Reservoir Outlet Works (Part - 4) - Hydraulic Structures - Civil Engineering (CE) PDF Download

Intakes for irrigation 

Two types of intakes are generally used for outlet works meant for releasing irrigation water. These are: 

1. Run-of-the-river type intakes, and
2. Reservoir type intakes. 

Run-of-the-river type intakes are those which draw water from the fresh continuous river inflows without any appreciable storage upstream of the diversion structure. A typical sketch of intake to meet special characteristics, such as steep slopes, high peaks and short duration flood flows and high sediment loads, is shown in Figure 10. A canal head regulator (discussed in Lesson 4.3) is a typical example of this type of intake constructed upstream of a barrage. 

Figioa. Run-Off River Type Intake (General Layout)

Figure 10(B) Details of Intake and Sediment Exclusion Device through Sluice

Reservoir type intake is provided where discharges for irrigation are drawn from storage built up for this purpose. Depending on the head, this is further categorized as under: 

1. Low head (up to 15 m),
2. Medium head (15 to 30 m), and
3. High head (above 30 m). 

Intake in concrete or masonry dams: In the case of concrete dams, irrigation intake structure can be located either at the toe when operating head is low or in the body of the dam itself when operating head is medium or high. Typical section of such an intake is shown in Figure 11.  

FIGURE 11. Typical intake through a concrete dam

Intake in earthen dams: When the reservoir is formed by an earthen dam, the irrigation tunnel is laid below it or in the abutment. The intake structure for such situations will be a sloping intake or tower type of intake. Typical layouts for sloping and tower type intakes are shown in Figure 12 and 13 respectively. As far as possible, reinforced cement concrete pressurized system should be avoided in the body of the earth dam. Measures like provision of steel liners and suitable drainage downstream of core, provisions of joints for differential settlements when not founded on rock should be considered in case pressure conduits are provided under earth dams. 

Figure12. Typical Installation in an Earth Dam-Sloping Intake

Figure 13 Typical Installation in an Earth Dam of Tower Type Intake

Intakes directly from the reservoir through abutments: In this case, the dam is separated from the intake structure. The dam may be of any material (concrete, earth, etc.) but the intake is constructed by grading the left or right abutments and leading the outlet pipes through the surrounding hills. Figures 14 (a) through (c) show the typical layout, section and plan of such an intake. 

Figure 14 (B) Semicirculer Type Intake Structure - Elevation

Figure 14(C) Semicircular Type Intake Structure-Plan

The hydraulic design of the various components of an intake, like the elevation of the centre-line, trash rack structure, bell mouth shape and transition details, etc. may be found from the Bureau of Indian Standards code IS: 11570-1985 “Criteria for hydraulic design of irrigation intake structures”. 

Intakes for hydropower 

Similar to the irrigation intakes, the hydropower intakes are also of two types: 

1. Run-of-the-river type intakes, and
2. Reservoir type intakes. 

However, it may be mentioned that on the whole, these intakes are quite similar to those constructed for serving irrigation requirements. The Bureau of Indian Standards code IS: 9761-1995 “Hydropower intakes – criteria for hydraulics design” may be referred to finalise details about the hydraulics design of hydropower intakes.