Identification of Areas with Significant Flood Risks in Counties along the Danube River in Serbia and Their Risk Assessment

Sustainable development cannot be achieved unless flood risks have been considered by strategic planning in a timely manner. Flood risk mechanism has often been described by the source-path-receptor model [1], where the source can be heavy rain or high sea level, and the path can be watercourses or land routes, through which floodwater makes its way to the receptor, i.e., people and property. Although the sources or root causes of floods (rainfall and sea levels) are natural phenomena and essentially uncontrollable (with the exception of man-made drivers of climate change), the pathways, through which these phenomena are transformed into floods and flood damages, are subject to the influence of local or regional human activities. These activities and their impact can be controlled and can significantly increase or decrease the flood risks to property and infrastructure [2]. Related responsible bodies within the United Nations, led by the Economic Commission for Europe, prepared the document the Guidelines for Sustainable Flood Prevention [3], with recommendations and best practices for flood prevention and control areas, which emphasized the adjustment of land use and risk assessments in regions with immediate flood danger.

Uncontrolled development is not desirable, and population growth in urban areas has increased the likelihood of excessive land use in flood-prone areas [4]. Therefore, timely actions must be taken to deal with the constantly developing flood risks in some areas, such as construction of embankments [5] and increasing natural retention.

After huge floods occurred in Europe in 2002, an expert group was established, which produced a document on best practices in flood risk management (EU, 2003). Then the Integrated River Basin Management (IRBM) promoted the sustainable management of watercourses and all environmental segments in the river basin. But it turned out that concrete tools for long-term water management have been missing in most cooperative management agreements, involving 106 of the world's 263 international basins [6]. In addition, the practical value of the 1997 United Nations Convention on the Right to the Non-Navigational Use of International Watercourses has been questioned because of its unclear and sometimes contradictory language and slow progress in ratifying its legal framework [7].

The European Flood Alert System (EFAS), the first international system for forecasting floods of the Danube and providing an early flood warning, was launched in 2008 by the International Commission for the Protection of the Danube River (ICPDR) and the Joint Research Center (JRC) of the European Commission. Several countries, namely, Austria, Bulgaria, Czech Republic, Germany, Hungary, Moldova, Serbia, Slovakia, Slovenia, and Romania, signed the memoranda of understanding for the EFAS development. The SoFPAS 1 project created both vulnerability and flood risk maps for the left and right sides of the Danube River between the Belgrade Municipality of Zemun (1175 km) and the upstream end of the Iron Gate Gorge (1040 km), including parts of Belgrade City along the Danube, i.e., municipalities Zemun, New Belgrade, Stari Grad, Palilula and Grocka areas on larger rivers in the Velika Morava basin. In addition, IPA 2014-2020 flood recovery project in Serbia created both vulnerability and flood risk maps, which identified remaining significant 74 flood areas in Serbia.

Floods and climate change have affected urban and rural areas in Serbian counties along the Danube and have begun to affect their economic, health and social situation, requiring intensive disaster risk management. In 2001, 2002, 2010 and 2013, the regional authorities in Serbia had to protect the population and property from the biggest floods of all time on the Danube. (IPA II indicative strategic document for Serbia, 2014-2020).

The Water Framework Directive as part of EU environmental legislation must be fulfilled by all EU member states in order to protect their resources. The Management Plan for the period 2021-2027 was prepared in Serbia, which achieved a turning point in water protection policies. In addition, climate verification of flood risk measures will be considered by Serbia in the Flood Risk Management Plan that is being prepared.

This paper briefly described the latest situation in the Danube region of Serbia and analyzed some adaptation projects and strategies, which have been implemented. In addition, this paper emphasized the importance of strategic planning in reducing the impact of floods [8] and that of geographic information and technology in flood and coastal risk management [9], [10] as well as the advantages of mapping this natural hazard [11], [12], [13]. The paper tried to answer several questions: Do the countries along the Danube have a long tradition in this field? Have EU countries benefited from joint management and responsibility of natural flood hazards? What are the European experience and literature on flood risk management? What is the current state of watercourses, water management and related jurisdiction in Serbia? What are the main critical factors to consider in order to achieve successful flood protection in Serbia and how to consider to make changes? What is the importance of Geographic Information System (GIS)?

In the process of answering the questions, this paper did qualitative research and analyzed statistical and modeling data, aiming to formulate the theoretical-applicative construction of the research model more precisely, thus achieving the goals and tasks postulated in the framework of the counties along the Danube River and flooding risks. The information is mainly from statistical data, data of competent institutions, European and national documents, reports, communications, legislation and institutions' websites.

The Danube passes through mountain gateways, agricultural lands, wetlands, and deltaic interlacing's of inland and water near the river's terminus, forming the Danube basin (Figure 1).

The research scope is the Danube area, which consists of Nomenclature of Territorial Units for Statistics (NUTS) 3 districts in Serbia, which are directly connected to the Danube (Figure 2). Each NUTS 3 district is a statistical unit with 150,000 to 800,000 inhabitants. In accordance with the regulation on the nomenclature of statistical territorial units (Official Gazette of the RS, No.109/09 and 46/10, Article 5), each NUTS 3 district is made of local self-government units within administrative districts. Territorial units are part of a certain area. The counties along the Danube River have very favorable geographical and traffic locations and are characterized by cross-border and neighborhood cooperation, developed economy, infrastructure (waterways, ports, piers, roads, railways, energy infrastructure, telecommunications, and urban and communal infrastructure in settlements), and an abundance of natural resources (hydropower potential of the Danube, i.e. Đerdap I, Đerdap II and the planned Đerdap III, coal reserves in the Kostolačko-Kovina basin, agricultural land, natural resources and conditions for tourism, water resources, favorable locations for residential production plants, etc.) [14], [15], [16], [17].

Pollution of water, groundwater and soil, reduced availability of clean drinking water. Insufficient development of regional and housing-communal infrastructure was caused by several factors, such as, high unemployment rate, low level investment, different degrees of development, unfavorable demographic structure, existence of national parks and other protected areas (e.g., IBA, IPA, RAMSAR), improper treatment and disposal of industrial and mining waste, etc. There is an excellent potential for agricultural development, such as fertile soil, favorable climate and geographical location, availability of services, and pastures in protected areas (grade II and III protection). Sustainable land use and agricultural development has many obstacles, such as occupation of land planned for construction of traffic and other infrastructure, industrial pollution (land, water and air), mining near large agrocomplexes, unresolved issues of wastewater treatment, underdeveloped irrigation systems and so on. In addition, forest resources have a significant potential for the sustainable development of counties along the Danube, such as preservation of habitats and biodiversity, possibility of increasing the natural stability and self-renewal of forests and so on.

As the main rivers of the Danube in Serbia, Tisa, Sava and Morava (Figure 3) are exposed to a significant increase in water levels during heavy rain period and are also affected by weather conditions in other countries because of their international nature.

In Serbia, counties along the Danube have a big potential for water management development, especially the hydropower potential, which is about 8.35 TWh/year or about 42% in the total 19.7 TWh/year usable potential, greater than all countries along the Danube.

There are favorable factors, such as sources of drinking water (Šalinac, Godomin and Kovin-Dubovac stretch of alluvium intended to supply South Banat, etc.), protection systems against external and internal waters (line systems against large (external) waters of the Danube, and systems against internal waters), possibility of expanding the functions and renewing the HS DTD, regulation of water regimes for larger irrigation systems of high-quality land with the Danube as a water catchment, and possibility of constructing hot water ponds in the depressions near the Danube (spatial plan of the special-purpose area of the international waterway E80 - Danube, Pan-European Corridor VII).

However, there are limiting factors, such as probability of more uneven water regimes of the Danube upstream of the HPP "Đerdap" dam and its most important tributaries, increase of large water volume due to canalization of the Danube in the upper reaches (excluding inundations), worsening of non-stationary precipitation phenomena due to climate change, increasingly long periods of low water (partly due to climate change and increasing water intake in the upstream countries, particularly in low-water periods), poor sanitation of settlements without WWTP, landfills with hydraulic influence of springs, discharge of industrial waste water without purification, unplanned construction in the zone of springs and even in their narrow protection zone, threats to protective systems from large and internal water lines (e.g. illegal construction), additional slowdown compared with the initial "zero" state caused by backfilling of the HPP "Đerdap 1" reservoir, insufficient maintenance of the coastal protection system, flood control measures affected by water soil threats due to unplanned construction, especially along the defended coast embankment, and division of power in water management area of Serbia, etc. [15], [16], [17].

The Ministry of Agriculture, the Forestry and Water Management (Republican Institute of Water Management), the Public Water Management Company Srbijavode, and local governments (municipalities and cities) are responsible for water management in Serbia, including water management policies and regimes, risk management, water protection, rational use of water, management of river regimes, water supply and other responsibilities prescribed by the Water Law ("Official Gazette of RS", No.30/2010, 93/2012, 101/2016, 95/2018 and 95/2018 and other laws). Duties of other ministries overlap in water resources management, such as the Ministry of Environmental Protection, the Ministry of Health, the Ministry of State Administration, local self-government and the Ministry of Infrastructure. In Vojvodina, related water management activities are entrusted to the Public Water Management Company Vode Vojvodine. The local authorities are responsible for managing local water supply systems, natural lakes, springs, and public wells in municipal areas. Water regimes are maintained and improved according to the Water Management Strategy of Serbia.

In the Danube region, the areas with flood risks have the highest proportion in Srednjebanatski County (1,708km²) and the lowest proportion in Borski County, as presented in Table 1.

In accordance with the ESPON TITAN project, 2013 [18], the flood hazard indicator shows the percentage of flooded land area per NUTS 3 for riverine floods in Danube area in Serbia (Table 2).

Multilateral cooperation in the Danube basin takes place within the framework of the Convention on Cooperation on the Protection and Sustainable Use of the Danube River, signed by eleven countries along the Danube and the EU in 1994 in Sofia, which was later ratified as the Convention on the Protection of the Danube River. The Decree on Promulgation of the Law on the Convention on Cooperation on the Protection and Sustainable Use of the Danube River was adopted in 2003. Many transboundary water management international agreements had been signed, namely, the Agreement on Transboundary Waters (1955), Navigation Agreement (1955) and Fishing Agreement (1961) with Romania, the Convention on Cooperation for the Protection and Sustainable Use of the Danube, by the ICPDR (1994), and Tisza River Basin Forum (2001, Budapest Declaration). For Serbia, climate verification of flood risk measures will be considered in the Flood Risk Management Plan, which is being prepared.

Water protection infrastructure in this Danube area is evident. The Danube-Tisa-Danube canal system was constructed for flood prevention and irrigation, but the efficiency is not good. The priority is being given to the reconstruction of protection structures in cities of Novi Sad, Zemun, Pancevo, Smederevo, Veliko Gradiste and Golubac. Reconstruction has also been planned on the left bank of the River Sava (City of Belgrade and Sremski County). In addition, the same priority has been given to Tisa riverbed [16]. Barrage system, dams, proposed works on dikes, and pier walls are shown in Table 3 and Table 4.

Although spatial planning deals with future spatial arrangement [19], [20], [21], [22], its role in flood mitigation was often neglected in practice. Planners are responsible for planning general land use, even in flood areas, and implementing it at all levels, while local risk management agencies have less decision-making power. Development control in flood-prone areas can also be realized through land planning [20], [21]. Although there are three active flood protection measures as follows:

• Reservoirs, which aim to produce electricity and irrigate, apart from retaining the top of the flood wave;

• Retention of less accumulation along watercourses, and prevention of embankment collapse and flooding;

• Relief channels, which are artificial channels that drain excess water from the river;

In Serbia, river valleys are occupied by both legal and illegal construction. In addition, there are problems in retention of reserving areas for flood defense, expropriation, and construction of reservoirs, which takes time to solve.

"Determining the flood risk, either from a national dataset (once available) or through a specific assessment, is essential to determine the existing and potential future locations and degrees of flood hazard, taking into account the potential impacts of climate change. Based on this information, zones for controlled, and importantly, appropriate development may be set to avoid placing flood-sensitive development in flood-prone areas" [2].

In accordance with the Law on Water ("Official Gazette of the RS" No.30/10, 93/12, 101/16, 95/18 and 95/18, etc.), the risk management of harmful effects of water includes preparation of a preliminary flood risk assessment, creation of flood risk maps, as well as creation and implementation of flood risk management plans. Flood hazard is assessed in many countries at national level as part of a flood risk or hazard mapping program. In Serbia, the public water management company prepares both hazard maps and flood risk maps for the territory within its jurisdiction for a six-year period and then review and update them. Maps for areas with significant flood risks are determined by the Preliminary Flood Risk Assessment.

Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 (from Danube Atlas - Flood Hazard and Risk Maps 2012) are corresponding flood hazard maps for areas along the Danube in Serbia [23], which show areas exposed to flood hazards and associated potential damages and flood risks, priority measures to be taken within the EU Floods Directive, affected population and possible damages in extreme floods and predicted inundation depth in graded blue colors.

Corresponding flood hazard maps for areas along the Danube in Serbia by the ICPDR [23] are as follows:

Effective risk management is not possible unless the risks and the necessary database have been completely understood. Successful flood risk assessment and management include knowledge of locations with problems, natural conditions, climate vulnerability, and changes of land use. Information on the volume of flood waves can be used to reduce risks of those areas by planning construction conditions on time. Planning of certain land uses should be limited by local and regional plans in flooding zones. In addition, larger scale destruction and damage can be prevented by using information on the extent, depth, speed, frequency, mechanism and possible impact of floods. Therefore, there is a need for risk assessment in areas where flooding may be a problem.

When flood risk information is used as part of planning process, timely decisions on future land uses can be made.

GIS tools can be used for visualization, visual inspection and synthesis of different types of data, analysis of flood waves, and determination of flood zones, movement of river sediments and changes in the river bed, as well as for water embankment designers in Serbia to check their solutions even before flood waves. As the analysis shows, though many models and calculations have been made for risk management and mitigation, concrete application of measures are still missing, because the financial resources of water management are often used for other purposes.