6.1 Retzbach (Site 1)
6.1.3 Results: Physical Habitat Characterization
6.1.3.1 Reach 1/1
Figure 32: Niederbach, reach 1/1.
Figure 33: Impoundment of the Retzbach river.
Reach 1/1
1% 7%
4%
4%
81%
3%
Cascade Glide Lateral Scour Pool Plunge Pool Trench Pool Riffle
Reach 1/1
12%
9%
21%
18%
27%
3% 3% 5%
2% Bedrock (rough)
Boulders (large) Boulders (small) Cobbles Gravel (coarse) Gravel (fine) Sand Fines Concrete
The right tributary of the Retzbach flows through a V-shaped valley. Its course is heavily constrained by a gravel road and the hillside. A fence hinders hikers to enter the nearby private property.
Mouth of the Niederbach into the Retzbach at the impoundment of a small hydropower plant. The slow flowing water is about 2-3m deep. The Niederbach has created a sediment bank, mostly cobble and coarse gravel.
Even though the reach consists of different types of habitats, it is dominated by riffle sections, followed by pools in a variety of shapes.
The major substrate classes are gravel and cobble. Sand and fines play an insignificant role.
Even if the substrate composition may appear natural at the first sight, the impact of the adjacent road must not be neglected. A culvert under the gravel road is made out of concrete.
Cover Percentage
0 0 0 2
0
10
4
0 15
0 4 8 12 16 20
Filamentous Algae
Macrophytes
Woody Debris >0.3m
Brush/Woody Debr. <0,3m
Live Trees/Roots
Vegetation overhanging <1m
Undercut Banks
Boulders
Artificial Structures
Figure 35: Reach 1/1 - Fish cover.
Fish find cover mainly under boulders and overhanging vegetation. In general, fish cover is rare what could be observed during the field work when fish tried to find a place to hide.
55 52
25
5
15
43
33
0 10 20 30 40 50 60 70
Big Trees >0.3m Small Trees <0.3m Shrubs/Saplings Herbs/Grasses/Forbs Shrubs/Saplings Herbs/Grasses/Forbs Barren/Bare Dirt/Duff
Canopy >5m high Understory 0.5 - 5m high Ground Cover <0.5m high
Figure 36: Reach 1/1 - Riparian vegetation cover - left bank.
Canopy >5m high
91%
9%
Mixed None
Understory 0.5 - 5m high
27%
64%
9%
Deciduous Mixed None
Percentage
The left bank of the reach is densely covered by trees of a mixed hillside forest. Trees higher than 5m with a DBH >0.3m are as frequent as trees with a DBH <0.3m. The understory is not significantly pronounced and mixed at 64% of the transects, at 27% of the transects it is deciduous. Ground cover is dominated by herbs, grasses, and forbs, followed by barren, bare dirt, and duff. Small shrubs and saplings play a minor role.
16 16
5
16
6
29
57
0 10 20 30 40 50 60 70
Big Trees >0.3m Small Trees <0.3m Shrubs/Saplings Herbs/Grasses/Forbs Shrubs/Saplings Herbs/Grasses/Forbs Barren/Bare Dirt/Duff
Canopy >5m high Understory 0.5 - 5m high Ground Cover <0.5m high
Figure 37: Reach 1/1 - Riparian vegetation cover - right bank.
Due to the gravel road riparian vegetation cover is not in good condition on the right bank.
Canopy cover, that is at some transects nearly absent, is dominated by mixed vegetation.
The understory is even less developed and characterized mainly by deciduous small trees and shrubs. 57% of the ground cover is not vegetated and consists mainly of gravel.
Canopy >5m high
9%
73%
18%
Deciduous Mixed None
Understory 0.5 - 5m high
64%
18%
18%
Deciduous Mixed None
Percentage
0.3
0.5
0 0.3
0 0 0 0 0
0.1 0.1
0 0.3 0.6 0.9 1.2 1.5
Dike/Revetment/Riprap Buildings
Pavem
ent/Cleared Lot Road/Railroad
Pipes (Inlet/Outlet)
Landfill/Trash Park/Lawn
Row Crops
Pasture/Range/Hay Field
Logging Operations Mining Activity
Mean Weighting
Figure 38: Reach 1/1 - Human disturbances and influences - left bank.
The left bank of the reach is not heavily influenced by human impacts. The upper section is artificially altered because of a culvert under the gravel road.
1.1
0.2 0.3
0 0.3
0 0 0 0 0
1.4
0 0.3 0.6 0.9 1.2 1.5
Dike/Revetment/Riprap Buildings
Pavem
ent/Cleared Lot Road/Railroad
Pipes (Inlet/Outlet)
Landfill/Trash Park/Lawn
Row Crops
Pasture/Range/Hay Field
Logging Operations Mining Activity
Mean Weighting
Figure 39: Reach 1/1 - Human disturbances and influences - right bank.
The gravel road has led to heavy disturbances of the right bank and the adjacent area. Due to logging transportation and regular maintenance measures a development of a near-natural condition is not possible.
6.1.3.1.2 Summarizing Presentation of Conclusions and Results
This section demonstrates the correlations between the results of the NÖMORPH method and the Physical Habitat Characterization method with the help of the detailed characterizations of the 5 summarizing parameters (see Table 25 and section 7 Discussion).
Left bank
The left side of reach 1/1 is not heavily influenced by human impacts. This is illustrated by the NÖMORPH results as well as by the measurements and estimations of the Physical Habitat Characterization.
The riverbed evaluation resulted in condition class 2 due to occasional alterations along the riverbed and of the substrate composition caused by concrete (substructure of a bridge) that also influences the hyporheic interstitial (see also Figure 34).
The connectivity of water and the riparian area is sporadically disturbed by riprap and concrete which leads to a slightly modified condition (1-2). Even though large woody debris is absent (see Figure 30), Figure 35 shows that fish cover is present, mainly composed of boulders, overhanging vegetation, and undercut banks.
Vegetation cover of the riparian zone and the surroundings is near-natural. This conclusion is also affirmed by Figure 36 and Figure 38: Canopy, understory, and ground cover are consisting of mixed and native plants. Logging operations and agricultural areas are absent.
Right Bank
The right bank is significantly influenced by a gravel road as illustrated by Figure 39. The results are slightly to heavily modified conditions of the summarazing parameters (see Table 25).
Concerning channel geometry and flowability dynamic processes are limited and the river course is restricted because of riprap (see Figure 39).
The riverbed evaluation resulted in condition class 2 due to occasional alterations along the riverbed and of the substrate composition caused by concrete (substructure of a bridge) that also influences the hyporheic interstitial (see also Figure 34).
The connectivity of water and land is characterized by the significant limitation of lateral dynamic processes and the sporadical lack of natural structures.
The typical characteristics of the bank and the riparian zone are heavily altered because of riprap and the gravel road. The vegetation cover is disturbed - canopy, understory, and vegetated ground are nearly absent (see Figure 37).
The vegetation of the surroundings is also modified as there is no vegetation buffer and no understory.