IS 11551:1986 is the Indian Standard (BIS) for criteria for design of canal structures: flumes. This standard provides criteria for the hydraulic design of flumes, which are constricted channel sections in canal systems. It covers the design principles for flumes operating under both sub-critical and super-critical flow conditions, with a major focus on the geometry and energy loss calculations for inlet and outlet transitions.
Provides criteria for the hydraulic and structural design of flumes in canals for flow measurement or crossing obstructions.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Converging Transition Splay (Angle) | 1 in 3 (approx. 18.4°) | Typically 1 in 4 to 1 in 2.5 (14° to 22.5°); angles around 12.5° are also common. | USBR Design of Small Canal Structures |
| Diverging Transition Splay (Angle) | 1 in 5 (approx. 11.3°) | Flatter slopes are preferred for better energy recovery, typically 1 in 6 (9.5°) to 1 in 10 (5.7°). | USBR Design of Small Canal Structures |
| Minimum Freeboard at Flume Entry | Greater of 15 cm or one-third of the head loss (HL/3) above FSL. | Typically a function of discharge, e.g., 0.3m for small flows (<3 m³/s) up to 1.0m for large canals. | USBR Design of Small Canal Structures |
| Modularity Limit for Parshall Flumes | Not explicitly defined; states modularity should be ensured. | 0.7 for throat widths from 1 ft to 8 ft. | ISO 9826:1992 |
| Location of Upstream Head Measurement (Ha) | At a distance of 2 to 3 times the upstream head (H) from the beginning of the transition. | At a specific distance 'A' from the flume crest, where A is 2/3 of the converging section length. | ISO 9826:1992 (for Parshall Flumes) |
| Side Wall Height in Throat | Should be equal to the upstream total energy line (TEL). | Should be at least the upstream water depth (y1) or slightly higher to contain flow variations. | USBR Design of Small Canal Structures |