Concern for the impacts of stormwater litter has increased in recent times, especially for dangerous items such as syringe needles, but also for the huge quantities of cigarette butts.

Recently Victorian councils have embarked on Stormwater Management Plans that outline the risks to and possible solutions for pollution in our creeks and waterways. The plans often include suggestions of potential locations for stormwater litter traps (or gross pollutant traps) and have led to an increased number of litter traps being installed in Victoria.

Approximately one billion items of litter find their way into Melbourne's waterways each year. About one third of these are cigarette butts: approximately one in ten butts smoked reaches a waterway.

Trapping litter from the stormwater system is a difficult and expensive task, particularly for small items such as cigarette butts. Litter in stormwater can be almost anything, in different quantities, sizes and densities. The amount of water flowing and litter loads vary enormously in stormwater systems making the trapping task very difficult.

Many items can also change their characteristics the longer they are in water. The challenge is to trap the litter yet allow water to flow through the stormwater system and not to increase flooding risks.

There is a range of litter traps for the stormwater system that can treat water at different scales. These are:

• side entry pit traps (to capture litter as it falls in from roadways)
• underground litter traps that can treat blocks to small suburbs (up to 200 hectares)
• large litter traps intended for open channels and treating very large flows
• floating litter traps that capture the most buoyant litter items from estuaries.

Within the range of stormwater litter traps there are many that can capture cigarette butts (some offer capture of items down to 1 mm in size). However, there are no agreed standards for assessing the capture rates of litter traps. Caution should be used when assessing vendor claims as litter traps require substantial investment, but can have very different capture performances for cigarette butts depending on the design.

Generally, a tender process for a litter trap installation will ensure that a range of technologies are represented. It is also important to consider the maintenance required for any litter trap. Maintenance is often the most overlooked issue and the cause of poor performance of a trap.

The choice of which litter trapping system is best suited to a particular location is governed by the size of the area to be treated, available resources for installation and maintenance, as well as assessing any flood risks.