Hydrological System of the Plitvice Lakes—Trends and Changes in Water Levels, Inflows, and Losses

Josip Rubinić,Maja Radišić,Andrijana Brozinčević,Igor Ružić

doi:10.3390/hydrology8040174

Abstract

The Plitvice Lakes National Park is inscribed on UNESCO’s World Heritage List. The lake system is composed of 16 cascading lakes of different sizes separated by tufa barriers, which are the park’s key phenomenon. The lakes are characterized by highly diverse trends of the characteristic hydrological indicators—mean annual water levels, discharges, and tufa barrier growth. The analyses carried out in this paper identified that in the period before the early 1990s, Kozjak Lake had a trend of decreasing discharges, together with a trend of increasing water levels and growing tufa barriers. In contrast to this, in the period after 2001, a trend of increasing discharges was recorded, as well as a trend of decreasing water levels and decreasing tufa barriers. A potential cause of the barriers decreasing in size were the extremely high discharges during the last decade, which resulted in increased erosion of the tufa barriers. Losses of water due to the sinking from the lake system as well as the upper Korana course were confirmed, and it was identified that during the analyzed period the losses had not changed significantly. It was determined that the losses of water from Kozjak Lake occurred during low-water periods; however, they depended not only on the quantity of water flowing through the lakes but also on the hydrological conditions underground. The analyses carried out and the methodological procedures used in the analyzed area of the Plitvice Lakes are useful examples for the performance of analyses at similar lakes in karst formed by tufa deposition processes.

Highlights

Tufa precipitation and sedimentation processes in water systems cause the formation of tufa barriers with various morphological characteristics
The run-off dynamics are affected by the total volume of the lakes, which makes the system almost lag behind the current precipitation and hydrological conditions, in relation to the intra-annual oscillations of the lake system and the possibility for a certain quantity of water to be retained in the active volume of particular lakes above the flow over the barriers
The study identified that the regime of fluctuating water levels in the lakes and the flow of water through the lakes was affected by the morphological changes in the geometry of the lakes themselves due to the variable growth of the tufa barriers that form the lakes

Summary

Introduction

Tufa precipitation and sedimentation processes in water systems cause the formation of tufa barriers with various morphological characteristics. The barriers formed in such environments are specific water systems, often recognized as very valuable phenomena and protected as unique natural systems. Many of these systems are inscribed on UNESCO’s World Heritage List [1], such as Pamukkala (Turkey), Jiuzhaigou (China), Yellowstone National Park (USA), Badad-e Surt (Iran), Band-e Amir (Afghanistan), Huamlong (China), the rivers of the Barkly karst (northern Australia), Hierve el Aqua (Mexico), Hanging Lake (USA), and Plitvice Lake (Croatia), which was the focus of the research presented in this paper. The formation of the barriers is largely connected with thermal springs and the chemical precipitation of tufa at locations with suitable physical conditions (temperature, water flow, etc.). To the authors’ knowledge, estimation of the growth and erosion of the barriers based on the distributed hydrological estimations for the whole profile of the barriers has only been carried out at the Plitvice Lakes [15] and Krka River [16]

Methods

Results

Conclusion