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Improve of flood protection and water balance PDF Print E-mail

Water balance and flood protection

Modern waterways are based on fully autonomous “circulation” of water thanks to pumping water. Pumping is a procedure, during which it is possible to eliminate any interference with hydrological regime of parallel streams. This “neutral” role of canals can still be changed into an active one when a canal connects areas with different water resource. It can improve a water-resource balance in regions where the lack of water endangers not only economic development, but the environment as well.

First of all, it is useful to describe transporting the water of the Danube through the Main – Danube canal in neighboring Germany which is in operation from 1993. This system is the most similar to opportunities offered by the D-O-E water corridor. The major initiator of this solution was the Bavarian State Ministry for the Regional Development and the Environmental Issues. The territory of the Free state of Bavaria is divided into two different parts from the point of view of water resources. The southern part located in the catchment area of the Danube and its alpine affluents is abundant in resources, while the northern part in the Main catchment area is relatively drier. Taking into account the population, the difference is particularly significant. Streams in the north are able to feed about a third of water per capita compared to the south. The disproportion is even bigger in dry periods.

Such an amount of water could not be held by any reservoirs in the densely populated area with a minimum of usable possibilities of the dam realization. Due to the insufficiency of the above solution, the attention of water management experts has shifted to the Main – Danube waterway, which was being built at that time. Its locks and dams should include pumps with the output of 14 m3/s for ensuring the traffic. It would be enough to increase the output by further 21 m3/s, i.e. install five instead of two machine sets and solve the water-resource problem for good. 

Water management functions of the Rhine-Main-Danube Waterway is an effective, energy-efficient and carefully thought-out combination of the interests of transport, water management and environmental care. 

Obnovený malý jez Eisenhammer na říčce Roth. Snímek ze srpna 2003, tj. z období mimořádného sucha, dokumentuje stav průtoku na říčce, která by byla bez přívodu vody z Dunaje téměř vyschlá. 

The renewed small dam Eisenhammer on the Roth Creek. The photo from August 2003, i. e. during an extreme drought, shows the creek discharge as it had almost dried out without water supply from the Danube. The weir rise is used in a small hydropower station at the former iron-mill, reconstructed as a museum of historical technology. 

The level in them is almost always stable, which is favorable for recreational use and for creating shallow zones, strictly divided from recreational facilities. These zones compensate the decrease of natural wet biotopes that happened in the aftermath of intensive utilization of the environment. In suitably modified boundary parts of these reservoirs, preserved natural and bird areas stretching almost 400 ha were declared. The approach of Bavarian authorities to revitalization of streams fed by the Danube water from the canal was similarly sensible. The whole amount of water is not led via the bed of the canal just to the Nuremberg agglomeration, but smaller streams are fed if necessary as well. These streams were revitalized at the same time, the existing historical water projects renewed and conditions for periodical irrigation of meadows were created. The conditions for fish migration were improved as well. It might seem that increasing discharges by pumping is energetically costly and economically disadvantageous. The opposite is true, though: in the case of the Main – Danube waterway we can say that the energy balance of the whole system is positive.

The currently valid concept of the water-resource utilization in Czech Republic is trying to solve balance deficiencies in a conventional way, i.e. by building further reservoirs. Further worsening of the water-resource balance and increasing of the number of sections with passive balance is expected in this section in the future as the “demanding” part of the balance will undoubtedly increase as a result of further economical development that will lead to higher take-outs of the water. The southern Moravia holds an unpleasant record as for how long the continuous dry periods last. The longest drought was recorded between February 1932 and February 1935, i.e. for 37 months. Similar disastrous periods had been recorded in numerous old chronicles as well. The water-resource balance does not worsen only due to the increase of demands, but also due to the decrease of resources, which is even a more important problem. It is connected with global changes of the climate, i.e. with the ever more discussed issue.

Srovnání charakteristických průtoků Dunaje, Moravy, Labe a Odry.

A comparison of characteristic discharges of the Danube, Morava, Elbe, and Oder Rivers.

 

Water is becoming a strategic resource. For a water function is water corridor DOE irreplaceable, and in three areas:

1. Flood protection

of adjacent areas and large industrial and urban areas. Estimations lead to a conclusion that if the D-O-E water corridor had been in place in 1997, the inhabitants of Olomouc, Přerov, Troubky and other towns and villages would have known the impacts of the flood still just from TV screens. 

Moravská brána včetně města Přerova by měla být v budoucnu ochráněna vodním koridorem D-O-L před povodněmi. Foto: Miroslav Raudenský

Moravian Gate including City of Přerov (on the picture) should be protected against the floods in future by water corridor DOE. Photo: Miroslav Raudenský

July flood in 1997, which affected vast areas along the Morava, Bečva and Oder and reminded them how illusive can be the feeling of safety that was evoked by a very long time without huge discharges. The enumerable material damages reached CZK 62 billion and there were also 52 deaths due to that disaster. It was very difficult to express non-economic damages too. 

In connection with that disastrous flood and another, even more damaging one in the Vltava and Elbe catchment areas, a lot of experts share the opinion that there will be a higher probability of flood occurrence in the Czech Republic in the upcoming decades. Up to 1997, possible impacts of floods were underestimated even by some experts for water management and engineers responsible for the D-O-E water corridor concept. It was thought that this project did not necessarily have to fulfill a flood measure function. The July 1997 flood affected most of the area along the waterway route and urged a revision of the general opinion of that time. The results were surprising.  

The attention was first concentrated on a canal sections of the waterway that led parallel with larger streams on which flood discharges could occur. The water does not flow through pools under normal circumstances – if we ignore slight flows due to filling or emptying locks or due to pumping, the water surface is practically horizontal. What would happen if we stop traffic for a short period of time and transfer a part of a flood discharge to a canal, though? The pools would see a flow of discharges which volume would depend on how much higher level of water would be admitted on the upper end of the pool. The calculations prove that it would be possible to transfer 500 ms3/s of water. Reduction of flood effects can also reach by "cutting off" the top of flood wave in the retention of water in enough large reservoir - eg polder. 

An optimum concept of a flood control reservoir on the Bečva at Teplice. The water corridor D-O-E, constituting its northern border (red line), can fully protect a main railway (purple line), a first class road (yellow line), and the townships of Milotice and Hustopeče nad Bečvou.

 

2. Keeping the water in the landscape

Positive Water Balance of DOE water corridor will be best reflected in the areas of southern and central Moravia. But generally, the water corridor DOE will ensure that "no drop" of water don't drain from the Czech part of the Morava, Oder and Elbe river basins above the mouth without the benefit for a man and nature. 

Přivaděč vody do vodohospodářského systému průplavu Rýn-Mohan–Dunaj pod nádrží Brombach má v některých případech tvar umělých a vzájemně propojených jezírek. 

Water supply of the water management system of the Main–Danube Waterway below the dam Brombach sometimes takes shape of interconnected small artificial lakes. 

 

3. Pumping of water

Water corridor DOE would allow to pumping of water through reversible pumping stations on the each navigation locks from only rich water source in Central Europe, from the River Danube. This practice is verified on the Rhine-Main-Danube waterway, where is pumped 21 m3 /s from river Danube. 

Stupeň Berching na průplavu Rýn-Mohan-Dunaj. Vpravo je přečerpávací stanice, která zajišťuje jak vodu pro provoz na průplavu, tak zásobování vodou toků v Norimberské oblasti. 

Navigation lock Berching on the Rhine-Main-Danube Waterway. A view of the lower approach and gate of the navigation lock Berching on the Main–Danube Waterway On the right, a pumping station with an intake structure, also serving as a guiding wall. The pumping station has 2 units with the capacity of 2 x 7 m3/s, which fully provide for needs of navigation, and 3 units of the same capacity for water management purposes. Altogether there are 5 units installed.