Spatio-temporal variations of runoff and baseflow components using isotopic methods

Abstract: The quantification of runoff and base flow components of hydrograph in terms of water fluxes and chemical composition is an important issue in catchment hydrology. Particularly in a riverine system contribution of hydrograph components depends on the initial state of the various hydrological reservoirs and on the characteristics of the hydrological input (precipitation). Baseflow reacts slowly to precipitation and is usually associated with water discharged from groundwater storage. By separating the baseflow (pre-event water) from the stream discharge the contribution of surface and groundwater can be quantified using stable isotope tracers.

The stable isotopes of water namely 18O and 2H, which are part of the water molecule, are typically considered in the hydrological investigations owing to their spatio-temporal variations resulting from isotope fractionations along different phase changes of water cycle and diffusion. Various atmospheric processes such as advection, condensation and evaporation directly impact the composition of stable water isotope, which consequently influence the groundwater isotopic composition. As a part of the Isotope Hydrograph Separations (IHS), study has been done for Kabini catchment by applying end member mixing analysis (EMMA) to quantify the pre-event water and event water.