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46 Wirkung von Habitatsstrukturen auf die Benthoszönose
1998, Tittizer et al. 2000). To enable a further recovery of the aquatic fauna, besides
chemical also the physical improvement of habitat quality becomes increasingly important.
Main attention of this study was to assess the environmental changes within groyne
fields induced by two new groyne forms. Carabid beetles and macrozoobenthos taxa were
monitored prior to and after groyne modification to evaluate effects of different flow
velocities and resulting sedimentary deposition on the distribution patterns of the species
assemblages and the stenotopic species Bembidion velox and Gomphus flavipes.
Design and function of modified groynes
Two new groyne forms have been developed by means of model investigations (1D-, 2D-
HN, large scale physical model (1:30), (Henning 2000). A v-shaped groyne inclined on the
bank side and declined on the river side (type I, Fig. 4.4 D), and an inclined groyne which
is lowered by 1.20 m below mean water level on the riverbank side (type II, Fig. 4.4 G)
were found to diverse flow patterns and to slow down siltation in groyne fields (Fig. 4.4,
Hentschel & Anlauf 2001).
Regular Type (damaged)
exposed
submerged
A)
Type I
50 m
B) C)
D)
50 m
E)
72
°
F)
Type II
8 - 12 m (depending on groyne hight)
mean water level
1:3
1:3
mw - 1.2 m
G)
Fig. 4.4:
H) I)
Aerial view of the groynes (A: regular inclined, partially damaged, D: v-shaped),
geometry of the lowering (G), flow patterns in groyne fields with regular groynes (B:
exposed, C: submerged), modified type I (E: exposed, F: submerged), modified type II
(H: exposed below mean water, I: exposed above mean water). Arrows: Direction of
water current. Survey with Acoustic-Doppler-Current-Profiler (ADCP) and Acoustic-
Doppler-Velocimeter (ADV) (Simpson 2001).