Integrated Catchment Management

Sediment generation, delivery and impacts

 Research Status: Ongoing
Bank erosion - Motupiko River

Bank erosion - Motupiko River


Sediment may have a range of impacts on the ecology and habitat of both freshwater and marine ecosystems. To understand and manage these impacts it is important to determine the major sources of sediment generation as well as establish changes in riverbed characteristics important to maintenance of the trout fishery, and delivery of sediment to the marine environment.

From 1985 until the late 1990s there was a widespread and significant decline in the abundance and biomass of trout in the Motueka River as measured by drift diving carried out by Nelson-Marlborough Fish and Game and by angler experience. This decline has been linked to increased input of fine sediment into the river and its direct and indirect effects on trout habitat and trout populations. A key property influencing trout populations is the proportion of sand and silt in the bed of the river, which is believed to have increased in many parts of the river system.

Trout numbers in the Motueka River have rebounded over recent years.

The exact causes of these major fluctuations in trout numbers is not well known scientifically. There is little data on riverbed characteristics throughout the Motueka, variation in rates of sediment supply, the time scale for sediment movement through the river system, the major sources of sediment and the relative role of natural erosion and that related to land-use (forestry or pasture), and the long-term impact of large storms.

Previous scientific work on sediment has focused largely on sediment generation from forestry activities on Separation Point Granite. This has demonstrated earthworks associated with roads and landings are the main sediment producing areas and landslides are the biggest sediment contributors. However, on a whole catchment basis (such as the Dart or Wangapeka) natural erosion rates are higher than those induced by disturbance. Recommendations to reduce disturbance-related erosion included regulation of landing size, regulation of roading and cutbank formation, safe storage of excess sidecast material, avoidance of stream crossings by use of appropriate culverts, and promotion of revegetation.

Recent discussions with a range of people with interests in sediment issues in the Motueka suggest there are a variety of factors influencing present sediment characteristics of the Motueka River including the long-term impact of large storms, sediment generation from both natural erosion and that related to forestry activities on Separation Point Granite, the long-term impact of past forestry management practices, and river bank stability.

Research Approach

To establish changes in riverbed characteristics important to maintenance of the trout fishery, and to determine the major sources of sediment input and options for managing the rate of sediment supply.

Research Results

A number of reports and documents have been produced covering suspended sediment monitoring, changes in river bed cross-sections, bank erosion, gravel extraction, river bed substrate characterisation, and the impacts of fine sediment on biota.

One of the other things to be done has been to produce a report that outlines the conceptual issues which need to be addressed in developing an erosion-sediment model for the Motueka catchment. It is based on analysis of sediment dynamics within the Motueka catchment resulting from the sediment source mapping that has been undertaken, and the findings of the review of the effects of fine sediment on river biota.

Intensive monitoring of turbidity and flow has been undertaken at 4 sites in the Motueka catchment from December 2002 to November 2009. This data has been used to calculate sediment yield on a storm event and long term basis. The following data sets were updated in June 2010 and archived:

Kikiwa - erosion from Easter 2005 flood Fine sediment at Motueka Gorge from Easter 2005 flood

Kikiwa - erosion from Easter 2005 flood

Fine sediment at Motueka Gorge from Easter 2005 flood

Recent Publications

Year Title File Size
2012 A Summary of Outcomes and selected formal publications from the Integrated Catchment Management (ICM)research programme:2000 – 2011
pdf       1.08MB
2011 Integrated Catchment Management – Special Issue of the NZ Journal of Marine & Freshwater Research  
2009 Motueka Forest sediment study: data report July 2006 to June 2008 and analysis of sediment yield pdf       1.32MB
2008 River bank styles and effects of vegetation on bank stability – a pilot assessment doc       9.50MB
2006 Stream bank erosion: a review of processes of bank failure, measurement and assessment techniques, and modelling approaches pdf       2.62MB
More publications on this topic »
All ICM Publications »

Recent Presentations

Year Title File Size
2007 Sediment dynamics and biological impacts in the Motueka River, New Zealand. pdf       0.56MB
2006 Gravel-related research in the ICM programme. pdf       0.08MB
2006 What are other regional councils doing to improve gravel extraction management. pdf       0.08MB
2006 Advances in understanding bed level trends and gravel volume changes in the Motueka River. pdf       0.37MB
2006 Ecological effects of gravel extraction. pdf       0.13MB
More presentations on this topic »
All ICM presentations »

BMPs, BEPs and Guidelines

Title Description
Gravel Extraction Guidelines – Wellington  
Soil Conservation Technical Handbook The Soil Conservation Technical Handbook is a comprehensive collection of know how about soil conser...More »  
Clean Streams: A Guide to Managing Waterways on Tasman – Marlborough Farms From booklet:
This booklet provides information about how to manage waterways to improve water...More »  
New Zealand Environmental Code of Practice for Plantation Forestry The E CoP is an essential tool for anyone involved in forest management. Developed by the NZFOA, and...More »  
Erosion and Sediment Control Guidelines Canterbury  
Shelter for Hill Country Farms: Part 2 shelterbelt trees From Booklet:
Once you have decided where a shelterbelt will be planted see Environment Topic ...More »  
ANZECC Guidelines for Sediment A chapter fron the ANZECC guidelines pertaining to sediment...More »  
Controlling Gully Erosion with Debris Dams A guide for building debris dams to stabilize gully erosion....More »  
Small Flood Detention Dams Guide for the construction of detention dams for flood control....More »  
Protecting Infilled Valley Bottoms from Gullying A guide to controlling gully erosion....More »  
All BMPs, BEPs & Guidelines »

Primary Contacts:

Image - Les Basher Les Basher  EmailSend email to BasherL
Phone: 03 545 7708
Fax: 03 546 1082
More details»
Landcare Research
Soil science, geomorphology, erosion processes
Image - John Dymond John Dymond  EmailSend email to dymondj
Phone: 06 353 4955
Landcare Research
land and water models, GIS, remote sensing
Image - Chris Phillips Chris Phillips  EmailSend email to phillipsc
Phone: +64 3 321 9775
More details»
Landcare Research
Erosion processes, slope stability, effects of forestry, catchment management, knowledge management
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Page last updated Thursday, 1 July 2010

Related areas

Fine sediment: bringing the geomorphology and biology together River plume ecosystem Sediment learning group Stream health – invertebrates

Related Website(S)

Caesar sediment model New Zealand Landcare Trust NZ society of soil science Sednet