Pondage usually refers to the comparably small water storage behind the

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

of a

run-of-the-river hydroelectric Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amo ...

power plant. Such a power plant has considerably less storage than the reservoirs of large dams and conventional hydroelectric stations which can store water for long periods such as a dry season or year. With pondage, water is usually stored during periods of low electricity demand and hours when the power plant is inactive, enabling its use as a

peaking power plant Peaking power plants, also known as peaker plants, and occasionally just "peakers", are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power ...

in dry seasons and a

base load power plant The base load (also baseload) is the minimum level of demand on an electrical grid over a span of time, for example, one week. This demand can be met by unvarying power plants, dispatchable generation, or by a collection of smaller intermittent en ...

during wet seasons. Ample pondage allows a power plant to meet hourly load fluctuations for a period of a week or more. As a daily hydropeaking cycle of a hydro power plant with pondage results in fast rising river levels downstream, environmental regulations often restrict the full use of the dispatchability as a peaker.

Calculation

Because of the possibility of limited pondage, calculating its effect on power generation is important in determining how often the plant can be operated. The ''pondage factor'' is a rough index of the amount pondage needed when the stream flow is constant and the plant is operational during specific periods. It is calculated by the ratio of total inflow hours per week to the hours the power plant will be operated in that same period. For example, if a river has an inflow for seven days a week and the plant operates for five of those days for eight hours: :

\frac = 4.2

24-hour inflows and plant operation would have a pondage factor of one. If power is used for twelve hours per day and during the inactive hours, relatively all inflows can be stored, then power can be doubled during active hours. In 12 hours there are 43,200 seconds and in there are . This gives an estimation and guide that for twelve hours of pondage, there must be as much storage available in the pond as cubic feet per section received.

References

{{Reflist Hydroelectricity Power station technology