River Basin Studies as a Basis for Flood Risk Management Planning: the Kolubara River Basin Case Study

Marina Babić Mladenović1, Vasiljka Kolarov1

 

1 Jaroslav Černi Institute for the Development of Water Resources, Jaroslava Černog 80, 11226 Pinosava, Belgrade, Serbia; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

Abstract

Preparation of the Flood Risk Management Plan for the territory of the Republic of Serbia has been initiated by the Ministry of Agriculture and Environmental Protection. This Plan shall contain measures for the reduction of flood risks in all Areas with Potential Significant Flood Risk. Given that those areas are different in nature, especially regarding the hydrological regime of rivers and societal conditions, each of them should be given sufficient attention. Besides taking into account local conditions, it is also necessary to assess how measures implemented in one area contribute to flood risks in the downstream and upstream areas. Therefore, the best results are achieved when applying an integrated approach on a sub-basin level, such was implemented in the Study on Flood Management Improvement in the Kolubara River Basin.

Keywords: Flood Risk Management Plan, Sub-basin level, Study on Flood Management Improvement.

 

Introduction

Being one of the most frequently occurring hazards in Serbia, floods have always attracted a great deal of attention from experts. While the traditional flood management involved construction of hydraulic structures like levees and river training works, as of the end of XX century efforts have been made to keep rivers in their natural state as much as possible, following the initiatives and experiences from all around the world, and especially in the countries of the European Union. This way, while existing structures remain, the most important component of a flood protection system, more attention is being given to non-structural measures, which are focused on society and do not affect the environment.

Following the recommendations of the EU Floods Directive (2007/60/EC) and the requirements of the Law on Water (Official Gazette of the Republic of Serbia, 30/2010) a three-step approach has been proposed which includes (1) Preliminary Flood Risk Assessment, (2) preparation of flood hazard and flood risk maps and (3) development of the Flood Risk Management Plans.

The Preliminary Flood Risk Assessment for the Republic of Serbia (PFRA, adopted in 2012) resulted in the identification of 99 Areas with Potential Significant Flood Risk (APSFR), representing river sections along which floods are likely to occur and cause damage to society and environment.

While flood hazard and flood risk maps for those areas are being prepared through several projects and studies, preparation of the Flood Risk Management Plan for the territory of the Republic of Serbia (FRMP) is in its initial stage. The Plan shall include measures for the achievement of appropriate objectives for the management of flood risks for the identified APSFRs. The Plan shall be completed by the Ministry of Agriculture and Environmental Protection - Republic Directorate for Water by the end of 2017. On the course of the Plan preparation the competent authority shall encourage active involvement of interested parties.

Given that the territory of Serbia covers a relatively large area, with diverse natural and societal conditions, each river basin should be given the necessary attention and its specifics should be studied in detail. Results of the recently completed Study on Flood Management Improvement in the Kolubara River Basin (JCI, 2016) justifies such an approach.

 

Preparation of the Flood Risk Management Plan for the territory of the Republic of Serbia

The purpose of the Flood Risk Management Plan is to provide flood risk management by reducing potential adverse consequences on human health, environment, cultural heritage and economic activities.

Based on the contents listed in the Law on Water and in the EU Floods Directive, the Plan should contain at least: the conclusions of PFRA with a map showing the APSFRs; flood hazard and flood risk maps; objectives for the reduction of flood risks; list of flood protection measures with their prioritisation, description of the monitoring means for their implementation, competent authorities, necessary funds and proposed projects; description of coordination with the River Basin Management Plan for the Danube River (DRBMP) and coordination at the international level for international river basins; description of the impacts of climate changes on the occurrence of floods and of the process of public information and consultation.

The focus of the FRMP is on a set of measures needed for the achieving objectives for the protection from fluvial floods. The objectives set by the national Water Management Strategy and confirmed in DRBMP are as follows:

  • Development of a flood protection system,
  • Efficient and coordinated active flood defence,
  • Efficient and coordinated defence from ice and ice floods,
  • Regular maintenance and monitoring of the state of hydraulic structures for flood protection,
  • Efficient and permanent monitoring and forecasting of hydro-meteorological phenomena,
  • Adequate use of water land and floodplains,
  • Improvement of water retention in the river basin.

The FRMP shall include both structural and non-structural measures. While structural measures are commonly used to modify flood hazard (including flood frequency, depth of inundation, and flood extent), as one of the risk elements (Figure 1), a wide range of non-structural measures is applied to reduce exposure to flood hazard through land use control but also to decrease vulnerability to exposure. Structural measures have an impact on the environment, while non-structural measures are focused on society.

 

Fig01
Figure 1: Set of flood risk management measures (Kobayashi and Porter, 2012)

 

Structural flood control works modify flood hazard in different ways (Babić Mladenović, 2016): (1) Flood control reservoirs and flood detention basins reduce flood discharges downstream, directly modifying the physical characteristics of floods in terms of spatial extent of inundation, depths of flooding, and flood flow velocities; (2) Levees and river training works directly modify the spatial extent of flooding, also affecting flood depths and flow velocities; (3) Flood diversion channels modify the spatial distribution of flooded areas, reducing hazard in the areas where more people and assets are exposed. Watershed management (including erosion control and torrent control measures) is an important structural measure, aiming at runoff and sediment regulation.

It is important to pass the message that flood hazard can only be reduced, but never fully eliminated. After the implementation of different structural measures, there is still the residual risk due to possible failure of flood protection structures (levee breach, etc.), failure of a reservoir or severe flood exceeding a design standard (levee overtopping). It is especially important to keep in mind the residual risk in areas protected by levees, where particular risk from rapid arrival of fast-flowing and deep water flooding exists, with little or no warning if defences are overtopped or breached. Furthermore, implementation of structural measures encourages fast development in the protected area, and the value of property and number of people at risk increase because residents and users of the protected area do not understand that the risk is only changed and has not been eliminated.

Exposure is a human component of flood risk, and it is permanently growing. People who live and work in, or transit through, as well as private properties, commercial assets, and public infrastructure in flood hazard areas are exposed to floods. Flood risk increases with increasing exposure (higher intensity of land use, rising value of property or assets located in flood-prone areas, and growing population that live or work in the endangered area or use it for other purposes). Development on floodplains is usually in the interests of national and social progress, and must be permitted, but these areas should be managed wisely – through adequate spatial planning. Regulation of land use is most effective when directed at future development, and includes residential development (appropriate types of buildings, limitations, proper locations of public services like schools, hospitals, emergency services, etc.), permitting of enterprises (storage of hazardous materials should be prohibited), planning of public infrastructure (routing and/or locations of key infrastructure – electricity substations, water supply, water treatment, and sewerage facilities). Regulation of land use relies on flood hazard maps, where different zones or categories of flood hazard are defined.

Measures to manage vulnerability in flood risk management are always non-structural. These measures are especially important for management of the residual risk. This set of measures requires careful planning, regular reviews of plans to maintain preparedness and swift mobilization of planned actions during flood emergencies.

Adequate precautions can reduce vulnerability to floods, if applied prior to flooding: (1) Established support services (flood forecasting and decision support systems); (2) Developed reliable communications systems and flood warning data networks; (3) Determined evacuation routes and temporary refuge facilities; (4) Advance planning and training of emergency management procedures.

Emergency response to flooding includes: (1) Supply of materials, telecommunications, transport, and power for flood defence emergency measures and flood fighting units; and (2) Evacuation and rescue, together with other actions necessary to manage public safety and security.

A very important set of non-structural measures relates to the after flood recovery activities: (1) Delivery of the material needs of the flood victims, including a temporary supply of food and shelter; (2) Support services such as assistance in clean-up, prevention of epidemics and waterborne diseases, and counselling to overcome personal distress and financial problems; (3) Repairs and rehabilitation of public infrastructure; (4) Financial assistance for incurred losses, housing repairs and businesses.

All structural and non-structural measures shall be selected from the Catalogue of Measures, which shall be adopted in advance by the competent authorities and included in the FRMP.

Besides the national FRMP which is to be prepared by the Ministry, according to the Law on Water, public water management companies shall prepare flood risk management plans for water districts. Current water districts are delineated according to administrative borders, while the Amendments to the Law on Water envisaged a new delineation of water districts, based on sub-basin borders. Since these plans need to be more detailed than the national Plan, they would benefit even more from the preparation of river basin studies focusing on the improvement of flood management.

 

Study on Flood Management Improvement in the Kolubara River Basin

The consequences of disastrous floods that affected the Republic of Serbia, including the entire Kolubara region, from 14 to 16 May 2014, highlighted the need to improve flood management in the Kolubara River Basin. Although this river basin has suffered multiple devastating flash floods over the past twenty years (in the more recent past in 2001, 2006 and 2010 in the Kolubara River Basin, and especially in 1999, 2006 and 2009 in the Tamnava River Basin), the most recent flood in 2014 was exceptional in terms of both human casualties and the extent of damage.

The geomorphological and hydrological characteristics of the Kolubara River Basin (Figure 2) are such that it is prone to the formation of voluminous flood waves. Although flood protection schemes are present and include almost 350 km of levees and river training works, a dozen of small reservoirs, and erosion and torrent control measures, frequent floods in the Kolubara River Basin are posing a threat to human health, personal property, infrastructure, industrial facilities and farmland.

The central part of the Kolubara River Basin hosts the Kolubara Mining Basin (Kolubara MB), comprised of large open-pit mines and associated infrastructures, whose operation depends to a large extent on the water regime and water management in the Kolubara River Basin. These are extremely valuable assets, of major significance to Serbia's steady electric power supply, meaning that a high level of flood protection is essential. On the other hand, Kolubara MB facilities and related flood protection solutions have a major impact on the formation of flood waves downstream. In this context, the City of Obrenovac is especially vulnerable, as it is located at the downstream part of the river basin, on low-lying ground and in highly complex hydrographic conditions (under the influence of the Kolubara, Tamnava and Sava rivers).

 

Fig02
Figure 2: Kolubara River Basin

 

Fig03
Figure 3: Flooded open-pit coal mine

 

Fig04
Figure 4: Flood in Obrenovac

 

In May 2014, the Tamnava West Field open-pit mine was flooded with about 190 million m3 of water and mud (Figure 3). Besides, entire settlements were literally submerged having as a consequence human losses, thousands of people in collective shelters, destroyed houses and infrastructure. Obrenovac (one of the municipalities of the City of Belgrade) was flooded because levees on the tributaries were breached some ten kilometers upstream of the city. In parts of the flooded area, the water was several meters deep (Figure 4). The Obrenovac water supply source was also, and endangering Serbia's main electric power production facility – TPP Nikola Tesla was endangered.

After this flood, the competent authorities initiated the preparation of a study with the main objective being to define a concept for integrated flood protection in the Kolubara River Basin, which implies combining structural and non-structural measures.

A team of experts was assembled to fulfil this objective, including hydraulic engineers, hydrologists, forestry engineers for erosion and torrents control, geotechnical and geodesy engineers, spatial planners, economists, IT experts, and others, employed by the Jaroslav Černi Institute, Faculty of Civil Engineering in Belgrade and the Institute of Architecture and Urban and Spatial Planning of Serbia. One of the key activities was permanent communication with a large pool of Study beneficiaries, including Public Water Management Companies such as "Srbijavode" and "Beogradvode", the Electric Power Industry of Serbia, ministries, the Republic Hydrometeorological Service of Serbia (RHMZ), 14 local administrations (municipalities) in the river basin, local businesses, citizens, experts, and the media.

The main computation tools were two hydrological models (IJC-FCE distributed the conceptual model designed for continuous hydrological simulations, and the HEC-HMS semi-distributed model) of the Kolubara River Basin (Figure 5) and, 1D hydraulic models of the Kolubara and all major tributaries (Figure 6).

About 410 km of rivers, most of them previously defined as APSFR, were modelled based on all available morphological data, but also on the results of a new and extensive field survey campaign.

 

Fig05
Figure 5: Scheme of the Kolubara RB used in hydrological models

 

Fig06
Figure 6: Hydraulic models covering all APSFR in the Kolubara RB

 

Hydrological and hydraulic models were used for the reconstruction of the May 2014 floods and for simulation of extreme hydrological conditions. The results revealed that the statistical ranks of peak flows in May 2014 in the middle and lower parts of the basin were between 300 and 500 years. Simulations of 1% and 0.1% floods enabled comparison of such extreme water levels with crest elevation of 350 km long levees in order to assess the present status of flood protection. The assessment also included the condition and functions of existing erosion and torrent control structures, and of 10 small reservoirs and retention basins.

The next stage of the Study focused on determining measures for upgrading the flood protection system in the Kolubara River Basin. For that purpose, firstly flood hazard maps (for 100- and 1000-year floods, as well for 2014) were prepared for all APSFR within the basin.

In the next step, potential flood damage was assessed by using the extent of the 2014 flood and risk data at present (2015) and in the future (2035), for 2 scenarios: "do nothing" and "upgrade flood protection system". This analysis revealed that an urgent upgrade of the flood protection system is needed because a new catastrophic flood would cause 50% greater damage than the 2014 flood, if the planned developments in the river basin were to be fulfilled by 2035.

The most important part of the Study was an analysis of possible new structures and measures to attain the planned level of flood protection in the Kolubara River Basin, and evaluation of their overall effectiveness.

A system of structural measures included new structures for attenuating flood waves (29 flood retention reservoirs in the upper parts of the Kolubara's tributaries and 3 lowland flood retentions), erosion control measures and measures for natural retention of water in the basin and reconstruction/construction of levees in order to increase the level of protection of the most important areas. Ultimately 20 flood retention reservoirs were proposed (Figure 7), to be built in two phases (1st phase until 2025, 2nd phase until 2035).

 

Fig07
Figure 7: Proposed system of flood retention reservoirs (1st phase marked in green, 2nd phase marked in red)

 

The planned erosion control measures and measures for natural retention of water in the basin include technical measures (torrent barriers, consolidation belts), biotechnical measures (wattle works) and biological measures (afforestation, replenishment and melioration of forests, and grassing). Also, the introduction of best practices in forest management and agriculture (contour ploughing, etc.) is planned for at least 20% of the basin area, because farming is the predominant type of the land use in the Kolubara River Basin (at present approximately 60% of its total area).

 

Fig08
Figure 8: Proposed erosion and torrent control measures

 

The effects of the proposed system of retention basins and land management measures aimed at reducing runoff were tested for the case of the 2014 flood. A comparison of the observed and calculated hydrographs along the Kolubara River (Figure 9) lead to the conclusion that the flood risk will be considerably reduced by the year 2035, when the system becomes fully operational. It should be noted that the effects of the reservoirs on the flood regime along the tributaries of the Kolubara River are outstanding; they will minimize the existing flood risks.

The hydraulic calculations revealed that all levees that protect the Obrenovac area, 31 km long, should be reconstructed in order to achieve the planned security level and protect the city from a 1000-year flood.

Besides the abovementioned system of structural measures aimed at reducing the flood hazard (including flood frequency, depth of inundation, and flood extent), which require overall spending of as much as 200 million €, a variety of non-structural measures were proposed. These measures are needed to reduce flood hazard exposure through control of land use and vulnerability of society to floods, and should be implemented in the future by different institutions (water management, safety and rescue services, hydro-meteorological services, health services, spatial planners, nature conservation, municipalities), reservoir users, as well as citizens, non-governmental organizations, companies and entrepreneurs in potentially endangered areas.

 

Fig09
Figure 9: Comparison of the 2014 flood as observed (blue line) and after the implementation of the proposed measures (1st phase – green line, 2nd phase – red line, complete system – violet line)

 

The proposed solution was evaluated in terms of economic viability, as well as social and environmental impacts.

A GIS database of the Project contains all data used for calculations and analysis (DEM, existing objects, river network, etc.), as well as the results of the Study (planned structures, flood zones, etc.). It is expected that these will be implemented in the Water Information System of Serbia.

 

Conclusions

Flood risk management planning includes measures which focus on the prevention, protection, preparedness, recovery and review. The water sector is mainly in charge of the preventive measures, while the entire cycle of flood management planning requires cooperation between competent However, for unknown reasons, lack of data regarding this branchiobdellid worm includes even countries which almost fully or partially are situated in the area of the original distribution of A. leptodactylus (according to Souty-Crosset et al., 2006), and furthermore which branchiobdellid fauna is well studied, as Hungary (Kovács, Juhász. 2007) or Croatia (Klobučar et al., 2006). This cooperation should start in the early stages and at the river sub-basin level in order to be able to take into account local conditions, assess all receptors and include all actors in the assessment of risk and planning processes.

The Study on Flood Management Improvement in the Kolubara River basin is a good example of cooperation of experts from different fields, who worked together with competent authorities from local to national levels, and with all the main stakeholders in the area. The Study covered hydrological-hydraulic aspects of floods, as well as social and environmental impacts of floods, it gave estimates of potential damage in case of floods in conditions of increased development, as well as of costs for the measures and works required for the improvement of flood protection in the Kolubara River basin.

One of the main results of the Study is a set of measures which would contribute to the reduction of flood risks in the entire basin, and especially in the most downstream town, Obrenovac, which was also the most affected by the May 2014 flood. These measures will be included in Flood Risk Management Plans.

The Kolubara Study once again proved the importance of taking an integrated approach in the assessment of flood risk and definition of possible measures for its reduction, by studying natural and societal conditions in the entire river basin. Such an approach also required the cooperation of experts from different fields and cooperation with competent authorities at all levels of governance. Experiences gained in this process should be used in preparation of similar studies for other sub-basins in Serbia in order to provide information of the same quality for all sub-basins for the purpose of preparation of Flood Risk Management Plans for the territory of the Republic of Serbia and for water districts.

 

References

Babić Mladenović, M. (2016). Structural and non-structural measures in flood risk management. Proceedings of the Workshop on Flood Risk Management Measures & Links to EU WFD. ISRBC Secretariat, Zagreb, Croatia.

JCI (2016). Study on Flood Management Improvement in the Kolubara River Basin, Jaroslav Černi Institute, Belgrade, funded by Japan Government through UNDP.

Kobayashi, Y. and J. W. Porter (2012). Flood risk management in the People's Republic of China: Learning to live with flood risk. Asian Development Bank, Mandaluyong City, Philippines.