This information is for the higher rainfall (usually more than 450mm) areas of the lower south-west of Western Australia.
Steps to diagnose waterlogging
- Observe the signs of waterlogging in soils and plants.
- Note the soil type and landscape position.
- Check soil in the root zone for water content.
- Note yield changes against marked areas.
The best way to identify waterlogged areas is to look! In winter, if water is present at the surface (i.e. glistening in small depressions), the area is likely to be waterlogged. If waterlogging is suspected and not visible, dig a hole or two down to about 30cm and see if water flows into them; if it does, the soil is waterlogged.
Observe the signs of waterlogging
Waterlogging is most likely in winter after periods of heavy rainfall. Indications of waterlogging are:
- water ponding on the soil surface
- the surface staying wet and glistening
- dark, wet or slimy topsoil, often with algae on the surface
- boggy soils (you just lost the tractor!)
- yellowing crops and pastures
- weeds, such as toad rush, cotula, dock and Yorkshire fog grass.
Note the soil type and landscape position
Duplex soils are particularly susceptible to waterlogging, especially shallow duplexes on gentle slopes, change of slope or level areas. Waterlogging can also occur on flat valley floors and level plains. Sand over clay duplexes can have short-term root zone waterlogging without showing obvious signs.
Check soil in the root zone for water content
- Dig holes to about 30cm deep to see whether any free water flows into it: if it does, the soil is waterlogged and plant growth can be affected. See waterlogging: the science for more information on assessing the severity of waterlogging.
- Duplex soil can have very rapid onset and drainage of waterlogging. Daily monitoring may be needed to identify periods of waterlogging.
- Grey or greenish-coloured subsoil can indicate long-term waterlogged conditions.
- The degree of waterlogging can be very different over short distances (metres) and short periods (days).
Note yield changes against marked areas
Waterlogging that reduces crop or pasture yield is worth managing:
- Mark out the affected areas, either with posts laid on the ground or on an accurate map.
- At harvest time, observe where the crops are poor and check this against earlier observations.
Severity of waterlogging
The severity of waterlogging can be indicated by a Sum of Excess Water (SEW) value. SEW integrates waterlogging that occurs during the winter growing season in the primary root zone of the top 30cm soil layer (SEW30) (Setter & Waters 2003).
SEW30 is the sum of all daily values in centimetres (cm) of watertables closer than 30cm to the soil surface (in units of centimetre days [cm.days]). For example: 10 days rising to 10cm below the surface (20cm above the 30cm depth measured) is 10 x 20 = 200cm.days. See Table 1 for waterlogging classes.
|Waterlogging class |
(in terms of drainage)
|SEW30 index |
(cm.days in an average growing season)
|Moderately well drained||30–100|
|Moderately poorly drained||500–1200|
|Very poorly drained||>2500|
Table 1 is derived from Bulletin 4343 Soil Guide: a handbook for understanding and managing agricultural soils (Note: this is a large PDF download).
Now you have diagnosed waterlogging, what next?
There are several ways of preventing or reducing waterlogging; see the managing waterlogging page.