Canal escape structures with sketch

An escape is a structure built in the side of a canal to release surplus water into a natural drain or stream. It protects the canal from damage, allows it to be emptied for repair, and removes silt.

Functions

1. Remove excess water caused by heavy rainfall, sudden closure of outlets or faulty operation of the head regulator.
2. Empty the canal quickly in an emergency (breach) or for maintenance.
3. Scour out silt deposited at the head of the canal (scouring escape).

Types

1. Weir type escape (surplus escape): a fixed weir wall with its crest at FSL, which automatically spills the excess water over its crest. Used where the excess flow comes from rain.
2. Escape with sluice gates: gates at bed level that can be opened to empty the canal quickly or to flush silt. Used at the tail of the canal or at silted reaches.
3. Syphon escape (a syphon spillway type): works automatically when the water level exceeds FSL.

Neat sketch

 Plan                          Section through escape
  canal ==>===+===>==            FSL ~~~~~|
              | escape                 ___|__ crest = FSL
              v                  bed __|    |
        ====== escape                floor, gates
        ====== channel to drain      d/s protection

• The head wall has its crest at the full supply level of the canal.
• A scour sluice at canal bed level discharges silt and drains the canal.
• A stilling basin and protection works are provided at the toe.
• The escape is located upstream of major structures, near natural drains, and upstream of the cross regulator.