A Novel Approach to Detecting Blockages in Sewers and Drains: The Reflected Wave Technique

Blockages in sewers and drains often result in overflows and flooding that cause significant environmental pollution and public health risks particularly in hospitals where the consequences can be catastrophic. Due to their low “visibility”, sewers and drains are inherently difficult to monitor and maintain, resulting in a reactive management approach whereby maintenance or repair is carried out only after a system failure has occurred. This study investigates the application of the reflected wave technique, a unique sonar-like monitoring system, capable of identifying changes to the geometry of closed-pipe-conduits, as a means of active system monitoring to enable maintenance to be conducted in a pro-active basis. An experimental setup was developed to simulate a horizontal drain using standard pipework of 100 mm diameter and 70 m length. Blockages representing 30% and 75% coverage of the drain’s cross-sectional area, with lengths from 30 mm to 3000 mm, were added to the drain. A sinusoidal air pressure wave of 10 Hz was applied and the resultant system pressure response recorded. All but the two smallest blockages (30% with 30 mm length and 30% with 100 mm length) were detected and located with good accuracy. The reflected wave technique could provide a novel and non-invasive method for blockage detection and overall system monitoring for sewers and drains.