Run-off river plants with pondage. The usefulness of this type of plant is increased by pondage. tail race conditions should be such that floods do not raise the tail race water level,thus reducing the head on the plant and impairing its effectiveness. Pondage is the storage at the plant which makes it possible to cope,hour to hour,with fluctuations ofload throughout a week or some longer period depending on the size of the pondage.With enough pondage,the firm capacity of the hydro-electric plant is increased.This type of plant can be used on parts of the load curve.as required,within certair limitations and is more useful than a plant without storage or pondage.