Sediment reduction and mitigation principles – a review of New Zealand literature

Report: TR 2023/28

Authors: John Drewry, Chris Phillips, Scott Graham Manaaki Whenua – Landcare Research

Project and client

• Waikato Regional Council (WRC) is producing a strategic document on erosion from farmland and other sources in the Waikato region.
• WRC contracted Manaaki Whenua – Landcare Research to undertake a literature review to provide information on erosion and sediment, and its control.
• This information will help WRC explain the impact of erosion and sedimentation on communities, and the consequent loss of natural capital and ecosystem services. It will also help to communicate the sediment story for different farming systems and civil defence issues.

Objectives

• The objective of this report was to conduct a general review of the New Zealand literature on erosion and sediment reduction, with a focus on literature relevant to the Waikato region.

Methods

• A literature search of New Zealand-based studies on erosion and reduction through mitigation was conducted.
• Studies relevant to the Waikato region were a particular focus. In the absence of such information, inferences from studies outside the region were applied to the local context.
• A review of modelling studies was out of scope.

Summary of key findings

Different combinations of erosion process and extent require different erosion and sediment control treatments. There are feasible treatments for most erosion problems, but they sometimes require a combination of biological and structural erosion mitigation and/or other land management practices (e.g. grazing intensity). Their effectiveness can vary widely.

Recommended erosion control treatments are based on type(s) of erosion, risk of erosion, current activity of erosion, land management, size and depth of feature, and extent of treatment required.