The Lugeon Test: Methodology, Interpretation, and Applications in Geotechnical Engineering

Canal falls are masonry or concrete structures constructed in irrigation canal systems primarily to manage changes in elevation and dissipate excess energy. They are necessary for several key reasons:

Adjusting Steep Ground Slope: When the available natural ground slope is steeper than the designed bed slope of the channel, canal falls are constructed to adjust this difference by introducing vertical 'drops' in the canal bed at suitable intervals. This prevents the need for excessive and costly earthwork in filling to maintain the canal's designed slope.

Dissipating Surplus Energy: Water falling from a higher elevation to a lower one liberates surplus energy. Canal falls are designed to destroy or dissipate this surplus kinetic energy through vertical impact into a cistern or by facilitating a hydraulic jump on a glacis. This energy dissipation is crucial to prevent erosion downstream of the structure and protect the canal bed and sides from damage.

Maintaining Designed Slope: Falls are constructed to lower the canal's bed level to maintain its designed slope when there is a change in the natural ground level. Beyond the fall, the canal can then resume its designed slope.

Regulating Water Flow and Level: They help to regulate water flow, maintain a stable water level in the canal, and improve water distribution and allocation to crops.

Reducing Risk of Flooding and Damage: By controlling the water level and dissipating energy, falls reduce the risk of flooding and damage to downstream infrastructure.

Economic Considerations: In systems like the Sarda Canal in U.P., economical falls were necessary for constructing a large number of smaller falls, especially where sandy stratum overlay sandy-clay and a minimum depth of cutting was desired. The location of a fall also considers economy in the cost of excavation and filling, aiming to balance earthwork on both sides to avoid costly unbalanced earthwork.

Cross-Drainage Works: Canal falls are also necessary in cross-drainage works when the difference between the canal's bed level and the drainage's bed level is small, or when the full supply level (F.S.L) of the canal is above the drainage bed level. In such cases, the fall helps to carry the canal water below the stream or drainage.

In essence, canal falls are critical hydraulic structures that ensure the stability, efficiency, and safety of an irrigation canal system by managing elevation changes and the associated energy of flowing water.