Small Hydroelectric Engineering Practice

Chapter 2

Scheme identification

Having identified a region with potential for hydropower generation, studies are

needed to identify the best site and the main features of the proposed scheme. The

route and cost of a transmission line from the power station to the load or the grid

also needs to be established.

2.1 PRELIMINARY STUDY

The study should commence with a thorough examination of the region using topo-

graphical and geological maps, satellite photography from Google Earth and other

sources, and aerial photography followed by investigations into rainfall and stream

flows. Once there is good understanding of the lie of the land and likely flow, sites

with sufficient flow and an adequate head can be identified. Head can be created –

usually expensively – by building a dam with a power station at its base but for small

hydropower it is more common to divert the water out of a river valley and then con-

vey it to a power station further downstream. In many cases head can be developed by

diverting the flow around a waterfall or a section of rapids. In some cases, tunneling

through a hill or building a canal to an adjacent deeper valley is an excellent way of

achieving a higher head at a reasonable cost.

Establishing the available flow (hydrology) is important. If good flow records

are already available the job is fairly easy. More often, no records are available and

estimates must be made from rainfall records and run-off estimates, or from adjacent

catchments with similar characteristics.

Once a site has been identified, site visits are essential to obtain a more accurate

indication of the flow available, the topography and the geological conditions. At least

one survey should be done during the seasonal low-flow period to get some idea of the

minimum flow. During every visit the flow in the stream should be measured using a

flowmeter. Guesses are not good enough! For preliminary studies a log (speed meter)

used for measuring the speed of a yacht is a satisfactory alternative to an expensive

flow meter.

A geological overview is needed to establish the risk of landslides and settlement

of any structures. When these studies are complete, outline design of the headworks,

spillways and waterways can commence. For the powerhouse, the type of generating

plant and the number of units needs to be established so that the approximate size of