Components and layout of diversion headworks

A diversion headworks is a structure built across a river to raise the water level and divert the flow into a canal. It consists of a weir or barrage and the associated structures.

Layout (plan)

 Left       <-- river flow: Upstream to Downstream -->
 guide  ______________________________________  Right
 bund  |                                      | guide
       |  Weir   Weir   |D| Under-  |D| Head  | bund
  ~~~> |  (crest) bay   |W| sluices |W| reg.  |
       |=====================|======|====||===|--> canal
       |  Fish ladder   |<-- pocket -->|     |
       |  Divide wall (DW) separates weir/sluices
       |_______ Upstream & downstream aprons ___|
       Marginal / afflux bunds on both banks

(DW = divide wall; the head regulator is located at one end, with the silt excluder in front of it.)

Cross-section through the weir

  Pond level ~~~~~~~~~~~~~
  u/s apron     crest|\  d/s glacis
  ______________ ____| \_________ 
  cutoff (sheet pile)       |      d/s pile

Components and their functions

1. Weir or barrage proper – raises the river level to the pond level and passes the flood over the crest (weir) or through gates (barrage). It has a crest, u/s and d/s glacis, and a floor with cut-off walls.
2. Undersluices (scouring sluices) – gated openings at low level next to the canal head, which scour deposits in front of the head regulator and pass low floods.
3. Divide wall – separates the weir portion from the undersluice portion, protects the sluices from cross currents, and forms the still pocket.
4. Fish ladder – a sloping channel with baffles beside the divide wall, allowing fish to migrate.
5. Canal head regulator – controls the flow into the canal; its crest is higher than that of the undersluices to keep out bed silt.
6. Silt excluder / silt ejector – reduce silt entry into the canal.
7. Guide bunds (guide banks) – train the river to flow axially through the structure and prevent outflanking.
8. Marginal (afflux) bunds – protect the land and villages upstream from flooding caused by the raised water level (afflux) behind the structure.
9. Aprons and protection works – u/s and d/s concrete blocks with filters and launching aprons, to protect against scour.
10. Pile cutoffs / curtain walls – at the upstream and downstream ends of the floor, to lengthen the creep path and keep the exit gradient safe.
11. Piers, bridge, and shutters/gates – for operation of the gates and cross-communication.