# Geohydroology of a Reference Mediterranean Catchment (Cilento UNESCO Geopark, Southern Italy)
## 1 Introduction
EC-based estimates of the event water contributions to streamflow components have low measurement uncertainty [20] because, in contrast to the isotopic composition of the event and pre-event water, the difference in the EC of event and pre-event water can be very large, frequently two orders of magnitude and, occasionally, even three [21]. In addition, EC-based hydrograph separation is possible for nearly every event, and measurements of EC are still much cheaper and can be recorded continuously in the stream flow at a very high frequency [22]. This last advantage matches with one of the principal criteria suggested by the UNESCO's Biosphere2 Program, based on the simplicity and effectiveness of the techniques and monitoring system to be adopted in protected areas, moreover for that recognized as the Biosphere Reserve by UNESCO [3]. Following this suggestion, for complex catchments in terms of geology, geomorphology and hydrology and with a size over 1 km\({}^{2}\), the use of cheaper methods than the site-specific tracer, such as the EC method, are recommended. Clearly, EC-based hydrograph separations must be based on a well-defined (object-oriented) hydro-geomorphological identification of the source areas and flow pathways [4; 8]. The researchers in [8] suggested a modified mass balance method, applied to daily EC data, by using a \"cascade approach\" allowing the separation of the runoff in more than two components, performing a useful and simple daily hydro-geochemical analytic chart. The daily hydro-geochemical analytic chart was used also in [4] for the objective variable source area identification and mapping, using the GmS_UNISA object-based procedure applied to the research catchments. The low frequency hydro-geochemical data analysis in space and time does not allow for the full understanding of the biochemical and geochemical streamflow processes, which can only be characterized by high-frequency monitoring and real-time monitoring systems [23]. The high temporal resolution allows a more feasible detailed catchment analysis [18] helping to identify sources and pathways of nutrients [24]. From this perspective, after a daily-monitoring training period (2013-2014), from 2015 the Ciciriello catchment was further equipped with instrumentations for discharge (Q) and electrical conductivity (EC) measurements at 5-min intervals, in order to improve it as a reference experimental Mediterranean headwater catchment. The high frequency dataset was used for event scale analysis and it provided new insights on the geo-hydrologic behavior of the reference catchment. To this end, a comparative analysis was performed between the event hydro-chemograph at five-minute intervals and the location of the event data on the daily chart was used to characterize the event with respect to the runoff components and flow pathways. To improve the identification and the classification of runoff event types, an event scale hysteresis analysis was carried out. In fact, as for many natural phenomena, the EC more clearly featured nonlinear behavior when compared only to discharge (Q) or stage (H) data. This specific behavior, that was not described by linear models, is typically described with a hysteretic loop that, for such phenomenon, allows the identification of the events past history. Recent studies were focused on the hysteresis analysis to identify different source areas of solute contents in the runoff [25; 26; 27], sediment dynamics in the catchment [1] or the timing of the runoff component [22; 28]. The hysteretic relations can be analyzed with indices that allow the comparison of hysteretic loops at various space- and time-scales, to develop a classification of hysteretic patterns, to detect changes in hysteretic loops or to test the ability of models to reproduce the observed hysteretic behavior [29; 30; 31]. This paper aims at identifying a perceptual model of the experimental Ciciriello headwater catchment by using the hydro-geomorphologic surveys and monitoring system and the hydro-chemical analysis.