Recent hydrogeologic study of the Vis island

Abstract

The Vis Island belongs to the group of the Middle Dalmatian islands. It comprises an area of about 90.2 km 2 . Morphologically, three belts of highlands and two depressions with karst poljes are significant. The highest point on the island is Hum with 587 m a.s.l. the island's water supply is organized from the water-supply station "Korita", situated in the central part of island, in tectonically formed depression. There are two additional captured objects: the well K-l above the Komiža town and the spring "Pizdica". The most important hydrogeological role on the island have two hydrogeological barriers, one in the Komiža Bay, completely made of impermeable igneous and clastic rocks, and another one, the recently recognized relative barrier in the area of Dračevo, Plisko and Velo polje. Since the island karst aquifer is in permanent dynamic relation with seawater, classical geologic, structural and hydrogeologic investigations have been performed with application of hydrogeochemical methods taking into account the natural Chemical tracer content of groundwater and its variations in different hydrologic and vegetation conditions. Precipitation regime is very unfavorable with regard to the recharging of island's aquifer, because dry periods are usually very long. During the summer tourist season, when the number of inhabitants and fresh water consumption considerably increase, amounts of island's groundwater suitable for water supply and irrigation rapidly decrease. Sometimes, insufficient quantity of fresh water on the Vis Island causes restrictions. Concerning the development of tourist potential and the present agricultural activities, summer lack of water is a serious restrictive factor. Some results of the performed hydrogeological study, important as a basis for island's fresh water potential assessment, will be presented.

Hydrogeological Assessment and Modified Conceptual Model of a Dinaric Karst Island Aquifer

“…This aquifer is very heterogeneous, and consists of voids of different scales that are interconnected by fractures, cracks, and even karst conduits (Figure 5a,b). Similar examples have been recorded in comparable environments [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”

“…The fact that the dye injected into the BO-6 well did not appear at any of the monitored localities on the western coast of the island (Pizdica and Kamenice springs) proves that there is no groundwater flow from Korita toward the west. This means that the catchments of Korita and Pizdica are divided, and are not a single catchment, as previously hypothesized [16,38].…”

“…These SPZs were subsequently approved by the local authorities, such that the protective measures are being implemented, which is of vital importance as the island currently has no alternative water supply option. Previous research hypothesized the existence of a single catchment area for Korita and Pizdica [16,38], whereby the presumed groundwater flow was from the central aquifer and the area around Korita towards Pizdica (except for the area influenced by the radius of the wells). On the other hand, the research and analyses in the present study, including the tracer test, provided an improved insight into the system and divided it into two catchments that are separated by a zonal groundwater divide (Figures 4 and 10).…”

“…Groundwater and spring water samples for hydrochemical analyses were collected during two campaigns by previous researchers (Figure 6b): (1) during winter 1999 and (2) during summer 2000 [16,38]. From each location, one sample was taken at the hydrological minimum (in 2000) with respect to GWL, and one close to the maximum (in 1999).…”

Exceeding Turbidity versus Karst Spring Discharge during Single Rainfall Events: The Case of the Jadro Spring

“…A proposal for a technical solution to this problem can be found in [10]. Detailed hydrogeological and hydrological information about the Jadro Spring has been published in several publications, e.g., [44][45][46][47]. Below is a summary of previously published information relevant to this study.…”