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Best practice environmental guidelines - land drainage

TR 2006/06R

Note: This report was originally published in March 2007 as Technical Report 2006/06. This new edition corrects a minor data error which appeared in section 4.1 Aquatic Life - Mudfish. While addressing this error, the opportunity was taken to make some minor changes to data, based on updated methodology that has been developed since the original report was published. This makes no difference to interpretation or conclusions, but in the interests of data accuracy we are re-releasing this report.

The Waikato region has a large network of drains that among other things are managed to ensure adequate land drainage and alleviate flooding. Without adequate management of these waterways large areas would be unproductive or inaccessible.

In many areas the main focus has been to dig drains to lower the water table to improve pasture growth and to remove water as fast as possible from the land without much thought given to the environmental and economic impacts this may cause. It is now recognised that drains are also often important habitats, or could be important habitats, and have multiple uses and values. Drains have replaced wetlands in much of the Waikato region and some of the flora and fauna that used to inhabit wetlands now inhabit the drains. By following best practice guidelines people can achieve effective land drainage that is more environmentally sustainable and is cheaper to maintain in the long term.

These best practice guidelines have been prepared to assist regional and local authorities, landowners, consultants, and contractors with the creation of new drains and maintenance of existing land drainage. While focusing on environmental outcomes that can be achieved this document also recognises the operational need for maintaining drainage outfall and minimising long term costs.

By following the recommendations land drainage activities:

  • should have only minor adverse impact on the environment
  • will be consistent with the requirements of the existing Proposed Waikato Regional Plan
  • will not compromise the levels of service provided by Regional and District flood protection or land drainage schemes.

The topics covered by this best practice guideline include:

  • The Waikato Regional Plan
  • Land Drainage Schemes
  • Best practice design guidelines for achieving land drainage. 

Read or download the report

Best Practice Environmental Guidelines - Land Drainage [PDF, 2.3 MB]

Contents

1 Introduction
1.1 What is best practice?
2 Legislation
2.1 The Waikato Regional Plan
3 Land drainage schemes
4 Ecological considerations
4.1 Aquatic life
4.2 Effects on water quality
4.2.1 Unstable banks/sediment
4.2.2 Dissolved oxygen
4.2.3 Nutrient levels and biological contaminants
4.2.4 Water temperature
4.3 Native plant biodiversity
5 Existing drainage
5.1 Minimising the need for drain cleaning
5.1.1 Dealing with sediment
5.1.2 Dealing with nuisance plants growing in and along drains
5.2 Best management practices
5.2.1 Salt water flushing
5.2.2 Drain cleaning
5.2.3 Drain spraying
6 Peat drainage
6.1 Best management practices
7 New drainage
7.1 Wetlands – to drain or not to drain?
Appendix 1 Drainage district areas
Appendix 2 Decision support guideline – planting along drains
  References and cited references
  Definitions