TILE DRAINAGE: POTENTIAL RESEARCH DEMANDS AND
OPPORTUNITIES
Shokri, Ali,1
1
Lincoln Agritech Ltd, Private Bag 3062, Hamilton
Abstract
Artificial drainage, either tile drain, mole drain or open channel drain, is a common
practice to improve the aeration condition of the soil for agriculture. Before human
intervention, about 20% of New Zealand soils were wet, concentrated mostly in
Northland, Waikato, Canterbury and Southland. Fig 1 shows an overview of the
concentration of artificial drains in Waikato, New Zealand. With around 2 million ha of
poorly or imperfectly drained soils in New Zealand, artificial drainage plays a very
important role in improving the agricultural productivity of New Zealand. However, the
effects of artificial drainage on regional scale surface water and groundwater flows and
quality are not addressed adequately in the literatures.
In this study, six specific beneficial roles of artificial drainage are distinguished: soil
productivity, flood control, soil erosion, pesticide control, sustainable irrigation land use
and reduction in contaminants (e.g. phosphorus, potassium, organic nitrogen and
ammonium losses). On the other hand, increased nitrate leaching to surface water is
considered as the main disadvantage of the tile drainage practises. Moreover, it is
concluded that a combination of tile drainage with good drainage management practises
such as regular monitoring of tile drainage outlet, controlled drainage and sub-irrigation
may hugely reduce the volume of nitrate leached via tile drains.
Furthermore, some potential tile drainage research demands for New Zealand are
suggested: understanding the hydrological effect of tile drainage on catchment and
regional scales, understanding the effect of tile drainage practise on the regional
groundwater system, the needs of changing tile drainage designing criteria from
quantitative to qualitative criteria, opportunities of reusing the drainage water, and the
role of the tile drains on the irrigation projects sustainability.
Fig1 Overview of the concentration of artificial drains in Waikato region