Simplifying Construction of Multiple Drop Schemes 

Project: Guntur River:  Guntur Canal Capacity:  3 x 1250 kW
Click to Go Back State: Andhra Pradesh Energy:  17GWh/year
 For such schemes, the main goal was to simplify construction requirements. In general there are no major differences between the original and revised designs except where feasible to realign the channel to reduce the length of the water conveyance structures and to use closed conduits to obviate the need to permanently destroy agricultural land. Bascule gates or crest gates would be installed slightly upstream of the canal drop to control the water level in the canal and an intake which would be fitted with a trash rack and a stoplog. To maintain flows in the canal when the powerhouse is shut down, automatically regulated crest gates would be provided at the first drop structure.
The original proposal by the APSEB was to establish four schemes along a 10 mile section of the canal. The first scheme would utilize 3 drops (total head 6.9 meters) on the first mile of the branch canal; the second would combine 4 drops (total head 8.85 meters) along the second mile; the third, 2 drops ( total head 3.71 meters) along the fifth mile; and the fourth, 3 drops (total head 8.52 meters) along the ninth mile.

During the preliminary design and standardization process, it became apparent that the configuration of the second scheme could be changed from one scheme (i.e., combining 4 drops for total head 8.85 meters) to two schemes (i.e., combining 2 drops for head of 4.25 meters for each scheme). As a result, the length of the bypass channel was reduced by 250 meters, the cross-section of the by-pass channel was reduced, thereby allowing for significant savings in costs due to excavation of the channel and the powerhouse. 

Also, the change simplified the design of the intake structure and control mechanism (i.e, stop-log and trashrack) at the junction with the main canal. The construction period for the revised layout would be one year compared to three for the original layout. Details are indicated on the technical drawings for the scheme.

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