General characteristics of chosen karst springs

For the purposes of this study, some typical karstic springs were selected. The springs are chosen to represent the main hydrological zones of Bulgaria. The location of the springs is represented in Figure 1. The numbering of the chosen springs is in accordance with the system used in NHGN.

Spring no. 25, Glava Panega

This spring is one of the largest in Bulgaria. It drains the main part of the so-called Zlatna Panega karst basin (according to Antonov & Danchev 1980). The karst basin is built from Upper Jurassic limestone and is part of a large anticline that is highly dislocated. The drainage basin of the spring is situated in the northern part of the Stara Planina mountain and is characterized by mountain relief. An important role in the recharge of the spring is played by the Vit River, which loses an important part of its runoff 6.5 km ESE from the spring outlet. Other main sources of spring recharge are rainfall and snowmelt in the drainage basin. The recharge from snowmelt depends not only on snow distribution within the drainage basin of the spring, but also on the altitude. The delayed snow-melt process is related to large differences in the altitudes of the basin, ranging over 700 m. The water penetration is relatively fast due to numerous karst forms. A large number of vertical and steeply inclined caves is registered in the region. The location of the spring issue is determined by the contact between limestone and Lower Cretaceous marbles, which form a barrier for the karst water. The spring is concentrated, vauclusian, rising from a steeply inclined cavern 50 m deep.

Spring no. 396, Musina

This spring drains a part of so-called Lovetch-Tarnovski karst basin (Antonov & Danchev 1980) built from Lower Cretaceous limestone. The limestone forms a shallow syncline with fully outcropping carbonate rocks. The drainage basin is a low plateau with altitude 200-300 m a.m.s.l. The basin is located in the Fore-Balkan. On the surface many dolines are observed that contribute to the fast penetration to depth of water from rainfall and snowmelt. In this region, precipitation is the main source for groundwater recharge. Geological and geomorphological settings determine the spring location. The karst water flows out from a horizontal cave. The entrance of the cave is situated in the northern part of the outcropping limestone, in the bottom of the rock cliff.

Spring no. 48, Kotel

This spring is located in the lower part of the Eastern Stara Planina mountain. The karst basin is a well-drained syncline, and the karstified rocks are Senonian limestone. The karst is of mountain type with numerous surface and underground karst forms. The vadose zone is of considerable thickness and predetermines the existence of some of the deepest caves in Bulgaria (the maximum amplitude between the zones of recharge and drainage is almost 1000 m). The recharge of karst waters is due to rainfall. The total precipitation in the region is above the average value of the country. Areas with permanent and temporal water loss are registered within the karst basin. The karst spring is situated in the eastern part of the basin and develops several outlets that form a lake. There is hydraulic connection of the water in the lake with karst water in the neighbouring cave.

Spring no. 63, Malko Tarnovo

This spring occurs in the southern limb of the syncline. Karstified rocks are Triassic marbles, marble limestone and dolomites. The recharge of groundwater is mainly due to rainfall over outcropping carbonate rocks. The relief of the region as a whole is favourable for predominantly surface runoff. In this part of the country, the snow cover is not durable.

Spring no. 59, Jazo-Razlog

This spring drains a typical alpine karst basin, the so-called Razlog karst basin (Antonov & Danchev

1980). The basin is formed in a high horst-anticline with elevation of the highlands between 2500 and 2925 m a.s.l. The spring outlet is located at an altitude of 950 m a.m.s.l. The Proterozoic marbles are subject to the process of karstification, and are fissured and weathered. Due to the typical mountain climate, precipitation is abundant and predominantly of snow type; snow cover exists until late summer. This is a barrier spring, as the location of the spring outlet is predetermined by tectonic disturbances in the east. The water flows out through a coarse proluvial formation built mainly from boulders and marble pebbles, with minor participation of sand and clay. Another spring issues in the neighbourhood, draining the higher part of the phreatic zone in the same karst basin.

Spring no. 39a, Beden

This is a barrier spring. The spring outlet is located in the northern part of the outcropping Proterozoic marbles that are highly karstified. These marbles form the largest karst basin in the Rhodopes mountain: Nastan-Trigrad karst basin (Antonov & Danchev 1980). The basin is faulted into blocks and as a result several separate karst zones are formed. The recharge is mainly due to precipitation and loss of surface water including river runoff. The karst is of mountain type with large development of surface and underground karst forms.

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