SMALL HYDRO DEVELOPMENT
Civil Works –
Hydraulic Design Of Small Hydro Plants
Alternate Hydro Energy Center
Indian Institute of Technology Roorkee
Ministry of New and Renewable Energy
Govt. of India
AHEC/MNRE/SHP Standards/ Civil Works - Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011 1
GUIDELINES FOR HYDRAULIC DESIGN OF SMALL HYDRO PLANTS
This section provides standards and guidelines on the design of the water conductor system. This system includes; head works and intake, feeder canal, desilter (if required), power canal or alternative conveyance structures (culverts, pipelines, tunnels, etc), forebay tank, penstock and surge tank (if required) up to the entry of the turbine, tailrace canal below the turbine and related ancillary works.
HYDRAULIC DESIGN OF HEAD WORKS
In general head works are composed of three structural components, diversion dam, intake and bed load sluice. The functions of the head works are: Diversion of the required project flow from the river into the water conductor system.
Control of sediment.
Typically a head pond reservoir is formed upstream of the head works. This reservoir may be used to provide daily pondage in support of peaking operation or to provide the control volume necessary for turbine operation in the water level control mode. This latter case would apply where the penstock draws its water directly from the head pond. Sufficient volume must be provided to support these functions.
There are three types of head works that are widely used on mini and small hydro projects, as below:
Lateral intake head works
Trench intake head works
Reservoir / canal intakes
Each type will be discussed in turn.
Head Works with Lateral Intakes (Small Hydro)
Head works with lateral intakes are typically applied on rivers transporting significant amounts of sediment as bed load and in suspension. The functional objectives are:
To divert bed-load away from the intake and flush downstream of the dam (the bed load flushing system should be operable in both continuous and intermittent modes).
To decant relatively clean surface water into the intake.
To arrest floating debris at intake trashracks for removal by manual raking. To safely discharge the design flood without causing unacceptable upstream flooding.
AHEC/MNRE/SHP Standards/ Civil Works - Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011 2
The following site features promote favourable hydraulic conditions and should be considered during site selection:
The intake should be located on the outside of a river bend (towards the end of the bend) to benefit from the spiral current in the river that moves clean surface water towards the intake and bed load away from the intake towards the centre of the river.
The intake should be located at the head of a steeper section of the river. This will promote removal of material flushed through the dam which may otherwise accumulate downstream of the flushing channel and impair its function.
Satisfactory foundation conditions.
Ideal site conditions are rare, thus design will require compromises between hydraulic requirements and constraints of site geology, accessibility etc. The following guidelines assume head works are located on a straight reach of a river. For important projects or unusual sites hydraulic model studies are recommended. A step by step design approach is recommended and design parameters are suggested for guidance in design and layout studies. Typical layouts are shown in Figures 2.2.1 to 2.2.3.
Data Required for design.
The following data are required for design:
Site hydrology report as stipulated in Section 1.3 of this Standard giving: - Qp
(design flood flow, small hydro)
(design flood flow, mini hydro)
(data on suspended sediment loads)...