Groundwaters of the "Valjevo Karst" Area (Western Serbia)

. " Valjevo karst" is an area of about 780 km2 in a broader sense, while the uncovered karstified limestone makes about 330 km2. It is a part of the Inner Dinarides (Western Serbia). In the litho-stratigraphic view, the karstified limestones of Middle-Upper Triassic dominate, in which karst aquifers are formed. Analysis and systematization of the available data of hydrogeological and other relevant research is carried out. A branched network of groundwater traces between swallow holes and discharge points is presented as well as main features of sixteen karst springs (or scattered discharge zones) and nine (group of) wells, divided into five sectors. Average karst aquifer discharge of the whole area is calculated on 5.18 m3/s. Total minimum flow rate of the analysed karst springs and discharge zones is estimated at 1.2 m3/s, while the total flow rate of the analysed wells is estimated at about 0.3 m3/s, which makes about 1.5 m3/s of total (minimum) discharge. All analysed waters are low-mineralized (<1 g/l), while temperatures range from 9-35 °C. Use of the waters is multipurpose: municipal and local water supply, commercial bottling, recreational pools etc.


IV-
Northern karst oasis. The source for municipal water supply of Lazarevac and Lajkovac (loc. Nepricava) (Fig. 2) is based on the six deep (120-350 m) drilled wells that capture app. 1201/s of karst ground waters (D okmanovic et al., 2012). Total thickness of overlaying Miocene and alluvial deposit is 20-100 m.

V-
Southern karst oasis. Two springs are note worthy in the southern oasis, in the contact zone with the Paleozoic formation (Fig. 2, Fig 3): Gornja Tresnjica (Qav=80 1/s) and the Taor springs (dis charge zone), that is partially captured for munici pal water supply of the Kosjeric village. The flow rate of non-captured part of the Taor springs varies in the range 17-250 1/s (Petrovic, 2013). Supple ment water supply of Kosjeric is based on the cap ture of karst water by a drilled well (Fig. 2), during the recession of Taor springs.

Groundwater quantity
There is no continuous ( where: D-runoff; P-precipitation; Er-evapotranspiration; R-surface runoff; Ie-infiltration (in karst aquifer) Evapotranspiration was calculated according to the Turc formula: "L" parameter is calculated as: where ,,T" is the average annual air temperature.    II andIII (2000-2015).

Conclusion
An analysis and systematization of available data derived from previous researches is given in the paper.
VK is an area of about 780 km 2, while the uncov ered karstified limestone makes about 330 km 2. Ac cording to the spatial distribution of the most important discharge points and zones of the karst aquifers as well as available data of proven ground water traces, the area is divided into five sectors. A branched network of groundwater traces between swallow holes and discharge points is presented as well as main features of sixteen karst springs (dis charge zones) and nine (group of) wells. Average karst aquifer discharge of the whole area is calcu lated on 5.18 m 3/s. Total m inim um flow rate of the analyzed karst springs and discharge zones is esti mated at 1.2 m 3/s, while the total flow rate of the analyzed wells is estim ated at about 0.3 m3/s, vvhich makes about 1.5 m3/ s o fto tal (minimum) discharge.
All analysed vvaters are low-m ineralized (<1 g/1], while tem peratures range from 9 -3 5 °C. Use of the w aters is m ultipurpose: municipal and local w ater supply, commercial bottling, recreational pools etc. There is no adequate (system ic) quantitative monitoring of karst groundwater, neither in term s of spatial schedule of points, nor in term s of continuity.
None of the springs or discharge zones is observed, and there is only one observed hydrometric profile (Degurić, on the Gradac river).
Regulation of (unfavourable) natural discharge of Paklje and Gradac springs (sector I) have been considered by some researchers, but the realization did not happen given that the construction of the "Stubo-Rovni" dam and reservoir (on the Jablanica and Sušica rivers) was planned several decades ago, for the w ater supply purpose of the entire Kolubara district. In other sectors regulations have been successfully carried out at several sites by drilled deep wells, for municipal w ater supply, therm al w ater use and commercial bottling.
Regardless of the national and district w ater m anagem ent plans, the VK aquifers should be kept under continuous quantitative (discharge rates of springs/w ells and GWL) and qualitative (because of high vulnerability and pollution hazard) monitoring, in order to preserve and keep this exceptional natural water reservoir in good status.