of the Müglitz ca t ch ment (Ea stern Ore Mo un ta ins)

Sa xon Aca de my of Scien ces and Hu ma ni ties Wor king gro up „Na tu ral Ba lan ce

and Re gio nal Cha rac te ri stics“

Neustädter Markt 19, D-01097 Dre s den ro e der-m@rcs.urz.tu - dre s den.de

Flo od mi ti ga tion stra te gies – de mands and re a li ty de mon stra ted by a case stu dy

of the Müglitz ca t ch ment (Ea stern Ore Mo un ta ins)

Stra te gie ³ago dze nia po wo dzi – wy ma ga nia i rze czy wi stoœæ.

Na przyk³ad zie stu dium zle w ni Müglitz (Ru da wy Wschod nie)

Abstrakt: W ostatnich latach klêski powodzi spowodawa³y ogormne straty infrastrukturalne i spo -

³eczne. W rezultacie przywi¹zuje siê obecnie wielk¹ wagê do ³agodzenia powodzi. W artykule dokonano przegl¹du s³u¿¹cych realizacji tego celu zasad i metod. Potrzebne s¹ strategie kompleksowe, uwzglêdniaj¹ce zagadnienia in¿ynierii wodnej, ekstensywn¹ poprawê naturalnej retencji wodnej, ograniczenie potencjalnych szkód, zapobieganie niebezpieczeñstwu i edukacjê ludnoœci. Dla osi¹gniêcia najlepszych efektów ³agodz¹cych konieczne jest po³¹czenie budowy zbiorników retencyjnych i opracowywania zestawu miar krajobrazowych, mo¿liwych do zastosowania na du¿ym obszarze.

Kompleksowe badania ekologiczno-krajobrazowe s¹ konieczne dla podwy¿szenia naturalnej retencji wodnej. Studium „badania ekologiczno-krajobrazowe w zlewni Müglitz” ma na celu opracowanie i rekomendacjê konkretnych, realizycznych kroków prowadz¹cych do tego celu. Co wiêcej, powinno pomóc w lokalizacji i zarz¹dzaniu obszarami, na których powstaj¹ powodzie, optymalizacji u¿ytkowania ziemi i kwantyfikacji hydrologicznych efektów proponowanych miar krajobrazowych.

Oce na fun kcji pe³nio nych przez krajo braz jest wa ¿ na dla okre œle nia, jak zmia na po mie rzo nych pa ra me trów wp³ywa na krajo braz. Do brym na rzê dziem s³u¿¹cym za po bie ga niu kon fli ktom jest wie lo kie run kowa opty ma li za cja krajo bra zu ko m pu te row¹ me tod¹ LNOPT. Wzo r ce wy ko rzy sta nia krajo bra zu two rzo ne przez ten sy stem wspo ma ga nia de cy zji s¹ kompromisem miêdzy ró¿nymi funkcjami krajobrazu.

Nie ste ty, zna cze nie uzy ska nych wy ni ków nie jest po wszech nie akce p to wa ne. Co wiê cej, w obe cnych wa run kach eko no mi cz nych trud no o wiel koob sza ro we zmia ny u¿y t ko wa nia te re nu.

Dla te go za le ca siê wpro wa dze nia pro po no wa nych zmian w ob rê bie po wie rz ch ni klu czo wych. Dla ziden tyfi ko wa nia tych w³aœ nie te re nów, bêd¹cych ob sza ra mi powstawania powodzi, stworzono now¹ metodê empiryczn¹.

Key words: flo od mi ti ga tion, wa ter re ten tion, lan d s ca pe fun c tion, op ti mi sa tion, flo od ori gin, de ci sion sup port system (DSS)

S³owa klu czo we: ³ago dze nie po wo dzi, re ten cja wod na, fun k cja krajo bra zu, opty ma li za cja, po cho dze nie po wo dzi, sy stem wspomagania decyzji

Warszawa 2006

In tro du c tion

Du ring re cent ye ars many di sa stro us flo ods have oc cur red, not only in Ge r ma ny but also in Cen tral Eu ro pe. For exa m p le Po land was af fe c ted by the Odra flo od in 1997 and the Wis³a flo od 2001. In Ge r ma ny the big ri vers Rhe in, Elbe and Do nau are the main fo cus of pu b lic at ten tion. In con trast to that, the ri ver Müglitz is a small tri bu ta ry of the Elbe. Its ca t ch ment area is lo ca ted in the Ea stern Ore Mo un ta ins in Sa xo ny (fig. 1).

The ri ver Müglitz is known for its di sa stro us flo ods du ring sum mer. Spe cial we at her con di tions, so cal led 5b-cy c lo nes, of ten ca u se in ten si ve he a vy ra ins.

Di sa stro us flo ods took pla ce in 2002, 1957, 1927 and 1897. A spe cial fe a tu re of the flo od wa ves in the Müglitz ca t ch ment is the ir high spe ed and high crest, like a tor rent. The con se qu en ces are eno r mo us amo unts of da ma ge to in fra struc tu re and many hu man ca su a l ties. In Au gust 2002 the he a vy rain la sted abo ut 3 da ys brin ging abo ut 300 mm of wa ter, a third of the ave ra ge an nu al pre ci pi ta tion for this re gion. The re su l ting ru noff amo un ted to 370 m³/s in con trast to the no r mal 2,5 m³/s (LfUG 2004). 7 pe o p le died and the da ma ges amo un ted to 202 mil lion Euro (fig. 2).

Fig. 1. The lo ca tion of the Müglitz ca t ch ment in Ge r ma ny

A ge ne ral phe no me non of flo ods is the ir bro ad im pact on so cie ty. Di re c t ly af fe c ted are the po pu la tion (the ir he alth, ho u ses and po sses sions), in du stry and tra de (fa c to ries, sto ra ge and trans port), the in fra stru ctu re, the wa ter ma na ge ment, agri cu l tu re and fo re stry (esp. ha r vest loss and tree cut ting) and at last cultural values (for example archives).

In con trast to so cie ty, flo o ding is not a pro blem for na tu re. Na tu ral and se mi na tu ral bio co e no ses in ri ver val le ys are ad ap ted to spe cial con di tions.

Some eco sy stems (e.g. al lu vial fo rests) need pe rio di cal flo o ding for su r vi val.

Ex tre me flo ods al ter the se eco sy stems but also cre a te new con di tions for revi ta li sa tion. Da ma ges oc cur only in in ten si ve ly in ha bi ted are as.

Cha rac te ri stics of the Müglitz ca t ch ment

The Müglitz ca t ch ment is lo ca ted in the low mo un ta in ran ge. Its who le area is abo ut 214 km² and the al ti tu de dif fe ren ce is 636 m. The to tal length of the ri ver Müglitz amo unts to 48,1 km. The dra i na ge pat tern is ge ne ral ly di re c ted to the north. Most of the ri ver val le ys are

sur ro un ded by ste ep slo pes. So they are small and deep wi t ho ut ex pan ded flo od p la ins.

La r ge pla te a us are si tu a ted ou t si de of them.

Unfo rtu na te ly most of the large settlements are located in the valleys.

The ge o lo gi cal stru c tu re of the ca t ch ment area is do mi na ted by me ta mor p hic rocks (gne iss) fo r ming lo a my so ils rich in de tri tus.

Land use is hi g hly spe cia li sed. Abo ut 50%

of the who le area is uti li sed for agri cu l tu re (fig. 3). The hi g her the al ti tu de, the more Fig. 2. Glashütte

du ring the flo od in Au gust 2002

Fig. 3. Land use in the Müglitz ca t ch ment

gras s land is cu l ti va ted. Ara b le land is con cen tra ted on fe r ti le si tes. One third is fo rest lo ca ted ne a r ly exc lu si ve ly on the slo pes. Me dium pre ci pi ta tion and me dium tem pe ra tu re are ty pi cal for the low mo un ta in ran ge in Mid d le Europe.

But more frequent intense rains are possibly determined by climatic changes.

Flo od mi ti ga tion stra te gies

As a re sult of the flo od di sa sters du ring re cent ye ars, gre at va lue is cur ren t ly at ta ched to flo od mi ti ga tion. The re fo re, the prin ci p les and in stru ments are ei t her ne w ly cre a ted or re vi sed. For exa m p le the new Wa ter Law of Sa xo ny con ta ins re gu la tions con ce r ning flo od p la ins and flo od ori gi na ting are as. Flo od pro te c tion plans have been wor ked out for all ri ver ba sins and are co u p led with the land use plan ning in stru ment. Fi nal ly, the in fo r ma tion, warning and alert systems are improved due to the new demands.

In Sa xo ny flo od pro te c tion stra te gies are ba sed on four main in stru ments.

The se are hy dra u lic en gi ne e ring, the im pro ve ment of wa ter re ten tion in the who le ca t ch ment area, the re du c tion of po ssi b le da ma ges, the ave r ting of dan ger and education of people (tab. 1).

Tab. 1. In stru ments and me a su res of flo od pro te c tion in Sa xo ny

in stru - ments

hy dra u lic en gi ne e ring

im pro ve ment of wa ter re ten tion

re du c tion of po ten tial

da ma ges

ave r ting of dan ger and edu ca tio nal

ad ve r ti sing me a su res •flo od de ten tion

ba sins

•dyke con stru c tion

•op ti mi sed ru noff

•land use op ti mi sa - tion

•ra in wa ter ma na ge - ment

•re du ce of se a ling

•re na tu ra tion

•ban and re stri c tion of con stru c tion

•re lo ca tion of thre a - te ned go ods

•ac qu i re ment of land

•wa r ning and alert su r vey

•con tin gen cy plan

•“wa ter bri ga de”

•edu ca tion

ma in fo cus

wate rco u r ses flo od ori gi na ting are as

flo od pla ins

Hy dra u lic en gi ne e ring

The con cepts of flo od mi ti ga tion are ex ten si ve, but the re a li ty is one - si ded.

Hy dra u lic en gi ne e ring is still the most ef fe c ti ve but cost -in ten si ve me t hod for flo od mi ti ga tion, the re fo re it is fa vo u red re gar d less of the as so cia ted pro blems and of ten re gar d less of ot her po ssi bi li ties. In Müglitz ca t ch ment the re is one re ten tion ba sin completed and three more are plan ned. The se ba sins are ne ces sa ry to achie ve pro te c tion from a cen ten nial flo od event. The re fo re se ve ral alte r na ti ves are un der di s cus sion. Ho we ver the bu d get is low and many con flicts exist, for example between nature conservation, transport infrastructure and natural scenery.

A spe cial cha rac te ri stic of the Müglitz ca t ch ment is the exi sten ce of dif fe rent pro te c ted are as. Na tu re pro te c tion are as and fauna- flora- habitat -are as

are exa m p les of such are as. Some bio to pes and lan d s ca pe ele ments (e.g. the hi sto ri cal sto ne- ri d ges) are stron gly pro te c ted as well. In ad di tion to that, the re exist are as of ex ten si ve lan d s ca pe pro te c tion. Unfo rtu na te ly most of the plan ned si tes for the flo od de ten tion ba sins are within pro te c ted are as. This is the re a son why lan d s ca pe eco lo gi cal re se arch is re qu i red to show ways to im p le ment improvement of water retention outside of basins as flood mitigation measurements.

Wa ter re ten tion

Co m p lex lands cape-e colo gi cal in ve sti ga tions are ne ces sa ry to ove r co me the sho r t co mings men tio ned abo ve. Our stu dy “Lan d s ca pe eco lo gi cal in ve sti ga tions in the Müglitz ca t ch ment” is ai med to de sign a set of re com men ded con c re te and re a li stic steps to im pro ve wa ter re ten tion in the who le ca t ch ment area du ring flo od events. Mo re o ver, it shall help to lo ca li se and ma na ge flo od ori gi na ting are as, to op ti mi se land use, and to qu an ti fy hy dro lo gi cal ef fects of the pro po sed me a su res (fig. 4). Se ve ral lands cape-e colo gi cal me t hods (for exa m p le the ap pro ach of lan d s ca pe fun c tions for lan d s ca pe op ti mi sa tion) are to be co m bi ned with hy dro lo gi cal mo del ling and with eco no mi cal as ses s ments to find out the best way to im pro ve wa ter re ten tion, con si de ring the multi -func tiona li ty of the lan d s ca pe. This is done with the help of sce na rios.

Fig. 4. Lands cape-e colo gi cal in ve sti ga tions in the Müglitz ca t ch ment

De ta i led kno w le d ge of ru noff formation pro ces ses, dri ven by land use and he a vy rain events, can be ga i ned with precipi tation- runoff- mo dels. Using sce na rios it is po ssi b le to esti ma te hy dro lo gi cal ef fects and to get a fe e d back of the ir ef fi cien cy. Mo del ling of flo od peak re du c tion by af fo re sta tion (LTV 2003) and by abandonment of plo u g hing (Zim me r ling & Schmidt 2002) show that flo od peak abandonment is po ssi b le but the ef fects of land use chan ges are low. Neve r t he less, in some ca ses they may be im po r tant. The kno w le d ge of the pro ba bi li ty of re cur ren ce of flo o ding pla ys an im po r tant role for the po ssi b le flo od peak reduction. The effect is low during very rare events and better during events which occur often.

Lan d s ca pe op ti mi sa tion

All lan d s ca pes are mul ti func tio nal. With re gard to the pra cti cal ap p li ca tion of lan d s ca pe eco lo gy, the con cepts of lan d s ca pe fun c tions and na tu ral po ten tials are he l p ful ap pro a ches to ana ly se and as sess lan d s ca pe, espe cial ly from a hu man po int of view. We have to di stin gu ish be twe en eco lo gi cal fun c tions, eco no mic fun c tions and so cial fun c tions. It is ne i t her po ssi b le nor ne ces sa ry to con si der all of them in eve ry case. The cho i ce of fun c tions sho uld be co or di na ted with the aim of in ve sti ga tion. The fol lo wing fun c tions have been as ses sed in our pro ject: ru noff re gu la tion fun c tion, wa ter sto ra ge ca pa ci ty of so ils, soil ero sion by wa ter, fi l ter- and buf fer fun c tions of so ils, biotic yield potential, habitat function, potential for protection of species and potential of natural recreation.

The as ses s ment of lan d s ca pe fun c tions was a pre con di tion for the land use op ti mi sa tion using a mat he ma ti cal mo del. Op ti mi sa tion of wa ter re ten tion alo ne, as a sin gle lan d s ca pe fun c tion, wo uld lead to many eco lo gi cal and so cial con flicts, which wo uld re sult in the non- ful fi l ment of va rio us ot her fun c tions.

A mul tic ri te ria lan d s ca pe op ti mi sa tion is su i ta b le to pre vent such con flicts. For this pu r po se Gra ba um (Me y er & Gra ba um 2003) has de ve lo ped the com pute r- ba sed me t hod LNOPT, a de ci sion sup port sy stem which pro du ces land use pat terns. The pat terns are the re sult of a co m pro mi se be twe en dif fe rent lan d s ca pe fun c tions. LNOPT is ba sed on the game the o ry (Monte -Car lo-Me t hod). It is possible to involve all functions theoretically, but in practice limits are reasons for selection.

The ap p li ca tion of the LNOPT as De ci sion Sup port Sy stem in the Müglitz ca t ch ment sta r ted with a se le c tion of four lan d s ca pe fun c tions. Af ter that, de ve lo p ment of we ll-fo un ded sce na rios is im po r tant for set ting li mits of op ti mi sa tion. For exa m p le re stri c tions are to be de fi ned and the ma xi mum and mi ni mum per cen ta ge of are as for land use ty pes are to be wor ked out.

Weighting of landscape functions is also to be done.

One of the sce na rios, cal led the “re a li stic sce na rio” con ta i ned the fol lo wing as su m p tions:

– ma xi mum in cre a se of fo rest area up to 10%,

– con se r va tion of the ra tio of ara b le land and gras s land, – re du c tion of bu i l ding land to 50%,

– ex c lu sion of pro te c ted and va lu a b le are as.

Maps which con ta in an op ti mi sed land use (fig. 5) and the ca l cu la tion of ef fects on ot her lan d s ca pe functions are the ou t put of the op ti mi sa tion.

Af ter op ti mi sa tion it is ne ces sa ry to so l ve three main pro blems:

1. How to re a li se land use chan ges in pra cti ce?

2. Which eco no mi cal con se qu en ces will oc cur?

3. Which ef fects on flo od mi ti ga tion are po ssi b le?

All re sults are to be as ses sed and to be im p le men ted into lan d s ca pe plan ning. The eco no mic con se qu en ces for fa r mers and fo rest en te r pri ses are of ten un k nown and sub sequ en t ly a quan ti fi ca tion of hy dro lo gi cal ef fects un der se ve ral cli ma tic con di tions is ne ces sa ry. It is ad vi sa b le to re a li se the con cept in test are as at first. For this, flo od ori gi na ting are as are fa vo u red, be ca u se of the ir si g ni fi cant con tri bu tions to flo od formation.

Flo od ori gi na ting are as

The se are as of ori gin are exp li ci t ly men tio ned in the new Wa ter Law of Sa xo ny. The Law (§ 100b) de fi nes them as fol lows: “Wi t hin flo od ori gi na ting are as ... se rio us su r fa ce ru noff can oc cur as a con se qu en ce of he a vy rain or me l ting of snow du ring a short time, which po ssi b ly en dan gers life, he alth and pro per ty. In flo od ori gi na ting are as the na tu ral abi li ty of wa ter re ten tion and Fig. 5. Land use op ti mi sa tion with LNOPT (ori gin: S. Ger ber)

in fi l tra tion has to be pre se r ved and im pro ved”. As a re sult of the law, it is necessary to locate and to manage these areas.

In or der to iden ti fy flo od ori gi na ting are as, a new em pi ri cal me t hod was de ve lo ped (Röder & Ad olph 2005). It is re la ted to the as ses s ment pro ce du re of ru noff re gu la tion fun c tion by Zepp (1992). The me t hod is ba sed on the ap p li ca tion four pa ra me ters (field ca pa ci ty, in fi l tra tion ca pa ci ty, slo pe, CN-va lue) and a fi nal cor re c tion step. The CN-va lue, ac cor ding to the U.S.

Soil Con se r va tion Su r vey (SCS-me t hod, Ma niak 1997), is a pa ra me ter to se pa ra te pre ci pi ta tion which is ef fe c ti ve for ru noff, from the who le pre ci pi ta tion. It de pends on land use and soil parameters and it was separated from soil influence by calculating medium values.

Our ba sic mo du lar con cept is to di stin gu ish be twe en re la ti ve ly con stant na tu ral pa ra me ters to de fi ne a na tu ral pre fe ren ce of ru noff fo r ma tion, the chan ging land use as the pa ra me ter for the an thro po ge nic im pact, and pa ra me ters of the flood events like heavy rain.

Pa ra me ter Re sult 1 Re sult 2 Fi nal re sult

field ca pa ci ty in fi l tra tion ca pa ci ty slo pe

CN-me dian pre ci pi ta tion / ru noff

}

ru noff fo r ma tion

}

are as

}

The re sult of the as ses s ment pro ce du re is a po int va lue with a mi ni mum of three and a ma xi mum of 20. The or di nal va lu es have to be clas si fied into clas ses, which have to be ad ju sted to the pe cu lia ri ties of the ca t ch ment area (fig. 6). Fi nal ly, pa r tial ca t ch ment are as have to be con si de red to di stin gu ish be twe en are as of dif fe rent flo od pro ba bi li ty, with the help of thre s holds. Most su i ta b le pa ra me ters are the spe ci fic di s cha r ge du ring flo od events and sta ti sti cal cha rac te ri stics of pre ci pi ta tion fre qu en cy and in ten si ty. If not available, medium annual total runoff or medium annual precipitation are also applicable.

Ma na ge ment

The are as of high risk co m bi ned with high flo od pro ba bi li ty sho uld be sub ject to ur gent land use ma na ge ment and to test con ce p tion of in te gra ted flo od mi ti ga tion. Unfo rtu na te ly the ac ce p tan ce of such flo od mi ti ga tion me a su re ments is di ve r se. Some me a su re ments are im pro ba b le or very difficult, other are more realistic.

For exa m p le ex ten si ve af fo re sta tion will not take pla ce be ca u se of dif fi cu l ties in ac qu i ring of land, ho we ver the re bu i l ding of mi xed fo rests clo se to na tu re is a pro cess which is al re a dy go ing on. The chan ge of ara b le land into gras s land is dif fi cult be ca u se of the eco no mic ne ces si ties of agri cu l tu re, but re du c tion of plo u g hing is on a par from a hy dro lo gi cal po int of view.

In set t le ments, ex ten si ve re mo val of se a ling is very cost -in ten si ve, but lo cal rain wa ter ma na ge ment is sup po r ted by the Sa xon au t ho ri ties. Also ef fe c ti ve is the mo di fi ca tion of se wa ge and dra i na ge sy stems. The re na tu ra tion of de stru c ted mo ors in the Ea stern Ore Mo un ta ins is mo st ly im pos si b le be ca u se of the ir high gra de of deco m po si tion, but we tland revi ta li sa tion is de si red for na tu re pro te c tion. Af ter all, the reestablishment of historical structures of the landscape is impossible. A new programme for waterside edges will bring us some of them back.

Fig. 6. Flo od ori gi na ting are as in the Müglitz ca t ch ment

Con c lu sions

Co m p le te pro te c tion from flo ods is im pos si b le. We need co m p lex flo od mi ti ga tion stra te gies, which in vo l ve hy dra u lic en gi ne e ring, ex ten si ve im pro ve ment of na tu ral wa ter re ten tion and re du c tion of po ten tial da ma ges.

The con stru c tion of de ten tion ba sins and lar ge -a rea me a su res are to be co m bi ned for op ti mal mi ti ga tion ef fects. Un der the cur rent eco no mic con di tions, lar ge -a rea land use changes are difficult, but land use adjustment is possible.

Re fe ren ces

Lande stal sperren verwal tung des Fre i sta a tes Sa ch sen (LTV 2003): Ho chwas sers chutz - konzept Müglitz. Mskr. Dorsch Con sult.

Ma niak U., 1997: Hy dro lo gie und Wasse rwir t s chaft. Eine Einführung für In ge nie u re. 4.

Aufl. Sprin ger- Ve r lag Ber lin- Heide l berg.

Me y er C.B., Gra ba um R., 2003: Multi kri te riel le Lands chaft sopti mie rung – reif für die Pra xis? IÖR-Schriften, Bd. 40: 105 –118.

Röder M., Ad olph B., 2006: Lo ka li sie rung und Ma na ge ment von Hochwas serent - stehungs gebie ten. “Wasse rwir t s chaft”, Bd. 96, H. 5: 22–26.

Sächsisches Lan de samt für Um welt und Ge o lo gie (LfUG 2004): Erei gni sana ly se – Ho - chwas ser Au gust 2002 in den Osterzgebirgsnebenflüssen. Ma te ria lien zur Wasse r - wir t s chaft: 188.

Sächsisches Was se r ge setz (SächsWG) vom 18. Okto ber 2004, SächsGVBl, 2004: 482.

Zepp H., 1992: Abfluss regula tions fun ktion [in:] Marks R., Müller M. J., Le ser H., Klink H.-J. (Hrsg. 1992), An le i tung zur Be we r tung des Leistungsvermögens des Land schaftshaushaltes. Forsch. z. de ut s chen Lan de skun de Bd. 229, Trier, 2. Aufl.:

86–90.

Zim me r ling B., Schmidt W., 2002: Be i trag der kon ser vie ren den Boden bear be i tung zum vor be u gen den Ho chwas ser s chutz [in:] Be ri ch te aus der Pflan zen pro du ktion. Schri - ften re i he der Sächs. “Lan de sanstalt für Land wir t s chaft“, Bd. 7, H. 11: 23–51.