A Large-Scale Flood Event in 1994 from the Mid-Canterbury Plains, New Zealand, and Implications for Ancient Fluvial Deposits

  1. I. Peter Martini2,
  2. Victor R. Baker3 and
  3. Guillermina Garzón4
  1. G. H. Browne

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304299.ch7

Flood and Megaflood Processes and Deposits: Recent and Ancient Examples

Flood and Megaflood Processes and Deposits: Recent and Ancient Examples

How to Cite

Browne, G. H. (2002) A Large-Scale Flood Event in 1994 from the Mid-Canterbury Plains, New Zealand, and Implications for Ancient Fluvial Deposits, in Flood and Megaflood Processes and Deposits: Recent and Ancient Examples (eds I. P. Martini, V. R. Baker and G. Garzón), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304299.ch7

Editor Information

  1. 2

    Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada

  2. 3

    Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721–0011, USA

  3. 4

    Dpto de Geodinámica, Fac. de Geología, Universidad of Complutense, 28040 Madrid, Spain

Author Information

  1. Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, New Zealand

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 10 FEB 2002

ISBN Information

Print ISBN: 9780632064045

Online ISBN: 9781444304299

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Keywords:

  • large-scale flood event in 1994 from mid-Canterbury plains, New Zealand, and implications for ancient fluvial deposits;
  • meteorological conditions related to flooding;
  • observations made from January 1994 floods;
  • sediment deposited during 1994 floods;
  • downstream changes in clast size;
  • implications for ancient fluvial deposits;
  • post-depositional introduction of clay bands;
  • implications for fluvial petroleum reservoirs

Summary

Major flooding occurred in mid-Canterbury rivers of the South Island of New Zealand on 9 January 1994. Maximum flood discharges of 5594 cumecs were recorded in the Rakaia River, the highest in this river in over 40 yr of recordings. Flooding in the large braided rivers of mid-Canterbury is related to heavy orographic rainfall in the west, in alpine catchments of the Southern Alps. Over a three-day period immediately preceding and subsequent to the flooding, areas on the west coast of the South Island received 80–85% of their average January rainfall. On one of those days (8 January 1994, the day prior to the flooding event in the Canterbury rivers), the daily precipitation exceeded 190 mm for one of these west coast sites, some 40% of the average total monthly rainfall for January.

At the height of the flood, a 400-m-wide flood channel was created at the mouths of the Rakaia and Rangitata rivers, with flood discharge eroding the gravel beach normally fronting the rivers to the Pacific Ocean. This flood channel was subsequently modified and eventually was plugged by littoral sediment transported northward by longshore drift. Extensive chipping, scratching, and pitting of large boulders in the rivers indicates that mechanical abrasion of fluvial clasts is an important agent in downstream clast-size reduction.

Analogue strata of last glacial to latest Pleistocene age exposed in coastal cliffs adjacent to the Canterbury Plains show little evidence of fine-grained (silt- and clay-size) sediment. Where present, fine-grained sediment is confined to discrete permeability-controlled layers or clay bands (such as along foreset stratification). Based on observations of flood deposits in the modern deposits, these ancient sediments were probably deposited with considerable fine-grained sediment. It is inferred that fines are removed from the fluvial deposit, aeither by aeolian transport, or by interstitial water movement, some being concentrated in the distinct clay-bands.