Deposits have a number of negative consequences on the operation of drainage networks, all of which are also associated with economic disadvantages. They also contribute to water pollution. Impact of the deposits on the operation of the sewer systems are:

• Deposits lead to a reduction in the hydraulic performance of the sewer system by increasing the operational roughness reducing the flow area and the capacity of the sewer system. These circumstances can lead to flooding and backups during rain events which can significantly interfere with the operation of the entire network and its components.

• Deposits can also reduce the retention capacity of a sewer system, which can lead to problems during heavy rain events that wouldn’t normally occur [Macke87].

• Increased expenditure for sewer cleaning.

• Increased risk of biogenic sulphuric acid corrosion (BSAC) in partially filled channels and structures made using cement binders, which can result in reduced service life or destruction of these systems [Bock84] [Biele87a] [Schre85] [Klose80] [Lohse95].

• Adverse health effects on the operational personnel as a result of the gas formed by the decomposition of the deposits.

• Wear related stresses on the channels and in particular the moving parts of the sewer system and treatment plants, such as pumps, valves, gates, etc.