9* International Symposium on Lowland Technology September 29-October 1,2014 in Saga, Japan
ONLINE ESTIMATION OF FLOOD DAMAGE IN THE NETHERLANDS
O.A.C. Hoes', M.A.U.R. Tariq^ andN.C. Van de Giesen^
ABSTRACT: This paper presents a recently developed model in the Netherlands for the online estimation of damage caused by floods. The model attempts to fill the lack of a consistent framework for the assessment of damage for all water authorities and all floods in the Netherlands. A framework was necessaiy to be able to evaluate the cost and benefit of measures, and moreover, needed to be consistent in order to be able to compare results from different water authorities. Our model estimates both direct - water induced - damages and indirect economic damages such as the interruption of production during the period needed for recoveiy measures and detour time caused by blocked roads. The presented model is featured by a high resolution land use map and elevation data for the whole country in combination with economic data, data on flood characteristics and stage-damage functions. The usefulness of the model is demonstrated in a case study estimating expected flood damage in a flood-prone polder area in the Netheriands.
Keywords: Flood damage, stage damage curves
INTRODUCTION
Worldwide many approaches exist on how flood control is arranged from designing levees and structures such that they are able to withstand a water level with a certain return period towards more sophisticated flood risk approaches within which one aims to combine the probability and damage in case of flooding. Regardless the method, knowledge about the potential damage in case of flooding is of great importance for flood control. As one way or another, the cost of the measures has to be somehow in equilibrium with the expected damage.
Common practice is that a land-use map, stage damage curves and an inundation depth map are combined to estimate the damage in case of flooding. These stage damage curves describe for each specific class of the land-use map the relationship of the flood damage to the stage of flooding. Existing models usually only establish a relationship between inundation depth and damage. Not that people do not realize that the damage depends on more than just the depth, but because there is not more information available.
Existing damage models are therefore fairiy coarse. Often a distinction is made between micro, meso and macro approaches. The micro level is an object-oriented approach which distinguishes in e.g. single buildings. At the meso level land-use functions are aggregated to e.g. residential areas and industrial areas. At macro level, damages are estimated for administrative units (e.g.
municipalities). The number of models at the micro level, however, is rather scarce. When they exist micro models usually cover specific sites, e.g. one catchment or they designed to test ex post a new concept. There are hardly any examples on a national scale. One of the examples has been described by Hall et al. (2003) for England and Wales.
In the Netheriands, the hitherto most used national scale damage model HIS-SSM was developed by the ministiy of public works. The model is a meso model, which calculates the damage with a 100 m resolution water depth and averaged damage values on six digit Postal Code areas. A six digit Postal Code area consists of 25 addresses; roughly the maximum amount of letters a post man can carry in one hand while delivering the mail.
For small-scale flooding - with water depths of a few centimeters - this model is too coarse. Furthemore, for all land use functions the HIS-SSM model only takes the water depth into account although the flood duration is implicitly hidden in the depth. For a widely applicable model however, an explicit method is desired, which does not only have the depth, but for example also the duration of the flooding or the season included in the stage damage curves. Thus, the Dutch Water Authorities needed a far more detailed model. This need was further enhanced, because unlike the past, the water authorities no longer blindly design and maintain all infrastructure just to meet a certain standardized return period. The
' lALT member, Delft University of Technology, Stevinweg 1, 2628 CN, THE NETHERLANDS, o.a.c.hoes@tudelft.nl ^ Mohammad Ali Jinnah University, Islamabad Expressway, Kahuta Road, Zone-V, Islamabad, PAKISTAN
combination of increased economie value, expected future climate changes and present economic crisis make that citizens expect that the water authorities spend their tax money carefully. Nowadays, when a measure is intuitively expensive for the problem it solves, one aims to estimate more than previously the costs and benefits of this measure to base the decision to reject or proceed with a project.
The Netherlands has 25 regional water authorities. To avoid that every water authority develops his own method, it was decided to develop an online application which allows all water boards to calculate the damage for all floods in a uniform, reproducible and transparent manner. This new damage model calculates the damage for 60 land use classes spread over buildings, infrastructure and crop damage.
In this article successively first flood damage models are clarified. Next, the power of an online model is explained, then our damage model is discussed and illustrated with details on the stage damage curves and how the damage amounts are derived. Last, the model is illustrated in a case study.
DAMAGE MODELS
Types of Damage
Flood damage is normally divided into tangible and intangible damages. Intangible damage arises from adverse social and environmental effects caused by flooding, such as stress and anxiety, which can not be assigned monetary values. Tangible damages are monetary losses directly attributable to flooding. They may occur as direct or indirect flood damages.
Direct flood damages are caused by the floodwater wetting the possessions and structures. When items are damaged iiTeparably, the direct damage is equal to the pre-flood value of the item or its replacement cost. Otherwise the damage is equal to the cost of repairs plus the loss in value of the repaired item.
Indirect damages are additional financial losses that arise from the disruptions to physical and economic activities caused by flooding, for example the cost for temporai-y accommodation for evacuees, loss of sales, reduced productivity and the cost of alternative travel i f road and rail links are broken.
Susceptibility to damage
The susceptibility of a land-use function to damage depends on factors as season, inundation depth, flood duration, duration of repair measures, water quality, flow velocity, wave impact, and the velocity with which the
Table 1 Damage parameters per land use
Buildings Crops Infi-a
Inund. Depth direct direct
Flood duration direct
Season direct
Duration repairs indirect indirect
water level rises. Depending on the type of land-use one or more of these factors influence the amount of damage significantly, and therefore should be within the before mentioned stage-damage curves.
A coarse first subdivision in land-use functions consists of buildings, crops and infrastructure (See Table 1). The water depth is the main parameter for the direct damage to the inventory and also structure of buildings. While the indirect damage depends mainly on the time needed to cany out the repair work and restarting production.
For crops not the depth, but the season and flood duration determine the direct damage. The actual inundation depth is much less important: a persistent fully saturated root zone is sufficient for the crops to decay and rot. Indirect damage due to damage to crops consists of business interruption at suppliers and customers. This indirect damage is hard to estimate as it depends on the extent of the flood, scale of the considered economy and the interconnectedness of the lost hai-vest with this economy.
The parameter for the indirect infrastructure damage (roads, railways) is extra travel time caused by blocked roads. For major highways and railways connecting cities with harbors and aiipoits this indirect damage can be a multiple of the direct damage which consists of removing silt and repair work.
Existing Flood Damage Models
Nine models were examined prior to the construction of our new model. This is in order to try to benefit from the experience of these models. GIS is an Australian model developed in 2002 that assesses flood migration and floodplain developments from an economic point of view for fluvial floods. GIS only takes the flood depth in account for buildings and infrastructure and has a resolution of 5*5 meter (Belts 2002). AIR is a company that made a model in 2008 to price and underwrite the risk of floods for Germany as well as for Great-Britain. The model of Great-Britain was assessed for this research because it takes pluvial flooding into account. The model focusses on damage to buildings due to fluvial and pluvial floods, and takes the depth, duration and recovery period into account. The resolution is
Online damage calculation
10*10 meter (AIR 2008). The next model is HAZUS from 2006 which is rather complete compared to the previous models. HAZUS considers buildings, infrastructin-e and crops. The stage damage cui-ves contain inundation depth, flood duration, recovery time and seasonality on a 10*10 meter resolution (Scawthorn 2006). AGDAM is developed by the US Corps of Engineers in 1985 and calculates the annual damage due to fluvial floods. The model is set up to specifically calculate the damage of crops and takes inundation depth, fiood duration, recovery time and seasonality into account (CEIWR-HEC 1985). The next evaluated model is Adapt developed in 2010 for fluvial floods. Adapt is a model that assesses adaption measures with an integrated decision tool. Within Adapt all the land-use functions buildings, infi-astructure en crops are considered. The stage damage curves contain inundation depth, flood duration, recoveiy time and seasonality on a 2*2 meter resolution (Giron 2010). Another model with a 2*2 meter resolution is HOW AD-PREVENT, which makes assessments for pluvial flood damages to buildings. To do so it takes depth and duration into account (Sterna 2012). HIS-SSM was developed in 2003 by the Ministry of Public Works in the Netherlands and estimates the expected damage and casualties of coastal and fluvial floods. It is a very general model that takes water depth and velocity into account on a resolution of 100x100 meters (Huizinga 2004). The Loss estimation model is a model developed at the University of Tokyo, li calculates losses on a 50*50 meter resolution for buildings, infrastructure and crops; and takes depth, duration and seasonality into account (Duta 2003). The last model is called A new damage index, which is specified on calculating the replacement value of buildings. It is a very specialized model which only takes the flood depth for buildings into account (Blong 2003). Within these 9 models a trend is present. The newer the model, the higher the resolution and the more parameters are considered for the determination of the damage.
ONLINE FLOOD DAMAGE MODEL
Why An Online Model?
The new damage model developed is a web-based model and can be accessed via www.waterschadeschatter.nl (water schade schatter is Dutch for water damage estimator). In order to start a calculation one need to upload the relevant flood infonnation to the website. The calculation is then divided over several multicore servers, after which the user will receive an email with a link to the results of his
calculations. There were several reasons which made it preferable to choose for an online application. First of all, with an online application anyone (water authorities, municipalities, consuhants, and universities) can use the program without installing any software. Second, by using the calculation power of several muhicore servers in parallel, these calculations can be done several times faster than on a desktop PC. Thirdly, with an online model version control becomes unnecessary as anyone is always working with the latest version of the land-use map, digftal elevation model, stage damage cui-ves and damage values. Fourthly, the database that contains all elevation and land use data of the Netheriands which has been used for this damage model has a resolution of 0.5 * 0.5 meter. This makes in total around 2 TB of data for the whole of the Netheriands, which is beyond the amount of information that fits on a desktop PC.
Elevation Data
The most detailed digital elevation model (DEM) of the Netherlands is named the AHN2, which was collected during 5 winters between 2007 and 2012 by a helicopter with a laser altimeter mounted under it. The winter was chosen as deciduous trees do not have leaves between November and March, what allows the laser beam to obsei-ve the true surface beneath the trees.
The dataset flown contains 20 to 40 points per m^ with their respective x,y,z location. From these data, first all buildings, ti-ees, cars and other objects that are not part of the surface were fihered. This filtered point dataset was then converted to a raster file of 0.5 * 0.5 meters (0.25m^). In order to be able to calculate water in buildings, one wants to (theoretically) measure the elevation of all ground floors of all buildings individually. However, the building database ('BAG register') used contains all buildings within the Netherlands. To circumvent a laborious and long lasting
survey the footprint of all buildings with a residential, office, industrial, hospital, church or shop fimction was lifted 15 cm above the mean elevation within a 1 meter buffer around these buildings. As we assumed that the floor level within buildings is 15 cm higher than the surrounding surface level. Buildings with a secondary function, like sheds, were not lifted.
Land-use Map
There was no land-use map available which distinguished sufficient land-use categories at a resolution of 0.25m^. What made that a new land-use map was created by combining the best of four existing maps:
1) The 'BAG register' is a cadastral polygon shape file from the Land Registry and Mapping Agency and contains the footprint of each of the 7 million buildings in the Netherlands. The file distinguishes 10 building types: dwellings, offices, industcy, shops, prisons, hotels, education, sports, health care and miscellaneous. The quality of the BAG-register compared to other maps is primarily that the perimeter of each individual building is accurately drawn.
2) 'TOPIONL' is the most detaüed topographical database from the same Land Registry and Mapping Agency. We used this file solely for the watercourses and roads. For the roads the file distinguishes between primary, secondary and tertiary roads. Primary roads are ranways of airports, highways and railways. Secondary roads are all provincial roads and main roads. With the inundation of primary and secondary roads damage occurs as extra travel time to drive around. Tertiary roads are roads in residential areas. This map is very accurate in space, but the legend contains 'agricultural land' and 'buildings', without any further subdivision.
3) 'CBS-bodemgebmik' is the land-use map of Dutch Statistics. Compared to the other maps, the map of Dutch Statistics is very specific on relatively rare land-use types, like courtyards, cemeteries, industrial sites, allotments.
4) The last map is the 'LGN6' land-use map from Alterra, which is a raster map on 25m * 25m. The map distinguishes different crop types: grass, potatoes, beets, grains, flower bulbs, orchards, greenhouses, nature.
The resulting map has 70 land-use categories. The level of detail of the resulting map is better than the separate maps. Plots with potatoes enchcled by ditches, for example, have in the original LGN6 map a rather coarse resolution of 25*25 meter, while in the new map the plots encircled by ditches and roads from map 2) were assigned the dominant land use type from map 4).
Table 2 Damage per dweUing of 50 m^ in euros
low avg Max rent submersible pump 50 50 50 rent water vacuum cleaner 200 200 200 rent construction dryer 500 500 500 rent storage and transport 500 500 500 removal and disposal of 1000 1000 1000 carpet, cupboards etc
new carpeting 1500 5000 9000
new kitchen cupboards 750 1250 1750 plaster and painting 2000 2250 2500 fridge contents/ couch 1000 1750 2000 total for 50 7500 12500 17500
unit price per 150 250 350
Damage Values
For each of the land-use categories a direct and indirect damage value was determined. For buildings, crops, or roads different sources for the values were selected. For builduigs the replacement cost for the inventory and repafr cost for the structural damages were collected (See Table 2). The crop data were derived from Dutch Statistics and Wageningen University. Both conduct annual surveys on crop yields and market prices. The 2000-2010 data were corrected for inflation and VAT to deteimine average, minimum and maximum damage values per hectare (See Table 3). Indirect damages for crops were set to null. Of course, there may be a loss at customers and suppliers, but this is for the economy as a whole assumed to be compensated by higher revenues for the other farmers outside the flood zone. For roads and railways, the direct damage was esthnated as € 0.20/m for cleanmg the roads with a vacuum track. The indirect values are caused by the cost for extra travel time, and based on earlier studies on the damage due to blocked highways in case of flooding (Adviesdienst Verkeer en Vervoer 2006).
Three Stage Damage Curves
For each land use type three stage damage curves
Table 3 Damage for different crop types per hectare
low avg max
Hay / grass
e
951 € 1 008 € 1 108 Com € 1 575 € 1 923 63 071 Potatoes € 2 014 € 6 654 €14 189 Beets €3 387 € 4 120 € 4 702 Cereals € 931 € 1 557 €2 410 Orchards €50 190 €54 679 €59 855 Flower bulbs €22 577 €25 653 €29 349 Green houses €326 411 €398 948 €818 833Fig. 1 The new map was constructed by merging the best layers from 4 existing maps
Online damage calculation
were constructed: inundation deptli, flood duration, and season. Depending on the stage, a factor between 0 and 1 was assigned. Moreover, the damage was calculated consistently by: damage = max € • fdepth ' gduratioa" A^season For a land-use type one the parameters needed to be ruled out, the curve is simply set to 1 for all stages. Fig. 2 shows an example for different crops. The furst stage damage curve increases from 0 to 1 around a 0.0 m inundation depth. The second curve shows flood duration. Grass and cereals need to be flooded for 20 days to be flilly lost, while the other crops do not survive three days of flooding. The third curve shows how the damage depends on the season. In December and January most crops will hardly experience any damage, while in June and July the loss reaches 100%. The mmor
S 1Ö 13 1-1 16 19 20
damage in the winter is not due that there are any crops sown, but the flood deteriorates the soil condition and rinses out nutrients.
CASE HERTOGIN HEDWIGE POLDER
The Hertoging Hedwige Polder is a 340 hectare small polder in the south of the Netheriands (N51.342° E 4.215°). The polder is adjacent to the Westerschelde water, which connects the harbor of Antwerp to the North Sea. The polder is interesting as it contains, despite its small size, different types of land use: grass, com, potatoes, beets and cereals, three farmhouses and two roads (See Fig. 2). The average surface level in the polder is +1.7 to 2.0m MSL, while the mean high water level (MHW) at the adjacent Westerschelde is +2.8 m MSL. The polder is protected with a levee with its crest at +9.7 m MSL, which corresponds with a return period of 1:4000 year.
A calculation at the website starts with entering an email address and selecting a type of calculation. The website provides multiple types of calculations, which changes the required input. E.g. one can upload an ASCI-file with the maximum water level for an event, or multiple ASCI-files for each tune step of an event, or muhiple ASCI-files with different return periods, which makes that the model will calculate, next to the damage per return period, an expected annual damage map. This way the model satisfies the demands of the different users within the Netherlands.
To illustrate the model an ASCI-file with the maximum water level of +1.9 m MSL was uploaded. Next, the model requires input fi'om the user about the duration of flooding, month of the floodmg, recovery duration for the road network, recovery duration for the buildmgs, and whether one wants to calculate the
Fig. 2 Three stage damage curves for different crop types
H R o c " - - j ' , l o i \ ' C c m > ; ! c r v
H F i r l i V H o r t ï c u I r j ' T
Table 4 Damage in the Hedwige Polder at +1.9 m MSL
Category Inundated max
Dwellings 0.1 €1459 Sheds (> 50m^) 0.1
e
70 327 Secondary roads 0.1e
87 544 Tertiary roads 0.6 €377 Hay / grass 23.2 € 9 289 Com 10.2 € 19 457 Potatoes 21.3 €42 498 Beets 17.5 € 70 942 Cereals 54.7e
33 755 Miscellaneous 24.7 € 130 056 agriculture Other grass 2.6 € 1 026 TOTAL 155 ha € 466 728damage with minimum, average or maximum damage values. As an example we choose a flood duration of 72 hours, August, 5 days for the recovery period of the roads, 10 days for the recovery period of the buildings and average damage values.
A 340 hectare small polder contains over 13 million cells of 0.5*0.5 meter. The calculation time is approximately 3 minutes as the calculations are conducted parallel on a sei-ver cluster. The results contain an inundation map on Google Maps, a damage map on Google Maps, a damage I<ML file for Google Earth, a table with the flooded surface and damage per land-use (See Table 4) and an ASCI-file with the damage per pixel.
The total damage amounts € 466 000. The largest contributor is miscellaneous agriculture, which consists of plots at which the crops grown are vegetables, but the type of vegetables is not consistent and might change by the year.
CONCLUSION AND RECCOMMENDATION
The aim of this research was to give insight in a recently for The Netherlands developed model to estimate the damage in case of flooding. Our model is the first model in the world in which one can fulfill online damage calculations on a national scale. The database behind the model contains over 2 TB of data of land-use and elevations, which makes it impractical to conduct calculations on a desktop computer. Moreover, it is also the model vi'ith the highest resolution we laiovi' of Compared to the existing models, our model needs water levels as input, and calculates its own inundation depth mapwhich allows us to fulfill all calculations -regardless the resolution of the input - on a 0.5*0.5 meter resolution.
The model calculates both direct water induced -damages and indirect economic -damages for buildings, infrastmcture and crops. For each of the categories it takes water depth, flood duration, season, and recovery period into account.
For the near fiiture, our model will be updated with improved stage damage curves, based on a literature review and comparison of existing models and expanded to also calculate victims in case of flooding.
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