Sewer Condition and Blockage Detection Classification Using Novel Acoustic Instrumentation

In the UK, the sewer system is ageing, poorly monitored and around 300,000 km long. The system is subject to increasing capacity demands because of increased urbanisation, more stringent environmental regulation and the consequences of climate change in the form of more frequent and intense rainfall events. OFWAT, the economic regulator for the water industry, imposes a legal duty on water companies to maintain the structural and operational conditions of their sewer systems and also to progressively reduce flooding incidents from sewers. In 2004 OFWAT identified 5700 sewer flooding incidents and an additional 11600 properties with a 10% annual risk of flooding. In approximately 90% of these cases, flooding was caused by an obstruction in a section of sewer pipe. Consequently, monitoring pipes for obstructions and then rapidly removing them could form an important part of an effective programme to reduce sewer flooding. The aim of this project is to develop novel acoustic technology (sensor and software) to produce a near market prototype that can be used in a live sewer to measure rapidly and objectively in-pipe condition and identify blockages and damage. Sewer monitoring is currently limited to the interpretation of CCTV pictures or the use of LightLine surveys. These methods require a mobile trolley with camera to be inserted and travel up a pipe section acquiring images which are then manually examined and defects/obstructions classified according to the standard Sewer Rehabilitation Manual document. Discussions with sewer operators in the UK indicate that they CCTV survey around 2% of their networks every 5 years. This project will develop an alternative fast method for analysing objectively the condition of a sewer and locating blockages. Recent research at the University of Bradford (EPSRC grant EP/D058589/1) has proved that the area of pipe blockage, extent of cracks, water level and positions of lateral connections can be measured in the laboratory pipes using an acoustic method of inspection. In this way the pipe condition of a sewer could be determined between manholes in the airborne regime. The key element of this acoustic device is a small multi-sensor array and advanced, real-time signal processing algorithm which overcome the effects of ambient noise and reverberation in the manhole environment. The key barriers to transferring this technology to the commercial sector are: (i) construction of an intrinsically safe, robust instrument; (ii) acquisition of sufficient field data to demonstrate clearly to potential users that acoustic sensors can reliably identify defects and obstructions in sewers (iii) demonstration that the acoustic technology can provide data that is compatible with the conventional CCTV methods and can be mapped onto the existing sewer condition classifications and sewer databases used by UK water companies. The data collected in the field will be critical in determining the nature and extent of the industrial funding and commercial interest from potential stakeholders. The investigators are in contact with four commercial organisations who support this work: Richard Long Associates, Mouchel Parkman, Yorkshire Water Services and Thames Water. It is generally agreed that CCTV surveys take between 2 and 4 hours per 100m length for measurement with a similar time for image analysis. This costs between 2 and 40 per linear metre depending on the access constraints. Acoustic measurement potentially reduces the measurement and analysis time to tens of minutes per 100m. Significant efficiencies can be achieved. This would enable operators to survey more of their network more frequently so would allow for better monitoring strategies to be developed, the earlier identification of defects and especially blockages leading to fewer flooding incidents and better planned maintenance.