GROUND-WATER STORAGE CALCULATION IN KARST AQUIFERS WITH ALLUVIUM OR NO-FLOW BOUNDARIES

Abstract: The determination of water-budget parameters, such as change in storage and subsurface inflow and outflow, is costly and unreliable due to heterogeneities of karst aquifers. Some karst aquifers may have one or a combination of boundaries such as impermeable formations, alluvial aquifers, and known ground-water divides. Karst water only discharges through springs or flows to the adjacent alluvium. A new procedure is proposed to estimate volume of storage in region during the dry season in these settings. The subsurface inflow and outflow can be measured in the adjacent alluvium using equipotential and flow lines, cross-sectional area, and transmissivity of the alluvial aquifer. The dry season makes it possible to calculate the karst spring recession coefficient and karst aquifer dynamic volume at the beginning and end of the hydrological year. The change of storage is the difference between the dynamic volumes of the karst aquifer at the beginning and end of the hydrological year. The volume of water which flows to the adjacent alluvium or spring is measured by plotting the discharge as a function of time and estimating the recession coefficient at the beginning (or end) of the hydrological year. Known equations are used to calculate the dynamic volume of springs. A general equation is proposed to calculate the dynamic volume of a karst aquifer when there is a combination of springs, and subsurface inflow and outflow from the karst aquifer. The proposed method is applicable to the Zagros Folded Zone in Iran