The largest European fish pass in Geesthacht Design and construction Dipl.-Ing. Christof Neumann

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1 The largest European fish pass in Geesthacht Design and construction Dipl.-Ing. Christof Neumann In order to improve the passability for migratory fish an efficient fish pass is constructed in the river Elbe at the north side of the weir structure in Geesthacht. During the design phase of the facility numerous new and innovative solutions were developped that also are interesting for future design. Initial situation In the river Elbe there is only one transverse structure on German ground: The barrage in Geesthacht. The weir consists of four weir fields with 50 m effective width and of two unused fields and a fixed weir threshold that were kept available for the construction of a hydropower plant at the time. The construction of the weir in 1957 to 1960 caused a significant decimation of fish fauna. Many fish species hardly reach their spawning grounds in the middle and upper Elbe. In the 1990s a fish pass constructed at hte southern bank improved the situation there but isn t efficient enough. The company Vattenfall Europe Generation AG decided upon the recommendation oft he involved experts to construct a fish pass at the nothern bank of the weir in order to limit the damage of potential intrusions caused by the construction of a power plant. The company Knabe Enders Führkop Ingenieure GmbH in Hamburg was commissioned with the design. Basics of design At the site in addition to the conditions of the river Elbe, e.g. the tidal influence outside the weir, floods, storm floods and ice conditions, there are Natura protection areas as well as specific fish fauna to be considered. Therefore, different experienced experts had tob e included in the design team. An essential basis for the design and dimension if the facility were the new design regulations for fish passes in the DWA (German Association for Water, Waste Water and Waste) fact sheet that has been published as a yellow paper [DWA 2010]. 1

2 The requirements included in this paper were considered in de design and planning of the facility. Fish pass north Headwaters Tailwater Fig. 1: Situation of the fish pass at the weir Vattenfall To allow the fish to find a fish pass in the tailwater and to transverse it to the headwaters without too much effort and without interruption different parameters have to be adjusted depending on the fish species that is aimed at. The geometry of the facility is defined by the largest species and the maximum flow speed by the weakest swimmers. As decisive largest specie the adult Atlantic sturgeon was defined measuring about 3 m in average. This definition was decided on the basis of the resettlement programme for the Atlantic sturgeon implemented by the Sturgeon Association in Berlin. Furthermore, the facility also is adapted fort he whole spectrum of species in the Elbe. 2

3 Chosen Option Nature-oriented designs weren t possible due to the hydraulic parameters that could not have been respected. So a double-slot pass was chosen. Slot passes are constructed with success all over the world based on comprehensive research result concerning geometry. In contrast to a single slot pass the double-slot pass has a higher efficiency and less turbulences. The length of the facility and the maximum velocities in the slots mainly result from the defined differences in altitud per slot transverse wall. Fig. 2: Flow pattern in the double-slot pass [KIT 2009] In table 1 the main dimensions of the facility are documented. It is very important to respect the exact slot and basin geometries in order to assure the stability of the characteristic flow corridors. In between flow corridors large areas with low flow velocities will appear allowing the fish to regenerate if necessary. Basin width = 16 m Basin length = 9,3 m Slot width = 1,20 m Numer of basins = 45 Length in total approx m Water depth approx. 1,75 m Table 1: Main dimensions of the fish pass 3

4 Redirection of water to create a guiding current New bank line to guide fishes Access to the fish pass with culvert and bridge Free weir fields for potential hydropower use Eel pass via 4 eel ladders in the branch Branch Inflow to the double slot pass Fig. 3: General plan of the measure, Vattenfall Regarding the alignment of the facility in the headwaters of the weir it was decisive that the access was designed in a line with the transverse structure to be easier to find for the fish. (See Fig. 1). An undercrossing of the weir bridge is possible as in the nothern part under the road that is placed on piles free weir fields with fixed weir threshold do exist. Extensive preliminary investigations of the site and the construction conditions showed that the alignment in an existing bight with screw shape design is the optimal solution. It was found that neither sharp bends nor 180- degree redirecting basins were realized in this construction, and thus detailed studies on the development of appropriate basic elements and dimensions were required. Working with an experienced institution and complete evidence with a hydraulic model experiment turned out to be an essential prerequisite for ensuring a flawless function. In operation since mid-2010 functionality of the system was fully confirmed. 4

5 The channel walls are made of steel sheet pile walls in order to respect statics and csot efficiency. The transverse walls are realised with pre-cast reinforced concrete parts and fixed by steel piles in the ground. At first sight the design doesn t seem to be close to nature for the human eye but fortunately this isn t of any relevance for the users. The sole is built with bed substrate made of natural stone and is connected to the existing river bed at the tail- and headwater. Adaption to tidal influence According to the design criteria defined in the DWA fact sheet [DWA 2010] the facility has to be fully operational for at least 300 days per year. This is also true in conditions as they can be found in Geesthacht influenced by the tide. The tidal curve leads to retention in the facility during high tide resulting in higher water levels and consequently in a reduction of the flow velocity also in the slots. During extensive model tests it was found that the defined minimum velocities were underrun in the flow corridor and in the access in the tailwater. As a consequence it is harder for the fish to find access to the facility. For already existing facilities additions of water were realised in order to reach the minimum velocities in the access area. For the present project a new approach was chosen using model tests to determine entry points where water quantities are added regulated by floats. Consequently it is easier to find the access and the necessary minimum velocity is assured. Fig. 4: Dotation regulated by floats 5

6 Eel pass In addition to the fish pass an efficient eel pass is created. The so-called glass and European eels coming from the sea are very weak swimmers and move mainly near to the surface and close to the banks. The fish pass can t be passed by them. For the eel pass channels of about 40 cm width with brushlike inlays at the potential arrivig points of the eels. The channels are covered until they reach a storey structure with a monitoring station. The eels then reach the headwaters via a branch with reduced flow. The channels are kept wet with special armatures in order to offer optimal conditions to the eels. Fig. 5: Eel ladder (here still without cover) 6

7 Function control The proof of function of the fish ladder is accomplished on the basis of a monitoring program that was set by the licensing authority. For this purpose, a catching device jointly developed with fish ecologists was built at the plant which can take up large amounts of fish with its fish trap measuring 3 x 4 m. After one year of operation we ca state that a large variety of fish passes the fish pass from little fish weak in swimming like the stickleback and the smelt up to large fish like the salmon. Execution For the construction in total were carried out: about to steel sheet pile walls, 46 bulkheads mad of pre-manufactured, approx m³ earth works, ca to embankment and bed protections. Pile driving was carried out mainly from a spud carriage pontoon. Fig. 6: Pile driving 7

8 For the execution appropriate accuracy requirements are to be complied with. Moreover, for works with floating machines above the weir regulations of the Water and Shipping Authority have to be respected.. To increase security, a special security concept consisting of dolphins and fishing ropes has been developed. For this purpose, a catching device jointly developed with fish ecologists is built at the plant. Sources: [DWA 2010]: Fact sheet DWA-M 509, Fish ladders and fish pass structures Design and quality control [KIT 2009]: 3D-Calculations of the KIT, University of Karlsruhe Dipl.-Ing. Christof Neumann Knabe Enders Dührkop Ingenieure GmbH, Hamburg Gasstraße 18, Haus Hamburg c.neumann@ked-ingenieure.de 8