[[file:icon_sediment.png|right|150px|link=[[Sediments]]]]
=Introduction=
[[file:sediment_bypass_locations.png|thumb|250px|Figure 1: Sediment pass-by tunnel with two different locations of the intake: a) intake located at the reservoir head, b) intake located inside the reservoir. Longitudinal sections (top) and plain views (bottom) are provide (click to expand).]]

Dams act as a barrier for sediment transport in river systems. Sediment-laden inflows transport sediments from the upstream catchment that will be trapped when reaching the reservoir. Sediments deposit in the bottom of the reservoir and reduce its storage capacity. In geographical areas with very high sediment concentrations, reservoirs can be filled after some years, rendering the infrastructure useless. Consequently, sediments are not transported past the dam, resulting in sediment starvation in the downstream river reach. Lack of sediments can induce severe morphological and ecological impacts.

Sediment by-passing is a measure which aims at routing bed load and part of the suspended sediment load through or around the reservoir (Morris et al. 1998). The objective is to maintain the storage capacity of the reservoir in addition to insure sediment continuity in the river and avoid morphological and ecological impacts (Hauer et al. 2018; Boes et al. 2019).

Sediment by-pass consists in diverting bed load and part of the suspended load around the reservoir to prevent them from entering the reservoir. The sediment-laden inflows are diverted through a tunnel at the entrance of the reservoir and conveyed to the river reach downstream of the dam. A weir or a guide wall located at the upstream head of the reservoir re-directs the water to the tunnel during periods of high flow and high sediments loads, and allows water entering the reservoir during periods with low sediment loads (Fig. 1a). Alternatively, the intake structure can be located inside the reservoir, leading to some deposition in the upstream part of the reservoir (Fig. 1b).

An alternative to bypass sediments through a tunnel is in transporting them with trucks or boats. Accumulated sediments are excavated from the reservoir, bypassed around the reservoir via trucks or boats, dumped downstream of the dam and transported downstream by flood flows.

=[[Methods, tools, and devices]]=

==During planning==
The design of bypass tunnels depends on catchment characteristics like topography, geology, hydrology and the reservoir's shape and size (Tiger et al. 2011, Hauer et al. 2018, Boes et al. 2019). They function well in small reservoir with steep slopes as the gradient of the diversion channel needs to be sufficiently large to insure the transport of sediments. The use of bypass tunnels with intake located at the reservoir head is a measure that does not interfere with hydropower operations since it does not require a drawdown of the reservoir. In contrast, if the tunnel intake is located in the reservoir, a partial reservoir drawdown is required to transport incoming sediment to the tunnel guiding structure (Fig. 1). In addition, sediment routing through bypass tunnels induces less impacts on the downstream ecosystems than reservoir flushing or sluicing. However, bypass structures are not well adapted to flood control reservoirs as they undercut the main role of these reservoirs (Kondolf et al. 2014).

==During implementation==
Construction of bypass structures (canals or tunnels) have relatively high investments costs. They should be built at the time of reservoir construction to minimize technical efforts.

==During operation==
The main challenge of bypass tunnels is abrasion. The intense bed load transport degrades the invert of the tunnels and can induce deep abrasion of the material. High-strength concrete or hard natural stone materials such a sgranit are recommended for the invert protection of the sediment bypass tunnels (Müller-Hagmann et al., 2020).

=Relevant MTDs and test cases=
{{Suitable MTDs for By-passing sediments}}

=Classification Table=
{{By-passing sediments}}

=Relevant Literature=

[[category:Sediment measures]][[category:Measures]]
Boes, R.M., Müller-Hagmann, M., Albayrak, I. (2019). Design, operation and morphological effects of bypass tunnels as a sediment routing technique. Proc. 3rd Intl. Workshop on Sediment Bypass Tunnels, pp. 40-50, National Taiwan University, Taipei, Taiwan.
Müller-Hagmann, Albayrak, M., Auel, C., I. Boes, R.M. (2020). Field Investigation on Hydroa-brasion in High-Speed Sediment-Laden Flows at Sediment Bypass Tunnels. Water 12(2), 469, https://www.mdpi.com/2073-4441/12/2/469.

2020-04-28T09:21:53Z

Robert Boes: /* Gallery */

[[Category:Test cases]]
{{Fact box for Schiffmühle}}
{{Relevant SMTDs for Schiffmühle}}

=Introduction=
The hydropower plant (HPP) Schiffmühle is a run-of-the-river HPP located on the 35 km long stretch of the Limmat river in the communities of Untersiggenthal and Turgi near Baden, some 27 km downstream of Lake Zurich. Between lake Zurich and Schiffmühle there are seven HPPs, namely in flow direction Letten, Höngg , Dietikon, Wettingen, Aue, Oederlin and Kappelerhof. There are three more HPPs between HPP Schiffmühle and the junction with the Aare river, namely Turgi, Gebenstorf and Stroppel. The lowest and highest points of the Limmat river are 330 m and 406 m asl, respectively. The surface area of the whole catchment amounts to 2384 km2, of which 0.7 % are glaciated.

On river Limmat, the mean monthly discharge increases from March to June and then decreases from July to October. The annual discharge in 2015 was 89 m3/s, while the long-term average is 101 m3/s (1951-2015).

=About the hydropower plant=
At Schiffmühle, hydropower is exploited in two run-of-river HPPs, namely the main powerhouse located at the end of a headrace channel on the right shore and the residual flow HPP situated next to a flap gate at the upstream end of the weir on the left shore (see Gallery, layout of HPP Schiffmühle). In the scope of FIThydro, the residual flow HPP is the investigated case study HPP. This HPP has an installed capacity of 0.5 MW and a mean annual output of 1.9 GWh. It operates with a bevel gear bulb turbine.

===The Operator: Limmatkraftwerke AG (LKW)===
LKW produces environmentally friendly and local electricity from four main and two residual flow hydropower plants on river Limmat between Baden and Turgi. The company is owned by the Regionalwerke Holding AG Baden (60%), a local utility company, and the regional power company AEW (40%). The Regionalwerke AG Baden is responsible for the operation of the HPPs and all technical and energy management issues. The administrative and financial management are performed by Axpo AG. The average annual energy output is around 91 GWh. The company fulfills the standards according to ISO 9001 and the production of renewable energy is certified by TÜV SÜD Erzeugung EE.

=Pressures on the water body's ecosystem=
The river Limmat is located in the Rhine river catchment, which was historically one of the most important Atlantic salmon rivers in Europe. The upstream migration of salmons (Salmo salar) in the Rhine catchment became almost impossible due to transverse structures such as hydropower plants. In the past few years a number of HPPs on the Rhine, Aare and Limmat rivers have been equipped with state-of-the-art fish passage facilities for upstream migration. However, downstream migration measures and sediment management strategies have hardly been realized. Furthermore, the Limmat river is highly influenced by HPPs and densely populated areas and considered as a heavily modified water body. The river has a moderate ecological potential. Various measures for sediment control, fish migration, flow changes, habitat in-channel and morphology off-channel have been implemented in the water body.

=Test case topics=
===Fish population===
All of the existing fish species in the Limmat river (at least 22 species) face potential mortality during their downstream migration, some of which also have difficulties to migrate upstream. Some of the most important species are: Eel (Anguilla anguilla), Brown trout, Common barbel (Barbus barbus), Grayling, Spirlin, Nase, Chub, Bleak.

===Downstream migration===
At the residual flow HPP Schiffmühle, an angled fish guidance structure with horizontal bars, termed Horizontal Bar Rack (HBR), has been implemented in 2013 to shield fish from the turbine intake and guide them into a bypass and to the tailwater. The rack is positioned parallel to the main flow to have a lateral intake. The HBR has a length of 14.6 m and a spacing of 20 mm between the bars, which are positioned in a vertical angle of 90°. At the end of the rack there is the bypass inlet with three openings in a vertical chamber in different water depths (close to the bottom, central and close to the surface). From there, a 25 cm diameter pipe bypasses the fish downstream, letting them out at about 0.20 m above the tailwater level. The discharge in the bypass is 170 l/s.

For monitoring downstream migrating fish, 1 PIT-tag antenna has been installed at the bypass pipe inlet.

===Upstream migration===
HPP Schiffmühle has a combination of a nature-like and a technical fish pass (vertical slot) for upstream migration. The entrances of the nature-like fish pass and the vertical slot pass are located approx. 36 m and 2 m downstream of the turbine's suction tube outlet, respectively. The technical and the nature-like fish passes merge at an elevation of 336.83 m a.s.l. (see figures in the Gallery). From there on upwards, fish use the nature-like pass. The total discharge in the fishway is 0.5 m3/s.

To monitor upstream migration and fish behavior in the migration facilities, 5 PIT-tag antennas have been installed in the technical vertical slot fish pass and in the nature-like pass.

===E-flow===
The residual flow HPP Schiffmühle supplies up to 14.6 m3/s of turbine water and 0.67 m3/s of the water in the fish passage facilities (upstream and downstream) to the downstream river reach as e-flow. Moreover, during high river discharges, additional water is supplied over the frontal weir at the HPP and over the side weir along the headrace channel to the residual flow reach.

===Sediment management===
An innovative vortex tube for bed load transport connectivity has been installed in 2002 in the headrace channel to guide bed load to the residual flow stretch of the Limmat river during floods. Additionally, sediment can be flushed via the weir flap gate.

=Research objectives and tasks=
The studies at HPP Schiffmühle address various aspects of the upstream and downstream fish passes, downstream habitat and sediment transport. The findings of the studies will have a wide range of applications for other HPPs and will give answers to the fundamental questions on fish behavior at fish passes.
===Research tasks===
The research tasks and field studies conducted at HPP Schiffmühle are:

* Field campaign: hydraulics, habitat, attraction flow and Lateral Line Probe in upstream fish pass
* 3D numerical model of the HPP perimeter
* Fish monitoring
* Bed load monitoring at vortex tube
* Habitat and sediment modelling

=Results=
The flow conditions at the entrance of the nature-like fishway of the residual flow HPP Schiffmühle is more attractive for all monitored fish species than the flow condition at the entrance of the vertical slot fishway close to the draft tube outlet. However, the fish entrance efficiency is higher for the vertical slot fishway. Overall, the passage efficiency of the fish pass system is high (> 80 % for most species monitored), indicating an appropriate design and a good functionality.

Regarding downstream fish migration, velocity measurements and fish monitoring results show that the attraction flow to the bypass of the fish protection and guidance structure (Horizontal Bar Rack-Bypass System) is inefficient and needs to be upgraded and optimized. The results indicate that the design, location and operation of a fish guidance rack-bypass system is of prime importance for a successful implementation and a high guidance efficiency. Using a 3D numerical model, alternative bypass designs in terms of layout and inlet location have been investigated.

=Gallery=
<gallery mode=packed>
Schiffmühle_aerial.png|Aerial overview of Schiffmühle HPP; flow direction from top to bottom
schillmuhle_spillway.jpg|Residual flow HPP (left), flap-gated weir (centre) and headrace channel to the main HPP Schiffmühle (right); view to downstream
schillmuhle_fishway.jpg|Nature-like fishway at Schiffmühle HPP
Layout-Picture_Schiffmühle_CVAW_ETHZ_web-scaled.jpg|Layout of Schiffmühle HPP
schillmuhle_upstream-migration-devices_c_ETHZ_web-scaled.jpg|Overview of fish migration devices at Schiffmühle HPP
schiffmuhle_vertical_slot_fishway.jpg|Vertical slot fishway at Schiffmühle HPP
schiffmuhle_downstream-migration-devices_photo_2.jpg|Schematic of fish migration devices at Schiffmühle HPP
schiffmuhle_sediment-management_vortex_tube_photo_4.jpg|Outlet of sediment vortex tube at Schiffmühle HPP
schiffmuhle_sediment-management_vortex_tube_setup.jpg|Setup of the sediment vortex tube at Schiffmühle HPP
schiffmuhle_Calibration-of-sediment-monitoring-system-for-vortex-tube.jpg|Calibration of the sediment vortex tube monitoring system at Schiffmühle HPP
</gallery>

2020-04-27T15:23:35Z

Robert Boes: /* Pressures on the water body's ecosystem */

[[Category:Test cases]]
{{Fact box for Bannwil}}
{{Relevant SMTDs for Bannwil}}

=Introduction=
The Bannwil hydropower plant (HPP) is a run-of-the-river HPP on the river Aare located in the community of Bannwil, some 46 km downstream of Lake Biel. There are two upstream HPPs on the Aare river below Lake Biel, HPP Brügg at the lake outflow and HPP Flumenthal about 12 km from Bannwil.

The river Aare is a 291 km long tributary of the Rhine and the longest river within Switzerland. The Aare River passes through three major lakes: Lake of Brienz, Lake of Thun and Lake of Biel.

In total there are 10 hydropower plants between Lake of Biel and the junction with the Rhine river.The other nine HPPs as well as two nuclear power plants are located downstream of the Bannwil HPP.

The altitude of the lowest and highest points of this river reach are ca. 312 m a.s.l. and 429 m a.s.l., respectively. The average altitude of the whole catchment amounts to 1060 m a.s.l. and the whole catchment area is 17687 km2, of which 1.4 % are covered by glaciers. On the river Aare, the mean monthly discharge increases from February to June and then decreases from July to October. The annual discharge in 2015 was 260 m3/s.

=About the hydropower plant=
There are in total 12 HPPs on the Aare river stretch between Lake Biel and the junction with the Rhine river, and two nuclear power plants with water abstraction for cooling.
The Bannwil weir is located on the right side of the river, while the powerhouse is located on the left side. The reservoir impoundment is about 7 km long. With thre bulb turbines, HPP Bannwil has an installed capacity of 28.5 MW and an average annaul production of 150 GWh. The gross head amounts to 5.5 - 8.5 m, depending on the up- and downstream water levels, with a designed discharge of 450 m3/s. The annual production is about 150 GWh.

===The Operator: BKW===
HPP Bannwil is operated by the BKW group. The group plans, builds and operates infrastructure to produce and supply energy to businesses, households and the public sector, and offers digital business models for renewable energies. [https://www.bkw.ch/en/about-us/company/about-us/ Read more.]

=Pressures on the water body's ecosystem=
The river Aare is located in the Rhine river catchment, which was historically one of the most important Atlantic salmon (Salmo Salar) rivers in Europe. The upstream migration of salmons in the Rhine catchment became almost impossible after intense hydropower plant constructions, including the Aare river catchment. All of the occurring fish species present in the Aare river (total of 44 fish species) face potentially high mortality during downstream migration or difficulties during upstream migration.

Furthermore, the river Aare is highly influenced by hydropower and considered as a heavily modified water body. Moreover, there are three nuclear power plants on the Aare river, two of them reintroducing the used cooling water, which induces an increase of the river water temperature. The river has a moderate ecological potential. Measures for sediment control, fish migration, flow changes, habitat in-channel and morphology off-channel have been implemented in the water body.

=Test case topics=
===Fish population===
There are a total of 44 fish species in the river Aare, some of which are: Eel (Anguilla anguilla), brown trout (Salmo trutta), chub (Squalius cephalus), grayling (Tymallus Thymallus), spirlin (Alburnus alburnus), common barbel (Barbus Barbus). Salmon is expected in the next 10 - 20 years.

===Upstream migration===
The current fish pass is pool design with bottom and top openings. The entrance is located at the left side of river shortly downstream of the powerhouse. The bottom slope of the technical fish pass is on average 6 %. Most of the head difference is accomplished in the first half of the fishway. It consists of chambers with a spiral fishway. The upper part of the fishway consists of near horizontal canal that lead to the exit roughly 100 m upstream of the HPP. The mean discharge in the fishway amounts to 350 l/s.

The fish pass needs to be restructured to accommodate larger fish in the near future. Current plans include replacing the lower part with a vertical fish pass design and the upper part with a nature like open channel.

=Research objectives and tasks=
At Bannwil, downstream fish migration measures are investigated by means of field and numerical studies. The current situation and the efficiency of spill flow or water release as an operational measure at the HPP Bannwil will be investigated through field monitoring and 3-D numerical modelling in the area near the powerhouse and weir. Applying this model to different structural and/or operational scenarios will allow to come up with solutions to improve fish migration at reduced energy losses. Dynamic pressure fluctuations experienced by fish during the turbine and spillway passages will be studied at HPP Bannwil using a Barotrauma Detection System (BDS) developed at TUT. Based on the data a CFD-model will be developed, which can then be used to evaluate the fish passage in order to judge the possibility of adapting the hydropower operation for certain time periods
===Research tasks===
The research tasks and field studies conducted at Bannwil are:

* Velocity & hydraulic measurements
* 3D Turbine & HPP models with Biological Performance Assessment and Barotrauma Detection System
* Fish monitoring; Survey of fish movement using ARIS Sonar and radio telemetry techniques
* Variant Study
=Results=

=Gallery=
<gallery mode=packed>
HPP Bannwil River Aare.jpg|Aerial view of Bannwil power plant/dam.
HPP Bannwil River Aare2.jpg|Downstream view of Bannwil power plant/dam [1].
HPP Bannwil River Aare3.jpg|Downstream view of Bannwil power plant/dam [2].
Bannwil Layout.png|Layout of the Bannwil power plant/dam and surrounding area. The yellow arrow indicates the powerhouse.
</gallery>

Bannwil test case

2020-04-27T15:21:10Z

Robert Boes: /* About the hydropower plant */

[[Category:Test cases]]
{{Fact box for Bannwil}}
{{Relevant SMTDs for Bannwil}}

=Introduction=
The Bannwil hydropower plant (HPP) is a run-of-the-river HPP on the river Aare located in the community of Bannwil, some 46 km downstream of Lake Biel. There are two upstream HPPs on the Aare river below Lake Biel, HPP Brügg at the lake outflow and HPP Flumenthal about 12 km from Bannwil.

The river Aare is a 291 km long tributary of the Rhine and the longest river within Switzerland. The Aare River passes through three major lakes: Lake of Brienz, Lake of Thun and Lake of Biel.

In total there are 10 hydropower plants between Lake of Biel and the junction with the Rhine river.The other nine HPPs as well as two nuclear power plants are located downstream of the Bannwil HPP.

The altitude of the lowest and highest points of this river reach are ca. 312 m a.s.l. and 429 m a.s.l., respectively. The average altitude of the whole catchment amounts to 1060 m a.s.l. and the whole catchment area is 17687 km2, of which 1.4 % are covered by glaciers. On the river Aare, the mean monthly discharge increases from February to June and then decreases from July to October. The annual discharge in 2015 was 260 m3/s.

=About the hydropower plant=
There are in total 12 HPPs on the Aare river stretch between Lake Biel and the junction with the Rhine river, and two nuclear power plants with water abstraction for cooling.
The Bannwil weir is located on the right side of the river, while the powerhouse is located on the left side. The reservoir impoundment is about 7 km long. With thre bulb turbines, HPP Bannwil has an installed capacity of 28.5 MW and an average annaul production of 150 GWh. The gross head amounts to 5.5 - 8.5 m, depending on the up- and downstream water levels, with a designed discharge of 450 m3/s. The annual production is about 150 GWh.

===The Operator: BKW===
HPP Bannwil is operated by the BKW group. The group plans, builds and operates infrastructure to produce and supply energy to businesses, households and the public sector, and offers digital business models for renewable energies. [https://www.bkw.ch/en/about-us/company/about-us/ Read more.]

=Pressures on the water body's ecosystem=
The river Aare is located in the Rhine river catchment, which was historically one of the most important Atlantic salmon (Salmo Salar) rivers in Europe. The upstream migration of Salmons in the Rhine catchment became almost impossible after hydropower plant constructions. This includes the river Aare. All of the occurring fish species present in the Aare river (total of 44 fish species) face potentially high mortality during downstream migration or difficulties during upstream migration.

Furthermore, the river Aare is highly influenced by hydropower and considered as a heavily modified water body. Moreover, there are three nuclear power plants on the Aare river, two of them reintroducing the used cooling water, which induces an increase of the river water temperature. The river has a moderate ecological potential. Measures for sediment control, fish migration, flow changes, habitat in-channel and morphology off-channel have been implemented in the water body.

=Test case topics=
===Fish population===
There are a total of 44 fish species in the river Aare, some of which are: Eel (Anguilla anguilla), brown trout (Salmo trutta), chub (Squalius cephalus), grayling (Tymallus Thymallus), spirlin (Alburnus alburnus), common barbel (Barbus Barbus). Salmon is expected in the next 10 - 20 years.

===Upstream migration===
The current fish pass is pool design with bottom and top openings. The entrance is located at the left side of river shortly downstream of the powerhouse. The bottom slope of the technical fish pass is on average 6 %. Most of the head difference is accomplished in the first half of the fishway. It consists of chambers with a spiral fishway. The upper part of the fishway consists of near horizontal canal that lead to the exit roughly 100 m upstream of the HPP. The mean discharge in the fishway amounts to 350 l/s.

The fish pass needs to be restructured to accommodate larger fish in the near future. Current plans include replacing the lower part with a vertical fish pass design and the upper part with a nature like open channel.

=Research objectives and tasks=
At Bannwil, downstream fish migration measures are investigated by means of field and numerical studies. The current situation and the efficiency of spill flow or water release as an operational measure at the HPP Bannwil will be investigated through field monitoring and 3-D numerical modelling in the area near the powerhouse and weir. Applying this model to different structural and/or operational scenarios will allow to come up with solutions to improve fish migration at reduced energy losses. Dynamic pressure fluctuations experienced by fish during the turbine and spillway passages will be studied at HPP Bannwil using a Barotrauma Detection System (BDS) developed at TUT. Based on the data a CFD-model will be developed, which can then be used to evaluate the fish passage in order to judge the possibility of adapting the hydropower operation for certain time periods
===Research tasks===
The research tasks and field studies conducted at Bannwil are:

* Velocity & hydraulic measurements
* 3D Turbine & HPP models with Biological Performance Assessment and Barotrauma Detection System
* Fish monitoring; Survey of fish movement using ARIS Sonar and radio telemetry techniques
* Variant Study
=Results=

=Gallery=
<gallery mode=packed>
HPP Bannwil River Aare.jpg|Aerial view of Bannwil power plant/dam.
HPP Bannwil River Aare2.jpg|Downstream view of Bannwil power plant/dam [1].
HPP Bannwil River Aare3.jpg|Downstream view of Bannwil power plant/dam [2].
Bannwil Layout.png|Layout of the Bannwil power plant/dam and surrounding area. The yellow arrow indicates the powerhouse.
</gallery>

Bannwil test case

2020-04-27T15:12:12Z

Robert Boes: /* Introduction */

[[Category:Test cases]]
{{Fact box for Bannwil}}
{{Relevant SMTDs for Bannwil}}

=Introduction=
The Bannwil hydropower plant (HPP) is a run-of-the-river HPP on the river Aare located in the community of Bannwil, some 46 km downstream of Lake Biel. There are two upstream HPPs on the Aare river below Lake Biel, HPP Brügg at the lake outflow and HPP Flumenthal about 12 km from Bannwil.

The river Aare is a 291 km long tributary of the Rhine and the longest river within Switzerland. The Aare River passes through three major lakes: Lake of Brienz, Lake of Thun and Lake of Biel.

In total there are 10 hydropower plants between Lake of Biel and the junction with the Rhine river.The other nine HPPs as well as two nuclear power plants are located downstream of the Bannwil HPP.

The altitude of the lowest and highest points of this river reach are ca. 312 m a.s.l. and 429 m a.s.l., respectively. The average altitude of the whole catchment amounts to 1060 m a.s.l. and the whole catchment area is 17687 km2, of which 1.4 % are covered by glaciers. On the river Aare, the mean monthly discharge increases from February to June and then decreases from July to October. The annual discharge in 2015 was 260 m3/s.

=About the hydropower plant=
The run-of-river hydropower plant is located in Bannwil, downstream of Lake Biel and the HPP Brügg and Flumenthal. There are 9 more power plants between HPP Brügg and the junction with Rhine river as well as two nuclear power plants with water abstraction for cooling.

The weir is located on the right side of the river, while the Powerhouse is located on the left side. The reservoir is about 7 km long. With thre bulb turbines, the HPP has an installed capacity of 28.5 MW and an average annaul production of 150 GWh. The gross head amounts to 5.5 - 8.5 m depending on the up- and downstream water level with a designed discharge of 450 m3/s. The annual Production is about 150 GWh.

===The Operator: BKW===
The HPP Bannwil is operated by the BKW group. The Group plans, builds and operates infrastructure to produce and supply energy to businesses, households and the public sector, and offers digital business models for renewable energies. [https://www.bkw.ch/en/about-us/company/about-us/ Read more.]

=Pressures on the water body's ecosystem=
The river Aare is located in the Rhine river catchment, which was historically one of the most important Atlantic salmon (Salmo Salar) rivers in Europe. The upstream migration of Salmons in the Rhine catchment became almost impossible after hydropower plant constructions. This includes the river Aare. All of the occurring fish species present in the Aare river (total of 44 fish species) face potentially high mortality during downstream migration or difficulties during upstream migration.

Furthermore, the river Aare is highly influenced by hydropower and considered as a heavily modified water body. Moreover, there are three nuclear power plants on the Aare river, two of them reintroducing the used cooling water, which induces an increase of the river water temperature. The river has a moderate ecological potential. Measures for sediment control, fish migration, flow changes, habitat in-channel and morphology off-channel have been implemented in the water body.

=Test case topics=
===Fish population===
There are a total of 44 fish species in the river Aare, some of which are: Eel (Anguilla anguilla), brown trout (Salmo trutta), chub (Squalius cephalus), grayling (Tymallus Thymallus), spirlin (Alburnus alburnus), common barbel (Barbus Barbus). Salmon is expected in the next 10 - 20 years.

===Upstream migration===
The current fish pass is pool design with bottom and top openings. The entrance is located at the left side of river shortly downstream of the powerhouse. The bottom slope of the technical fish pass is on average 6 %. Most of the head difference is accomplished in the first half of the fishway. It consists of chambers with a spiral fishway. The upper part of the fishway consists of near horizontal canal that lead to the exit roughly 100 m upstream of the HPP. The mean discharge in the fishway amounts to 350 l/s.

The fish pass needs to be restructured to accommodate larger fish in the near future. Current plans include replacing the lower part with a vertical fish pass design and the upper part with a nature like open channel.

=Research objectives and tasks=
At Bannwil, downstream fish migration measures are investigated by means of field and numerical studies. The current situation and the efficiency of spill flow or water release as an operational measure at the HPP Bannwil will be investigated through field monitoring and 3-D numerical modelling in the area near the powerhouse and weir. Applying this model to different structural and/or operational scenarios will allow to come up with solutions to improve fish migration at reduced energy losses. Dynamic pressure fluctuations experienced by fish during the turbine and spillway passages will be studied at HPP Bannwil using a Barotrauma Detection System (BDS) developed at TUT. Based on the data a CFD-model will be developed, which can then be used to evaluate the fish passage in order to judge the possibility of adapting the hydropower operation for certain time periods
===Research tasks===
The research tasks and field studies conducted at Bannwil are:

* Velocity & hydraulic measurements
* 3D Turbine & HPP models with Biological Performance Assessment and Barotrauma Detection System
* Fish monitoring; Survey of fish movement using ARIS Sonar and radio telemetry techniques
* Variant Study
=Results=

=Gallery=
<gallery mode=packed>
HPP Bannwil River Aare.jpg|Aerial view of Bannwil power plant/dam.
HPP Bannwil River Aare2.jpg|Downstream view of Bannwil power plant/dam [1].
HPP Bannwil River Aare3.jpg|Downstream view of Bannwil power plant/dam [2].
Bannwil Layout.png|Layout of the Bannwil power plant/dam and surrounding area. The yellow arrow indicates the powerhouse.
</gallery>