oder-lisflood assessment of the effects of engineering, land use and climate scenarios on flood risk...

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ODER-LISFLOOD

Assessment of the effects of engineering, land useand climate scenarios on flood risk

in the Oder catchment

Ad De Roo, Guido Schmuck

ODER-LISFLOOD scenarios De Roo & Schmuck

ODER-LISFLOOD

Assessment of the effects of engineering, land useand climate scenarios on flood risk

in the Oder catchment

Ad De Roo, Guido Schmuck

July 2002

Institute for Environment and SustainabilityJoint Research CentreEuropean Commission

Ad de Roo & Guido SchmuckIspra, July 2002

Contacts: Dr. A.P.J. de Roo & Dr. G. SchmuckEuropean Commission, Joint Research CentreInstitute for Environment and SustainabilityLM Unit, Natural Hazards ProjectVia E. Fermi, TP261, 21020 Ispra (Va), ItalyTel: ++39-0332-786240Fax: ++39-0332-785500Email: ad.de-roo@jrc.it / guido.schmuck@jrc.it

CONTENTS

Executive summary …………………………….………………………….…………… vShrnutí -Executive Summary (Cz) …………........................................................…… ixPodsumowanie - Executive Summary (P) …………………………….……….…… xiiiZusammenfassung - Executive Summary (D) ………………………..……………. xvii

Introduction ……………………………………..………………………….…………... 1

1. The LISFLOOD modelling system ..………………………………….……….. 2

2. Validation ……………………………………………….……………..…..…… 7

3. Scenarios …………………………………………………………………….… 14

3.1 Scenario Building Stones ……………..………………………………..…. 14

3.2 Scenarios for calculation with LISFLOOD ……………..……….…..….. 16

3.3 Scenario reporting ………………………………………..……….…..….. 18

3.4 Scenario results …………………………………….………..…….……… 19

Reference scenarios ……….….……….………………………. 20IKSO scenarios ……………….………..……………………… 23Reservoir scenarios …………..………….……………………. 33Historic land use scenarios …..………….……………………. 40Land use change scenarios …..………….……………………. 45Brandenburg scenarios ………..…………..………………….. 53Climate change scenarios ….….……………..……………….. 62Combination scenarios ……..……….………………..………. 71

Conclusions ……………..……………………………………………….………….…. 72

Recommendations …………………………………………………………………….. 76

References ……………….……………….……………………………………………. 77

Appendices ………………..…………………………………………………………… 79

Executive Summary

BackgroundIn July 1997, an extreme flood hit the Oder and its tributary rivers, resulting in 114deaths, 195.500 people evacuated and approximately 4600 Million Euros damage.Following the extreme flood, the Joint Research Centre of the European Commissionstarted a model simulation study called ODER-LISFLOOD. This study is the EUcontribution to the ‘Workgroup Floods’ within the framework of the InternationalCommission for the Protection of the Oder river (IKSO), which was established after theflood and officially ratified in April 1999. Since its official start in January 1999, aninternational multi-disciplinary collaboration is brought together, consisting of:• European Commission, Joint Research Centre (JRC), IES-LM Unit, Ispra, Italy• Czech Hydro-Meteorological Institute (CHMI), Prague, Czech Republic• Institute of Meteorology and Water Management (IMGW), Wroclaw, Poland• Regional Water Development Authority (RWDA), Wroclaw, Poland• Landesumweltamt Brandenburg (LUAB), Potsdam, Germany• Sächsisches Landesamt für Umwelt and Geologie (SLUG), Dresden, Germany

The Oder-LISFLOOD projectThe most important objectives of the project are:• to investigate the effects of land-use change on flood risk (historic land use changes

and future developments)• to assess the effects of possible flood defense measures - scenarios . The scenarios

were proposed by the IKSO and experts from the Water Authorities in the CzechRepublic, Poland and Germany

• to assess the consequences of climate change trends on flood risk.

These objectives were realized by the development of a flood simulation model for theOder basin with the following phases:• development of the LISFLOOD model including special modifications for the Oder;• development of a high-resolution GIS for the Oder basin;• testing and validation of the LISFLOOD model for the floods of 1977, 1985 and 1997• simulation of scenarios to assess the effects of possible flood defense measures.

The Workgroup Floods of the IKSO has defined a list of 81 scenarios with flood defensemeasures.

The LISFLOOD modelLISFLOOD can simulate floods in medium-size and large river basins. Contrary to mosthydrological models LISFLOOD can simulate large areas while maintaining a highspatial resolution, proper flood routing methods and physical process descriptions.Through its nested approach – LISFLOOD consists of a catchment water balance model,a catchment flood simulation model, and a flood inundation simulation model – the

model is capable to simulate both the effects of land use change and climate change, andengineering flood defense methods.

MethodologyFor this study the Oder catchment upstream of the Warta confluence has been simulatedon a regular grid of 1km2. The total area of this part of the Oder catchment is 53.787 km2.A Digital Elevation Model (DEM) with a horizontal spatial resolution of 75 m togetherwith digital maps of the actual rivers has been used to determine the flow network.Especially for this project, a soil database on the scale of 1:250,000 has been developedfor the Oder, in cooperation with the European Soils Bureau of the EuropeanCommission. The Corine land cover database - developed under the PHARE Programmeof the European Commission – with a resolution of 100m - has been used. Furthermore,JRC and GISIG developed a digital historic land use database, containing the land use inthe Oder of around 1780, based on the Schmettau maps.

Rainfall data, discharge data, cross-section geometry and roughness values, groundwaterdata and evapotranspiration estimates have been obtained from the cooperating waterauthorities within this project (CHMI, IMGW, LUAB, SLUG) and partly from JRCdatabases.

Three historic flood events have been selected to test the LISFLOOD model: the floodsof August 1977, August 1985 and July 1997. In general, the results show that theLISFLOOD model simulates both the overall water-balance of the Oder and the threeflood events with reasonable quality, sufficient to be used as a model for the analysis ofscenarios. It can be observed that the results improve from 1977 to 1997 due to betterinput data: more precipitation and climate stations.

A set of 81 scenarios has been defined to investigate the effects of flood defensemeasures and also of expected future trends of climate and land use change. Thesescenarios can be divided into eight groups:• Reference scenarios, which reflect the current situation• Engineering scenarios as defined by IKSO until the year 2030• Scenarios on water reservoir management• Scenarios of historic land use• Scenarios of future expected land use changes and land use manipulation for flood

defense• Scenarios of Brandenburg retention areas• Scenarios of climate change• Combination scenarios

It has been decided to use the 1997 event as the reference condition. This means that allscenario results are valid for this extreme flood. For smaller events, or events with adifferent rainfall pattern, the results will be different.

For the purpose of this project, dyke-breaks are not taken into account, since it isunpredictable how dyke-breaks would develop – if they occur also – under a different

scenario. In order to be able to compare all scenarios equally, dyke-breaks are notsimulated: the river level is allowed to rise even higher than the maximum dyke height.

ConclusionsBased on the scenario calculations, it can be concluded that the proposed engineeringflood defense measures by IKSO until 2030, decrease flood peak discharges with 435 to1330 m3/s (14-46%) and decrease waterlevels between 80 cm and 300 cm for Poland.For Germany the IKSO measures decrease flood peak discharge with 58-466 m3/s anddecrease waterlevels between 27 cm and 79 cm. In the Czech Republic, the effects areless (-69 m3/s). This conclusion is valid for the 1997 flood event, and is compared withsimulations using the 2001 reference conditions.

In the Czech Republic, in addition to the new reservoirs planned, an extra flood peakreduction could be achieved through reforestation (-84 m3/s) and changing theoperational management of water reservoirs towards flood control. Throughoptimization of the water reservoirs, a total flood peak reduction of 266 m3/s can beachieved at the Odra/Olse station. Extra afforestation would increase this reduction withapprox 80 m3/s.

In Poland, the planned polders and reservoirs reduce the flood risk. Also here, animproved operational management of water reservoirs towards flood control will reduceflood risk even more. For polders the time of activating them determines theireffectiveness. Care has to be taken with the planned cross section changes, since many ofthe proposed changed reduce the storage potential in the river cross section thusincreasing waterlevels and discharge. Increasing dyke heights or building new dykesreduces local flood risk, but can cause problems downstream in other regions. Crosssection changes that increase storage capacity within the cross section do not havenegative downstream effects.

In Germany, the planned polders of Ziltendorf and Neuzell can help in reducing floodrisk near Frankfurt and further downstream, if the polders are activated at the right timejust before the flood wave arrives. An increase of the storage capacity of the floodplainreduces waterlevels with approximate 60 cm. Combinations of the new polders and thefloodplain storage reduces peak discharge at Frankfurt/Slubice with 141 m3/s or 71 cm.

Expected urban growth within the next 30 years will lead to a slight increase in peakdischarge (max. +43 m3/s). When planning future flood defense measures, it isrecommended to take this into account. It should be noted that during the 1997 event, thehighest rainfall was not in urbanized areas, but in more rural and mountain areas. If ahigher amount of rainfall falls in urbanized areas, the effect of urban growth will belarger.

It has been demonstrated in this study that land use changes between 1780 and presenthave increased peak discharges in the Oder. This is mainly caused by urban growth. Thetotal area of forests has grown between 1780 and present, except in regions with intense

urban development. Again it should be noted here that the effect of urban growth wouldbe larger if the spatial pattern of rainfall would have been different, more in urban areas.

Expected effects of climate change are difficult to estimate, because the results ofdifferent climate change scenarios are highly variable. Although it is expected thatworldwide precipitation will increase, the spatial pattern and magnitude of these changesis still unclear. The number of extreme rainfall events could increase, leaving theirmagnitude unchanged, or the number of extreme rainfall events could stay the same, buttheir magnitude could increase. Because of these uncertainties, for this study onlysimplistic climate change scenarios based on common trends were proposed. In general, atemperature rise is quite likely to occur, leading to decreased peak discharges andincreased evapotranspiration: a 1 degree temperature rise (scenario tp1) leads to a drop inmaximum discharge of 51-197 m3/s, corresponding to 13-29 cm waterlevel. A combinedscenario (+15% precipitation, + 1 degree temperature) causes an increase in flood peak(500-700 m3/s for all sites), but as mentioned before, it can be questioned if this scenariois realistic. However, the results suggest that in the planning of flood control measurespossible effects of climate change should not be ignored.

Shrnutí

ÚvodV červenci 1997 proběhla na Odře a jejích přítocích extrémní povodeň, která způsobilasmrt 114 lidí, 195 tis. lidí bylo evakuováno a materiální ztráty byly ohodnoceny ve výši4,6 mld €. V návaznosti na tuto povodeň zahájilo společné výzkumné centrum (JointResearch Centre) Evropské Komise práce na vývoji simulačního modelu nazvanéhoODER-LISFLOOD. Tyto práce představují vklad EU pro pracovní skupinu „Povodeň“,která byla ustavena po povodni v r. 1997, oficiálně schválena v dubnu 1999 a kterápracuje v rámci Mezinárodní komise pro ochranu Odry před znečištěním (MKOOpZ).Od ledna 1999, tj. od zahájení prací, byla navázána mezinárodní interdisciplinárníspolupráce mezi :▪ Evropskou Komisí, Joint Research Centre (JRC), IES-LM Unit, Ispra, Itálie

a▪ Českým hydrometeorologickým ústavem (ČHMÚ), Praha, Česká republika,▪ Institutem pro meteorologii a vodní hospodářství (IMGW), Wroclaw, Polsko▪ Regionální správou vodního hospodářství (RZGW), Wroclaw, Polsko▪ Zemským úřadem pro životní prostředí v Braniborsku (LUAB), Postupim, Německo▪ Saským zemským úřadem pro životní prostředí a geologii (SLUG), Drážďany,

Německo

Projekt ODER-LISFLOODNedůležitější cíle projektu jsou :▪ výzkum změny obhospodařování půdy (vegetačního krytu) na povodňová rizika

(změny v minulosti i budoucnosti);▪ vyhodnocení efektů možných scénářů protipovodňové ochrany navržených MKOOpZ

a eksperty z českých, polských a německých úřadů a institucí, zabývajících sehospodařením vodou;

▪ vyhodnocení důsledků trendů klimatických změn na povodňová rizika.

Tyto cíle byly dosaženy vývojem simulačních modelů pro povodí Odry v těchto krocích :▪ rozšíření modelu LISFLOOD jeho přizpůsobení na podmínky Odry;▪ vývoj profesionálního GIS pro povodí Odry;▪ testování a kalibrace modelu na povodních z let 1977, 1985 a 1997;▪ simulace scénářů pro vyhodnocení efektů možných protipovodňových opatření.

Pracovní skupina MKOOpZ „Povodeň“ sestavila seznam 81 scénářů protipovodňovéochrany.

Model LISFLOODLISFLOOD je schopen simulovat povodně v povodích středních a velkých toků. Narozdíl od většiny hydrologických modelů, LISFLOOD umožňuje simulaci velkých územípři zachování vysoké přesnosti a správnosti zobrazení průběhu a postupu povodňové vlnya fyzických procesů. Postupným zahrnutím vodní bilance povodí, simulace povodnív povodí a zátopových území, byl LISFLOOD zpřesňován a zdokonalován. Model je

schopen simulovat jak důsledky změn vegetačního krytu, tak i klimatických změn arovněž důsledky proti-povodňových opatření stavebně – technického charakteru.

MetodikaPro účely modelu je povodí Odry nad ústím Warty o ploše 53 787 km2 simulovánopravidelnou výpočtovou sítí s rozlišením 1 km2 . Pro průtoky byl použit model terénupomocí sítě s rozlišením 75 m a aktualizovaná digitální mapa říční sítě. Pro účelyprojektu, ve spolupráci s Evropským úřadem půd Evropské Komise, byla pro povodíOdry zpracována databáze údajů o půdách v měřítku 1:250 000. Rovněž byla využitadatabáze o využití půd Corina s přesností 100 m, vypracovaná v ramci programuPHARE. Mimo to JRC a GISIG využívaly databázi historického využívání půd v pvodíOdry od roku 1780, vycházející z map Schmettau.

Pomocí spolupráce s úřady a institucemi zabývajících se hospodařením vodou (ČHMÚ,IMGW, LUAB, SLUG) a s využitím údajů JRC byly shromážděny údaje o srážkách,zásobení, vodách podzemních, evapotranspiraci, příčné profily, parametry drsnosti a pod.

Pro testování modelu byly vybrány 3 historické povodně: ze srpna 1977, srpna 1985 ačervence 1997. Obecně možno konstatovat, že výsledky potvrzují, že model LISFLOODsimuluje s odpovídající, pro účely modelování scénářů postačující přesností jak celkovoubilanci vody, tak i testovací povodně. Viditelné zlepšení výsledků mezi obdobím roku1977 a roku 1997 je výsledkem zkvalitnění vstupních údajů zvýšením počtu měřícíchstanic.

Pro hodnocení dosažených efektů opatřeními protipovodňové ochrany a důsledků změnklimatických a vegetačního krytu, bylo definováno 81 scénářů rozdělených do 8 skupin:▪ scénáře referenční, zobrazujících současný stav▪ scénáře technických opatření definovaných MKOOpZ až do roku 2003▪ scénáře týkající se manipulací na přehradních nádržích▪ scénáře týkající se změn vegetačního krytu v minulosti▪ scénáře týkající se budoucích předpokládaných změn vegetačního krytu z hlediska

protipovodňové ochrany▪ scénáře týkající se retenčních ploch v Braniborsku▪ scénáře klimatických změn▪ scénaře kompilační

Jako referenční byla přijata povodeň z roku 1997, to znamená, že výsledky všech scénářůjsou porovnávány s touto extrémní povodní. Pro menší povodně, nebo s jinýmrozložením srážek budou výsledky odlišné.

Protože se nedá předvídat, zda vůbec, a pokud ano, tak kde, kdy a v jakém rozsahu můžedojít k protržení hrází, neuvažuje se ve scénářích projektu s žádným poškozením hrází.Aby mohly být scénáře vzájemně porovnatelné, není simulováno žádné přetržení hrází:hladina vody v řece je pak dokonce nad úrovní hrází.

ZávěryNa základě propočtů scénářů je možno konstatovat, že navrhovaná stavebně-technickáprotipovodňová opatření definovná MKOOpZ až do roku 2030 sníží kulminačníhodnotu povodňového průtoku od 435 do 1330 m3/s ( 14 ÷ 46 % ), a vodní stavy napolském území od 80 do 300 cm. Na německém území se sníží kulminační průtok od 58do 466 m3/s, a vodní stavy od 27 do 79 cm. Na českém území bude efekt menší ( - 69m3/s ). Závěr se vztahuje k povodni z roku 1997 a byl porovnán se simulacemireferenčních podmínek roku 2001.

Na českém území, je možno za předpokladu vybudování plánovaných novýchpřehradních nádrží dosáhnout opětovným zalesněním a změnou řízení povodňovéhoodtoku na přehradních nádržích zaměřenou na povodňovou ochranu snížení kulminacepovodňové vlny ( - 84 m3/s ). Optimalizací povodňového řízení na přehradních nádržíchje možno snížit kulminaci povodňové vlny na Odře o 266 m3/s v profilu Odry pod Olší.Maximálně možné zalesnění by mohlo znamenat další redukci o cca 80 m3/s.

Na polském území plánované poldry a retenční nádrže redukují povodňová rizika.Změnou řízení povodňového odtoku na přehradních nádržích ve prospěch povodňovéochrany se dále redukuje povodňové riziko. Čas aktivace funkce poldrů ovlivňuje jejichúčinnost. Je třeba věnovat pozornost na plánované změny říčních profilů, protože řadanavrhovaných změn snižuje kapacitu profilu a vede ke zvýšení vodních stavů. Zvýšeníhrází, nebo výstavba nových hrází snižuje lokální ohrožení, ale může vyvolat problémyv níže položených oblastech. Změny profilů zvyšující jejich průtočnou kapacitu, seneodrážejí negativně níže po toku.

Na německém území mohou plánované poldry v Zilterdorf a Neuzell přispět ke sníženípovodňového ohrožení ve Frankfurtu/O a pod ním za předpokladu, že budou aktivoványtěsně před příchodem povodňové vlny. Zvýšení rozsahu zátopových území snižuje vodnistavy o přibližně 60 cm. Kombinace nových poldrů se zvýšením rozsahu zátopovýchúzemí snižuje hodnotu kulminačního průtoku ve Frankfurtu/Slubicích o 141 m3/s, čemužodpovídá snížení vodních stavů o 71 cm.

Při plánování budoucích protipovodňových opatření by mělo být vzato v úvahu, žev nejbližších 30-ti letech očekávaný nárůst urbanizace vyvolá určité zvýšeníkulminačních hodnot ( max. + 43 m3/s ). Je třeba si všimnout toho, že v průběhu povodně1997 se nejvyšší srážky vyskytly v nezastavěných oblastech, tedy venkovských ahorských. Kdyby centrum srážek bylo na územích vysoce urbanizovaných, pak by vlivurbanizace byl vyšší.

V práci je dokumentováno, že změny ve využívání půd (hlavně zvětšení stupněurbanizace) od roku 1780 až po současnost, vedly ke zvýšení kulminačních průtoků.Celková plocha lesů se od roku 1780 zvýšila s výjimkou ploch rozvíjejícího seurbanismu. Mimo to je třeba mít na zřeteli, že význam urbanizace by byl větší, kdybaprostorové rozložení srážek bylo jiné, vyšší na urbanizovaných územích.

Je obtížné vyhodnotit vlivy klimatických změn, protože výsledky jejich různých scénářůse velmi liší. I když se očekává, že v globálním měřítku dojde ke zvýšení srážek, jejichprostorové rozložení a velikost nelze pro konkrétní menší území předvídat. Počet výskytůextrémních srážek např. může vzrůst při nezměněném úhrnu, nebo naopak. Z důvodutěchto nejasností byly v práci použity pouze zjednodušené scénáře klimatických změn,vycházející z obecných tendencí. Obecně, vzrůst teploty je pravděpodobný. To by vedloke vzrůstu evapotranspirace a snížení kulminačních průtoků. Například zvýšení teploty o1 stupeň (scénář tp1) by znamenal snížení maximálních průtoků o 51 ÷ 197 m3/s, čemužodpovídá snížení vodních stavů o 13¨÷ 29 cm . Kombinovaný scénář (nárůst srážek o 15% a teploty o 1 stupeň) vyvolá zvýšení kulminace (o 500 ÷ 700 m3/s pro všechna místa),ale jak vyplývá z výše uvedeného, výsledky získané na základě tohoto scénáře jsoudiskutabilní. Přesto však výsledky nabádají k tomu, aby klimatické změny nebylyignorovány.

Podsumowanie

TłoW lipcu 1997 r. na Odrze i jej dopływach miała miejsce ekstremalna powódź, w wynikuktórej 114 osób poniosło śmierć, 195.000 ludzi ewakuowano, a straty oszacowano na 4,6mld €. W związku z tą powodzią, Joint Research Centre z Komisji Europejskiejrozpoczęło wykonywanie opracowania zawierającego model symulacyjny, nazwanegoODER-LISFLOOD. Opracowanie stanowi wkład UE dla utworzonej po powodzi 1997 r.i oficjalnie ratyfikowanej w kwietniu 1999 r. Grupy Roboczej „Powódź”, działającej wramach Międzynarodowej Komisji Ochrony Odry przed Zanieczyszczeniem (MKOOpZ).Od początku sformalizowanej pracy w styczniu 1999 r. została podjętainterdyscyplinarna współpraca międzynarodowa pomiędzy:• Komisją Europejską, Joint Research Centre (JRC), IES-LM Unit, Ispra, Włochy,• Czeskim Instytutem Hydro-Meteorologicznym (CHMI), Praga, Czechy,• Instytutem Meteorologii i Gospodarki Wodnej (IMiGW), Wrocław, Polska,• Regionalnym Zarządem Gospodarki Wodnej (RZGW), Wrocław, Polska,• Landesumweltamt Brandenburg (LUAB), Poczdam, Niemcy• Sächsisches Landesamt für Umwelt and Geologie (SLUG), Drezno, Niemcy.

Projekt Oder-LISFLOODNajistotniejszymi celami projektu są:• zbadanie wpływu zmiany użytkowania (zagospodarowania) powierzchni ziemi na

ryzyko powodzi (zmiany użytkowania (zagospodarowania) powierzchni ziemihistoryczne i przyszłe),

• oszacowanie efektów możliwych scenariuszy ochrony przeciwpowodziowezaproponowanych przez MKOOpZ oraz ekspertów z czeskich, polskich i niemieckichurzędów i instytucji zajmujących się gospodarowaniem wodą,

• oszacowania konsekwencji trendów zmian klimatycznych na ryzyko powodzi.

Cele te były realizowane poprzez rozwój modelowania symulacyjnego dla dorzecza Odryw następujących etapach:• rozwój modelu LISFLOOD poprzez dostosowanie go do warunków Odry,• rozwój profesjonalnego GIS-u dla dorzecza Odry,• testowanie i kalibracja modelu LISFLOOD dla powodzi z lat 1977, 1985 i 1997,• symulacja scenariuszy dla oszacowania rezultatów możliwych działań ochrony

przeciwpowodziowej.

Grupa Robocza „Powódź” z MKOOpZ określiła listę 81 scenariuszy ochronyprzeciwpowodziowej.

Model LISFLOODLISFLOOD jest w stanie symulować powodzie dla dorzeczy rzek średnich i dużych. Wprzeciwieństwie do większości modeli hydrologicznych, LISFLOOD umożliwiasymulację wielkich obszarów przy zachowaniu wysokiej dokładności oraz właściwych

opisów przemieszczania się fali powodziowej i procesów fizycznych. Poprzez stopnioweprzybliżanie LISFLOOD zawiera model bilansu wodnego dorzecza, modele symulacyjnepowodzi w dorzeczu oraz zalewania terenu przez powódź. Model jest w staniezasymulować zarówno rezultaty zmian w użytkowaniu (zagospodarowaniu) powierzchniziemi oraz zmian klimatycznych, jak i inżynieryjnych metod ochrony przed powodzią.

MetodykaDla celów opracowania dorzecze Odry powyżej ujścia Warty o powierzchni 53.787 km2

zostało zasymulowane w regularnej siatce obliczeniowej o powierzchni 1 km2. Dlaokreślenia struktury przepływów został użyty model rzeźby terenu wraz z poziomymrozkładem przestrzennym co 75 m oraz zaktualizowaną mapą komputerową siecirzecznej. Specjalnie dla projektu, we współpracy z Europejskim Biurem Gleb z KomisjiEuropejskiej, opracowano dla Odry bazę danych nt. gleb w skali 1:250.000.Wykorzystano również rozwijaną przez program PHARE, posiadającą dokładność 100m, bazę danych Corina dot. pokrycia (zagospodarowania) powierzchni ziemi. PonadtoJRC i GISIG wykorzystywały opartą na mapach Schmettau bazę danych nt.historycznego użytkowania (zagospodarowania) powierzchni terenu nad Odrą od ok.1780 r.

W rezultacie współpracy z urzędami i instytucjami zajmującymi się gospodarowaniemwodą w ramach projektu (CHMI, IMiGW, LUAB, SLUG) oraz częściowo na podstawiebazy danych JRC pozyskano dane nt. opadów, zasilania, wód podziemnych iewapotranspiracji, przekroje geometryczne, parametry szorstkości.

Do testowania na modelu LISFLOOD wytypowano 3 historyczne powodzie: z sierpnia1977 r., sierpnia 1985 r. oraz lipca 1997 r. Generalnie można stwierdzić, że uzyskanerezultaty pokazują, że model LISFLOOD symuluje z odpowiednią, wystarczającą dlamodelowania scenariuszy dokładnością zarówno ogólny bilans wodny Odry, jak i 3powodzie. Można zauważyć poprawienie się rezultatów w okresie od 1977 do 1997 r.wskutek poprawy jakości danych wejściowych poprzez zwiększenie ilości stacjipomiarów opadów i klimatu.

W celu badań efektów ochrony przed powodzią oraz spodziewanych, przyszłych trendówzmian klimatycznych i w użytkowaniu (zagospodarowaniu) powierzchni terenuzdefiniowano 81 scenariuszy podzielonych na 8 grup:• scenariusze referencyjne, odzwierciedlające sytuację obecną,• scenariusze inżynieryjne zdefiniowane przez MKOOpZ aż do roku 2030,• scenariusze obejmujące zarządzanie zbiornikami zaporowymi,• scenariusze obejmujące oddziaływanie historycznych zmian w użytkowaniu

(zagospodarowaniu) terenu,• scenariusze dotyczące przyszłych, spodziewanych zmian w użytkowaniu

(zagospodarowaniu) terenu oraz w użytkowaniu (zagospodarowaniu) terenu podkątem ochrony przeciwpowodziowej,

• scenariusze dotyczące obszarów retencyjnych w Brandenburgii,• scenariusze zmian klimatycznych• scenariusze kompilacyjne.

Jako punkt odniesienia (warunki referencyjne) przyjęto powódź z 1997 r. Oznacza to, żewyniki wszystkich scenariuszy porównano z tą ekstremalną powodzią. Dla mniejszychpowodzi lub z innym rodzajem deszczu wyniki mogą być odmienne.

Ponieważ nie można przewidzieć, czy w ogóle, a jeśli tak, to gdzie i jakiej wielkościprzerwania wałów mogą wystąpić w poszczególnych scenariuszach, dla potrzeb projektuzałożono, że żadne wały nie zostaną przerwane. Aby umożliwić porównywaniewszystkich scenariuszy w jednakowy sposób nie symuluje się przerwań wałów: poziomwody w rzece jest podniesiony nawet powyżej wysokości wałów.

Wnioski:W oparciu o obliczenia scenariuszy można stwierdzić, że proponowana, inżynieryjnaochrona przeciwpowodziowa zdefiniowana przez MKOOpZ aż do roku 2030 zmniejszykulminację przepływu powodziowego od 435 do 1330 m3/s (14÷46 %), a poziom wodyna obszarze Polski od 80 do 300 cm. Dla Niemiec zmniejszenie kulminacji przepływuwyniesie od 58 do 466 m3/s, a poziom wody od 27 do 79 cm. W Czechach efekt będziemniejszy (-69 m3/s). Wniosek odniesiono do powodzi z 1997 r. i porównano zsymulacjami wykorzystującymi warunki referencyjne 2001 r.

W Czechach, przy założeniu wybudowania nowych, planowanych zbiornikówzaporowych, można osiągnąć redukcję kulminacyjnej fali powodziowej (-84 m3/s)poprzez ponowne zalesienie i zmiany w zarządzaniu zbiornikami zaporowymi(wodnymi) ukierunkowane na ochronę przed powodzią. Poprzez optymalizacjęzbiorników zaporowych (wodnych) można zmniejszyć kulminację fali powodziowej o266 m3/s w Odrze poniżej ujścia Olzy. Maksymalne możliwe zalesienie mogłobyspowodować dalszą redukcję o ok. 80 m3/s.

W Polsce planowane poldery i zbiorniki retencyjne redukują ryzyko powodzi.Udoskonalenie zarządzania zbiornikami zaporowymi (wodnymi) poprzezukierunkowanie na ochronę przed powodzią również spowoduje zmniejszenie ryzykapowodzi nawet w jeszcze większym stopniu. Czas uaktywnienia (podjęcia pracy)polderów warunkuje ich skuteczność. Powinno zwrócić się uwagę na planowane zmianyprzekroi, ponieważ wiele proponowanych zmian redukuje potencjalną pojemność wprzekroju poprzecznym rzeki powodując wzrost stanów wody i przepływów.Podwyższenie lub budowa nowych wałów zmniejsza lokalne zagrożenie powodziowe,ale może spowodować problemy w innych regionach poniżej. Zmiany przekroi, którezwiększają pojemność retencyjną w obrębie przekroju nie powodują negatywnegooddziaływania w dole rzeki.

W Niemczech planowane poldery w Zilterdorf i Neuzell mogą pomóc do zmniejszeniazagrożenia powodziowego w pobliżu Frankfurtu i poniżej niego pod warunkiem, żerozpoczną pracę we właściwym czasie tuż przed nadejściem fali powodziowej. Wzrostpojemności retencyjnej terenów zalewowych zmniejszy stany wody o ok. 60 cm.Kompilacja nowych polderów i retencji na terenach zalewowych zmniejszy kulminacjęprzepływu we Frankfurcie/Słubicach o 141 m3/s lub 71 cm.

Przy planowaniu przyszłych przedsięwzięć przeciwpowodziowych powinno się wziąćpod uwagę, że spodziewana w przeciągu najbliższych 30 lat urbanizacja doprowadzi doniewielkiego wzrostu kulminacji przepływu (max. + 43 m3/s). Należy zauważyć, żepodczas powodzi 1997 r. największy opad wystąpił nie w terenach zurbanizowanych,lecz na obszarach wiejskich i górskich. Jeśliby opad ten wystąpił na obszarachzurbanizowanych, rezultat wzrostu urbanizacyjnego byłby większy.

W opracowaniu zademonstrowano, że zmiany w zagospodarowaniu (użytkowaniu)powierzchni terenu (głównie urbanizacja) od roku 1780 do czasów obecnychzwiększyły kulminację przepływów w Odrze. Powierzchnia całkowita lasów zwiększyłasię od 1780 r. za wyjątkiem regionów z intensywnie rozwijającą się urbanizacją. Pozatym należy zauważyć, że skutek urbanizacji byłby większy, jeśli rozkład przestrzennyopadów byłby inny, tzn. większy na obszarach zurbanizowanych.

Przewidywane skutki zmiany klimatu są trudne do oszacowania, ponieważ rezultatyróżnych scenariuszy dot. zmiany klimatu są bardzo zmienne. Chociaż przewiduje się, żeopad w skali globalnej wzrośnie, jego zróżnicowanie przestrzenne i wielkość wciążpozostają niejasne. Ilość ekstremalnych opadów mogłaby wzrosnąć przy niezmiennej ichwielkości lub też ilość ekstremalnych opadów mogłaby pozostać niezmienna przy ichwzroście. Z powodu tych niejasności dla niniejszego opracowania zaproponowano tylkouproszczone scenariusze zmian klimatu oparte o ogólne tendencje. Generalnie, wzrosttemperatury jest całkiem prawdopodobny. Prowadziłby on do zmniejszenia siękulminacji przepływu i wzrostu ewapotranspiracji. Przykładowo, wzrost temperatury o 1stopień (scenariusz tp1) skutkowałby zmniejszeniem maksymalnych przepływów o51÷197 m3/s, co odpowiada 13÷29 cm poziomu wody. Scenariusz kompilacyjny (wzrostopadów o 15 % i temperatury o 1 stopień) powoduje zwiększenie się kulminacjipowodziowej (500÷700 m3/s dla wszystkich miejsc), jednak jak nadmieniono wcześniej,uzyskane na podstawie tego scenariusza rezultaty są wątpliwe (dyskusyjne). Pomimo torezultaty sugerują, że w planowaniu ochrony przeciwpowodziowej nie powinno sięignorować możliwych efektów zmiany klimatu.

Zusammenfassung

HintergrundIm Juli 1997 wurden die Oder und ihre Zuflüsse von extremem Hochwasser heimgesucht,bei dem 114 Menschen ums Leben kamen, 195.000 Menschen evakuiert wurden. DerGesamtschaden wird auf 4,6 Mrd. EURO geschätzt. Vor diesem Hintergrund begann dieGemeinsame Forschungsstelle der Europäischen Kommission das numerischeSimulationsmodell ODER-LISFLOOD zu entwickeln. Diese Studie ist ein Beitrag derEU zu den Arbeiten der Arbeitsgruppe 4 „Hochwasser“, die nach dem Hochwasser 1997im Rahmen der Internationalen Kommission zum Schutz der Oder (IKSO) eingerichtetwurde. Der Vertrag über die IKSO wurde im April 1999 ratifiziert. Nach der offiziellenEinrichtung der AG 4 begann die internationale multidisziplinäre Zusammenarbeit mit:• Europäische Kommission, Gemeinsame Forschungsstelle, (JRC), IES-LM Unit, Ispra,

Italien• Tschechisches Hydrometeorologisches Institut (CHMU), Prag, Tschechische

Republik• Institut für Meteorologie und Wasserwirtschaft (IMGW), Wroclaw, Polen• Regionale Wasserwirtschaftsverwaltung (RZGW), Wroclaw, Polen• Landesumweltamt Brandenburg (LUAB), Potsdam, Deutschland• Sächsisches Landesamt für Umwelt and Geologie (SLUG), Dresden, Deutschland

Projekt ODER-LISFLOODDie wichtigsten Ziele des Projektes sind:• Erforschung der Auswirkung von Landnutzungsänderungen auf das

Hochwasserrisiko (historische Landnutzungsänderungen und zukünftigeEntwicklungen)

• Untersuchung der Auswirkungen mehrerer Szenarien von möglichenHochwasserschutzmaßnahmen. Die Szenarien wurden durch die IKSO und Expertenvon wasserwirtschaftlichen Verwaltungen in der Tschechischen Republik, Polen undDeutschland vorgeschlagen.

• Untersuchung der Folgen von möglichen Klimaänderungen auf das Hochwasserrisikoin der Oder.

Diese Ziele wurden durch die Entwicklung eines Hochwassersimulationsmodells für dasEinzugsgebiet der Oder in folgenden Phasen umgesetzt:• Entwicklung eines an die Oder-Bedingungen angepassten LISFLOOD-Modells;• Entwicklung eines hochaufgelösten GIS für das Oder-Einzugsgebiet;• Testen und Kalibrierung des LISFLOOD-Modells für die Hochwasserereignisse

1977, 1985 und 1997• Szenariensimulierung zur Untersuchung der Auswirkungen von möglichen

Hochwasserschutzmaßnahmen.

Die Arbeitsgruppe Hochwasser der IKSO stellte eine Liste von 81 Szenarien mitHochwasserschutzmaßnahmen auf.

LISFLOOD-ModellAnhand des LISFLOOD-Modells können Hochwasserereignisse in mittleren und großenEinzugsgebieten simuliert werden. Im Gegensatz zu den meisten hydrologischenModellen kann LISFLOOD große Gebiete mit hoher Auflösung simulieren, und dabeigleichzeitig den Flutwellenablauf und die physikalischen Prozesse korrekt beschreiben.LISFLOOD-Modell besteht aus einem einzugsgebietsbezogenen Wasserbilanzmodell,einem einzugsgebietsbezogenen Hochwassermodell, sowie einemÜberschwemmungsgebiets-Simulationsmodell. Die drei Modelle sind in Reihegeschaltet, so dass die Ausgangsdaten des einen Modells die Eingangsdaten des nächstenModells werden. Dadurch kann LISFLOOD sowohl die Auswirkungen vonLandnutzungs- und Klimaänderungen als auch Methoden des technischenHochwasserschutzes simulieren.

MethodikFür diese Studie wurde das Odereinzugsgebiet oberhalb der Warthe-Mündung mit einerGitterweite von 1 km2 simuliert. Die Gesamtfläche dieses Gebiets beträgt 53.787 km2.Ein digitales Reliefmodell (DEM) mit horizontaler Raumgenauigkeit von 75 mzusammen mit Digitalkarten der wirklichen Flussläufe wurden für die Bestimmung derGewässernetzes benutzt. Speziell für dieses Projekt wurde eine Bodendatenbank für dieOder im Maßstab 1:250 000 in Zusammenarbeit mit European Soils Bureau derEuropäischen Kommission entwickelt. Weiterhin wurde die LandnutzungsdatenbankCorine – entwickelt im Rahmen des PHARE-Programms der Europäischen Kommission– mit einer Auflösung von 100 m benutzt,. Darüber hinaus haben JRC und GISIG einedigitale historische Landnutzungsdatenbank in Anlehnung an die Schmettau-Kartenentwickelt, die die Landnutzung an der Oder um das Jahr 1780 darstellt.

Angaben über Niederschlag und Abfluss, Profilgeometrie und Rauhigkeitswerte,Grundwasser, und Evapotranspiration wurden von den zusammenarbeitendenWasserverwaltungen im Rahmen dieses Projekts (CHMU, IMGW, LUAB, SLUG) undteilweise von JRC gewonnen.

Es wurden drei historische Hochwasserereignisse für das Testen des LISFLOOD-Modellsausgesucht: das Hochwasser im August 1977, im August 1985 und im Juli 1997. ImGrossen und Ganzen zeigen die Ergebnisse, dass das LISFLOOD-Modell sowohl diegesamte Wasserbilanz der Oder als auch die drei Hochwasserereignisse mit großerGenauigkeit simuliert, so dass es als ein Modell für die Analyse der Szenarien verwendetwerden kann. Eine Verbesserung der Ergebnisse im Laufe der Zeit von 1977 bis 1997kann festgestellt werden. Diese ist auf verbesserte Eingangsdaten zurückzuführen, vorallem auf die höhere Anzahl von Niederschlags- und meteorologischen Stationen.

Eine Liste von 81 Szenarien wurde aufgestellt, um die Ergebnisse derHochwasserschutzmaßnahmen sowie zu erwartende künftige Klimatrends undLandnutzungsänderungen zu ermitteln. Diese Szenarien können in acht Gruppen geteiltwerden:

• Referenzszenarien, die die aktuelle Situation wiedergeben

• Szenarien mit technischen Maßnahmen, vorgeschlagen von der IKSO bis 2030• Szenarien für Bewirtschaftungsregime der Staubecken• Szenarien der historischen Landnutzung• Szenarien für in der Zukunft zu erwartenden Landnutzungsänderungen und

Hochwasserschutzmaßnahmen durch Landnutzung• Szenarien für das Brandenburgische Retentionsgebiet• Szenarien für Klimaänderungen• Szenarienkombinierung

Das Hochwasser von 1997 wurde den Szenarien zu Grunde gelegt. Als Referenz dient dieSimulation, die das Hochwasser von 1997 mit den damals existierendenHochwasserschutzmassnahmen simuliert. Das bedeutet, dass alle Szenarienergebnissesich auf dieses Hochwasser mit der gegebenen Niederschlagsverteilung von 1997beziehen. Für weniger regenintensive Ereignisse oder Ereignisse mit einer anderenNiederschlagsverteilung würden selbstverständlich andere Ergebnisse erzielt.

Für den Bedarf dieses Projekts werden die Deichbrüche nicht berücksichtigt, weil esnicht vorauszusehen ist, wie sich die Deichbrüche im Falle der einzelnen Szenarienentwickeln, und ob sie überhaupt zustande kommen. Um die Szenarien einheitlichvergleichen zu können, wurden die Deichbrüche nicht simuliert: der Wasserspiegel imFluss kann somit sogar höher als die maximale Deichhöhe steigen. Die Ergebnisse zeigenin diesem Fall, dass unter der Annahme, dass kein Wasserverlust auftritt, keine Deichebrechen, und alle Hochwasserschutzmassnahmen simuliert werden, ein höhererPegelstand entstehen kann als 1997 gemessen wurde.

SchlussfolgerungenAuf Grund der Szenarienberechnung kann die Schussfolgerung gezogen werden, dassdie von der IKSO bis 2030 vorgeschlagenen technischenHochwasserschutzmaßnahmen den Hochwasserabfluss von 435 bis 1330 m3/s (14-46%) reduzieren, sowie den Wasserspiegel in Polen um 80-300 cm senken würde. FürDeutschland würden die IKSO-Maßnahmen den Hochwasserabfluss um 58-466 m3/sreduzieren sowie den Wasserspiegel um 27-97 cm senken. In der TschechischenRepublik sind die Auswirkungen geringer (-69 m3/s). Diese Schlussfolgerung gilt für dasHochwasser 1997 und wird mit der Simulation der Referenzbedingungen 2001verglichen.

In der Tschechischen Republik kann neben den neben geplanten Staubecken eineReduzierung des Hochwasserabflusses durch Aufforstung (-84 m3/s) und Änderung desoperationellen Bewirtschaftungsregimes zugunsten des Hochwasserschutzes erreichtwerden. Durch die Optimalisierung des Bewirtschaftungsregimes der Staubecken kannder Hochwasserabfluss auf dem Oder/Olse-Pegel um 266 m3/s reduziert werden.Zusätzliche Aufforstung würde diese Reduktion um ca. 80 m3/s erhöhen.

In Polen reduzieren die geplanten Polder und Staubecken die Hochwassergefährdung.Auch hier wird das verbesserte Bewirtschaftungsregime der Staubecken zugunsten desHochwasserschutzes die Hochwassergefährdung sogar mehr reduzieren. Die Zeit der In-

Betrieb-Setzung der Polder entscheidet über ihre Wirksamkeit. Bei der geplantenProfiländerungen muss aufgepasst werden, denn viele vorgeschlagene Änderungen dieKapazität des Flussprofils reduzieren, wodurch der Wasserspiegel und der Abfluss erhöhtwerden. Die Deicherhöhung oder Neubau von Deichen reduzieren zwar die lokaleHochwassergefährdung, sie können aber Probleme in anderen unterhalb gelegenenGebieten verursachen. Die Profiländerungen, die die Abflusskapazität auf den Profilenerhöhen, haben stromabwärts keine negativen Auswirkungen.

In Deutschland können die geplanten Polder in Ziltendorf and Neuzell bei derReduzierung der Hochwassergefährdung in der Nähe von Frankfurt und weiterstromabwärts helfen, wenn diese Polder rechtzeitig in Betrieb gesetzt werden, bevor dieHochwasserwelle kommt. Die Erhöhung des Retentionsvermögens derÜberschwemmungsgebiete reduziert den Wasserspiegel um ca. 60 cm. DieKombinierung der neuen Polder und der Retention im Überschwemmungsgebietreduziert die Hochwasserwelle in Frankfurt/Slubice um 141 m3/s beziehungsweise 71cm.

Die erwartete Entwicklung der Städte in den nächsten 30 Jahren wird zur leichtenErhöhung des Hochwasserabflusses führen (max. +43 m3/s). Bei der Planung derzukünftigen Hochwasserschutzmaßnahmen sollte dies berücksichtigt werden. Es mussdarauf hingewiesen werden, dass während des Hochwassers 1997 die größtenNiederschläge nicht in den besiedelten Gebieten, sondern auf dem Lande und in Gebirgenvorkamen. Sollten stärkere Niederschläge in den besiedelten Gebieten vorkommen,werden die Folgen der Städteentwicklung größer sein.

In dieser Studie wurde gezeigt, dass die Landnutzungsänderungen seit 1780 bis heutedie Hochwasserwelle in der Oder erhöht haben. Das wird vor allem durch dieEntwicklung der Städte verursacht. Die gesamte Fläche der Wälder wuchs von 1780 bisheute, außer in Gebieten mit intensiver Städteentwicklung. Es muss wieder bemerktwerden, dass die Folgen der Städteentwicklung größer wären, wenn größereNiederschläge vorwiegend in besiedelten Gebieten stattfinden würden.

Die erwarteten Auswirkungen der Klimaänderungen lassen sich schwer ermitteln, weildie Ergebnisse der Szenarien für verschiedene Klimaänderungen sehr variieren. Obwohlerwartet wird, dass die Niederschläge weltweit größer werden, ist die Raumverteilungund Größe dieser Änderungen noch immer unklar. Die Anzahl der extremenNiederschläge könnte wachsen, wobei die Regenmenge unverändert bleibt oder dieAnzahl der extremen Niederschläge könnte auf demselben Niveau bleiben, aber dieNiederschlagsmenge könnte wachsen. Wegen dieser Unsicherheiten wurden für dieseStudie nur vereinfachte Szenarien der Klimaänderungen auf Grund der allgemeinenTrends vorgeschlagen. Im allgemeinen könnte eine Temperaturerhöhung auftreten, unddas resultiert in der Senkung des Gesamtabflusses und Erhöhung der Evapotranspiration:die Erhöhung der Temperatur um ein Grad (Szenarium tp 1) führt zur Reduzierung desmaximalen Abflusses um 51-197 m3/s, das entspricht der Senkung des Wasserspiegelsum 13-29 cm. Ein kombiniertes Szenarium (+15% Niederschlag, + 1 GradTemperaturanstieg) verursacht eine Erhöhung des Hochwasserabflusses (500-700 m3/s

für alle Stellen), aber, wie oben erwähnt, ist es fraglich, ob dieses Szenarium realistischist. Trotzdem deuten die Ergebnisse an, dass mögliche Auswirkungen der Klimaänderungbei der Planung der Hochwasserschutzmaßnahmen nicht ignoriert werden sollen.

Introduction

In July 1997, an extreme flood hit the Oder and its tributary rivers, resulting in 114deaths, 195.500 people evacuated and approximately 4600 Million Euros damage.Following the extreme flood, the Joint Research Centre of the European Commissionstarted a model simulation study called ODER-LISFLOOD. This study is the EUcontribution to the ‘Workgroup Floods’ within the framework of the InternationalCommission for the Protection of the Oder river (IKSO), which was established after theflood and officially ratified in April 1999. Since its official start in January 1999, aninternational multi-disciplinary collaboration is brought together, consisting of:• European Commission, Joint Research Centre (JRC), IES-LM Unit, Ispra, Italy• Czech Hydro-Meteorological Institute (CHMI), Prague, Czech Republic• Institute of Meteorology and Water Management (IMGW), Wroclaw, Poland• Regional Water Development Authority (RWDA), Wroclaw, Poland• Landesumweltamt Brandenburg (LUAB), Potsdam, Germany• Sächsisches Landesamt für Umwelt and Geologie (SLUG), Dresden, Germany

The most important objectives of the project are:• to investigate the effects of land-use change on flood risk (historic land use changes

and future developments)• to assess the effects of possible flood defense measures - scenarios . The scenarios

were proposed by the IKSO and experts from the Water Authorities in the CzechRepublic, Poland and Germany

• to assess the consequences of climate change trends on flood risk.

These objectives were realized by the development of a flood simulation model for theOder basin with the following phases:• development of the LISFLOOD model including special modifications for the Oder;• development of a high-resolution GIS for the Oder basin;• testing and validation of the LISFLOOD model for the floods of 1977, 1985 and 1997• simulation of scenarios to assess the effects of possible flood defense measures.

1. The LISFLOOD modelling system

LISFLOOD is a model that has been developed at the Joint Research Centre (JRC,Institute for Environment and Sustainability - IES) of the European Commissionexplicitly for the simulation of floods in large European drainage basins. One of itspurposes is to serve as a reference model to assess the influences of European policies onflood risk. Unlike most other hydrological models – such as MIKE-SHE (Abbott et al,1986), TOPMODEL (Beven & Kirkby, 1979) or HBV (Lindstrom et al 1997) -, it iscapable of simulating large areas, while still maintaining a high resolution, proper floodrouting methods and physical process descriptions. Since the physical processdescriptions are universal, no or little additional calibration is needed if applied in a newcatchment. LISFLOOD is also especially designed to simulate the effects of change in aeasy and realistic way: land-use changes, modifications of the river geometry, waterreservoirs, retention areas and effects of climate change. LISFLOOD is embedded in aGIS and is using readily available European datasets, such as Corine land cover, theEuropean Soils Database, and the 1km resolution European flow network (De Roo et al.2000b).

LISFLOOD simulates the hydrological processes at the surface, in the soil, and in theriver channel network on a regular horizontal grid (figure 1), usually using a highresolution compared to the catchment size: LISFLOOD can easily handle 100,000 gridsor more. In the vertical a total of 4 different are considered. For each grid point a value iscalculated at every time step.

Figure 1: Schematic view of a catchment in LISFLOOD including two soil layers and twogroundwater zones.

The processes simulated in LISFLOOD

The theory of the model is described in detail in publications from De Roo et al. (2000a),De Roo et al. (2000c) and De Roo et al. (2001). In the following, only the basic processesare summarised

• At the surface, the predominant processes are the division of precipitation into rainfalland snow, snowmelt, glacier flow, interception by vegetation and evapotranspiration.Seasonal variations of the vegetation cover are also taken into account. The amount ofeffective precipitation is divided into overland flow and infiltrated water.

• Precipitation data from individual stations can be used in LISFLOOD, whichare then interpolated using an inverse distance method using the closeststations. Precipitation is corrected for altitude effects, based on precipitation-altitude relations found in the catchment to be simulated.

• Snowfall is simulated when the average daily temperature is lower than 1.0degree Celsius. Minimum and maximum daily temperature values fromstations are interpolated using an inverse distance method of the closeststations, and on each pixel are corrected for altitude.

• Interception of rainfall by the vegetation is simulated using the method of VonHoyningen-Huene (1981) for all land use except forests, for which theapproach of Shuttleworth and Calder (1979) is used. The equations are basedon the Leaf Area Index of the vegetation. Seasonal changes of LAI are takeninto account.

• Evapotranspiration is simulated using the Penman-Monteith method, asapplied in the WOFOST model (Supit et al., 1994, Van Der Goot, 1997).Meteorological variables used are temperature, wind speed, sunshine duration,cloud cover and actual vapor pressure, which are all interpolated from stationdata using an inverse distance method and where appropriate corrected foraltitude. The Leaf Area Index of each simulated pixel is used to calculateactual evapotranspiration from potential evapotranspiration.

• Snowmelt is simulated using a degree-day method (Baumgarter et al., 1994),when the average daily temperature is above 0 degrees Celsius.

• In the soil, LISFLOOD calculates the vertical transport of water in two soil layers.The flow rate depends on soil parameters such as soil texture the percolation to thegroundwater and storage of groundwater is also simulated. Also, lateral subsurfaceflow is simulated.

• Infiltration is simulated using the Smith-Parlange equation (Smith andParlange, 1978). The capillary drive value is based on topsoil texture.Saturated hydraulic conductivity values are based on topsoil texture and landuse. In city areas and on water bodies no infiltration takes place.

• Soil freezing is simulated using a degree-day method (Molnau and Bissel,1983). If the soil is frozen to a certain degree, infiltration is reduced to zero

• Vertical transport of water in the two soil layers is simulated using a one-dimensional form of the Richard’s equation. Soil water retention andconductivity curves are described by van Genuchten's (1980) relationships.Pedotransfer-functions from the HYPRES project (Wosten et al, 1998) areused to calculate the water retention and conductivity curves from soil texture.Both soil texture and soil depth are derived from the European Soils Database(Finke et al., 1998) or local soil maps.

• Lateral flow is simulated using a simplified Darcy approach.• Percolation to the groundwater store is calculated using the Darcy equation.• Groundwater storage and transport to the channel system are simulated with

an upper and a lower groundwater zone, and groundwater is then routed usinga response function similar to the one adopted in the HBV model (Lindströmet al., 1997).

• The routing of overland flow water and river water can be calculated with a kinematicwave or a dynamic wave, depending on data availability and channel bed gradient.LISFLOOD can also simulate special structures such as water reservoirs and retentionareas by giving their location, size and in- and outflow boundary conditions(maximum storage volume, minimum and maximum outflow, reservoir managementparameters).

• Overland flow and transport to the channel system is simulated using a four-point finite-difference solution of the kinematic wave (Chow et al. 1988)together with Manning's equation.

• Channel flow is also simulated using a four-point finite-difference solution ofthe kinematic wave (Chow et al. 1988) together with Manning's equation. Asolution of the dynamic wave equation can be used for lowland river systems,such as the lower Oder or Rhine. The channel and floodplain dimensions(width, shape and depth) are used to calculate the wetted perimeter.

• Special structures such as water reservoirs and retention areas can be simulated bygiving their location, size and in- and outflow boundary conditions (maximum storagevolume, minimum and maximum outflow, reservoir management parameters).

Input data for LISFLOOD

Meteorological input data can either be given as point data (from weather stations) or asgridded data (as from radar measurements or meteorological forecast models). Otherinput data are needed to define the surface (topography, slope gradient) and the canopy(land-use, leaf area index, rooting depth), the soil (soil texture, soil depth, manningcoefficient), and the channel network (dimensions of the channel and the floodplain suchas width and depth, bedslope, manning). The rule holds that the better the quality of theinput data the better the model results. Inputs used are readily available European datasetssuch as Corine land cover, a 1km resolution DEM, a 1km resolution European flownetwork (De Roo et al, 2000b), the 1m and 250k scale European soils database (European

Soils Bureau, 1998), the HYPRES soil hydraulic properties database, and the JRC-MARSmeteorological database.

LISFLOOD output

The LISFLOOD output can be any variable calculated by the model. The format can behydrographs at user-defined locations in the catchment - usually those locations wherealso observations exist, time-series of for example evapotranspiration, soil moisturecontent or snow depth, and maps such as water source areas, discharge coefficient, totalprecipitation, total evapotranspiration, total groundwater recharge and soil moisture maps(fig. 2).

LISFLOOD is programmed and embedded in the PCRaster GIS dynamic modellinglanguage (Wesseling et al, 1996), which makes the model user-friendly and its resultseasy to export and to compare with other data sources. Depending on the time step,LISFLOOD can operate as a waterbalance model (daily time step, simulating timeperiods of the order of one to several years) and as a flood simulation model (hourly timestep, simulating time periods of the order of days to weeks). The waterbalance model caneither stand alone or serve to provide the initial conditions for the flood model. Coupledto the flood simulation model LISFLOOD can also be a flood plain inundation model,which then calculates with a time step of the order of seconds how a floodplain may beinundated during a flood (time period of the order of 1 hour to days) (Bates & De Roo,2000).

Figure 2 : Examples of LISFLOOD input and output data.

Simulating reservoirs

Water reservoirs are simulated as points, with a given water storage potential in Mm3,and outflow operation rules. For every water reservoir, the user defines the total storagevolume, the conservative storage volume, the flood storage volume, and the normalstorage volume. Depending on the fraction of the reservoir filled, the outflow in m3/s iscalculated based on the user defined minimum outflow, the normal outflow and the non-damaging outflow.

Simulating polders

Polders are also treated as points, with a user-defined storage potential. If discharge in theriver adjacent to the polder reaches a user-defined level, the polder starts to be active untilit is filled. Next, if discharge in the river drops to another –lower– user-defined value, thepolder is emptied gradually.

Limitations of the model

Every hydrologic model is made for a specific purpose and scale. LISFLOOD is made forlarger catchments. The maximum catchment area is limited to computer power only. Alsoone should take into account that the grid-size used should correspond to the dataavailability, and not be chosen too coarse. For example, the model would be suitable tosimulate catchments such as the Danube or the Rhine with a 1km grid too. The minimumcatchment size is not so much an issue: even very small catchments (50 km2 or so) couldeasily be simulated with smaller grids (100*100 m). What becomes more important is thetimestep. As for now, LISFLOOD runs with an hourly or daily timestep. For very smallcatchments, with a very fine gridsize (5-25m), the timestep of the model has to bedecreased.

Limitations of LISFLOOD as it is used in the Oder catchment, are partly based on dataavailability limitations: the number of available river cross sections, the number ofprecipitation stations and climate stations could all be increased to obtain improvedresults. Also, mainly daily weather data were used here. The use of hourly data wouldalso improve the results probably. Furthermore, reservoir management operations weremore or less automated in this study, whereas in reality humans are in control, who maytake different decisions for reservoir outflow.

The algorithms used in the model were chosen carefully to match the spatial and temporalresolution of the catchment and the data available, and the spatial and temporal scale ofthe most important hydrological processes. However, a model is always a simplificationof reality.

2. Validation

LISFLOOD-FS is a flood simulation model with an hourly timestep. The model has beencalibrated and validated in the Oder catchment for three historic flood events: August1977, August 1985 and July 1997. To estimate the initial conditions, water balancemodels (LISFLOOD-WB, daily timestep) have been run for the previous two years ofeach flood event: 1976-1977, 1984-1985, and 1996-1997.

The following input data – obtained from JRC databases and through cooperation withthe national institutes - have been used for validation and testing of the model:• 137 precipitation stations (sources: JRC-MARS database, IMGW and CHMI) (figure

3)• 14, 17 or 23 weather stations (temperature, windspeed, actual vapour pressure,

sunshine duration, cloud cover) (source: JRC-MARS database) (figure 4)

Figure 3. Precipitation stations used for the model simulations.

• 1 km resolution Digital Elevation Model• 1 km resolution flow network, based on a 75 m Digital Elevation Model and GIS data

on actual rivers• 1 km resolution slope gradient map, based on calculations using the 75m DEM• 1 km resolution land use map (CORINE). Sub-grid information based on 100m

resolution maps used for urban and forest coverage

Figure 4. Meteorological stations used for the simulations.

• 1 km resolution maps of soil texture and soil depth to bedrock or the groundwatertable, based on the 1:250,000 scale soils database of the Oder catchment (source:European Soils Bureau, JRC)

• 158 River and floodplain cross sections. For the Oder on the German/Polish borderthe high resolution DEM from LUAB was used to extract the cross sections at everyriver km (sources: IMGW, CHMI, LUAB, Sachsen).

• From 11 water reservoirs inflow and outflow data were available. From these dataand additional information on the reservoirs, the reservoir operation rules (minimumstorage, minimum outflow, non-damaging outflow, flood storage volume etc) wereestimated (sources: IMGW and CHMI) (figure 5)

• For 111 locations along the Oder and its tributaries, Manning roughness coefficientswere provided by IMGW.

For the validation 71 gauging stations with observed discharge have been used. 22stations in Poland with estimated potential evaporation (Jaworski method) have beenused to validate the potential evapotranspiration estimates of LISFLOOD.

During the testing of the model in the Oder catchment, it has been decided to calibrateLISFLOOD on the following parameters only:• Groundwater parameters (conductivity of upper and lower zone, transport from upper

to lower zone)• Evapotranspiration correction (for 1977 and 1985 event only)

Figure 5. Current and planned reservoirs in the Oder catchment used in this study.

On the next pages graphs with observed and simulated discharge are shown for the threeflood events for the stations Dehylov (Cz), Miedonia (P) and Frankfurt/Slubice (D/P).

Figure 6. Observed and simulated hydrograph at Dehylov (Cz) for the 1977 flood.

Figure 9. Observed and simulated hydrograph at Miedonia (P) for the 1977 flood.

Figure 12. Observed and simulated hydrograph at Slubice (P) for the 1977 flood.

Figure 15. Observed and simulated total discharge for all Oder tributaries and theOder upstream of Bohumin (Cz) from 1-1-1996 until 31-10-1997,simulated with the LISFLOOD Waterbalance model.

In general it can be concluded that LISFLOOD simulates the overall water balance of theOder catchment (figure 15) with reasonable quality, sufficient to be used as initialconditions for the flood simulation model. Layers with initial boundary conditions thatare used for the flood simulation are: soil moisture in the upper and lower soil layer,groundwater amounts in the upper and lower zone, snow depth, soil freezing conditions,the initial amount of discharge in rivers and overland flow, and the storage of water inreservoirs.

For the LISFLOOD flood simulation model (figures 6-14) it can be concluded thatLISFLOOD in general simulates the response of the Oder and its individual tributariessatisfactory for the three flood events.

3. Scenarios

3.1 Scenario Building Stones

Based on the discussions and meetings within IKSO (27 July 2001 in Wroclaw) and theOder-LISFLOOD partners (CHMI, IMGW, LUAB) (11 October 2000 in Wroclaw), anumber of scenarios have been defined for estimating the effects of measures on floods.

Figure 16. Scenario building stones can be combined to form the final scenario forsimulation

For this study, a scenario can consist of multiple so-called ‘scenario building stones’(figure 16). The building stones are individual measures or items, as discussed during themeetings. A final scenario for calculation with LISFLOOD can consist of multiplebuilding stones. Like this, combinations of multiple measures can be simulated in anintegrated way.

A list of the scenarios building stones is given in Tables 1-4. This list contains 9 itemsrequested from the Czech Republic, 46 items requested from Poland and 16 itemsrequested from Germany.

Table 1. Scenario building stones requested from the Czech Republic delegates.

Table 2. Scenario building stones requested from the Polish delegates.

Table 3. Scenario building stones requested from the German delegates.

Table 4. Scenario building stones requested from the German delegates, to besimulated with the flood inundation models.

3.2 Scenarios for calculation with LISFLOOD

From the building stones listed in tables 1-4, scenarios for calculation with LISFLOODhave been assembled (Table 5). For clarity reasons, these scenarios have been organizedin 7 groups:- ‘IKSO’: a group of scenarios simulating all measures until 2010, 2020 and 2030

as discussed during the IKSO meetings, finalized at the meeting on 27 July 2001in Wroclaw

- ‘reservoirs’: a group of scenarios varying reservoir operational management, asrequested by CHMI

- ‘historic land use changes’: a group of scenarios estimating the effects of historicland use changes in the Oder, based on JRC studies of changing land use

- ‘land use changes’: a group of scenarios on land use changes, as requested byCHMI, IMGW and OderRegio project partners

- ‘Brandenburg’: a group of scenarios with all possible combinations of 4 measuresalong the border of Germany and Poland, as requested by LUAB

- ‘climate change’: a group of scenarios on expected climate change, as requestedby IMGW.

- Combination scenarios: specific combinations of scenarios

Table 5. List of scenarios simulated in this study.

3.3 Scenario reporting

Following the agreements of the IKSO meeting on 27 July 2001 in Wroclaw, the resultsare summarized in the following way (table 6). Results will be presented for 5 stations:Odra/Olse, Miedonia, Opole, Wroclaw/Trestno and Frankfurt/Slubice (figure 17). Todemonstrate the consequences of some scenarios, Nysa is included in the list.

It has been decided to report the maximum discharge (Q) of the scenario, the maximumwater level (H), the total amount of discharge (m3) during July and August 1997, and theduration of the flood (days). For the duration, a threshold discharge value has beenestimated.

Figure 17. Discharge stations for reporting the results of the scenarios.

Table 6. Stations and variables included in the reporting of scenario results.

3.4. Scenario results

The results of the scenarios are first individually presented using a standard template,including the name of the scenario, the building stones used in the scenarios, the institutethat requested it, the results – including a graph, and if appropriate comments by JRC onthe results.

Following the individual results, several graphs are presented summarizing results ofgroups of scenarios together

As an appendix, all detailed results are listed in 5 tables: peak discharge (m3/s),maximum water level (m), water level changes (cm), total discharge (m3), and floodduration (days).

Reference Scenarios

Scenario - Nr.:1997ref

Scenario Proposed by:IKSO

Date:27-07-2001

Scenario Description:

Reference simulation of the July 1997 flood, without dyke-breaks, and with reservoiroperations simulated

LISFLOOD input data, specific for this scenario:

Based on the observed weather data, both for the waterbalance and the flood model.Based on the cross sections as delivered by IMGW, CHMI and LUAB.Based on reservoir parameters as delivered by IMGW and CHMI.The Sleska Harta reservoir has been simulated as emptyThe waterbalance model is run from 01/01/1996 until 30/06/1997.The flood model is run from 01/07/1997 until 31/08/1997.No dyke-breaks simulated.Reservoirs outflow simulated.

Summary description of LISFLOOD results:

Hydrographs showing 1997val (observed reservoiroutflow) and 1997ref (simulated reservoir outflow)

To maintain a possibility tocompare scenarios (dykesmight not fail anymore ifsufficient measures aretaken) dyke-failures werenot simulated. Simulateddischarges are thereforehigher than observed duringthe 1997 event.Also, reservoir operationsare simulated with generaloperating rules, based on thedata provided. Thus,simulated reservoir outflowcan be different from realreservoir outflow.

JRC comments on results:

Estimating reservoir outflow and not simulating dyke failures have to be done in order toobtain an objective comparison between scenarios.

Scenario - Nr.:2001ref

Date:27-07-2001

Reference simulation of the July 1997 flood, including several measures taken until 2001

As 1997ref scenarioReservoir management in the Nysa and Otmuchow reservoirs changed: the storagevolume before the flood is changed to the proposed values (0.376 and 0.390 fillingfractions as compared to 0.453 and 0.485 in the 1997ref scenario).The Sleska Harta reservoir (CZ) is now filled 40% (0.400 as compared to 0.000 in the1997ref scenario).

Summary description of LISFLOOD results: Simulated discharge islarger for Odra/Olse andMiedonia because of theincreased initial filling inthe Sleska Harta reservoir.Simulated discharge isslightly smaller at Nysabecause of the reservoiroperation changes in theOtmuchow and Nysareservoirs.The combined effect of thechanges at Opole, Trestnoand Slubice is a slightincrease in discharge (50-60m3/s).

Only the above three reservoir changes have been taken into account. If there have beenadditional changes between 1997-2001, they have not been simulated because data onthose changes were not communicated to JRC.

Scenario group ‘IKSO’

Scenario - Nr.:2010c

Date:27-07-2001

As 2001ref including all cross section changes until 2010

As 2001ref scenario, including P4-P5Cross section changes: P9-P20

Summary of LISFLOOD results:General increase ofdischarge and waterlevel(+30-60 cm) in Polandupstream of Wroclaw.A moderate decrease indischarge and waterlevelfurther downstream on thePolish/German border (-30cm).

Proposed cross section changes decrease local flood risk by constructing higher dykes butcause a faster transport of water and higher water levels due to the generally reduced totalcrosssection area and the floodplainwidth.

Scenario - Nr.:2010cb

Date:27-07-2001

As 2010c, plus the planned Raciborz polder (P1)

As 2001ref scenario, including P4-P5Cross section changes: P9-P20Polders: P1

Summary of LISFLOOD results:Moderate decrease ofdischarge at Miedonia (350m3/s). Capacity of Raciborzreservoir alone is notenough to store all waterduring the peak of the flood(polder Bukow is notincluded here).Downstream of Miedoniadecreases of discharge andwaterlevels compared to2001ref

Raciborz reservoir as stand alone measure not sufficient. Polder Bukow is needed as anadditional storage polder.

Scenario - Nr.:2010crb

Date:27-07-2001

As 2010cb, also including new planned reservoirs in Czech Republic (C1 – NoveHerminovy) and Poland (P2-P3: Topola and Kozielno)

As 2001ref scenario, including P4-P5New reservoirs: C1, P2-P3Cross section changes: P9-P20Polders: P1

Summary of LISFLOOD results:Decrease of peak dischargeat Olse/Odra (66 m3/s) andNysa (101 m3/s) and amoderate decrease furtherdownstream as a result ofthe new reservoirs

Scenario - Nr.:2010crp

Date:27-07-2001

All measures proposed until 2010: cross section changes, reservoirs, polders

As 2001ref scenario, including P4-P5New reservoirs: C1, P2-P3Cross section changes: P9-P20Polders: P1, P6-P8

Summary of LISFLOOD results:Strong decrease of dischargeat Miedonia and a moderatedecrease furtherdownstream.Upstream of Raciborz slightdecreases of dischargecompared to 2001ref

Scenario - Nr.:2020c

Date:27-07-2001

All measures proposed until 2010 and cross section changes until 2020 (P32-P37)

As 2001ref scenario, including P4-P5New reservoirs: C1, P2-P3Cross section changes: P9-P20, P32-P37Polders: P1, P6-P8

Summary of LISFLOOD results:Compared to 2010crpscenario, slight increase indischarge and waterleveldue to general cross sectionarea reduction.

Scenario - Nr.:2020cr

Date:27-07-2001

As 2010c and new reservoirs between 2010 and 2020 (C2-Bukovec, P24-P25: Kamienicand Raclawice)

As 2001ref scenario, including P4-P5New reservoirs: C1-2, P2-P3, P24-P25Cross section changes: P9-P20, P32-P37Polders: P1, P6-P8

Summary of LISFLOOD results:Compared to 2020cscenario, decrease ofdischarge at Nysa (-334m3/s) due to new reservoirs.As a consequence, alsodecrease of dischargedownstream of NysaKlodzka confluence with theOdra. Neglible effect of theBukovec reservoir (C2).

Scenario - Nr.:2020crp

Date:27-07-2001

All measures proposed until 2020, including new polders (P26-P31, D1-D2)

As 2001ref scenario, including P4-P5New reservoirs: C1-C2, P2-P3, P24-P25Cross section changes: P9-P20, P32-P37Polders: P1, P6-P8, P26-31, D1-D2

Summary of LISFLOOD results:

Hydrograph showing 2001 reference situation at Slubiceplus all measures until 2010 and 2020

Compared to 2020crscenario, decrease indischarge and waterlevel atSlubice (-97 m3/s) due tonew polders in Poland (P26-P31) and Germany (D1-D2).Slight decrease of dischargeat Trestno (-22m3/s) andOpole (-2 m3/s)

Scenario - Nr.:2030r

Date:27-07-2001

All measures proposed until 2030, including new Czech reservoir (C3)

As 2001ref scenario, including P4-P5New reservoirs: C1-C3, P2-P3, P24-P25Cross section changes: P9-P20, P32-P37Polders: P1, P6-P8, P26-31, D1-D2

Summary of LISFLOOD results:Compared to the 2020crpscenario, slight decrease indischarge at Olse (-4 m3/s)due to new Horni Lomnareservoir. The effect islarger at Miedonia (-36m3/s), Opole (-5 m3/s) andTrestno (-4 m3/s). No effectat Slubice on Qmax.

The results of the ‘IKSO’ scenarios show a decrease of flood peak discharges with 435 to1330 m3/s (14-46%) and decrease waterlevels between 80 cm and 300 cm for Poland andGermany. In the Czech Republic, the effects are less (-69 m3/s).

Figure 18. Maximum discharge (m3/s) for all ‘IKSO’ scenarios until 2030 for 6stations in the Oder catchment.

Figure 19. Waterlevel changes (m) for all ‘IKSO’ scenarios until 2030 for 6 stationsin the Oder catchment.

Scenario group ‘Reservoirs’

Scenario - Nr.:rnon

Scenario Proposed by:CHMI

Date:11-10-2000

As 2001ref, but without water reservoirs

As 2001ref scenarioReservoirs not simulated (C4)

Summary of LISFLOOD results:If reservoirs would not bepresent, discharge peaks inthe upstream parts of theOder would be higher. Forthe 1997 case, the dischargepeaks in the downstreamparts of the Oder would besmaller, because the severaltributary contributionsarrive at different times anddo not coincide anymore.The ‘Nysa-Klodzka’ peak isnow earlier than the‘Miedonia’ peak.

The result obtained here with the decreased peak discharge at Slubice is caused by thegeometry of the Oder catchment and the temporal development of the 1997 storm. Foranother event results could be different.

Scenario - Nr.:remp

Date:11-10-2000

As 2001ref, but with reservoirs empty before the 1997 flood

As 2001ref scenarioReservoirs empty before the flood (C5). During the flood, reservoirs are operated torelease part of the water to free the flood storage potential.

Qmax if all reservoirs would be empty as compared to the2001ref scenario

Flood peak discharges arelower because reservoirshave more storage potential.Effect is relatively smallbecause reservoirs aresimulated to release part ofthe water during the flood tofree the flood storagepotential.

Scenario - Nr.:rnrm

Date:11-10-2000

As 2001ref, but water reservoirs filled to normal storage level (flood storage level allavailable)

As 2001ref scenarioReservoirs filled to normal storage level (C6)

Qmax if reservoirs are filled at ‘normal storage level’ ascompared to the 2001ref scenario.

If reservoirs would havebeen filled to the normalstorage level – i.e. floodstorage volume empty – thepeak discharges would behigher than compared withthe 2001ref scenario.This is because thereservoirs were in generalemptier than the normalstorage level.

Scenario - Nr.:rff

Date:11-10-2000

As 2001ref, but with water reservoirs reacting to a flood forecast

As 2001ref scenarioReservoirs start outflow at ‘non-damaging-discharge’ on the 3rd of July 1997 because aflood warning is given (C7), and are maintained at a high filling level.

Qmax if reservoirs are reacting already 2 days before theflood if a good flood forecast would be available.

Lower peak dischargesbecause reservoirs arestarting outflow at ‘non-damaging discharge’ 2 daysbefore the flood.For some reservoirs, twodays time is not sufficient toempty the reservoir with theoutflow discharge equal to‘non-damaging-discharge’

Scenario - Nr.:rffemp

Date:11-10-2000

As rff, but water reservoirs are now emptied completely, and kept filled during the flood:reservoirs optimized for flood control

As rff scenarioReservoirs are emptied before the flood event because a flood warning was available(C7), and are kept filled at approx 90%

Qmax if reservoirs are optimized for flood control, ascompared to the 2001ref scenario

Lower peak discharges ifreservoirs are optimized forflood control: if reservoirsare emptied before a floodand are kept filled at a levelof approximately 90%Better results than with ‘rff’and ‘remp’ scenarios: ‘rff’empties reservoirs too slow;‘remp’ releases alreadywater during the flood tofree flood storage. With agood flood forecast it couldbe decided to keep to floodstorage partially filled,because no further extremedischarges are expected.

The effect of water reservoirs on flood risk is in general that water reservoirs in generalhave a buffer capacity to store a part of the flood water. If they would not exist, floodpeaks in upstream areas would be larger (scenario rnon). For downstream areas, due tothe geometry of the subcatchments in the Oder, flood peaks are lower (!) withoutreservoirs.If reservoirs would be emptied before a flood event – if for example a good flood forecastwould be available – this storage capacity is much larger. An issue is also when to startemptying a reservoir after a flood event. If they are not emptied – as in scenario rff – asecond flood peak as in the 1997 event cannot be buffered anymore. If they are partially(down to 90%) and slowly emptied at ‘non-damaging-discharge’, the thus created bufferis sufficient to reduce the second flood wave. It is clear that if reservoir operations areoptimized for flood control, peak discharges can be reduced.

Figure 20 Peak discharges for all ‘reservoir’ scenarios.

Figure 21 Reservoir filling fractions for the Nysa reservoir, Poland. If reservoirs arenot emptied after a flood, as in the ‘rff’ scenario, there is no buffercapacity.

Scenario group ‘Historic Land Use Changes’

Scenario - Nr.:1780

Scenario Proposed by:JRC

As 2001ref, but land use as in 1780. Reservoirs not taken into account

As 2001ref scenarioLand use (including urban and forest sub-grid maps) as in 1780 (source: historic maps)Reservoirs not taken into account

Summary of LISFLOOD results:Compared to the 2001refscenario, a first dischargepeak will appear sooner inTrestno, because reservoirsare not present. Thedifferent land use in 1780causes a smaller maximumdischarge. Around 1780there was less (!) forest andless urban area compared topresent day. The smallerurban area is responsible forthe lower discharge.

Scenario - Nr.:1975

As 2001ref scenarioLand use (including urban and forest sub-grid maps) as in 1975 (source: Landsat MSSsatellite images).Reservoirs not taken into account (for comparison reasons)

land use changes between 1780 and present

The land use changesbetween 1780 and 1975cause an increasedmaximum discharge.Around 1975 there is aslight increased (!) forestarea, a decreased pasturearea and an increased urbanarea, as compared to 1780.The changes in urban areaand pastures seem to causethe discharge increase.

Scenario - Nr.:1992

As 2001ref scenarioReservoirs not taken into account (for comparison reasons)

Changes in peak discharge due to land use changes

Between 1975 and 1992,there seems to be a slightreduced flood risk based onthe land use changes.Around 1992 the forest areaslightly increased (!), thepasture area increased andthe urban area increased.The changes in forest andpasture area are responsiblefor the slight dischargereduction.

Since between 1780 and 1975 the urban area increased, and the area of pasturesdecreased, the flood risk between 1780 and 1975 increased, despite the fact that the areaof forests has increased between 1780 and 1975.

Between 1975 and 1992, the area of forests and pastures has grown, by which the floodrisk has decreased slightly, despite the ongoing urban growth.

Figure 22. Peak discharges for historic land use change scenarios.

Scenario group ‘Land Use Changes’

Scenario - Nr.:mor

Date:11-10-2000

As 2001ref, land use changes according to ‘Morava study’

As 2001ref scenario, but land use now according to ‘Morava study’ (C9): 15% ofagricultural land is changed: 5% into forests, 10% into meadows and pastures. Based onthis concept, land use for the entire Oder catchment is changed. A random method is usedto select the 15% agricultural land, and which part is converted to forests or meadows.

Qmax for Morava land use change as compared to 2001refscenario

A decrease of peakdischarge in the order of 30-50 m3/s for all reportedstations

Scenario - Nr.:for

Date:11-10-2000

As 2001ref, but all areas above 500m – except urban area - converted to forests

As 2001ref scenario, but all areas above 500m – except urban area - converted to forests(C8). The 1km resolution Digital Elevation Model is used to select the target area.

Qmax after a reforestation above 500 m altitude

Decrease of flood peakdischarge with 15-100 m3/s.

Reforestation influences the complete annual waterbalance, and can also have effects forwater availability in dry summer periods.

Scenario - Nr.:fordie

Scenario Proposed by:IMGW

Date:11-10-2000

As 2001ref, but the effect of forest die back simulated in a part of Poland

As 2001ref scenario, but upstream Piechowice (Kamienna river) and Mirsk (Kwisa river)forest dieback is simulated. Below 700 m altitude, 10% of the forests are converted toshrubland, using a random procedure. Above 700 m altitude, 100% is converted toshrubland.

Slight increase of peak discharge at Slubice (+3 m3/s).Other areas not affected because no changes weresimulated

Slight increase of peakdischarge at Slubice (+3m3/s). Other areas notaffected because no changeswere simulated.

Scenario - Nr.:urb04

Scenario Proposed by:OderRegio

Date:11-12-2000

As 2001ref, urban growth according to ‘Polish Official Statistics’

As 2001ref scenario, including urban growth. From ‘Polish Official Statistics’ (Lavalle,2002) it is estimated that the population in urban areas will grow 4% between present andthe year 2030. The assumption is made here that urban area will grow with the same rate.

Slight increase in peak discharges (5-18 m3/s) for allreporting stations

Slight increase in peakdischarges (5-18 m3/s)

Estimations of population growth and urban growth are subject to uncertainties andshould be interpreted carefully.

Scenario - Nr.:urb22

Scenario Proposed by:OderRegio

Date:11-12-2000

As 2001ref, , urban growth according to ‘Polish Official Statistics’

As 2001ref scenario, including urban growth. From ‘Polish Official Statistics’ (Lavalle,2002) it is estimated that the number of households in urban areas will grow 22%between present and the year 2030. The assumption is made here that urban area willgrow with the same rate.

Peak discharges for urban growth scenarios as comparedto 2001ref scenario

Increase in peak dischargesfrom +9m3/s (Nysa) to +43m3/s (Slubice)

Estimations of population growth and urban growth are subject to uncertainties andshould be interpreted carefully.

Scenario - Nr.:setasd

Date:11-10-2000

As 2001ref, but with ‘set aside’ land use changes in specific Polish areas

As 2001ref scenario, but with ‘set aside’ land use changes upstream of Miedzylesie (NysaKlodzka river and tributaries), upstream Ladek (Biala Ladecka river), Kamienna Gora(Bobr river), Piechowice (Kamienna river). 25% of the agricultural land below 500 maltitude is converted to shrubland. Above 500 m altitude 50% is converted.

No effect at all, as compared to 2001ref scenario

The fact that this scenario has no effect depends also on the magnitude of the event. Setaside will influence the infiltration capacity of the soil and evapotranspiration. Obviouslyfor this event the evapotranspiration change does not play a role. Also, the event is solarge, that also a change in infiltration capacity, which is incorporated in the model, hasno effect: water will come down anyway, as overland flow or as subsurface flow. Therecould be an effect on soil erosion rates, but that is not taken into account by LISFLOODat present.

Land use changes do influence flood risk. The afforestation scenario (‘for’) shows adecrease in peak discharge especially visible at Olse, Miedonia and Opole. The ‘Morava’scenario shows also a reduced flood risk. Urban growth causes a slight increase in floodrisk.

Both the forest dieback and set aside scenario have hardly any effects, because the size ofthe area where they were implemented is small compared to the size of the Odercatchment.

Figure 23 Peak discharges due to land use change scenarios

Scenario group ‘Brandenburg’

Scenario - Nr.:d-n

Scenario Proposed by:LUAB

Date:27-07-2001

As 2001ref, but with Neuzell polder

As 2001ref scenario, but with Neuzell polder activated (D1)

Discharge at Slubice with and without the Neuzell polderactivated.

The Neuzell polder isactivated here if thewaterlevel in the Oder is750 cm. It takes a part of theflood wave away.In combination with theother measures (Ziltendorfplus floodplain measures)this is enough to influencethe peak discharge, but as astand alone measure thetime of activating should bedelayed to a later stage.

Scenario - Nr.:d-z

Date:27-07-2001

As 2001ref, but with Ziltendorf polder

As 2001ref scenario, but with Ziltendorf polder activated (D2)

Discharge at Slubice with and without the Ziltendorfpolder activated

The Ziltendorf polder isactivated here if thewaterlevel in the Oder is750 cm. It takes a part of theflood wave away.In combination with theother measures (Neuzellplus floodplain measures)this is enough to influencethe peak discharge, but as astand alone measure thetime of activating should bedelayed to a later stage.

Scenario - Nr.:d-3

Date:27-07-2001

As 2001ref, but with a floodplain enlargement of 300 m downstream of Ratzdorf

As 2001ref scenario, but with a floodplain enlargement of 300 m downstream of Ratzdorf(D3)

Discharge at Slubice with and without floodplainenlargement of 300m downstream Ratzdorf

Floodplain enlargement of300m downstream Ratzdorfleads to a shift of thehydrograph of 6 hours. Soflow is delayed for 6 hours.Effects on maximumwaterlevel and peakdischarge are minimal,because the extra 300 m isfilled already in an earlystage during the flood

Scenario - Nr.:d-1

Date:27-07-2001

As 2001ref, but with a floodplain storage increase of +1m (D4)

As 2001ref scenario, but with a floodplain storage (depth) increase of +1m downstreamRatzdorf (D4)

Waterlevels at Slubice with and without a 1 m. deepeningof the floodplain downstream Ratzdorf.

A floodplain deepening of 1m downstream of Ratzdorfleads to a drop in waterlevelof 58 cm at the time of thepeak. Peak discharges aremore or less equal.

Scenario - Nr.:d-nz

Date:27-07-2001

As 2001ref, but with Neuzell and Ziltendorf polders

As 2001ref scenario, but with Neuzell and Ziltendorf polders activated (D1-D2)

Discharge at Slubice with and without the Neuzell andZiltendorf polders activated

The two polders take a partof the flood wave away, butpeak discharge is still moreor less the same. If thesepolders should be used asthe only measure, the timeof activating (waterlevel =750 cm), should be delayed

Scenario - Nr.:d-31

Date:27-07-2001

Combination of d-3 and d-1

As 2001ref scenario, with floodplain enlargement (300m) and deepening (1m) (D3-D4)

Waterlevel at Slubice with and without the floodplainenlargement and deepening

Decrease of waterlevel atthe moment of the floodpeak of 53 cm

Scenario - Nr.:d-nz31

Date:27-07-2001

As 2001ref, but with combination of Neuzell and Ziltendorf polders, and the floodplainenlargement and deepening

As 2001ref scenario, but with Neuzell and Ziltendorf polders activated, and floodplainenlargement (+300m) and deepening (-1m) downstream Ratzdorf (D1-D4)

Discharge at Slubice with the Neuzell and Ziltendorfpolders, as well as the floodplain enlargement anddeepening, as compared to the 2001ref scenario.

If all 4 measures arecombined, the flood peakdischarge is reduced with141 m3/s or 71 cm.

The four scenario building stones proposed by LUAB (polders Neuzell, Ziltendorf, 300mfloodplain enlargement, 1m floodplain deepening) have been simulated in all possiblecombinations. The maximum effect can be obtained if they are all combined (scenariodnz31), leading to a reduced peak discharge at Frankfurt/Slubice with 141 m3/s or 71 cm.

It is important to activate the polders at the right time just before the flood wave arrivesto optimize its effectiveness.

Figure 24. Maximum waterlevel at Slubice for all LUAB scenarios

Scenario group ‘Climate Change’

Scenario - Nr.:pp15

Date:27-07-2001

As 2001ref, but with a precipitation increase of 15% before and during the flood period

As 2001ref scenario, but a precipitation increase of 15%. The observed daily precipitationof 1996 and 1997 is multiplied by 1.15 (P38). The waterbalance model is also run toobtain the changed initial conditions

Maximum Discharge (m3/s) for a scenario with 15% moreprecipitation.

Sharp increase in maximumdischarge for all sites: +600-900 m3/s

It is expected that worldwide precipitation will increase due to climate change, but thespatial pattern and the magnitude of these changes is still unclear. The number of extremerainfall events could increase, leaving their magnitude unchanged, or the number ofextreme rainfall events could stay the same, but their magnitude could increase. It is notknown if this scenario is realistic.

Scenario - Nr.:pp30

Date:27-07-2001

As 2001ref, but with a precipitation increase of 15% in the July and August and a 30%increase before

As 2001ref scenario, but a precipitation increase of 15% during July and August and a30% increase before. The observed daily precipitation of 1996 and 1997 is multiplied by1.30, during July and August by 1.15 (P39). The waterbalance model is also run to obtainthe changed initial conditions

Discharge at Wroclaw/Trestno for two climate changescenarios (pp15 and pp30) as compared to the 2001refscenario.

Higher discharges (50-190m3/s) than with the pp15scenario

Scenario - Nr.:pm10

Date:27-07-2001

As 2001ref, but with a precipitation decrease of 10%

As 2001ref scenario, but a precipitation decrease of 10%. The observed dailyprecipitation of 1996 and 1997 is multiplied by 0.90 (P40). The waterbalance model isalso run to obtain the changed initial conditions

Maximum discharge for the pm10 scenario: reducingprecipitation by 10%

Decrease of discharges, withpeak discharges decreasedwith 426-556 m3/s.

Scenario - Nr.:pm15

Date:27-07-2001

As 2001ref, but with a precipitation decrease of 15%

As 2001ref scenario, but a precipitation decrease of 15%. The observed dailyprecipitation of 1996 and 1997 is multiplied by 0.85 (P41). The waterbalance model isalso run to obtain the changed initial conditions

Maximum discharge for the pm15 scenario: reducingprecipitation by 15%

Decrease of discharges, withpeak discharges decreasedwith 590-810 m3/s.

Scenario - Nr.:tp1

Date:27-07-2001

As 2001ref, but with a temperature increase of 1 degree

As 2001ref scenario, but a temperature increase of 1 degree. The observed dailyminimum and maximum temperatures of 1996 and 1997 are increased by 1 degree (P42).The waterbalance model is also run to obtain the changed initial conditions

Maximum discharges if temperature rises 1 degree, ascompared to the 2001ref scenario

Decrease of peak dischargeswith 52-197 m3/s.

Scenario - Nr.:tm1

Date:27-07-2001

As 2001ref, but with a temperature decrease of 1 degree

As 2001ref scenario, but a temperature decrease of 1 degree. The observed dailyminimum and maximum temperature of 1996 and 1997 are decreased by 1 degree (P43).The waterbalance model is also run to obtain the changed initial conditions

Maximum discharge if temperature drops 1 degree, ascompared to the 2001ref scenario.

Increase of peak dischargeswith 27-229 m3/s.

Scenario - Nr.:pp15tp1

Date:27-07-2001

As 2001ref, but with a precipitation increase of 15% and a temperature increase of 1degree

As 2001ref scenario, but a precipitation increase of 15%. The observed daily precipitationof 1996 and 1997 is multiplied by 1.15. Daily minimum and maximum temperatures areincreased with 1 degree. (scenario building stone P44). The waterbalance model is alsorun to obtain the changed initial conditions

Maximum discharge if precipitation increases with 15%and temperature with 1 degree

Peak discharges increasewith 565-697 m3/s

Expected effects of climate change are difficult to estimate, because the expected climatechanges themselves are still not known precisely. In general, a temperature rise is quitelikely to occur, leading to decreased peak discharges and increased evapotranspiration: a1 degree temperature rise (scenario tp1) leads to a drop in maximum discharge of 51-197m3/s, corresponding to 13-29 cm waterlevel. It is expected that worldwide precipitationwill increase also, but the spatial pattern and the magnitude of these changes is stillunclear. The number of extreme rainfall events could increase, leaving their magnitudeunchanged, or the number of extreme rainfall events could stay the same, but theirmagnitude could increase. The scenario calculated here (+15% precipitation, + 1 degreetemperature) causes a increase in flood peak (500-700 m3/s for all sites), but it can bequestioned if this scenario is realistic. However, ignoring effects of climate change whenplanning flood control measures is also not wise.

Figure 25. Maximum discharge for all climate change scenarios

Scenario group ‘Combinations’

Scenario - Nr.:combi

Date:27-07-2001

All IKSO measures until 2030, expected climate change (precipitation increase of 15%,temperature increase of 1 degree), and expected urban growth (22%)

Combination of scenarios 2030r, pp15tp1 and urb22. The waterbalance model is also runto obtain the changed initial conditions

Maximum discharges of a combined scenario of all IKSOmeasures until 2030, urban growth and climate change, ascompared to the 2001ref scenario

Peak discharges increasewith 18-362 m3/s.The proposed measures until2030 are not sufficient tobalance the effects of theclimate change and urbangrowth scenarios.

Scenario - Nr.:2030ropt

Date:11-10-2000

All ‘IKSO’ measures taken until 2030, but with reservoir operations optimized for floodreduction

As 2030r scenario, with reservoirs optimized for flood control (rffemp): they are emptiedon time just before the flood starts

Qmax if all measures until 2030 are implemented andreservoir operations are ‘optimized’ for flood control.

In general, a sharp decreasein peak discharge can beobtained if reservoirs areoptimized for flood control.

Conclusions

The proposed measures by IKSO until 2030, simulated here with the 2030r scenario,decrease flood peak discharges with 435 to 1330 m3/s (14-46%) and decrease waterlevelsbetween 80 cm and 300 cm for Poland and Germany. In the Czech Republic, the effectsare less (-69 m3/s).

In the Czech Republic, in addition to the new reservoirs planned, an extra flood peakreduction could be achieved through reforestation (scenario ‘for’: -84 m3/s) and changingthe operational management of water reservoirs towards flood control, as demonstrated inscenario rffemp and 2030ropt. Through optimization of the water reservoirs, a total floodpeak reduction of 266 m3/s can be achieved at the Odra/Olse station (scenario 2030ropt).Extra reafforestation would increase this reduction with approx 80 m3/s.

In Poland, the planned polders and reservoirs reduce the flood risk. Also here, animproved operational management of water reservoirs towards flood control will reduceflood risk even more. For polders the time of activating them determines theireffectiveness. Care has to be taken with the planned cross section changes, since many ofthe proposed changed reduce the storage potential in the river cross section thusincreasing waterlevels and discharge. Increasing dyke heights or building new dykesreduces local flood risk, but can cause problems downstream in other regions, asdemonstrated in the scenarios 2010c and 2020c. Cross section changes that increasestorage capacity within the cross section do not have negative downstream effects.

In Germany, the planned polders of Ziltendorf and Neuzell can help in reducing floodrisk near Frankfurt and further downstream, if the polders are activated at the right timejust before the flood wave arrives. An increase of the storage capacity of the floodplainreduces waterlevels with approximate 60 cm. Combinations of the new polders and thefloodplain storage reduces peak discharge at Frankfurt/Slubice with 141 m3/s or 71 cm.

Expected urban growth within the next 30 years will lead to a slight increase in peakdischarge (max. +43 m3/s). When planning future flood defense measures, it isrecommended to take this into account.

Expected effects of climate change are difficult to estimate, because the expected climatechanges themselves are still not known precisely. In general, a temperature rise is quitelikely to occur, leading to decreased peak discharges and increased evapotranspiration: a1 degree temperature rise (scenario tp1) leads to a drop in maximum discharge of 51-197m3/s, corresponding to 13-29 cm waterlevel. It is expected that worldwide precipitationwill increase also, but the spatial pattern and the magnitude of these changes is stillunclear. The number of extreme rainfall events could increase, leaving their magnitudeunchanged, or the number of extreme rainfall events could stay the same, but theirmagnitude could increase. The scenario calculated here (+15% precipitation, + 1 degreetemperature) causes a increase in flood peak (500-700 m3/s for all sites), but it can be

questioned if this scenario is realistic. However, ignoring effects of climate change whenplanning flood control measures is also not wise.

Recommendations for future improvements of flood simulations in the Odercatchment

Based on the experiences in this study, the authors believe that the simulation of floodevents in the Oder catchment can be further improved if the following input data wereadded or modified:

• The use of more hourly rainfall data – instead of daily data - to improve thesimulations. For large events such as 1997 this is less important, but still desirable;

• The use more temperature stations (especially for snowmelt flood modelling)compared to the number of stations used for this study;

• The use of a denser and high quality set of cross sections, including floodplaindimensions;

• The use of hourly observed reservoir outflow data instead of daily data.

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APPENDICES

Appendix A: Maximum discharge (m3/s) for all scenarios.

Appendix B: Maximum waterlevel (m) for all scenarios.

Appendix C: Water level changes (cm) for all scenarios.

Appendix D: Total discharge (Mm3) for all scenarios.

Appendix E: Flood duration (days) for all scenarios.

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