Complex sentence: A plant without pondage has no storage and is, therefore, subject to seasonal river flows and may operate as an intermittent energy source while a plant with pondage can regulate water flow and serve either as a peaking power plant or base load power plant.
Split into simpler sentences: A plant without pondage has no water storage and is, therefore, subject to seasonal river flows. Thus, the plant will operate as an intermittent energy source while a plant with pondage can regulate the water flow at all times and can serve as a peaking power plant or base load power plant.