mikimiki. (2) Frequency of annual maxima (1979-1982, 1996-2014) fitted by a Gumbel distribution (1998 flood peak = 356 m3/s). (3) Stage versus velocity relationship (1996‑2014) for Waipoua river at Mikimiki. (4) Frequency of annual maxima (1979-1982, 1996-2014) fitted by a Gumbel distribution (1998 flood peak = 400 m3/s). (5) Comparison of daily rainfalls for 1947 and 1988 storms.
 
Citation proposal
Alistair McKerchar (NIWA). .
 

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Date ( Creation )
2015-06-18T05:31:00
Date ( Revision )
2015-06-18T05:31:00
Purpose
Estimation of the magnitude and frequency of the flood peak of 20th October 1998 at the Waipoua River at Mikimiki hydrological recording station is central to the assessment of potential flood plain inundation in Masterton. Thus an analysis of the size and return period of the 1998 flood at the Mikimiki site was undertaken. 
Credit
Griffiths, G.A.; McKerchar, A.I. (2015). Estimation of flood peak magnitude and return period: Waipoua River at Mikimiki 20th October 1998. Funded by and prepared for Masterton District Council. March 2015. NIWA Client Report No. CHC2015-016. NIWA Project: SCJ155REG/15. p. 14. 
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Completed  

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Vector  
Topic category
  • Inland waters
Description
Wellington Region 
N
S
E
W


TimePeriod
1998-10-20T00:00:001998-10-20T00:00:00 
  • Flood peak, Waipoua River, water flow
NIWA Project Codes
  • SCJ155REG
Use limitation
Data ownership is as follows: Stage, rating, flow and slope-area data for this study were provided by the Greater Wellington Regional Council (GWRC). Historical information about flooding in the Masterton area was supplied in part by Masterton District Council (MDC). The New Zealand Meteorological Service and NIWA provided records of daily rainfalls. Permission is required from the above data-owners. Contact through NIWA first, using point-of-contact details above. 
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Title
Griffiths, G.A.; McKerchar, A.I. (2015). Estimation of flood peak magnitude and return period: Waipoua River at Mikimiki 20th October 1998. NIWA Client Report No. CHC2015-016. NIWA Project: SCJ155REG/15. p. 14. 
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Larger work citation  
Language
English  
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Jobs Regional Councils SCJ155REG/15

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893a2042-6e1b-8d5f-0c3f-b5f8a1bbc3d7

Language
English  
Character encoding
UTF8  

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Dataset  
Date info ( Creation )
2015-06-22T09:07:05
Title
ISO 19115-3 
 
 

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