Assessing Sensitivity Factors of Irrigation Delivery Structures

The flow behavior along an open-channel irrigation network can be assessed by determining the sensitivity of the irrigation structures. The importance of governing factors of the sensitivity and proportionality indicators is analyzed using a theoretical approach as well as practical results from historical data on a gated system in Sri Lanka and a gated and structured system in Pakistan. The influence of the discharge on the sensitivity indicator varies with the type of flow (overshot-undershot). For a common offtake (e.g., an orifice followed by a crest), sensitivity is at its peak at maximum discharge. The available head through the structure appears to be the most influential factor for sensitivity; the greater the head, the lower the sensitivity is. The submergence of the flow downstream of the structure is a reducing factor of the sensitivity that is important to consider for sensitive structures. Different methods for assessing the governing factors of sensitivity are discussed and illustrated using case studies. It is recommended that the sensitivity indicator be determined for the full supply depth in the parent canal and the maximum discharge through the offtake.