Source: Water Resources Research
Surface-water reservoirs tend to attenuate flood peaks by storing and, therefore, slowing the release of flood waters to the river downstream. In many cases, it is common for multiple reservoirs to be located one river reach in the same catchment, complicating the calculation of flood-peak attenuation at some location downstream of two or more reservoirs.
Previously, existing methods would require complex, data-intensive models of the complete reservoir system or one would have to use a simpler method that only provided a qualitive approach to understanding the effects. Cipollini et al.  provide a new index – termed the attenuation index – based on the concept of the equivalent reservoir, which allows for a quantitative, physically-based assessment of flood-peak attenuation for a multiple-reservoir system arranged in a series without the difficult and, often unobtainable, data requirements of more complex models. The equivalent reservoir term, R, approximates the joint effect of multiple reservoirs by accounting for the relative positions of the reservoirs in the system; the storages in the systems, including the temporal delay between waters from upstream and downstream reservoirs; and climatic conditions. The authors also provide an example and offer practical guidance for the application of the attenuation index to a practical example.
Citation: Cipollini, S., Fiori, A., & Volpi, E. (2022). A new physically based index to quantify the impact of multiple reservoirs on flood frequency at the catchment scale based on the concept of equivalent reservoir. Water Resources Research, 58, e2021WR031470. https://doi.org/10.1029/2021WR031470
—Georgia Destouni, Editor in Chief, Water Resources Research