tributaries Yugoslavia Rumania
5.4 Flood Control
Jn t h e following, a s h o r t review will b e given, f o r e a c h Danube country, about t h e flood c o n t r o l situation along t h e Danube.
FederaL RepubLic of G e r m a n y
Flood protecting l e v e e s built in 1849-1897 from 2,540 km (Dillingen) t o 2,510 km (Donauworth) hindering henceforth t h e floods t o overflow t h e banks and inundate t h e t e r r i t o r y covering t h e a r e a of about 115 km2. Flood protecting l e v e e s from 2,460 km Ongolstadt) to 2,427 km (Eining) were built in 1913-24 and fortified in 1965-75. They p r o t e c t an a r e a of 80 km2. Flood protection l e v e e s from 2,376 km (Regensburg) to 2,256 km (Hofkirchen) were constructed in 1930-56, protecting a n area of a b o u t 120 km2, b u t giv- ing only p a r t i a l p r o t e c t i o n f o r t h e t e r r i t o r y between Regensburg and Straubingen. On t h e basis of e x p e r i e n c e s gained during t h e floods in 1954 and 1965 t h e s e l e v e e s and t h e inland drainage have to b e improved.
Numerous completed dams and impounding r e s e r v o i r s took o v e r a p a r t of t h e flood protection by lowering flood peaks.
Improved flood p r o t e c t i o n s of Kehlheim and Regensburg are planned f o r t h e f u t u r e . The protection measures envisaged f o r P a s s a u should p r o c e e d a l s o in t h e f u t u r e through rebuilding of old houses and changing t h e utilization of t h e i r ground-floor.
A u s t r i a
Subsequent t o flood d i s a s t e r s i n 1830 and 1864 t h e f i r s t more extensive measures were performed in 1869-1875 f o r t h e protection of Vienna against floods. The c o r e of engineering works w a s a 26 km long r i v e r training work for which two l a r g e cut-offs had been established. For t h e f i r s t time in Cen- tral E u r o p e they were implemented o v e r t h e whole length and dredging t h e complete width, while in t h e p a s t i t was usual t o r e l y on t h e r i v e r itself t o perform t h i s work o v e r a long period. The amount of e a r t h moved in this operation was, t h e r e f o r e , a s high a s 16.5 mil.m3.
Other measures were a l s o included, such as closing s t r u c t u r e s f o r t h e Danube Canal, various flood control embankments and levees. Since 1898-99 a 180 m wide waterway in t h e regulated section w a s provided by means of groynes, securing navigation at low water stages.
From 1882 t o 1920 about 200 km of flood c o n t r o l levees were con- s t r u c t e d from Vienna down t o t h e March (Morava) r i v e r , in t h e Tullnerfeld and in Linz area.
Following t h e s e v e r e floods in 1954 flood protection in t h e town of Linz w a s i n c r e a s e d considering t h e flood with 500-year r e t u r n period as design value. The system was f u r t h e r improved p a r a l l e l to t h e construction of t h e b a r r a g e a t Abwinden-Asten.
The p r e s e n t flood c o n t r o l system in t h e Vienna area is being improved t o handle a d i s c h a r g e of 14,000 m3.s1, which c o r r e s p o n d s t o t h e peak d i s c h a r g e of a n e x t r a o r d i n a r y high flood. F o r t h i s purpose a r e l e a s e c a n a l will b e c o n s t r u c t e d , s e p a r a t e d from t h e Danube c a n a l by a 17 km long and 200 m wide island. In t h e downstream direction t h e l e v e e system i s dimen- sioned f o r a d i s c h a r g e of about 13,200 m3.s1, since in t h e case of more s e r i - o u s floods i t i s n e c e s s a r y to t a k e a l s o into consideration, with r e s p e c t t o t h e lower lying downstream c o u n t r i e s , t h e r e t e n t i o n of t h e March (Mora- vian) Field.
Czechoslovakia
Flood c o n t r o l embankments had been built a l r e a d y in t h e second half of t h e 1 9 t h c e n t u r y . Except f o r two s h o r t s t r e t c h e s where t h e banks are r e l a - tively h i g h e r a complete system of levees w a s built f o r t h e e n t i r e n o r t h e r n Danube bank and s o u t h e r n Little Danube bank. Disastrous floods, most r e c e n t l y in 1965, stimulated h e r e , as well as on t h e opposite bank, fortifica- tion a n d r a i s i n g of levees and improvement of d r a i n a g e within t h e p r o t e c t e d area.
Hungary
A q u a r t e r of t h e Hungarian t e r r i t o r y , about 23,000 km2, i s a potential inun- dation area from which 23% l i e s d i r e c t l y in t h e Danube valley. T h e r e f o r e , flood mitigation and protection i s of major importance in t h i s country. As e a r l y as in t h e 16th c e n t u r y protection levees were c o n s t r u c t e d t h e r e . A systematic construction of flood p r o t e c t i o n dykes s t a r t e d in t h e f i r s t half of t h e 19th c e n t u r y . Since 1840 t h e r e h a s been legislation t o r e g u l a t e t h e implementation of hydraulic s t r u c t u r e s , r i v e r training, construction and maintenance of flood control s t r u c t u r e s , and t h e n e c e s s a r y d r a i n a g e of
e x c e s s water. According t o t h i s regulation Water Associations were e s t a - blished unifying a l l i n t e r e s t e d p e r s o n s and organisations in a given region and a p a r t of t h e investments was c o v e r e d by t h e members. A decisive motive to complete t h e l e v e e system w a s t h e o c c u r r e n c e of s e v e r e floods in 1881 and 1888. By t h e end of t h e 19th c e n t u r y t h e p r o t e c t i o n system w a s p r a c t i c a l l y completed.
The straightening of t h e Danube between dykes caused a f u r t h e r i n c r e a s e of flood s t a g e s , s o t h a t many previous levees were too l o w a f t e r t h e completion of t h e whole system. In t h e f i r s t half of t h e 20th c e n t u r y t h e l e v e e s were r a i s e d and fortified, so t h a t a s a f e p r o t e c t i o n against floods of 60-year r e t u r n period w a s provided.
A t t h e beginning of t h e p r e s e n t s t a g e of flood c o n t r o l development t h e legal basis has been modified. Proceeding from t h e circumstance t h a t t h e s a f e t y of t h e main p r o t e c t i o n line h a s not only local, but also national signi- ficance, t h e state took o v e r t h e responsibility from t h e associations f o r important flood-control dykes. From t h e t o t a l main flood c o n t r o l line in Hungary, having a length of 4,183 km, 1,350 km lies along t h e Danube. I t is supplemented by t h e s e c o n d a r y lines of 260 km length a n d by t h e special p r o t e c t i o n of Budapest, t h e length of which is 1 8 km.
The significance of flood c o n t r o l in Hungary is evident from t h e follow- ing data: Within t h e potential inundation area live a q u a r t e r of t h e total population; about 30% of t h e railway network, and 20% of highways lie t h e r e .
Yugoslavia
L a r g e inundation areas r e q u i r i n g flood protection s p r e a d only along t h e middle Danube r e a c h in t h e Pannonian Basin. Systematic construction of flood c o n t r o l l e v e e s a l s o s t a r t e d in t h e 19th century. By World War I a con- tinuous protection system had been c o n s t r u c t e d linked t o t h e Hungarian levees, reaching on t h e l e f t bank down to t h e mouth of t h e Tisza (Tisa), and on t h e r i g h t bank t o t h e mouth of t h e Drau (Dravd). F u r t h e r downstream, t h e l e v e e system on t h e l e f t r i v e r bank w a s still deficient at t h a t time, while on t h e r i g h t bank flood c o n t r o l dykes were constructed only at P e t r o v a r a - din and Zemun.
In t h e p e r i o d between t h e two world wars t h e system of l e v e e s w a s expanded ( f o r i n s t a n c e , at P a n c e v o on t h e l e f t bank a n d at Smederovo a n d Godominsko P o l j e on t h e r i g h t bank).
After World War I1 some new s e c t i o n s were built t o complete t h e flood p r o t e c t i o n . A p a r t of old d y k e s was r a i s e d , f o r t i f i e d , a n d r e s t o r e d a c c o r d - ing t o e x p e r i e n c e s gained during t h e c a t a s t r o p h i c flood in 1 9 6 5 and b a s e d o n advanced soil mechanics.
A t p r e s e n t t h e r e i s a continuous system of d y k e s o n t h e l e f t bank from t h e Hungarian b o r d e r down t o t h e mountainous r e a c h of t h e I r o n Gate. Due t o l o c a l conditions o n t h e r i g h t r i v e r bank, i t was s u f f i c i e n t t o c o n s t r u c t l e v e e s at only a few sections: from t h e Hungarian b o r d e r down to t h e mouth of t h e D r a u (Drava), at P e t r o v a r a d i n and Zemun, as w e l l as at Smederevo.
The l a t t e r was a l s o r e q u i r e d b e c a u s e of t h e c o n s t r u c t i o n of t h e D j e r d a p I ( P o r t i l e d e F i e r ) b a r r a g e .
The crest of flood c o n t r o l dams i s usually 1.5-1.7 m a b o v e t h e water s t a g e of a food of 100-year r e t u r n period.
B u l g a r i a
Over t h e y e a r s from 1 9 3 0 t o 1950, a b o u t 300 km of flood c o n t r o l dams were c o n s t r u c t e d t o p r o t e c t a n area of a b o u t 72,600 h a . The h e i g h t of t h e l e v e e s was dimensioned a c c o r d i n g to t h e e x t r e m e flood in 1897.
Romania
The c o n s t r u c t i o n of flood c o n t r o l l e v e e s f o r p r o t e c t i o n of a g r i c u l t u r a l land w a s initiated i n t h e 1 9 t h c e n t u r y . The p r o t e c t e d area was i n c r e a s e d from ca. 50,000 h a in 1 9 4 0 to ca. 100,000 h a in 1960 a n d h a s b e e n f u r t h e r i n c r e a s e d up to t h e p r e s e n t t o ca. 400,000 ha. The t o t a l length of flood con- t r o l l e v e e s is 1 , 0 0 0 km (RZdD, 1986).
5.5 Barrages
The i d e a t o c o n s t r u c t a navigable waterway connecting t h e Main a n d t h e Danube a n d t h u s t h e North Sea with t h e Black S e a , d a t e d b a c k t o a n c i e n t times. A s e a r l y as 793, Charlemagne t r i e d to create a connection between t h e two r i v e r systems, c l o s e t o t h e town Treuchtlingen (FRG), w h e r e t h e dis- t a n c e between two t r i b u t a r i e s of t h e two systems i s only 2 km a n d t h e d i f f e r - e n c e i n a l t i t u d e i s only a b o u t 1 0 m .
From 1836 t o 1845 t h e 'Zudwig-Donau-Main Kanal" of 1 7 7 km long was built from Kehlheim to Bamberg with 100 navigation locks. Unfortunately, t h i s c a n a l soon lost i t s significance since t h e 120-ton vessels hauled b y h o r s e s could not stand t h e competition from t h e railway, which in those days w a s installed. In 1945, t h i s c a n a l was still in o p e r a t i o n and only in 1949 w a s i t finally abandoned.
Since 1959 t h e new Main-Donau-Kana1 h a s been u n d e r construction, i t s dimensions being: 5 5 m water level width, 31 m bottom width, 4.0-4.25 m water depth, 1 2 m wide and 1 9 0 m long navigation locks adequate f o r a p a i r of 1,500 ton and 90 m long Type Europe I1 b a r g e s . The 204 km long c a n a l between Regensburg a n d Bamberg is divided into 18 sectors from which 1 0 3 km with 1 0 s e c t o r s i s c a n a l with standing water, and 1 0 1 km is impounded s t r e t c h of r i v e r s .
In connection with t h e new Main-Danube waterway, t h e completion of which is envisaged f o r t h e f i r s t half of t h e decade 1990-2000, 15.0 m3.s-I of water should b e conveyed from t h e Danube t o t h e Main r i v e r basin. How- e v e r , water withdrawal should t a k e place only when t h e Danube d i s c h a r g e i s above t h e a v e r a g e low d i s c h a r g e MLQ.
In 1984 a 64 km long Danube-Black S e a c a n a l between Cernavoda and Constants (Romania) was completed, at f i r s t only f o r i n t e r n a l operation.
The mean width i s 90 m, d e p t h 7.5 m, both ends are provided with 310 m long and 25 m wide twin navigation locks. The navigation r o u t e was s h o r t e n e d by 370 km. This canal, t h e construction of which r e q u i r e d t h e removal of 300 million m3 of e a r t h (more than in t h e case of t h e Suez Canal: 275 million m3) a l s o provides water f o r irrigation of 700.000 h a of a r a b l e land in Dobrogea.
In t h e following, a s h o r t review about b a r r a g e s on the Danube is given f o r e a c h Danube country.
FederaL Republic of G e r m a n y
The Kachlet b a r r a g e (2,230 km) at Vilshofen, built in 1924-27 was t h e f i r s t member of t h e canalization system of t h e Danube. I t improved navigation in t h e r o c k y s t r e t c h of t h e "Hilgardsberger Kachlet". I t was followed by t h e b a r r a g e at Jochenstein, constructed in cooperation with t h e Federal Repub- l i c of Germany and Austria on the common b o r d e r in 1952-55. During t h e
period 1952-84 a continuous chain of 1 5 b a r r a g e s w a s built from Ulm t o Ingolstadt. In t h e majority of t h e s e schemes a p a r t of t h e f o r m e r inundation a r e a i s overflowed during flood events, t o p r e v e n t t h e unfavourable i n c r e a s e of flood d i s c h a r g e s in t h e downstream section. The releases t a k e place, in a regulated way through spillways and movable weirs. The alluvial f o r e s t s are often inundated, though t h e a g r i c u l t u r a l land i s submerged only during disastrous floods.
Three b a r r a g e s , Regensburg (2,381 km), Bad Abbach (2,401 km) and Geisling (2,354 km) were built with t h e purpose of extending t h e waterway on t h e Danube up t o Kelheim and to interconnect it with t h e Main-Danube canal.
A t p r e s e n t one b a r r a g e is u n d e r construction a t S t r a u b i n g (2,324 km), whose purpose is t o improve navigation conditions. Some o t h e r s are also planned (one t o extend t h e waterway until t h e Kachlet b a r r a g e and two more downstream from Ingolstadt to p r e v e n t t h e r a p i d scouring and deepening in t h i s r e a c h .
Austria
The systematic development of t h e Danube c a s c a d e s began with t h e con- s t r u c t i o n of t h e b a r r a g e a t Jochenstein, on t h e German-Austrian b o r d e r , completed in 1954. Up t o t h e p r e s e n t about 250 km of t h e 350 km long Aus- t r i a n Danube section i s canalized and t h e r e a r e plans t o f u r t h e r develop t h i s cascade system.
B a r r a g e s in flatlands of t h e Danube basin are supplemented by dyke systems t o provide protection f o r t h e densely populated inundation a r e a against floods. However, l a r g e r r e t e n t i o n a r e a s remain p r e s e r v e d , simi- l a r l y as in t h e German Danube section, also after t h e constrliction of b a r - r a g e s . In all five, completed water schemes situated in t h e plain high-water overflows were built into t h e p a r a l l e l l a t e r a l levees, t h u s making possible t h e overflow of water above a c e r t a i n flood-discharge o n t o t h e f o r m e r inun- dation plain. In t h i s way a t h i g h e r floods a significant portion of t h e flood r e t e n t i o n is maintained. In addition, t h e f o r m e r inundation conditions in t h e alluvial plains and f o r e s t s a r e p r e s e r v e d .
Czechoslovakia
Since 1978 t h e hydropower plant Gabcikovo h a s been construction jointly with Hungary. With i t s l a r g e derivation c a n a l i t d i f f e r s from all o t h e r com- pleted and planned water schemes on t h e Danube. The combined navigation and hydropower canal should d i v e r t a d i s c h a r g e of 5,200 m3.s" from t h e Danube at Dunakiliti, which r e t u r n s t o t h e main r i v e r bed only after a length of about 30 km. I t is planned to c o n s t r u c t in cooperation with Hun- g a r y downstream from Gabcikovo a n o t h e r water scheme at Nagymaros. Only a f t e r completion of t h i s b a r r a g e will i t b e possible t o create a complex water utilization scheme f o r peak hydropower production. The two b a r - r a g e s will a l s o provide a final solution of flood c o n t r o l on t h e Danube r e a c h concerned.
Hungary
The canalization p r o j e c t at Gabcikovo-Nagymaros, to b e c o n s t r u c t e d jointly with Czechoslovakia, h a s a l r e a d y been d e s c r i b e d above. More details can b e found in Annex 11.
Yugoslavia
F o r solving t h e s e r i o u s problems concerning navigation on t h e Danube and f o r utilizing of t h e hydraulic power potential, Yugoslavia and Romania con- s t r u c t e d jointly in t h e p e r i o d 1964-72 a t 942.94 km a dam of 32 m height, t h e "Hydroenergy and Navigation System Djerdap ( P o r t i l e d e F i e r I)". The backwater extends at low water s t a g e as far as 270 km to t h e mouth of t h e Tisza (Tisa). In case of flood, t h e head i s reduced t o 6.5 m, so t h a t at high floods t h e backwater ends a distance of a b o u t 120 km at Veliko Gradiste.
In. 1984 t h e b a r r a g e Gruia ( P o r t i l e d e F i e r 11) at 863 km w a s p u t in operation. I t s backwater zone i s linked with t h e scheme Djerdap ( P o r t i l e d e F i e r I), t h u s serving a s compensation r e s e r v o i r during t h e peak operation of t h e hydropower plant. This p r o j e c t w a s implemented a l s o as a common Yugoslav-Romanian scheme.
Romania
Both r i v e r power p r o j e c t s at t h e Iron Gate I and I1 have a l r e a d y been dealt with in connection with t h e development in Yugoslavia (RZdD, 1986).
5.6 Hydropuwer
In o r d e r t o c h a r a c t e r i z e t h e problems of b a r r a g e s from t h e viewpoint of e n e r g e t i c s , in Figure 1 1 , t h e longitudinal section of energy-potential (discharge multiplied with slope) of t h e Danube is shown. The diagram c l e a r l y indicates t h a t t h e highest specific power r e s o u r c e s are concen- t r a t e d in t w o r e a c h e s : between Passau and Gonyu, a n d downstream from Belgrade, in t h e I r o n Gate region.
The f i r s t r e a c h (between Passau and Gonyii) i s especially significant due t o its high slope of 1 5 0 m along about 435 km length of t h e r i v e r . A t t h e second r e a c h (downstream of Belgrade) t h e high e n e r g y potential i s d u e t o t h e g r e a t d i s c h a r g e s of t h e r i v e r .
A sudden b r e a k in t h e s l o p e of t h e r i v e r bed at Gonyu c a n b e s e e n in Figure 11. This r e s u l t s in problems of sediment accumulation at t h e break- point. Accordingly, t h e annual bed load t r a n s p o r t at Bratislava i s about 650,000 m3 while i t i s only 13,000 m3 above Budapest. This i s t h e r e a s o n f o r t h e well-known "bottle neck" in t h e navigation along t h e c r i t i c a l Czechoslovakian-Hungarian r e a c h (Benedek , 1986).
The plans f o r t h e complex utilization of t h e Danube's w a t e r r e s o u r c e s involve 49 r i v e r b a r r a g e s of which so f a r 31 have b e e n constructed. The sections and c a p a c i t i e s of t h e s e hydropower p l a n t s are listed in Table 11.
The locations of t h e s e hydropower stations according t o c o u n t r i e s i s shown in Table 12. The t a b l e s show t h a t t h e p r e s e n t utilization of t h e t o t a l capa- c i t y (61%) will b e gradually i n c r e a s e d to more t h a n 90% by t h e t u r n of t h e c e n t u r y (DoKW, 1985;
OVH,
1985). Figure 1 2 gives some information on t h e extensive hydropower utilization of t h e Austrian Danube section (DoKW, 1985).win
ABWINEN- ASTEN
0 planned