Wasteway, also known as return flow, is a canal used to drain excess water in the irrigation delivery system. This return flow can also be from overflows from distribution channels or fields that return to the irrigation system. Return flows can be used for recharging groundwater table.
Trenchless rehabilitation techniques such as cured-in-place pipe (CIPP) lining can be used to repair wasteway canals.
Trenchlesspedia Explains Wasteway
Streams are prone to flood flow before the gate settings can be adjusted, requiring an outlet at the upstream end of the canal. This outlet is the wasteway and can be a simple system for overflow with a channel for return flow to the stream.
The control system can be a check with underflow gates or a gate to another structure to ensure orifice flow. It can also be a concrete-lined section that will act as a weir for overflow to remove excess flow. Wasteway structures are also necessary at the downstream ends of the canal with a stop log controlled opening.
A long canal should be provided with a wasteway having a capacity equal to at least 10% of canal flow. It is also provided with an overflow section if the canal has a diversion coming from a stream.