Glossary of salinity terms
Aquifer: any water-bearing saturated layer of rock, earth or gravel capable of yielding ample supplies of water to bores or springs. Riverina Water pumps 70 per cent of Wagga Wagga's water supply from the deep aquifer under the Murrumbidgee flood plain. The aquifers involved with Wagga Wagga's urban salinity are usually shallower and are not connected to the flood plain aquifer.
Capillary rise: the upward movement of water caused by molecular attraction between soil particles and water. The action is like water being drawn into a dry sponge. Capillary rise occurs when groundwater is within 1-2 metres of the soil surface.
De-watering bores: During the late 1990s Wagga Wagga City Council installed ten de-watering bores in the area around Calvary Hospital. These bores were aimed at lowering the watertable in this discharge area to between 3-5 metres below the surface by pumping out some of the groundwater. When groundwater is kept below this level it does not affect the soil surface or underground services such as water pipes. The bores pump from an aquifer 40-65 metres below the surface where the groundwater is less salty than water closer to the soil surface. The water is piped to the Murrumbidgee River where it is closely monitored according to the requirements of the Department of Environment and Conservation. The Council has a licence to continue pumping until 2009. The results from piezometers in the area indicate that the de-watering bores have been effective in lowering the groundwater level within the immediate area.
Discharge area: an area where underground water reaches the soil surface. The showground and Charles Sturt University South Campus are two discharge areas in the Wagga Wagga urban area. Loss of vegetation, salt crystals on the soil surface, break up of roads and concrete paths, house brick deterioration, permanent wet areas and rusting underground pipes and metal fences are all signs of a discharge area. To control discharge area watertables, water entering recharge areas must be reduced.
Dryland salinity: can be found in dryland farming areas around Wagga Wagga. The situation is similar to urban and irrigation salinity where the water balance has been changed. Dryland salinity can occur when the amount of water entering the groundwater system is greater than the amount used by plants or drained away.
Evaporation basin: these usually large and shallow basins are used to safely dispose of salty groundwater pumped from high watertable areas. Wagga Wagga City Council built an evaporative basin next to Urana St to control the drainage of groundwater away from the Wagga Wagga Showground.
Groundwater: the water found in the ground in a saturated zone of soil. Groundwater height varies across the city. It is usually higher in lower parts of the catchment or where there is a change in slope. These areas are often the first sites to be salinity affected.
Piezomete: a non-pumping bore used to measure the level of groundwater below the surface and to allow collection of groundwater for salinity testing. It consists of a sealed PVC pipe 20-40 mm in diameter, with narrow slots cut in the bottom to let ground water enter the pipe. The pipes are usually more than 3 metres deep. The groundwater level readings obtained from piezometers can identify recharge and discharge areas. The Wagga Wagga 1996 Depth to Piezometric Surface Map was based on readings from 50 piezometers situated around Wagga Wagga.
Recharge area: where rainfall, irrigation, garden water or water from waterways seep into the ground and add water to the groundwater system. Rocky hills with thin soils such as Willans Hill are high recharge areas. Planting trees and shrubs on recharge areas will reduce the amount of water seeping past plant roots. Throughout Wagga Wagga we can help reduce recharge by being water wise in our gardens - mulch garden beds, use tap timers, plant low water using plants and reduce lawn area.
Rubble pits or sullage pits: these are backyard pits where stormwater collected from house roofs is drained slowly, but directly, into the ground. In recharge and discharge areas these pits can contribute to salinity problems. As part of their salinity strategy Wagga Wagga City Council is progressively connecting houses with rubble pits to the stormwater drain system.
Salinisation: is the accumulation of soluble salt within the soil. Soil salt content increases at discharge sites as groundwater evaporates and salts concentrate in the soil. It is harder for plants to remove water from salty soil. Eventually they may die and be replaced by salt tolerant plants such as couch grass and sea barley grass. These plants can be seen on Charles Sturt University South Campus oval.
Salinity: a term which refers to salt content in water or soil. It is usually measured in decisiemens per metre (dS/m). Groundwater salinity in Wagga Wagga ranges from 0.6 dS/m to 16.7 dS/m. The desirable salinity level for drinking water is 0.8 dS/m. Groundwater at 16.7 dS/m is usuitable for cereal crops, poultry, pigs, pears, apples, oil crops and most legumes. The salt concentration of groundwater depends on the salinity content of the soil and rock in which the water is found.
Soil sponge: the drying effect of plant roots drawing water from the soil. Before land clearing, native vegetation provided a soil sponge to a depth of 6 metres or more and a balance existed which prevented excess recharge. In the urban situation not only has our soil sponge been reduced, the amount of water applied has increased as water has been piped from the river.
Urban salinity: salinity occurring in urban areas. Wagga Wagga is experiencing urban salinity due to vegetation removal and replacement with shallow rooted high water-using plants, storm water draining into backyard rubble pits, leaking water pipes and over watering of gardens and public areas. Junee, Cootamundra, Leeton and Griffith are among the many NSW towns also tackling urban salinity.
Waterlogging: this occurs when the soil becomes saturated by rising watertables. Plant roots become oxygen starved and sensitive plants eventually die out. Plants more tolerant to saturated conditions such as pinrushes and dock then take over. Underground services are also affected with rusting of water and gas pipes requiring more frequent replacement. Once the watertable reaches the sewer pipe system, salt water can be channelled to the river via the sewerage treatment works.
Watertable: the upper surface of the groundwater. The zone immediately below the watertable is saturated. The aim of the Wagga Wagga Council's Urban Salinity Action Plan is to keep the watertable at least 3 metres from the soil surface. At this depth capillary rise is prevented and underground services are out of the saturated zone.
|Glossary developed with the assistance of the Wagga Wagga City Council|