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Coastal Sedimentation: What We Know and the Information Gaps

TR 2008/12

Report: TR 2008/12

Author: Hannah Jones


This report aims to bring together available information on coastal sedimentation, summarising what is known and identifying what is not known about the sources and the effects of coastal sedimentation.

Sedimentation in estuaries is a natural process that can be accelerated by changes in land use or land management within the catchment or by development of structures within the estuary. Estuaries are under increasing pressure from coastal development or catchment activities and development, such as farming, subdivision and vegetation clearance. Estuaries on the east coast of the Coromandel Peninsula are at high risk of infilling because of the erosive nature of their catchments (steep topography and frequent high intensity rainfall events) and the physical nature of the estuaries (sandbars or barriers narrow the harbour entrances). In addition, major land use changes have occurred on the Coromandel Peninsula following European settlement. Large scale deforestation in the late 19th century was followed by conversion to pasture (early to mid 20th century) and then exotic production forestry became established from the 1950s until present.

Some studies have provided information that is applicable to all east coast Coromandel estuaries.

Coastal Sedimentation: What We Know and the Information Gaps [PDF, 1.1 MB]

Glossary v
Executive summary xi
Introduction 1
    The issue 1
  The scope and structure of this report 2
The life of an estuary 2
The process of sedimentation in estuaries 3
The effects of sedimentation on estuaries 6
  Effects on plants 6
  Effects on benthic animals 7
  Wider effects 8
Sources and delivery of sediment 9
  Sediment generation 10
  Sediment yield 12
  Connectivity 13
  Sediment yield from catchments studied 13
  Sediment cores: X-Radiograph and isotope techniques 17
  Storage in streams 18
  Riparian vegetation 18
  How does land use (production forest, native forest or pasture) impact on erosion? 18
Case studies 21
  Tairua Harbour 21
  Whangapoua Harbour 23
  Whangamata Harbour 31
  Wharekawa Harbour 34
  Whitianga Harbour 39
Harbour and catchment comparison 43
Conclusions 45
Information gaps 47
Further research 48
References 50
Appendix 1: Catchment land cover 55
Appendix 2: Whangamata sediment core 56