[en] Karstic aquifers with their potentially high infiltration capacity comprise of important groundwater reservoirs, which are also prone to rapid contamination due to relatively high flow velocities. These aquifers almost always posses an extremely heterogenous distribution of geohydrologic properties and usually have unmeasurable hydraulic head distribution. Additionally, the mountainous karstic aquifers are highly tectonized and have complex flow geometry as dictated by the intercalation of permeable and impermeable geologic units. In such systems, groundwater flow dynamics can not be determined with the present knowledge of analytical or numerical approaches of flow dynamics as used in distributed parameter models. Lumped parameter models present an alternative way by handling the whole aquifer as a system whose internal details are not known. The 'system analysis' approach allows the use of environmental tracer data to analyze the groundwater residence time distribution provided that tracer input series and observations on system's output is available. In this approach, all parameters and processes affecting the transport of water mass or tracer are lumped into one single equation, the system response function, which is user-selectable. Developments in system analysis science and in associated mathematics enable the derivation of system response functions for more complicated conceptualizations under steady or unsteady state conditions (i.e. variable in/out flux, variable volume of system components). A bundle of 15 different lumped parameter models (LUMPED UNSTEADY 'LU'), which are capable of using ³H, ⁸⁵Kr, CFCs and SF₆, was developed to run under unsteady flow conditions. LU models are capable of simulating tracer transport in plug and exponential flow reservoirs, which may be connected in any combination of series or parallel fashion and may have by-pass flow and/or dead volume components. The LU models have been applied to mountainous Aladag karstic aquifer in the Eastern Taurids Range of southern Turkey. The aquifer lays over an area of 750 km², extends between 400 m and over 3500 m elevations and comprises of 5 carbonate nappe slabs separated by impermeable covers. The whole system is drained by several springs, which are located in tectonic windows of overlying impermeable ophiolitic nappe. The minimum total groundwater discharge was estimated to be 31.5 m³/sec. Our environmental tritium based lumped parameter modeling attempts in springs of shallow and deep groundwater circulation resulted in plausible residence time distributions and were in agreement with the hydrogeologic conceptualization of the flow systems. In general, the springs with shallow circulation conforms well to serially connected plug and exponential reservoirs with by-pass flow of varying degree while those of deep-circulation are in agreement with exponential (with some dead volume) and plug flow reservoirs. The same model runs with CFCs resulted in higher residence time values than those of tritium. The difference may be attributed to the presence of deep unsaturated zone, which might have caused by a time delay in transport of this tracer to water table. The results of unsteady and steady lumped parameter models for the same field cases were also discussed in view of uncertainties in the model inputs