Geosynthetics August/September 2021 - 44

FINAL INSPECTION
The geosynthetic-based fish ladder
(left) at the Schwabentorwehr in
Freiburg im Breisgau, Germany.
Photograph courtesy of NAUE
GMBH & Co. KG
Bentonite mats allow fish to migrate
T
PROJECT HIGHLIGHTS
FISH LADDER FOR A
SMALL DAM IN GERMANY
OWNER
City of Freiburg im Breisgau,
Germany
LOCATION
Dreisam River in Freiburg
im Breisgau, Germany
CONTRACTOR
Walther Keune-Bau GmbH &
Co. KG, Freiburg im Breisgau
DESIGN ENGINEER
UNGER ingenieure, Freiburg
im Breisgau
GEOSYNTHETICS PRODUCT
Bentofix BZ 13-B
GEOSYNTHETICS
MANUFACTURER
NAUE GmbH & Co. KG
he Schwabentorwehr (Swabian Gate Weir) in Freiburg im Breisgau, Germany, was in disrepair
and insurmountable for fish. With the help of bentonite mats, the fish now have a free run again.
The historic Schwabentorwehr on the Dreisam River was a federally listed building for monument
protection. However, the 1873-constructed building was not only in disrepair but was an
obstacle to the migration of fish. To improve the site while preserving its historic character, a natural
fish ladder was added to replace the ten steps of the weir's ramp, which was impassable for fish. A
bentonite mat/geosynthetic clay liner (GCL) was installed under the revetment to act as a water
barrier and seal the protected structure.
The European Union (EU) Water Framework Directive stipulates ecological continuity. While
other locations used fish bypasses along the river, the layout of the Schwabentorwehr in the middle
of Freiburg im Breisgau prevented this. There were a public footpath, a cycle path, federal roads (one
on each side of the site) and residential buildings. Planners had no choice but to rebuild the structure.
It was important for the designers to seal the building downward to reduce surface water losses.
Essential requirements for the sealing material were a very high puncture resistance and having
the ability to be installed underwater.
Based on the specific requirements, the designers opted for Bentofix BZ 13-B (bentonite mats/
GCLs) from NAUE GMBH & Co. KG. The bentonite mats are needlepunched, reinforced, versatile
geocomposites with immediate sealing efficiency. They combine two geotextile outer layers
and a core of high-swelling powder sodium bentonite clay. The bentonite mats encapsulate an
additional sand layer. Both the bentonite and the sand layer are fully needled and erosion-proof.
The result is a uniform, multidirectional, shear-resistant hydraulic barrier with self-sealing and
rehealing characteristics.
Bentonite mats were installed between the existing subsoil and the revetment. The bentonite mats
were laid directly on the subgrade with an overlap of 3.3 feet (1 m) in the flow direction. The bentonite
mats were then covered with a gravel-sand layer, followed by a gravel-scrap mixture and the revetment.
Now, fish can overcome the height difference of 10.8 feet (3.3 m) upstream. The new fish ladder
is particularly crucial for the salmon resettlement program. G
44
Geosynthetics | August September 2021

Geosynthetics August/September 2021

Table of Contents for the Digital Edition of Geosynthetics August/September 2021

Geosynthetics August/September 2021 - Cover1
Geosynthetics August/September 2021 - Cover2
Geosynthetics August/September 2021 - 1
Geosynthetics August/September 2021 - 2
Geosynthetics August/September 2021 - 3
Geosynthetics August/September 2021 - 4
Geosynthetics August/September 2021 - 5
Geosynthetics August/September 2021 - 6
Geosynthetics August/September 2021 - 7
Geosynthetics August/September 2021 - 8
Geosynthetics August/September 2021 - 9
Geosynthetics August/September 2021 - 10
Geosynthetics August/September 2021 - 11
Geosynthetics August/September 2021 - 12
Geosynthetics August/September 2021 - 13
Geosynthetics August/September 2021 - 14
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Geosynthetics August/September 2021 - 16
Geosynthetics August/September 2021 - 17
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Geosynthetics August/September 2021 - 19
Geosynthetics August/September 2021 - 20
Geosynthetics August/September 2021 - 21
Geosynthetics August/September 2021 - 22
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Geosynthetics August/September 2021 - 24
Geosynthetics August/September 2021 - 25
Geosynthetics August/September 2021 - 26
Geosynthetics August/September 2021 - 27
Geosynthetics August/September 2021 - 28
Geosynthetics August/September 2021 - 29
Geosynthetics August/September 2021 - 30
Geosynthetics August/September 2021 - 31
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Geosynthetics August/September 2021 - 33
Geosynthetics August/September 2021 - 34
Geosynthetics August/September 2021 - 35
Geosynthetics August/September 2021 - 36
Geosynthetics August/September 2021 - 37
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Geosynthetics August/September 2021 - 43
Geosynthetics August/September 2021 - 44
Geosynthetics August/September 2021 - Cover3
Geosynthetics August/September 2021 - Cover4
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 1
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 2
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 3
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 4
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 5
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 6
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