Preventing waterlogging through drainage
Permanent raised beds are widely used to grow traditional broadarea crops in irrigation country in the Eastern States of Australia. They represent a potentially practical and economic means of preventing waterlogging in wetter areas of the Western Australian grainbelt.
In irrigation areas the furrows get water onto the paddock and into the soil (via horizontal infiltration). Their use to prevent waterlogging reverses this operation by drawing excess water out of the beds (horizontal drainage) and conducting it from the paddock into open collector drains.
When to use raised beds
Raised beds are an option when:
- The probability of waterlogging is 50 per cent or more in the wettest months (usually June to August) when the emerging crops are most suceptible and on susceptible soils.
- Shallow water tables and large gravel contents in the soil reduce the soil’s capacity to absorb rainfall, resulting in a high frequency of waterlogging.
- Where hill slopes are greater than 3 per cent, waterlogging may not be a problem. In shallow or gravelly soils, however, waterlogging can occur on land with slopes greater than 3 per cent.
Susceptible soils are:
- Shallow sand, high gravel content soils and loam-over-clay soils situated in areas where the waterlogging frequency is greater than 50 per cent.
- Soils in areas with a shallow water table will also be suceptible but that land is likely to be salt-affected and reclamation of the salinity is likely to be difficult, even with the use of raised beds.
Raised beds may be an option in many situations and professional advice should be obtained before installing them.