LOCATION OF DIVERSION HEAD WORKS
The total length of the river may be divide into the following four stages.
1. Mountainous stage.
- The first length of the river originating from hills is know the mountainous stage of the river.
- The longitudinal slope in this stage is very steep and the velocity of the flow of water, very fast.
- The width of the river in this region is generally very small.
- This region is found most suitable for the construction of storage works like high dams.
- Large storages are possible very deep valleys are easily available here.
- Moreover, the length of the dam is also relatively small. Materials of construction are locally available.
- This stage is however not suitable for diversion works.
2. Sub-mountainous stage.
- The bed and banks of the river in this stage are made of gravel.
- The velocity of flow is considerable though smaller than first stage.
- The river water contains lot of silt load.
- The river generally does not flow in a single channel, but is form of small several channels.
- The longitudinal slope is less than first stage but still considerable.
- Diversion works can be located in this region of the river.
3. Alluvial or trough stage.
- This length of the river is in plains.
- The section of the river is made of alluvial soils or silt.
- The longitudinal slope of the river is small and velocity of flow moderate.
- This length of the river is the largest of all other lengths. Diversion works are mostly located in this length.
- The area to be irrigat lies very near to this length and thus reduces the overall length of the canal network.
4. Delta stage.
- This is the last length of the river before it falls into the sea.
- This length of river is only a few kilometres long.
- Here velocity of flow is very small and silting rate very high.
- Because of high rate of silting, the rivers frequently change their course.
- No diversion work is construct in this region.
- Secondly available command area near this region is also small.
- Canals cannot be taken from mountainous stage, lot of cuttings and fillings are involv and thus canal construction becomes very costly.
- Lot of falls will have to be construct adding still more to the cost. After having decid the region in which diversion head work is to be located.
The following additional points should also be taken into account:
- All the construction materials should be available in the vicinity.
- In order to keep the length of the canal minimum, diversion headworks should be locat near the area to be irrigat as possible.
- The elevation of the water in the river should be such that water may flow to the area under gravity.
- If the level of water is low, the position of the headworks should be shift a few kilometers upstream so that increase elevation of water is available.
- The canal should run in such a way that the canal is partly in cutting and partly in filling.
- The river at the site of diversion should be neither too wide nor too narrow.
- The river should neither be scouring nor silting.
- The river should be straight and flowing in one channel.
- Its bed and banks should be stable.
- The canal alignment should be such that minimum streams cross it.
- This will reduce the number of cross-drainage works to be construct.
- The canal should take off, either at 90° or greater than 90° with the river.
- The canal should not run parallel to the river.
- In such circumstances, the canal may be eroded during floods.