Urban salinity is mainly caused by rising groundwater bringing salts to the land surface. Towns are often located in areas prone to salinity (such as plains, valleys, or at the foot of a ridge). In addition to the regional causes a rise in groundwater levels (see dryland salinity), urban development itself can lead to localised salinity because of:
- Clearing of native vegetation for urban development
- Over-watering of gardens, parks and sporting fields
- Water leaking from pipes, drains, tanks
- Seepage from sullage pits, and
- Blocking or changing natural drainage paths (such as by building roads).
How does urban salinity occur?
Salt is naturally present in soil, rain and groundwater. Additional sources of salt in urban areas include swimming pools, food products, fertilisers, soaps and detergents, industry and building materials and effluent (sewage).
Recognising the solubility of salt in water is the key to understanding urban salinity processes. When water comes into contact with buildings and other infrastructure, salt can be carried with it. As the water evaporates (or dries) the salt crystals grow and expand, causing physical damage to bricks, mortar and other construction materials. The salt crystals often form a white crust on the surface of bricks. Homeowners often try to wash off the unsightly residue, but this only helps the salt crystals grow even bigger, worsening the problem.
Some building methods may also contribute to the development of salinity. Compacted surfaces can restrict groundwater flow and concentrate salt in one area. By cutting into slopes to build, groundwater or saline soil may be intercepted and exposed. In addition, fill used to build up an area may be a source of salt, or it may be less permeable, preventing good drainage.
What are the impacts of urban salinity?
Salinity damage shortens the life of urban infrastructure such as roads, buildings, water and sewage pipes. This leads to costly maintenance and repair by homeowners and councils.
The movement of excess water and salt in parks and gardens can affect plant growth and cause plant death. Sports grounds and recreation areas affected by urban salinity may become bare, unattractive and unusable. Soil properties can be altered significantly making it hard to revegetate these areas.
Pockets of native vegetation in and around urban landscapes may also be affected. This can have serious consequences including the disappearance of native flora and fauna and poor downstream water quality.
What is being done?
The NSW Salinity Strategy is a whole-of-government approach that is helping communities understand urban salinity. The three major urban salinity projects are:
1. The Local Government Salinity Initiative
The Local Government Salinity Initiative (LGSI) provides training, education and technical support to local government on urban salinity issues. As a part of the LGSI, a series of booklets have been produced to address urban salinity. They include:
2. Model planning guidelines
Guidelines have been produced to help local government avoid and manage salinity associated with urban development.
- Land Use Planning and Urban Salinity - presents an overview of the way land use planning can play an important role at council level in preventing and managing urban salinity.
- Best Practice Guidelines for Greener Subdivisions: Western Sydney (greenerSubdivisionsGuideline.pdf, 4MB) - provides a guide to the planner, designer and developer to inform of the need to incorporate sustainable practices in subdivision planning to ensure sustainable outcomes on the ground. Prepared in 2002 by NSW Department of Land and Water Conservation (now part of DECCW) specifically for Western Sydney local government areas within the Hawkesbury - Nepean catchment.
What can I do to manage urban salinity?
To manage urban salinity the problem normally needs to be addressed at both the catchment (the surrounding rural and urban landscape) and local levels. This is because the groundwater responds to both catchment and local factors. Management practices within an urban centre alone are not normally sufficient.
Management at the catchment level principally involves the maintenance of adequate vegetation cover and the implementation of appropriate land and water management practices (as outlined in Dryland Salinity Management).
At the local level, in the urban centre itself, there a number of management strategies that councils and residents could implement. These include:
- Avoiding over-watering public parks, sports fields, home gardens and lawns
- Planting large native trees and shrubs in open spaces
- Investigating the extent of leaking channels and pipes and implementing a pipe replacement program using corrosion resistant materials
- Assessing the likelihood that current and proposed water storages, artificial lakes and drainage basins contribute to groundwater recharge, with strategies to minimise where possible
- Ensuring that water drains away from infrastructure developments to avoid ponding
- Connecting septic tanks to piped sewerage systems where possible
- Connecting roof drainage to stormwater systems, rather than sullage pits
- Monitoring changes to watertable levels and groundwater quality by installing piezometer ('monitoring bore') networks, and
- Encouraging residents to establish gardens with low water requirements.
Direct treatment strategies
An engineering option for the management of urban salinity that may be considered in some locations involves groundwater pumping to keep the watertable greater than two metres below the surface. This may be a realistic option where localised areas of high-value infrastructure or community value are threatened. The saline waters could be pumped into special evaporation basins or, if not excessively saline, into local drainage systems. Wagga Wagga City Council has implemented a dewatering strategy like this to protect the city's infrastructure.
New houses, buildings or infrastructure in current or potentially salt-affected areas should be built to withstand the effects of salinity. Corrosion resistant materials should be widely used. Durable water-resistant membranes (eg. damp courses in houses) may often be appropriate. Various changes may be necessary to local Council and NSW Government building codes to ensure appropriate design, construction and use of new developments.
Assessment and planning strategies
Assessment and planning strategies that may lead to the better management of urban salinity problems include:
- Increasing knowledge and awareness of the problem within potentially affected Council areas (by using the Internet, for example)
- Developing strategies to educate planners, builders and developers about urban salinity prevention measures and building in a saline environment
- Joining or forming urban Landcare groups
- Preparing and implementing Urban Salinity Management Plans, as in several NSW towns, such as Wagga Wagga
- Conducting urban salinity monitoring, as well as assessment and research programs to examine trends, causes of the problem and potential risks
- Understanding the geology and hydrogeology of an area to identify and manage urban salinity.
- Ensuring appropriate zoning and management of lands with known or potential salinity or high watertables, and
- Developing a groundwater management strategy, including a focus on the impacts of effluent disposal.
References and resources
Page last updated: 26 February 2011