Preliminary Results of Hydrologic Reconstruction of the May 2014 Kolubara River Flood - page 01

Overview of Meteorological Conditions

In the first trimester of 2014, the territory of Serbia enjoyed relatively stable weather, without significant rainfall (Prohaska et al, 2014). In mid-April, a cold front caused moderate-intensity constant rainfall until the beginning of May. This rainfall episode lasted almost continuously for 21 days, which was registered on main meteorological stations Kuršumlija, Leskovac and Požega, while stations at Dimitrovgrad, Kruševac, Niš, Sjenica, Vranje and Zlatibor only registered one day without rain. On average, all 28 available main meteorological stations registered less than four days without rain during this rainfall episode.

The rainfall that caused the disastrous flood in May 2014 was a result of a cold air front that came over the Alps into the Mediterranean, and formed a cyclone at all altitudes, which shifted across the Adriatic Sea towards the Balkans on May 13th. From May 14th to 16th, the cyclone intensified at all altitudes and became stationary. The center of the cyclone followed a path from the Gulf of Genoa over the Apennine Mountains, south Adriatic, southern Serbia, Bulgaria and Romania, before making several cyclonic loops in the southeastern regions of the Pannonian Basin (northern Serbia, southeastern Hungary, northwestern Romania). This cyclone did not follow the usual path of Genoese cyclones, which is towards the Black Sea, where they usually dissipate. The areas most affected by rainfall were western Serbia, Republika Srpska and Slavonija. As the cyclone was stationary, according to data from RHMSS, between May 14th and 18th it caused heavy rainfall of over 200 l/m2 and in some places over 300 l/m2. As noted previously, this rainfall event was preceded by heavy rainfall events in April, when recorded rainfall over most of Serbia was between 120 and 170 l/m2, and in the southwestern part of the country even over 250 l/m2. This combination of circumstances caused disastrous flash floods, erosion and landslides, first on streams and small rivers, followed by medium-sized rivers (Kolubara), and finally raised water levels in large rivers, mainly the Sava River (Babić Mladenović and Kolarov, 2015).

 

The Course of the Flood and Sequence of Events

Stubo-Rovni Dam, located on the Jablanica River (one of two sources of the Kolubara River), has been fully constructed but filling of the reservoir had not yet begun by May 2014. On the evening of May 14th, senior officials accompanied by design engineers considered the possibility of completely closing the diversion tunnel to fully contain the flood wave of the Jablanica River. This plan could not be implemented due to the access roads to the diversion tunnel, and the diversion tunnel itself, being already fully flooded. On May 15th at 3pm the water elevation in the reservoir was observed at 312 m.a.s.l by witnesses, which is close to the maximum elevation during this event. The diversion tunnel was discharging at full capacity, which was estimated at 70 m3/s. Later in the evening, the water level in the reservoir began to subside. Preliminary analysis estimated that a maximum storage of 2.5 million cubic meters was achieved during the event.

Some riverside neighborhoods in Valjevo were flooded due to overflowing from the regulated Kolubara River channel. On the evening of May 14th, the neighborhood on the left banks of the Kolubara River near the railway station was flooded, while in the morning on May 15th the neighborhood surrounding the factory "Gradac" became flooded. The Kolubara River also overflowed downstream from the railway station where no river training works exist. The river began to subside in Valjevo on May 16th, and floodwaters retreated from flooded areas.

The Obnica River, a source of the Kolubara River, caused great problems due to a lack of flood protection systems. The Obnica River overflowed during the night between May 14th and 15th and flooded nearby neighborhoods, the Juvenile Correction Facility, damaged the main road M4 Valjevo-Loznica, destroyed three bridges and deposited large amounts of sediment. One casualty was confirmed.

In April, the Gradac River caused much damage to roads, bridges and watermills. Similar events occurred in May, when several bridges were overtopped and damaged and/or destroyed upstream of the concrete dam. Flooding and landslides damaged the railway line Belgrade-Bar in several sections along the left bank of the Gradac River.

The Kolubara River also overflowed its banks along the unregulated reach between Valjevo and Lajkovac, and breached the left embankment in Lajkovac. On May 17th, an attempt was made to drain flooded areas of Lajkovac by pumping, but due to high river stages of the Kolubara, this was not possible. Two persons lost their lives in the flood, and around 500 were evacuated.

The Ribnica River, a tributary of the Kolubara, did not overflow its channeled riverbed through the town of Mionica, while the banks of the unregulated riverbed downstream and upstream of Mionica were overflowed. Flood defense on the Toplica River was announced on May 14th, when the regulated riverbed was damaged and floodwaters reached Banja Vrujci and downstream areas.

Flood defense on the Ljig River and its tributaries Godevac and Kačer was also announced on May 14th. The regulated riverbed was damaged during the flood wave. The Garaši Reservoir on the Bukulja River, a tributary of the Kačer River, was not put into operation for flood protection. The reservoir was completely filled with the side spillway in operation. Large areas were flooded in the Ljig River basin, particularly along unregulated river reaches.

 

Embankments on the right banks of the Kolubara River between its tributaries the Ljig River and the Peštan River were also overtopped and damaged. On the section of the road Veliki Crljeni-Kalenić to the mouth of the Turija River, the Kolubara broke through the embankment on the right riverbank and flooded the open mine pit "Veliki Crljeni".

The Peštan River overflowed in the upstream unregulated part of the riverbed. Most of the river flowed through the right-bank floodplain, where the river flooded several villages and flowed along the road Lazarevac - Veliki Crljeni before flooding the open mine pit "Veliki Crljeni" with approximately 20 million cubic meters of water. Two casualties were reported in this region.

Another embankment breach occurred near the mouth of the Vraničina River on the left bank of the Kolubara River. Due to the embankment breach, nearly the entire discharge of the Kolubara River flowed upstream the Vraničina River channel and through the open mine pit "Tamnava - East Field" into "Tamnava - West Field". It has been estimated that about 185 million cubic meters of floodwater entered the open mine pit "Tamnava - West Field". In the Kolubara riverbed, along the reach from the Vraničina River to the mouth of the Lukavica River, numerous embankment breaches and severe erosion occurred at multiple locations.

The flood wave on the Tamnava River reached the town of Koceljeva on May 14th, when the municipal headquarters for emergency management made the decision to artificially breach the right riverbank embankment, downstream from the bridge on the main road, in order to divert floodwaters into agricultural fields and away from the town. On May 15th, when the bridge on the main road over the Tamnava River was destroyed, the body of the main road was also artificially breached, allowing the floodwaters to subside in the urban area just upstream. In May, Koceljeva Municipality suffered a total of 176 flooded and damaged houses, and the bridge on the main road Valjevo-Šabac was destroyed along with 15 smaller bridges.

The flood defense measures on the Ub River were also announced on May 14th. Preventive measures were initiated the day before, when Ub Municipality headquarters for emergency management ordered the artificial breach of the left, and later the right, embankments on the Ub River. The retention basin Bogdanovica was put into operation at 6 pm, which according to estimates retained around 500,000 cubic meters of water. Gates on the Dokmir retention basin were partly opened, receiving an estimated volume of 1,600,000 m3 of water.

Along the left riverbank of the Tamnava River, from the hydrologic station Ćemanov Most to the confluence into the Kolubara River, embankments were breached at multiple locations. The railway line Obrenovac-Veliki Crljeni was also damaged on the left banks of the Trstena River. The flood proceeded downstream through the floodplains, and once combined with the Kolubara River, overflowed embankments on the left riverbank.

In the upstream part of the Kladnica River basin, the earthfill dam Paljuvi Viš was built in 1985. Downstream, Kladnica Dam and retention basin were built in 2004 on the eastern edge of the open-pit mine "Tamnava - West Field", including a system for pumping stormwater from the retention basin back into the Kladnica River north of the coal mine. During the May 2014 floods, Paljuvi Viš Dam successfully withstood the flood, with the spillway operating at a crest depth of 1 meter. Kladnica Dam did not withstand the flood coming from the Paljuvi Viš and downstream subcatchment, and the northern edge of the dam was overtopped, breached and destroyed. The entire flood wave of the Kladnica River entered the open mine pit "Tamnava - West Field".

After receiving waters from its largest tributary, the Tamnava River, the Kolubara River overtopped the left-bank embankments near the village of Veliko Polje. The area was further flooded by the flood wave coming from the upstream inundation at the breach of Trstena River embankments. The waters that overflowed the left embankments of the Kolubara River flowed directly towards the city of Obrenovac and further to the Sava River, where it breached the right embankment of the Sava River near Zabrežje on May 17th at 2 a.m. At that point, the stage of the Sava River was lower than the stage of the flood in Obrenovac, and water flowed from the Obrenovac valley out into the Sava River. The city of Obrenovac was the hardest hit by this flood; water depth was 1-2 meters north of the road Belgrade-Šabac and up to 4 meters in the southern parts of the valley, for several days. Based on the water depth and affected area, it is roughly estimated that the volume of the flood in Obrenovac was 10-20 million cubic meters of water. According to municipal authorities, 7,000 houses were flooded, 200 of which were completely destroyed. Many apartment and office buildings were severely damaged, 3,500 cars were destroyed, 1,000 ha of agricultural land was flooded, etc. No official data have been issued on the total number of casualties.

 

Available Data

The most relevant data for the May 2014 Kolubara River flood reconstruction are:

  • Digital Terrain Model,
  • Hydrometeorological data,
  • Data on flooded buildings,
  • Data on the condition and performance of existing flood defenses,
  • Data on flooded settlements and damage to infrastructure.