Flow-duration analysis in the context of preliminary design of small hydropower plants: from uncertainty assessment to regionalization

The preliminary design of small hydropower plants is typically relied on empirically-derived flow-duration curves (FDCs). This approach allows for estimating characteristic quantities of interest, such as the mean annual energy production, the mean annual water volume captured by the turbines and the mean annual time of turbine operation. In this work, we aim to parameterize the daily FDCs in statistical terms, i.e. by fitting suitable distribution functions and express their uncertainty through confidence intervals. The fitting procedure emphasizes to the accurate representation of the main body of the distribution, since the high flows cannot be captured by hydropower plants without sufficient storage capacity, while the lower ones are reserved for environmental purposes. The parametric FDCs are next used to provide statistical predictions of the desirable design variables. The methodology is applied to a sample of Mediterranean catchments with different hydroclimatic and geomorphological characteristics. Based on the outcomes of this analysis, we also attempt to establish regional relationships, by associating key statistical and design quantities with lumped properties and hydrological signatures of the studied catchments.