Vegetation clearing since European settlement has altered the water balance of many catchments. Deep-rooted perennial vegetation has been replaced with shallow-rooted annual species that do not use water to the same extent, resulting in more water seeping through to the groundwater.
Annual pastures and crops do not use more than 400mm/year of water, and often much less. Over time, water tables can rise and concentrate dissolved salt within the rootzone of pastures, crops and trees. In areas at risk of salinity, it is important to monitor the levels of groundwater or water table heights as well as the salt concentration of this water.
Water tables form when water cannot move into, or pass through, a less permeable layer (for example, rock, clay or other hard layer). Water tables can be very localised and confined to small areas of a catchment. They can also be a part of a larger groundwater system covering many square kilometres.
It is important to speak to local experts — such as salinity extension officers or catchment management authority staff to understand if your farm is likely to be above a localised, intermediate or regional groundwater system.