Reservoirs are water management facilities that allow the regulation of the natural runoff regime. Depending on the natural characteristics of the hydrological system, the need for water and the volumetric capacity of the reservoir, and the characteristics of the evacuation organs, it is possible to manage the water resources of the basin. The increasing depletion of natural water resources and the increasing problems with meeting water needs have emphasized the need for the construction of reservoirs, often with multi-year equalization, as an integral element of integrated water resources management. Water resources management includes a number of activities such as planning, design, construction, management, maintenance, monitoring and control of constructed facilities, in order to assess and increase their efficiency. Accordingly, it is necessary to specifically plan all activities in relation to reservoirs as key facilities for managing the water regime of a basin. Keywords: multipurpose reservoir, water resources, sediment, catchment area, sedimentation, GIS modeling

In a series of exogenous and endogenous processes that cause enormous damage almost all over the world, land erosion and torrential flows occupy a special place. Torrential flows are formed practically unnoticed and represent a mixture of a large amount of eroded material from mountainous and hilly areas, which, together with water, flows down the ravines formed at a high speed into the lower parts. These streams, which in dry weather have very little flow or their beds are completely dry, in a short period of time destroy everything in front of them, from bridges, roads, to other buildings. They fill canals and agricultural land with silt, and often endanger populated areas, often with human casualties. A true example of the above was witnessed in the destruction of settlements in the municipality of Konjic and municipality of Jablanica in October 2024, where torrential rains caused huge human losses and material damage in a few hours.

The main task of the multi-purpose reservoir "Modrac" is to regulate the water regime in a given basin while making decisions on the amount of water released, as well as the amount of water that needs to be retained for future use. Decisions are made on the basis of available data and forecast data. Since no forecast model has been developed, the operator of these complex processes must rely on forecasts that are more or less precise. In practice, dam and reservoir operators, in most cases, usually follow the rules of the curves (volume, flow, etc.), which determine the actions to be taken depending on the current state of the system. With the construction of the Modrac dam in 1964, the reservoir of the same name was formed. The primary goals were to provide technical water for industry in the Tuzla region and mitigate downstream floods, as well as recreation and other purposes. The paper presents an analysis of the runoff coefficient in the correlation of annual precipitation and mean annual inflows for the catchment area of the multipurpose reservoir "Modrac" for the period 1999 - 2024. Keywords: multipurpose reservoir, runoff coefficient, precipitation, inflow, catchment area

Determining the erosion characteristics of a catchment area is very important in managing the catchment area itself, as well as in managing water resources, especially if it is a multipurpose reservoir. Factors that determine the erosion process in a watercourse catchment area, or the sediment regime of a watercourse, could be divided into those that practically do not change or those that do not change significantly over a period of several years, and factors that are subject to change during the year, depending on meteorological and climatic changes over the catchment area. For preventive action and prevention of erosion, and thus flash floods, and filling of reservoirs, it is necessary to analyze and determine precisely the erosion coefficient of the catchment area. On the other hand, water resources management includes a number of activities such as planning, design, construction, management, maintenance, monitoring and control of constructed facilities, in order to assess and increase their efficiency. Accordingly, it is necessary to specifically plan all activities in relation to reservoirs as key facilities for managing the water regime of a catchment area and processes within the catchment area. Keywords: erosion, sediment, meteorological changes, climate change, erosion coefficient, water resources, sediment, catchment area, deposition

Increasingly, and often mutually conflicting requirements for the use of water resources, there is a need for more complex management methods, including the management of the volume of reservoirs. Silt filling of reservoirs is one of the most well-known problems of river hydraulics. Dams and reservoirs, created by damming river flows, cause the retention of river sediment (drag and floating sediment) that comes from the gravitating basins, or sub-basins of the reservoir's tributaries. By analyzing the sediment transport on the tributaries, and the total amount of sediment deposited in the Modrac multi-purpose reservoir, real data are obtained on the amount of sediment introduced into the Modrac multi-pupose reservoir, the dynamics of sediment input, and the degree of pollution of this type of water body. The Modrac multi-purpose reservoir is the only available water resource in the region of Tuzla and its surroundings. Acknowledging the fact that the useful volume of the reservoir is limited, and that over time the reservoir is filled with dragged sediment and coal dust as floating sediment, and that consumers - the population, industry and others must be provided with a water supply with a high degree of safety. Excess water needs to be used to the maximum for the purpose of electricity production, and there is a need to optimize the system, i.e. more efficient management of the water resources of the reservoir, i.e. to prove the maximum utilization of the reservoir while continuously providing all the necessary amounts of water to which the Modrac multi-purpose reservoir is connected.

Multi-purpose reservoir Modrac is the most important water resource in Tuzla canton( northeastern Bosnia and Herzegovina). Ecologically acceptable flow on dam Modrac is not adjusted with the latest Rulebook about methods of determining ecologically acceptable flow. Modrac reservoir with upstream and downstream flow of Spreca river is categorized as a protected water resource due to its susceptibility to eutrophication and according to current legislation, requires a second level of ecologically acceptable flow assessment. This paper shows the methods used to determine ecologically acceptable flow on the Modrac dam, respecting the fact that reservoir Modrac is declared as protected water resource. The given calculation of ecologically acceptable flow is made for II level of evaluation

Mufid Tokić1 Anadel Galamić2 Jasmin Hrnjadović3 Omer Kovčić4 UDK: 556.1:627.81 DOI: 10.14415/konferencijaGFS2019.072 Summary: According to the available existing documentation and various previous studies, the flow of water into the "Modrac" accumulation is not defined directly, by measuring the flows on the main creek Spreca and Turija, but indirectly, over the level and volume of the accumulation, as well as data on the discharge of water from the reservoir. In this way, a series of average daily values of inflow into accumulation was obtained for the period from 1980 to 2012. year. Interpretation of these data was done in the form of variation of annual inflows in the observed period, as well as average flow curve curves. By reviewing the previous measurements and surveys, it can be concluded that there is a more pronounced cyclicality of inflows over a longer period of time, with driers of dry and rainy periods. On the other hand, having in mind the natural correlation between the inflow of water and the spread of the deposit, it is logical to hypothesize that at the time of the hydrological maximum, the input is higher in the accumulation. Another important indicator of the hydrological regime of the lake is the duration of the inflow into the accumulation "Modrac". This curve points to the vast hydrological regime of the watercourse in the basin of the reservoir. In this regard, it should be noted that all watercourses in Bosnia and Herzegovina and the region, with a basin area of up to 1000 km2, have such a regime. Bearing in mind the similarity of physical and geographical conditions in the region, this analogy is quite logical. The hectic hydrological regime is characterized by a short duration of large waters and a very long duration of small water, as well as a large flow range (Qmax / Qmin).

Jasmin Hrnjadović1 Anadel Galamić2 Mufid Tokić3 UDK: 519.6:628.1 DOI: 10.14415/konferencijaGFS2019.074 Summary: The water supply system is a planned and meaningfully connected set of facilities and activities aimed at ensuring sufficient quantity of water in the most economical way. Defining the functional dependence of the hydraulic parameters of the water supply system is crucial because it enables the calculation of unknown values based on the appropriate available or measurable values. „Spline“ interpolation is one of the methods by which it is possible approximately, but with sufficient accuracy, to define the functional dependence of hydraulic parameters if we have known values at certain characteristic intervals that can be measured or calculated by one of the numerical methods. "Spline" interpolation denotes the method of constructing a function within the range of a discrete set, which approximates the already known points. The result is a function, or set of functions, by which it is possible to calculate the value of an unknown function for any value of the variable at a defined interval. The specific application of this method will be shown on the example in this paper.