Inspecting Inverted Siphons

Inverted siphons are commonly used for transporting water under drainages, highways, and other structures. Siphons are very durable if well designed and constructed, but can experience problems such as pipe deterioration, cracking, leakage, or accumulation of rocks. Inspection can be difficult and dangerous. The Bureau of Reclamation (Reclamation) generally recommends that inspections be done at least every 6 years.

Siphons are designed to function with a specified normal water surface elevation at the intake, which should be indicated in the design drawing, or which may be estimated based on the freeboard required at the intake and in the canal upstream of the siphon. If this depth is exceeded, it may indicate that flow through the siphon is being restricted. Another indication of a problem is water flowing at an unexpected location or flow rate near the siphon, or which starts after the siphon is watered-up, which may indicate a leak.