Implementation of flow duration curves for evaluating the environmental flow

In this research work, the implementation of Flow Duration Curves (FDC) was assessed, as a mean of estimating the environmental flow (e-flow) in rivers segments in Greece. The FDC of fifteen river basins varying in size and geomorphological characteristics and covering a wide area of mainland Greece, were derived by using high quality monthly discharge measurements of two years period. The e-flows were first calculated by applying the current Greek regulation method, which makes use of measurements of only the summer and September months, and by relating the e-flow as a percentage of the Mean Annual Flow (MAF). The e-flows were then plotted upon the FDC and compared with specific quartiles. The results show that the e-flows calculated by both the Greek regulation methodology and the 10% of MAF are a very good approximation of the 90% quantile of the FDC (Q90) while the 30% MAF falls very close to the 70% quantile (Q70). Therefore this study suggests that the Q90 could be used insted of the Greek regulation method, as it produces quite similar but safer (higher) discharge values. It was also indicated, that a strong correlation of 10% MAF to Q90 and 30%MAF to Q70 exists.