Design procedure: cross and distributary head regulator

A cross regulator is placed across the parent canal d/s of an off-take, and a distributary head regulator is placed at the off-take. Both are gated structures with similar design steps.

Cross regulator

1. Data: parent canal discharge $Q_p$, off-take discharge $Q_d$, u/s and d/s FSL, bed levels and widths.
2. Discharge through the regulator: $Q_{cr} = Q_p - Q_d$.
3. Afflux: $\Delta h =$ u/s FSL $-$ d/s FSL (usually 0.15 to 0.3 m).
4. Crest level: at the d/s bed (or raised 0.3 to 0.5 m if the canal is silty). Provide gates and piers.
5. Waterway: from orifice flow, $B = \dfrac{Q_{cr}}{C_d\,D\sqrt{2g\,\Delta h}}$ with $C_d \approx 0.8$, or from the weir formula $Q = 1.7LH^{3/2}$; provide bays and piers.
6. Scour and cut-offs: Lacey's $R = 1.35(q^2/f)^{1/3}$; d/s cut-off at $1.5R$ below the d/s water level and u/s cut-off about $R$.
7. Floor: length by Khosla's exit gradient for the maximum static head $H_s =$ u/s FSL $-$ d/s bed; thickness from uplift.
8. Protection works: inverted filter, stone apron.

Distributary head regulator

1. Data: distributary discharge, parent FSL, distributary FSL and bed level.
2. Sill level: at the distributary bed level (raised 0.3 m to reduce silt entry if needed).
3. Waterway: orifice flow, $B = \dfrac{Q_d}{C_d\,D\sqrt{2g\,\Delta h}}$, $\Delta h = FSL_{parent} - FSL_{dist}$; provide bays and piers.
4. Cut-offs, floor length, thickness and protection as for the cross regulator, using the head $H_s =$ parent FSL $-$ distributary bed.
5. Alignment: the head regulator is set at an angle of about 60° to 90° to the parent canal, and a cross regulator is placed d/s to hold the water level.

 Plan:   parent canal  ===>===[CR]===>===
                         \ [HR]
                          \==> distributary
 Section: gates | piers | crest | floor | cut-offs