Inferring changes in dynamic groundwater storage from recession curve analysis of discharge data

Groundwater storage is an important element of terrestrial water storage. It influences the baseflow component of the river discharge which constitutes the majority of the outflow of Polish rivers. An evaluation of changes in the dynamic groundwater storage from point measurements of groundwater levels is usually a difficult task as groundwater data are scarce in time and space. Alternative approach involves recession curve analysis of discharge data. This study describes an approach to estimate the long-term changes in dynamic groundwater storage from daily discharges on a basin scale. Recession curve analysis is applied for identification of groundwater system functioning through derivation of master recession curve. The Master Recession Curve Tool developed by Lamb is used for automate analysis. Then results are coupled with a concept of nonlinear reservoir expressing discharge-storage relationship. As a result the volume of the groundwater storage and its temporal changes are derived on a yearly base, as a difference between highest values of storage during spring season and lowest values appearing in late summer or early autumn. The results show high annual variability of dynamic groundwater storage. The approach is presented on the example of lowland basin situated in central Poland, on the Mazovian Lowland (N 52°14' - N 52°14' and E 11°10' - E 11°10').