Basic Concept for Water Balance Assessment in Serbia
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Basic concept for water balance assessment in Serbia Brankica Majkic, Prof. Dr. Stevan Prohaska, Dr. Dragoslav Isailovic Institute for the Development of Water Resources “Jaroslav Cerni” Jaroslava Cernog 80,11226 Pinosava, Belgrade, Serbia [email protected] Abstract: This paper presents the basic characteristics of a developed concept for water balance assessment in Serbia. The starting point is a baseline water-balance equation which reflects all water inputs into a specific catchment area and, following the inclusion of all output and return components (water abstractions and discharges), the available water resources are obtained for a given territory during the discretization period of time. Specifically, the entire territory of Serbia has been divided into nineteen water management balance units to which the established water balance equations apply. The paper highlights interactions between water management balance units. Procedures for the definition of individual components of the established water balance equation are presented at the end of the paper. The paper illustrates a practical example in which the developed concept is used to assess the water balance for a water management balance unit within the territory of Serbia. Key words: water balance assessment, water management balance unit, water inputs, water abstractions, water returns, water discharges. Introduction This paper describes the methodology which was used to assess Serbia’s water balance. Since previous methodologies date back to the 1980-1988 period (1980 Methodology for Water Management Balance Assessments in the Republic of Serbia, Excluding Autonomous Provinces; 1984 Water Management Master Plan Development Methodology for the Autonomous Province of Vojvodina; and 1988 Water Management Master Plan Development Methodology for the Autonomous Province of Kosovo), they had to be re-assessed and new methodologies developed, which rely on new knowledge, current data, and the present institutional organization of Serbia. To develop a concept for the water management balance of Serbia, the types of data and methods for data collection and archiving had to be studied and evaluated. The water management balance of an area is generally prepared for the following major purposes: 1. Systematic monitoring of quantity and quality variations in available surface water and groundwater resources, and of water abstractions and discharges for and by all users; 2. Updating, to reflect current knowledge and international trends; 3. Systematic monitoring of changes in water resources and provision of reliable data for the preparation of water regime management plans and water management master plans, and for timely undertaking of measures aimed at the conservation, protection and development of water resources; 4. Evaluation of current methods and procedures for collection of data for all elements of the water management balance and for recommending data acquisition and archiving improvements; 5. Definition of principles to be used in the selection of balance profiles and the territorial division of the country for purposes of management of available water resources; 6. Assessment of the availability and quality of water resources within various territories; and 7. Making recommendations for inter-institutional integration of all factors relevant to the water balance. BALWOIS 2008 – Ohrid, Republic of Macedonia,-27,31 May 2008. 1 This paper presents the water balance equation and the division of Serbia into water management balance units. Methodology for water management balance assessment The development of a methodology for water balance assessment is difficult due to a number of practical problems. The methodology proposed for a water management balance assessment should apply to current conditions (problems associated with the scope and types of collected data), and should be adjustable to changes over space and time (problems associated with the requirements set out in the EU Water Framework Directive). Hydrologic cycle, water balance, and water management balance The hydrologic cycle is a global geophysical process which underlies the concept of hydrology; it reflects the principle of the maintenance of water mass in all of its three phases on Earth. In essence, the hydrologic cycle is a natural phenomenon which governs the global transformation of water between the atmosphere, biosphere and hydrosphere. Natural circulation of water constitutes the basis of renewable freshwater, in other words, the balance of water which is available for use in all human activities and by the plant and animal world on the planet. The major components of this balance are: the amount of water vapor in the atmosphere (W), precipitation (P), evaporation (E ), runoff (Q), variation in surface water and groundwater volume (W), and groundwater flow (G) during a specific time interval. The conventional and fundamental water-balance equation, which addresses all of the above parameters and applies to a limited watershed surface area (A), delineated by boundary (I), may be expressed as follows: ∂W 1 r E − P + Q + + Gndr = 0 (1) ∂t A ∫ Where, in addition to the above, n - is the unit vector perpendicular to the contour of the unit surface area, and t - is time. Taking this equation as a starting point, the general water-balance equation for a single time interval Δt and a limited real unit surface area of the watershed may be expressed as: P ─ E = Q + ΔG ± ΔW (2) Where: P - is the total precipitation which reaches the unit surface area of the watershed during a given time interval; E - is the total evapotranspiration from the same surface area during the same time interval; Q - is the total runoff from the same surface area during the same time interval; ΔG - is the total groundwater flow for the same surface area during the same time interval; and ΔW - is the total change in surface water and groundwater volume within the same surface area during the same time interval. The above parameters are known hydrologic quantities which can be calculated from hydrologic and meteorological data. However, from a water management perspective, the balance of water available within a watershed is only one of the major issues which water management and sustainable development address. The other major issue reflects the use of water in all spheres of human activity and water discharges from all types of water uses, which constitute a part of the so-called water management balance. In essence, as pointed out above, the water management balance is the ratio of available water resources (defined by the water balance) to used and discharged water, in terms of quantity and quality over time and space within a particular portion of the watershed, which results from the so-called Water Management Cycle, or the circulation of water from the point of abstraction for any type of use. Since the water is used but not expended, most of it returns to streams and the ground, whereby available water is increased by a level roughly equal to the difference between abstracted and discharged water. Based on the above, the total abstraction for various uses (ΔQw) should be subtracted and the total discharge from all types of uses (ΔQr) should be added to the baseline water-balance equation. Consequently, the general water management balance equation for a unit catchment area becomes: P ─ E = Q + ΔG ± ΔW + ΔQr - ΔQw (3) The securing of optimum and sustainable control of the water management balance over time and space within a territory constitutes the essence of sustainable development, use, and management of renewable water resources within that territory. Since a real catchment area or water district can have multiple inputs and outputs of surface water and groundwater, as well as several intakes for water uses and outlets of used water, the above water management balance equation acquires the following general form: NIJPEZPOV w ul i−+−=+ iz j p p e e z z pov pov (4) ∑∑∑∑∑∑∑(Δ= V )n (V ) (V ) (V ) (V ) (V ) (V ) n=======1111111 i j p e z pov Where: N w is the change in total volume of groundwater and surface water within the water ∑(ΔV )n n=1 district; I ∑(Vul)i is the total inflow of groundwater and surface water into the water district; i=1 J ∑(Viz) j is the total outflow of groundwater and surface water from the water district; j=1 P ∑(Vp) p is the total precipitation which reaches the water district; p=1 E ∑(Ve)e is the total evapotranspiration from the water district; e=1 Z ∑(Vz)z is the total abstraction of water for all types of water uses within the water district; z=1 and, POV ∑(Vpov) pov is the total discharge of water from all types of water uses within the water pov=1 district. These parameters of the water management balance reflect highly complex changes which occur during the process of formation, movement and use of water within a single water district. Some elements of these parameters are directly measurable (particularly quantitative and qualitative elements of surface water and abstracted/discharged water), while others are not measurable at all (such as those which relate to groundwater and evapotranspiration). Additionally, in nature, there is a major difference between the formation and movement of groundwater and surface water even though there is a direct interaction between them through infiltration and outflow processes. Keeping this in mind, the surface water balance and the groundwater balance are usually assessed separately in practice, but their interaction parameters are included in the water balance equations. Division of the territory of Serbia into water management balance units Serbia’s hydrologic network is very intricate because it consists of several major European rivers (such as the Danube, Tisa, Sava, and Drina) which flow across its territory, a number of cross-border rivers (such as the Pčinja, Dragovištica, Jerma, Nišava, and Visočica), and several rivers in Banat which originate in Romania (e.g. the Zlatica, Begej, Tamiš, Brzava, Moravica, Rojga, Karaš and Nera).