Karst Lake’s Dynamics Analysis as a Tool for Aquifer Characterisation at Field Scale, Example of Cryptodepression—Red Lake in Croatia

Abstract

This paper analyses complex hydrological and hydrogeological properties of a deep karstic lake and its surroundings. Red Lake (Croatia) is a cryptodepression in the karst massif rich in well-developed extreme surface karst forms and underground conduit system. It is interconnected with other close water bodies and offers information on groundwater movement and characteristics. The article analyses hourly data on precipitation and water levels in Red Lake and compares them with data on discharges from near Opačac Spring for a period of five years. Data gaps in the record caused by operational interruptions of the measuring equipment were compensated by the use of neural networks. The study of the hydrodynamics of karst surroundings under recession was conducted by observing the receding water levels and corresponding lake’s volumetry. By isolating recession periods from the record of integral water volume change, some of the common techniques in recession analysis were performed aiming to acquire new knowledge on the hydrogeological regime of the karst system at the field scale. Additionally, spectral analysis was used as another tool of karst system characterisation since it enables the signal decomposition in the frequency domain and detection of dominant flow processes.