Stormwater runoff will collect with it whatever trash and litter it finds in the built-up areas of the catchment that the system is serving. This can be anything from dirt, cigarette butts, plastic bags, leaves, or any other litter that people carelessly throw on the ground. If this trash is allowed to make its way into the natural water sources that stormwater is often led into, it can greatly increase the pollution of water.

It, therefore, becomes important to design any stormwater management system with devices and methods for removing trash from water before it is led into its final disposal areas. You can build in many such devices into a system, but a proper analysis of the quantity and nature of the trash will lead to a more efficient way to handle the problem of trash. This requires a properly planned trash strategy to be in place that has identified high trash zones, and all the outfalls and drainages that are bringing in the trash load. Once this is done, you can then choose the drainage areas that need treatment and the devices that will be the most efficient for removing the trash.

All these devices will require proper maintenance to remove the accumulated trash and require having placed a proper inspection schedule and methods to clear and dispose of the trash that has been removed from the water. Constant monitoring can help to judge any increase or decrease in load, that can then be used to make any needed modifications to the installed devices and methods for removing trash from water.

The most effective way of ensuring that trash does not enter the waterways is to institute structural control measures that can effectively trap the trash and preventing it from going further into the system. These can be in the form of screens, sediment tanks, detention ponds, and other techniques that use swirl control to separate the trash from the water. Screens installed need to be periodically cleaned to prevent their clogging, but there are screens available which have been designed to deflect the trash and force it to form a sediment, and thus reduce the need for constant maintenance.

Sediment tanks and detention or retention ponds retain the water for a fixed period and reduce the flow force to zero so that heavier articles that form the trash can settle down and form sediments. Sediment tanks will have several baffles that help in controlling the flow of stormwater that induce the trash to settle between barriers and allow the runoff to cross over them. Detention ponds and retention ponds separate the trash naturally, and their capacities, inlets, and outlets need to be designed to facilitate sedimentation of trash.

Swirl control structures use the force of the flow of the stormwater runoff to create a centrifugal force in the water that drives the trash to the edges of the container that then traps the trash and deposits it at collection points from where it can be removed.

A properly designed stormwater management system that incorporates the right structures for removal of trash can go a long way in preventing the pollution of natural water bodies into which stormwater finally finds its way.