Sediment Control in Canals

By:- Anil Kumar Pandey

8th sem civil(B.E) K.L.E.society college of engineering and

technology

Guidence:- Dr. R.V Raikar

Introduction:-

One of the major problem in the design of irrigation works and hydroelecric schems is the control of sediment entering irrigation and power canals. The slope of an irrigation canal taking off from the head works is usually smaller than that of parent strem, to enable water to reach the points above the stream where irrigation isrequired. Such a decrease in slope is required in the case of power canals also to obtain head for power generation. If heavy sediment load enters the canals, the canal will be unable to transport the entire load with such a small slope and part of the load will be deposited in the canals itself. A certain amount of fine sediment can always be tolerated in irrigation as well as power canals. Presence of fine sediment can always be tolerated in irrigation as well as power canals. Presence of fine sediment may even be desirable in the case of irrigation canals, since part of it gets deposited on irrigated lands, thereby increasing their fertility. It is necessary to keep the amount of coarse sediment carried by the canal to as low as possible. In case of power canals all the coarse material detrimenal to the life of turbine blades must be removed. The abrasive sand in sarda canal(india)water was responsible for the wearing out of the turbine blades of khatima power house.

The Effects of deposition of coarse sediment on the performance of Irrigation canals are:-Water supply for irrigation has to be stopped occasionally for clearing the sediment from the canals. Removal of deposited material is quite expensive. With the silting up of the canal, its capacity and command decrease. Silting encourages weed groth in the canals. In an irrigation-cum-navigation canal, the deposition of sediment reduces the draft.

Methods of sediment control:-

Sediment entering a canal can be controlled in a variety of ways. A large storage reservoir built on the stream automatically traps all coarser fractions of sediment and a large percentage of finer fractions. A canal supplied from such a reservoir will therefore have water which is free from sediment. While such a reservoir is usually constructed across nonperennial rivers normally envisages the construction of low weir or a barrage to control the water level and diverts the flow in to the canal. A typical headworks used on perennial streams in India. It consist of a weir or a barrage, scouring sluices( also called undersluices), divide wall, fish ladder and canal head regulator. The lake upstream of such barrages does not trap much sediment load and the canal is likely to be heavily charged with sediment. However, attempts are usually made to locate and construct the headworks in such a manner that the amount of sediment load entering the canal is small. A favourable location for the head regulator from sediment consideration is on the outside of a river bend.