1 July 12 th 2013 FLOOD DAMAGE SURVEY REPORT event 2013 Elbe and Danube Floods in Germany, Austria and Central and Eastern Europe Willis post-event field damage survey report As the flood wave travelled down from the headwaters of Rivers Elbe and Danube, members of the Willis Flood Team spent five days in the field surveying water depths and damages caused by the floods across the affected region. In addition, the teams assessed the effectiveness of flood defences along the banks of rivers in Germany, Austria, and Czech Republic. This report summarizes the findings from this damage survey, including the use of mobile technology, and details the development of the Willis Flood Footprint. Overview In June 2013, much of southern and eastern Germany, northern Austria and western Czech Republic were affected by significant flooding caused by prolonged heavy rainfall over the region. In many areas, these were the largest floods since the devastating Elbe and Danube floods of 2002 and in some locations along the Danube, Saale and lower Elbe, the floods were the worst in recorded history. As the flood wave travelled down Rivers Elbe and Danube, representatives of Willis and the Willis Research Network (WRN) spent five days in the field surveying the affected regions. The main objectives of the damage survey were to: a) survey flood depths and extents, b) assess the damage caused by the floods to individual properties, and c) assess the effectiveness of the flood defences throughout the region. Despite road closures and the remaining flood waters, the survey teams were able to visit a number of affected locations in Bavaria in Germany, Lower Austria, and Prague and surroundings in Czech Republic. In order to accurately track the location of the surveyed locations, the Willis survey teams used consumer mobile technology combined with ArcGIS Online. The ArcGIS Collector app for iphone allowed the survey teams to use the GPS and mobile data connections to upload the location, extent of damage and photographs to an online repository. In this way, Willis employees and clients in offices around the world could monitor the evolving flood and survey progress. The survey team in Austria observed many examples of well-drilled emergency services, highly efficient and effective flood defence structures and substantial natural floodplains and retention areas. In Prague, further examples of demountable flood defences were observed in addition to flooding behind these defences caused by high water levels and sewer surcharging. In contrast, the survey team in Germany visited locations where defence structures had failed and was able to survey a number of affected properties as flood waters had receded. Figure 1 shows the locations throughout the region visited by the Willis survey teams. Copyright 2013 Willis Limited / Willis Re Inc. All rights reserved: No part of this publication may be reproduced, disseminated, distributed, stored in a retrieval system, transmitted or otherwise transferred in any form or by any means, whether electronic, mechanical, photocopying, recording, or otherwise, without the permission of Willis Limited / Willis Re Inc. Some information contained in this document may be compiled from third party sources and we do not guarantee and are not responsible for the accuracy of such. This document is for general guidance only and is not intended to be relied upon. Any action based on or in connection with anything contained herein should be taken only after obtaining specific advice from independent professional advisors of your choice. The views expressed in this document are not necessarily those of Willis Limited / Willis Re Inc., its parent companies, sister companies, subsidiaries or affiliates (hereinafter Willis ). Willis is not responsible for the accuracy or completeness of the contents herein and expressly disclaims any responsibility or liability for the reader's application of any of the contents herein to any analysis or other matter, or for any results or conclusions based upon, arising from or in connection with the contents herein, nor do the contents herein guarantee, and should not be construed to guarantee, any particular result or outcome. Willis accepts no responsibility for the content or quality of any third party websites to which we refer.
2 Figure 1: Extract of field survey locations visited by the Willis Flood Teams throughout Germany, Austria, and Czech Republic with an example survey point Germany Damage Survey The Willis survey team visited Fischerdorf, Niederalteich, and Winzer near Deggendorf, some of the heaviest affected communities in southern Germany on 11 th June (see Figure 1 for locations). Fischerdorf were affected by levee failure along the Isar, while Niederalteich and Winzer were affected by a levee failure on the Danube downstream of the confluence with the Isar. In Bavaria, many 100 s of hectares were still inundated a number of days after the main floodwaters had peaked closing off the main highway to Passau (E56) and many smaller country roads in the wider area. Although the flood waters had receded and flood depths reduced, many streets and properties were still inundated. The standing water in most locations was less polluted than expected but in places, contained significant traces of oil and sulfate components. Figure 2: Flooding in Fischerdorf with a) receding flood waters from the Danube and b) a flood property with water marks on the buildings and surrounding trees. The survey team managed to gain access to properties in Fischerdorf while the clean-up was ongoing. The properties had been severely affected as a result of a defence breach. Water depths of up to 2 m from ground level were observed (Figure 3a) and surrounding properties on lower ground experienced water depths of 3 m above ground level (Figure 3b). Most residential properties surveyed were of masonry and reinforced masonry construction such that structural damage was limited despite the significant water depths. On the other hand, the majority of contents from basements and ground floors were a total loss (Figure 3c). In particular, electrical equipment such as washing machines and dishwashers were amongst the damaged goods. Upon inspection, many properties were pumping excess water out of basements, some of which was polluted with oil. Page 2 of 9
3 Figure 3: Survey findings from Deggendorf and surrounding area with a) water depths in ground-level of buildings up to 1.5m, b) water depths up to 3 m in other properties and c) total loss of contents from basements and ground floors Commercial damages in the area included a number of car dealerships and car rental companies in Fischerdorf, most of whom lost the majority of their stock. For instance, the local BMW dealer lost ~400 cars during the event. Flood Defence Integrity The wider Deggendorf area is protected by permanent flood defences but experienced at least two breaches along both Isar and Danube. In Winzer and Niederalteich many flood defences required additional reinforcement using sandbags or spare earth in order to protext communities during the event. In addition, high groundwater levels put significant pressure on already strained flood defences causing further weakening of defence structures and causing widespread flooding in basements. In places, defences were dismantled in order to relieve pressure points (Figure 4a). Demountable gate flood defences were also evident throughout the region protecting smaller parts of communities (Figure 4b) although flooding behind these defences was observed where defences had failed elsewhere (Figure 4b). Figure 4: Flood defences in Deggendorf and the surrounding area where a) flood defences close to Winzer were dismantled to relieve pressure and b) demountable flood defence gates built into a permanent dyke. Austria Damage Survey In most of the areas affected by flooding in Lower Austria, the emergency services restricted access to roads and buildings still under water and those at risk from further flooding. Figure 5 demonstrates the clear signage in operation throughout Austria for both major and minor roads where road closures were strictly enforced. The Willis survey team made their way from Mauthausen in Upper Austria to Klosterneuberg and Hainburg in Lower Austria along the banks of the River Danube, following the flood wave. Downstream of Mauthausen, many small country roads in Machland connecting Au an der Donau, Baumgarten and Mitterkirchen im Machland were closed to traffic due to high water levels from the Danube causing localised backwater flooding on the Rivers Naarn and Aist. Page 3 of 9
4 Figure 5: Clear signage and strict road closures were in operation throughout Austria In Grein, the 1 km long demountable flood defence protected the majority of the town with around a dozen houses affected by the high water levels on the River Danube. Outside the demountable defences, the affected houses were already starting the clean-up operation a day or two after the peak floodwave had passed. Figure 6a illustrates the impact of the flooding on contents and Figure 6b shows the clean-up process with emergency services and local residents working together. Figure 6: Flooding and clean-up operation in Grein where a) shows the impact on a flooded house and b) shows the emergency services clearing away flood waters and silt In the Wachau valley of the Danube River, the towns of Melk and Emmersdorf were badly affected by the flooding. In Emmersdorf, the local community and emergency services were clearing away the damaged contents and attempting to move the debris and waste left by the flood waters (Figure 7a). Water depths of up to 2-3 m were observed in both commercial and residential properties (Figure 7b) with significant damage to contents. Observed structural damage was limited due to mostly concrete or reinforced masonry construction types. Figure 7: Flooding in Emmersdorf with a) emergency services attempting to clear away the debris and b) water marks on commercial buildings Page 4 of 9
5 In Klosterneuberg, a few hundred properties were inundated up to 1 km from the main channel of the River Danube and in Kritzendorf, a number of properties by the river banks were under 2-3 m of water (Figure 8a). Downstream of Vienna, in Hainburg, a few hundred properties were flooded up to 2-3 m (Figure 8b) although emergency services were not as evident in the region. Figure 8: Flooded properties in a) Kritzendorf and b) Hainburg Flood Defence Integrity The area of the Machland was subject to significant flooding in 2002 as well as events in 1899 and As a result, the Machland Dike, a 36.4 km dike was constructed in 2012 to protect ~1,000 properties from Au to Mitterkirchen up to the 1-in- 100 year return period level. Figure 9a shows the structure. Figure 9b demonstrates the scale of the flooding from past events and the impact of the defence in 2013 as the Willis survey team was standing on dry ground Figure 9: The area of the Machland is protected by the 36.4 km Machland Dike shown in a) and b) shows the previous events to have affected the area before the construction of the dike The demountable defence in Grein protecting large parts of the town consisted of pylons spaced around ~1 m apart secured in the ground with metal sheets of 10 cm height and depth slotted in up to a height of ~6 m. The authorities estimate the standard of protection of such defences as ~1-in-100 year. The demountable defences protected the town successfully during this event. Page 5 of 9
6 Figure 10: Demountable flood defences structures in Grein protecting large parts of the town In the village of Theiß, the permanent earthen defence was under pressure and emergency services were shoring up the dyke with bags of gravel and sandbags (Figure 11a). In Hainburg, close to the Slovakian border, a combination of permanent and demountable defences protected the old town from the high water levels. Figure 11b shows the use of demountable metal sheets that slot into the gaps between permanent defence structures that form the abutment for the elevated railway line running along the river bank. Figure 11: Flood defences throughout Austria were important with a) emergency services shoring up defences in Theiß and b) demountable defences complimenting permanent ones in Hainburg Czech Republic Damage Survey The survey team visited large parts of the Old Town in Prague in addition to suburbs along the banks of the Vltava River (Velká Chuchle, Zbraslav). The damage to inundated buildings varied with construction type but a number of common patterns were observed. In general, water depths in severely affected properties ranged from meters and damage ratios to structures of up to 40% were observed (Figure 12a). Damage to contents at ground floor level was significant although the flood warnings allowed many residents to move their belongings prior to the arrival of the flood waters. Only one commercial property was observed to suffer damages close to 100% for buildings and contents (Figure 12b), being mostly attributed to a combination of high localised flood velocities and relatively weak construction type. The duration of flooding for the areas investigated varied from 1-4 days. The Willis survey team observed that basements were often inundated by the rising water table (Figure 13a) or by backwater effects from the stormwater and sewer network behind defences. In a number of neighbourhoods (e.g. Palmovka), a number of roads were inundated from water discharging out from basements. Page 6 of 9
7 Figure 12: Flooding in Prague and surrounding areas with a) properties affected up to 2 m depth, b) total loss to commercial building The main branch of the Vltava River is highly regulated, with a series of large dams built from the headwaters to Prague (Vltava cascade). As a result, the hydrological services in Czech Republic attenuated the flood peak and protected the highly exposed areas such as Prague. The Willis Flood team found that Prague along the Vltava (from Smíchov in the south to Holešovice to the north) was very well defended using temporary demountable levees resulting in minimal damages. Localised inundation was apparent in the Marina District and the Dock yards at Holešovice, at Troja (Prague Zoo) and at river islands such as Kampa (Figure 13b). Villages in Prague s periphery were significantly affected, especially where demountable flood defences were not present, such as at Chuchle and Lahovičky at the confluence of the Berounka and Vltava Rivers. Figure 13: Flooding around Prague of a) properties and basements caused by rising water tables and b) the Kampa Museum in Prague Flood Defence Integrity Since 2002, there has been significant investment in both large scale and small scale river management and flood defence schemes. As a result, the affected areas for this event in Czech Republic can be classified into two categories; a) areas significantly affected without flood defences and b) backwatering effects behind flood defences. The field investigation by the Willis Flood Team identified that the large majority of flood damages were limited to areas falling into the first category where flood defences and emergency protection measures were not present. The survey team found that demountable flood defences played a key role in protecting communities such as Prague and Zbraslav. Demountable flood defences, combined with pumping activity, allowed whole townships and neighbourhoods to reduce flood losses (Figure 14). However, it was found that the effectiveness of such temporary defences are limited to areas affected by simplified flood hydraulics. For example, in the township of Velká Chuchle, demountable flood defences placed along the banks of the Vltava River proved to be of little help to prevent inundation from the Berounka River which inundated properties by pushing flood waters behind the defences. Page 7 of 9
8 Figure 14: Demountable defences and pumping mechanisms in Prague Ground-truthing of Flood Extents The Willis Flood team acquired a number of datasets that captured the flood event. These include satellite data (PERILS, The Flood Observatory) and modelled data from the Willis flood model and the JBA Risk Management Ltd (JBA) model. Using the information obtained during the site investigation, Willis compared and evaluated the datasets. The results informed the Willis flood outlines for the June 2013 event. Comparing datasets From the evaluation the Willis Flood team undertook, it became apparent that modelled data (such as the JBA flood extents) and satellite data (such as the PERILS information) can be significantly enhanced by ground-truthing. For instance, in the Holešovice district of Prague (Figure 15a), PERILS data captured little of the flood extent, largely because the peak of the flood had receded when the satellite image was acquired. Similarly, areas in the Marine district of Holešovice (refer yellow shaded area in Figure 15a) were initially not captured by JBA modelled extents. In Deggendorf, the JBA flood extents were verified by the site inspection and informed the decision to disregard PERILS data for that particular area (Figure 15b). Overall, it was found that in areas where demountable flood defences were not affecting the flood patterns, modelled flood extents (such as JBA or Willis) captured the flood extents reasonably well. However, in cases where flood defences affected flood waters (e.g. Vienna), flood extents required amendment using the data collected on the ground by the Willis Flood team. In addition, the satellite data often contains artefacts around permanent water bodies (i.e. lakes) and a manual adjustment of the flood extents was undertaken in such cases. Figure 15: Willis Flood Footprint developed as a combination of PERILS, The Flood Observatory, JBA Risk Management and Willis site surveys shown for a) Prague and b) Deggendorf Page 8 of 9
9 Key Findings The June 2013 flood in central Europe affecting large areas of Germany, Austria, and Czech Republic was of similar magnitude to the flood events of 1954 and 2002 but with significant regional differences. However, the largest differentiator compared to the 2002 flood event was the increased preparedness and resilience of the communities affected. Significant investment in flood defences since 2002 has played an important role in the pattern of loss generation throughout the region. For example, Grein in Austria was left largely undamaged by the flood waters thanks to 6 m tall demountable flood defences, whilst other areas such as Fischbeck and Deggendorf were severely affected as a result of flood defence failures. Given that flood defences play such a significant role in loss generation, flood underwriting tools (e.g. ZUERS) and flood catastrophe models require regular updates to reflect changes in flood defence infrastructure as well as appropriately depict possible flood defence failure. The Willis Flood team examined the effect of flood defences along extensive stretches of waterways. Unless floodplain attenuation systems are constructed (e.g. wetlands, reservoirs) along with defence systems, the flood peak is simply migrated downstream, hence transferring the risk to communities downstream of the flood defences. This was observed in Magdeburg where the highest ever recorded water levels were observed with peak levels staying high a number of days. The reason is that the majority of the Elbe is defended and only in a few locations is water allowed to enter the floodplain and thus attenuate the flood wave. In contrast, the Danube in Austria has a large number of purpose-built and natural flood attenuation areas, such as Nationalpark Donauauen downstream of Vienna, which are regularly flooded. Conducting ground flood damage analysis by qualified hydrologists has proven to be beneficial in many ways. The Willis Flood team that inspected large areas of the affected communities, gathered detailed information that allowed them to: define more accurate flood extents and create an informed event flood footprint evaluate different data sets including modeled and satellite data and quantify their merits inform engineering flood damage curves for the region, allowing improved loss estimation for Willis equip Flood models Contact us Willis Flood Team Dr Timothy Fewtrell Dr Angelika Werner 51 Lime Street Nymphenburger Straße 5 London EC3M 7DQ München Phone + 44 (0) Phone Giorgis Hadzilacos Thomas Kiessling 51 Lime Street Nymphenburger Straße 5 London EC3M 7DQ München Phone + 44 (0) Phone Willis Limited, Registered number: England and Wales. Registered address: 51 Lime Street, London EC3M 7DQ A Lloyd s Broker. Authorised and regulated by the Financial Services Authority. Copyright 2010 Willis Re Inc. All rights reserved: The views expressed in this report are not necessarily those of Willis Re Inc., its parent companies, sister companies, subsidiaries or affiliates (hereinafter Willis ).This report and its contents are provided for informational purposes only, do not constitute professional advice and are not intended to be relied upon. Willis is not responsible for the accuracy or completeness of the contents herein and expressly disclaims any responsibility or liability for the reader s application of any of the contents herein to any analysis or other matter, or for any results or conclusions based upon, arising from or in connection with the contents herein, nor do the contents herein guarantee, and should not be construed to guarantee, any particular result or outcome. Page 9 of 9
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