The paper presents some procedures for identification of low flow required for taking preventive measures in the rivers with no comprehensive hydrological observations. Besides using time - space parameters, temparery or simultaneous hydrometric observations in the observed rivers are also recommended. The paper concludes with the presentation of relevant low flow calculation results for one river in Zlatibor region (Serbia, Yugoslavia), which has not been examined so far.

Withdrawal of water from surface water network should be concerned with preservation of the environment, meaning that the low flow regime in streams should be preserved within the range of natural regime. In order to formulate criteria for minimal allowed flows in streams, it was necessary to perform statistical analysis of low flows in rivers in Serbia (Yugoslavia). The criteria for water withdrawal are proposed on the basis of characteristic ratios between minimum and mean flows. Different criteria are proposed for cold and warm seasons.

In this paper we have pointed out the hydrogeological condition in the catchment area of the Jablanica river in the south Serbia (Yugoslavia). The two units are separately presented here. The first one is mountainous part of the catchment area upstream of the gaging station of Lebane and the second one is the part of the terrain in the plain down stream to the river mounth near Pecenjevac. The hydrogeological characteristics of the two mentioned regions are given to explain the reasons of existing the constant flow of the Jablanica to Lebane and its disappearing course in the period of recession in the plain downstream. The quality of water in the Jablanica river at Lebane is good. Down stream of this gaging station the waste water collector flows into the river. In the part of recession period the ratio between them is unfavourable. We have also discussed the quality of water at the gaging station of Pecenjevac and pointed out the function of sandy-gravel deposits in the process of natural purification of the Jablanica flow.

The paper shows available water resources potential of karsts spring waters of Carpatho-Balkan region of east Serbia. Basic elements of water balance are also given, as well as quantitative indicators of low flows. Karsts spring yield is compared to the domicile waters of Serbia. We can also read certain comments and see an estimation maximum usage of these karsts waters.

A new concept for the determination of reference low flows of natural watercourses - the guaranteed minimum - has recently been introduced into the water management practice. Appreciating the significance underlying the definition of low flows in all segments of water management (municipal and industrial water supply, wastewater discharge, irrigation, navigation, hydropower, water protection, etc.), the author believes that all aspects of the problem must duly be considered, examined and identified. The doubts and issues raised by the guaranteed minimum concept in the domain of random-probabilistic phenomena, such as river discharge, are discussed in the paper.

The paper contains description of potential approaches to better defining of distribution curves parameters for low water levels on water courses that sporadically dry up, also including additional information on the length of dry period. Computed results are given for the example of minimum annual discharge on several rivers in the Velika Morava basin, Serbia (Serbia and Montenegro).