Summary of site visits taken by the PLATINA 2 group of experts
The expert group convened at three different workshops to discuss relevant issues regarding
maintenance, to review the draft versions of the manual and to exchange experiences during onsite visits.
1. Danube: Bad Deutsch Altenburg, Austria (Host: viadonau, 15 Oct. 2014);
Topic: implementing structural measures to reduce maintenance efforts
At the first constitutional workshop, the group of experts visited the dredging site at the ford Bad
Deutsch Altenburg, situated in the free-flowing section of the river Danube east of Vienna. This
river stretch is characterised by high flow velocities and coarse sediment. The sediment regime is
disturbed by numerous hydropower plants. The hydropower plant operator is obliged to provide
residual (missing) sediment to stabilize the river bed. viadonau as waterway administration is
working on a project design to reduce necessary dredging interventions to a minimum by
implementing long term engineering solutions in the river (e.g. optimization of groynes and
training walls, removal of riprap, reconnection of side arms). Specific requirements are posed by
the location of the site in a national park (Danube floodplains). The sediment dredged at shallow
sections is loaded onto hopper barges, transported upstream and released back into the river at
specified sites to stabilize the sediment regime.
Figure 1: Maintenance dredging on the Austrian Danube (© Robert Tögel/viadonau) (left); the PLATINA 2
group on the Serbian Danube (© Luka Krivokuca/PLOVPUT) (right).
2. Danube: Belgrade, Serbia (Host: Plovput, 20 March 2015)
Topic: implementing structural measures and maximising possibilities of fairway realignment to
reduce maintenance efforts
During the second study visit, a surveying vessel of the Serbian waterway administration (Plovput)
took the participants to a critical section for navigation called “Preliv”, located in the free-flowing
stretch upstream of Belgrade. Here, the Danube has a sandy riverbed and is morphologically very
dynamic which creates numerous critical sections. Due to restricted budgetary resources, Plovput
prefers to realign the fairway (by re-setting the buoys) to optimise the available depth and width,
rather than to conduct repetitive dredging activities on locations with low back-filling rates. A main
element in this process is the corridor-oriented fairway marking database that has been
established in cooperation with partners from Croatia, Romania and Bulgaria ( Good Practice
Example will be presented in the manual). It provides a web-based overview of all current marking
signs, including coastal signs and buoys in use and enables quick updates and little reaction
times.
Thus implementing this database, malfunctions and updating of marking system can be
performed fast and efficient.
The visited river stretch consists of the main channel and a side arm which are divided by an
island. As the side arm is slightly shorter and wider than the fairway, skippers often prefer to take
this shortcut although fairway markings try to prevent the unauthorized side-arm passage. This
often results in groundings (river bed collisions) as the side arm is too shallow. Establishing a
physical connection between the island and the river bank to prevent passages of the side arm is
not possible due to nature protection requirements. Thus, the section is currently dredged if
necessary, but a more sustainable approach will be needed in the future. Plovput presented an
approach that envisages increasing flow velocities in the left and right bank area of the sidearm
by inserting a chevron close to the island and another one further upstream where another sand
bar reaches into the channel. At the same time, these structures would enable a controlled
sedimentation process in dedicated areas.
3. Rhine: Iffezheim & Gambsheim, Germany & France (Host: WSV & VNF, 17 Sept. 2015)
Topic: Artificial bedload supply
Iffezheim is the last hydropower plant on the Rhine before it flows downstream into the North
Sea. The free-flowing stretch downstream of Iffezheim is lacking sediment and has experienced
riverbed degradation for many decades. In order to avoid the construction of another barrage and
to support a more natural and ecologically valuable river, a sediment management programme
was set up (Good Practice Example will be presented in the manual). Gravel – corresponding to
the grain size composition of the original bedload material – is placed into the river. In order to
maintain the minimum fairway depth, the placement site has to be chosen carefully. Surveying
vessels accompany the loaded hopper barges and confirm the exact spot. Sometimes the
artificial bed load is dropped at once, at other times while in motion. After placement, the
morphology of the riverbed is surveyed again. Depending on the river discharge, multiple trips per
day might be necessary.
Figure 2: The surveying vessel leads the way to the exact placement spot (left), the hopper barge is opened to
release the material (right) (© Katja Rosner, viadonau).
Topic: Fish passes at locks
Iffezheim and Gambsheim are hydropower plants situated on the River Rhine. Grounded on the
European Water Framework Directive, waterway administrations and lock operators increased
their efforts to support natural fish migration around artificial and natural barriers. A fish pass
was built in Iffezheim in 2000, consisting of several pools that support fish to overcome the large
height difference and also allow them to rest in less turbulent corners. However, the velocity of
water falling over the steps must remain great enough to serve as attraction flows for fish to the
ladder. Three entrances were constructed from where the attraction flows are distributed over the
whole river width. 2014 was an exceptional year as over 50,000 fish travelled through the fish
pass by September. Prior to that, only about 25,000 migrated through it each year. The reason for
the sudden increase in 2015 still has to be evaluated. The fish pass is constantly improved and
the knowledge gained has also been used for constructing the fish pass in Gambsheim in 2006.
Topic: Lock management
A German-French treaty signed in 1969 enabled the construction of the Gambsheim lock which is
operated by the French waterway administrations („Voies Navigables France“). It is the largest
navigational river lock in France with a length of 270 m and a width of 24 m. A modern traffic
management system has been installed recently which is also used for disaster control. Action
plans for emergency situations, such as the leakage of dangerous goods, accidents or floods
have been set up. The station at Gambsheim also operates two polders which may only be
flooded and emptied according to the legally binding agreements with Germany.