Techniques for Sewer Condition Assessment

• Zoom cameras
• Closed-circuit television
• Digital scanners
• Laser profilers
• Remote sensing diagnostic techniques

Zoom cameras

• Cost and time saving preliminary inspections 

• Main premise is that most of sewer problems occur at or near maintenance holes 

• Provide good quality imagery up to 20-75 m pipe length
• Able to survey 150 to 1525 mm diameter sewers 

• Colour videos and digital images saved on optical storage devices

Closed-circuit television (CCTV)

• Most widely used technology for sewers in past 35 years 

• Depend on expertise, alertness and judgment of field technicians or camera operators for identification and classification of defects 

• Advances in coloured image enhancements, pan-and-tilt camera heads, steerable crawler systems
• A video camera along with a lighting unit mounted on a crawler 

• A cable drum with a counter to measure distance inside sewers connects camera to the surface 

• A computerized control unit for controlling camera, lighting, and crawler movement usually hosted in a van accompanies the CCTV system

Digital scanners

Flash Cameras

• Two high resolution cameras with 186 degrees wide-angle lenses are integrated at the front and rear ends of the system 

• Hemispherical digital images are put together to form a 360-degree spherical image 

• Defects and objects can be measured on unfolded images 

• Camera works in pipes of dia 200mm & up, operates at a speed of 20 metres per minute

Laser Profiler

• Employed in combination with CCTV camera to determine internal condition and measurement of defects and other features for sewers 

• A ring of laser light is projected onto the internal pipe surface, and laser image is captured by the CCTV camera
• Ring of light is analyzed using the laser profiler software and digital profile of pipe is produced