Estimation of specific yield in bedrock near-surface zone of hilly watersheds by examining the relationship between base runoff, storage and groundwater level

A catchment-scale method for estimation of specific yield (Sy) in the zone of groundwater level fluctuation is proposed. It is applicable to hilly watersheds, where deep groundwater discharge – not drained by local streams as baseflow – is small and can be neglected. Therefore, it is mostly employable for bedrock flow systems, dominated by shallow unconfined fractured rock aquifers. Method provides an estimate of specific yield (Sy) by combined analysis of streamflow recession, storage/runoff relationship and groundwater level fluctuation (Q-S-H). For groundwater storage (S) values evaluation, river discharge (Q) master recession curves are constructed and interpreted. The method produces as more reliable results as number of groundwater level observation sites increases. As example, it is demonstrated at the Levočský potok Brook watershed (Western Carpathians, Slovakia), built by fracture porosity dominated Paleogene sediments. Estimated characteristic Sy value is from the interval 0.001–0.002 and 0.002–0.005 for low and medium storage/runoff conditions – or bottom and middle part of GWL fluctuation zone – respectively.