Are hydrological indices capable of providing credible e-flow suggestions?

Hydrological index methods are among the pioneer methods of e-flow assessment and are bestowed by the limited requirements in terms of data, time and expertise. As a result, they serve as a way out in the studies that are circumscribed by these requirements, especially in countries like India where e-flow assessment is still at rudimentary level. However, these methods bring with them the flavor of intrinsic hydrological, meteorological, geomorphological as well as ecological set-ups of the region for which they were established through some observation based or hypothetical conditions. Based on either of the concept of i) Percentage of Flow (POF), ii) Range of Variability (RVA) and/or iii) Flow Duration Curve (FDC); these indices result in flow values that may or may not lead to similar effects on the hydrological, geomorphological and ecological settings as are expected for the region in which they are developed.

In this study, we attempt to verify the credibility of hydrological indices based on the concept of POF and RVA for e-flow assessment of 24 sub-systems of Ganga River Basin that represent spatio-temporally diverse hydro-meteorological conditions as well as enormous geomorphological and ecological diversity. Applicability of these indices is verified in terms of their ability to acknowledge the pronounced seasonality that underscores Ganga hydrology. Effectiveness of the indices in terms of their ability to provide suitable e-flow suggestion that can accommodate societal as well as ecological and geomorphological needs is also verified.