CCTV drainage survey

Method[edit]

Access is through an existing manhole, inspection chamber or rodding point. The line is usually cleaned first, because silt and deposits obscure the pipe wall and produce a survey that records the debris rather than the pipe. The camera is then run through the length, with distance logged continuously so that each observation is tied to a chainage from the access point.

The result is a defect-coded record rather than a narrative. Coding covers structural conditions such as cracks, fractures, deformation and displaced joints, and service conditions such as root intrusion, deposits and infiltration.^[1]

Relationship to leak detection[edit]

Drains are gravity systems, so a defect in one does not produce the pressurised escape that acoustic and correlation methods rely on. Leakage from a drain shows instead as infiltration into the pipe or exfiltration out of it, and as damp or washout in the surrounding ground.

Where a drain is suspected of leaking, a CCTV survey identifies candidate defects and their position, and a water or air test to BS EN 1610 establishes whether the length actually holds or not.^[2] A visible crack is not by itself proof of loss, and a length that passes a test does not need excavating because a camera saw a mark on it.

Limitations[edit]

The camera sees only the inside surface. Defects on the outside of a pipe, ground voids and the condition of a bedding are all invisible to it. A partly full or surcharged line cannot be surveyed usefully. Very small diameters, sharp bends and collapsed sections stop the camera and leave the remainder unsurveyed, which is recorded as a survey abandoned at a chainage rather than as a clear length.