Utilization of Reverse Slope to Increase Full Supply Level in Small Irrigation Channels

Abstract

In this study optimal limit of the reverse slope, downstream of an irrigation outlet, where flow is supercritical was studied to create sufficient working head required to irrigate elevated fields in the command area of a watercourse. Three different types of outlets (AOSM, Pipe and Open flume) were designed and constructed in the lab. Various values of reverse slopes were incorporated in one-meter and two-meter length of the watercourse bed downstream of the selected outlets at a constant value of canal Full Supply Level (FSL). It was observed that FSL of watercourse increased with increase in reverse slope. Reverse slopes -0.10 and -0.15 incorporated in a length of one meter were found most suitable for an outlet of one-cusec discharge. FSL of watercourse increased with increase in reverse slope value up to -0.15 and then started decreasing gradually at -0.20. The outlet discharge decreased slightly (3%) from -0.10 to -0.15 reverse slopes and significantly (26%) at -0.20 reverse slope by submerging the outlets. Reverse slope incorporated in one-meter length of the channel bed was more useful than incorporated in the two-meter length of the channel bed. The results obtained for AOSM and pipe outlets were identical. Open Flume outlets found not to be fit for reverse slope. The best hydraulic section for the reverse slope was with upstream width equal to the Bt of the outlet and then expanded in the direction of flow to join the designed width of the channel.