893a2042-6e1b-8d5f-0c3f-b5f8a1bbc3d7 eng utf8 dataset custodian NIWA National Institute of Water and Atmospheric Research +64 4 386 0300 voice +64 4 386 0574 facsimile 301 Evans Bay Parade Hataitai Wellington 6021 New Zealand curator@niwa.co.nz http://www.niwa.co.nz Website of the National Institute of Water and Atmospheric Research, New Zealand - Enhancing the benefits of New Zealand's natural resources. Data curator 2015-06-22T09:07:05 creation ISO 19115-3 urn:ogc:def:crs:EPSG::4326 OGP NZST/NZDT Estimation of flood peak magnitude and return period: Waipoua River at Mikimiki 20th October 1998. 2015-06-18T05:31:00 creation 2015-06-18T05:31:00 revision 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. 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. 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. completed pointOfContact NIWA George.Griffiths@niwa.co.nz George Griffiths Principal Scientist author NIWA Alistair McKerchar Scientist vector inlandWaters Wellington Region 176.564062,-40.81111 176.211252,-40.65921 175.268221,-40.768713 174.851416,-40.62859 174.603476,-40.895861 174.412973,-41.469383 175.42444,-41.795172 176.054712,-41.493254 176.564062,-40.81111 174.412973 176.564062 -41.795172 -40.62859 1998-10-20T00:00:00 1998-10-20T00:00:00 Flood peak Waipoua River water flow SCJ155REG theme NIWA Project Codes 2012-01-01 publication NIWA_ProjectCode 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. restricted 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. largerWorkCitation eng https://dc.niwa.co.nz/niwa_dc/srv/metadata/893a2042-6e1b-8d5f-0c3f-b5f8a1bbc3d7 WWW:LINK-1.0-http--metadata-URL Point of truth URL of this metadata record O Drive Christchurch Jobs Regional Councils SCJ155REG/15 dataset Flood peak data from Waipoua River at Mikimiki 20 October 1998 restricted