The case study was done in Salzburg, one of the nine provinces of Austria. The orographic features of Salzburg are characterised by the Alpine mountain range with its great variety of geological strata and parent rocks and by the pre-alpine region in the northern part of the province with moderate to hilly terrain conditions. Three road projects in the Alpine mountain range, different in respect to bedrock material and side slopes, were chosen to serve as study objects to cover favourable, intermediate as well as difficult terrain conditions for road construction by excavator.
Table 1. General information on forest area in Austria and in the province of Salzburg
Austria |
Salzburg |
|||||
Forest categories |
[ha] |
[%] |
[ha] |
[%] |
||
Commercial forest |
3 063 000 |
78 |
239 000 |
65 |
||
Protection forest with yield |
289 000 |
3 |
37 000 |
10 |
||
Forest without timber yield |
106 000 |
7 |
9 000 |
3 |
||
Protection forest without yield |
466 000 |
12 |
81 000 |
22 |
||
Total forest area |
3 924 000 |
100 |
366 000 |
100 |
Note: Forest without timber yield are areas dedicated to forest road, skid trail, landing, nursery, game management, route of mains, skiing ground, springwater catchment, avalanche path, virgin forest, nature reserve or wildlife preserve. These areas remain forest by law although they often do not have any tree cover. |
Geological, morphological and hydrological terrain features are not only responsible for different construction conditions but also widely determine the type of forest cover in interaction with climate conditions. Within the framework of the Austrian Forest Inventory (AFI) two main forest types are distinguished, namely, "production forest" and "protection forest without yield". The production forest comprises the categories commercial forest, protection forest with yield and forest areas which remain forest by force of the forest act although they are currently without timber yield. The areas of protection forest without yield, which also covers dwarf pine vegetation, are areas mainly located in the timberline zone. Soil protection and erosion control is the exclusive objective in management of those areas. General information on these forest categories is provided in Table 1.
In the province of Salzburg the precipitation varies considerably, not only with respect to mean rainfall year and rainfall intensities, but also with its distribution over the year which is of significant importance to understand watersheds' response in distinct geological regions and therefore to properly design and dimension road drainage facilities (Winkler, 1992).
Another important fact to be considered in road planning activities is the land ownership and land use pattern in the province of Salzburg. It is characterized by small private property (see Table 2), mainly held by farmers who often rely on alpine agriculture and forest harvesting activities to earn their living. In many cases forest roads do not just serve timber harvesting purposes but also provide access to alpine pasture areas above the timber-line. In some cases, forest roads form part of the planned network of public roads and become an essential component of the local level development infrastructure.
Table 2. Forest ownership in Austria and in the province of Salzburg
Austria |
Salzburg |
||||||||||||||
Forest type |
Production forest |
Protection forest without yield |
Production forest |
Protection forest without yield |
|||||||||||
Ownership |
[ha] |
[%] |
[ha] |
[%] |
[ha] |
[%] |
[ha] |
[%] |
|||||||
Smallholders |
1 884 000 |
56 |
164 000 |
35 |
127 000 |
46 |
40 000 |
49 |
|||||||
Forest properties |
1 026 000 |
31 |
173 000 |
37 |
33 000 |
12 |
12 000 |
15 |
|||||||
Federal forest |
442 000 |
13 |
130 000 |
28 |
115 000 |
42 |
29 000 |
36 |
|||||||
Total forest area |
3 352 000 |
100 |
466 000 |
100 |
275 000 |
100 |
81 000 |
100 |
Note: Private property comprises the category of smallholders (owners of less than 200 ha forest area) and the category of forest properties (owners of more than 200 ha forest area). Federal forest refers to state owned forest area. |
Private property, which comprises ownership by smallholders and forest properties, provides about 59 % of the province's production forest area which is low compared to Austria's average of 87 % for this type of ownership. The remaining part of the production forest area, about 41 %, and a major part of the protection forest without yield, about 36 %, are federal forest in the province of Salzburg. These state-owned forest areas in Salzburg are often characterized by having been exploited in the Middle Ages in order to provide fuelwood and charcoal for the salt-mining industry.
The growing demand for fuelwood and charcoal in the early salt-mining and iron industries in the Middle Ages resulted in the first forestry regulations (Sedlak, 1996) in order to avoid further forest exploitation and to guarantee continued wood supply to the industry. As a result of these early efforts in forest management Austria has gained a long tradition in forest harvesting on a sustainable basis. The Forest Act 1976, adopted in 1996, and several environmental regulations are a response to the growing importance of environmental issues and provide the legislative tool to keep the impact of forest harvesting operations, in particular permanent forest infrastructure, to the absolute minimum (Photo 1).
Sustainable Alpine Land Management, which meets the needs of the agriculture and forestry sector while serving the growing demand of multiple use of resources, requires careful planning and co-operation between different small landowners and other interest groups, to favour appropriate road alignment and design required from the economical, environmental and social point of view. An integrated approach in road planning activities will most likely contribute to a well-planned rural road network.
Photo 1. Well-planned alignment and proper design of forest roads provide acceptance of forest harvesting operations. - Perfect road alignment prevents scars inflicted on the landscape
Photo 2. Critics of forest roads often point to excessive road building, evident on many hillsides, due to lack of co-operation between landowners - failures in the past
Almost 80 percent of the Austrian road network of about 200 000 km, may be classified as low-volume rural roads (Litzka and Haslehner, 1995). The low-volume rural road network comprising all roads providing access to rural areas, that are neither federal nor provincial, may be divided into the following categories (Litzka and Haslehner, 1995) based on ownership and function:
· Community-owned roads outside villages and towns;
· Farm-to-market roads connecting farm areas, single farm houses, or small villages with the higher road network; and
· Forest roads.
In general, road construction and maintenance are the road owners' responsibility. Associations formed by potential road users, mainly found in small ownership, are an appropriate means for financing of construction and maintenance of farm-to-market and forest roads while serving the need for co-operation between adjacent landowners to shorten the total length of road (Photo 1) at the same time.
The Road Inventory, as a sub-programme of the Austrian Forest Inventory, has provided the information on forest access, by different types of low-volume rural roads (Winkler, 1998; FBVA, 1997), stated in Table 3.
The figures in Table 3 show that low-volume roads located at the forest edge, about 12 % on average for Austria and 8 % for Salzburg contribute significantly to forest access although mainly serving agricultural requirements. These edge roads reduce the need for roads located inside forests or at least help to reduce the forest road densities required.
Table 3. Accessibility of production forest by low-volume rural roads
Austria |
Salzburg |
|||||
Road location and ownership |
[km] |
[%] |
[km] |
[%] |
||
located inside forests |
||||||
private-owned |
50 400 |
54 |
3 600 |
58 |
||
community-owned |
32 200 |
34 |
2 100 |
34 |
||
located at forest edge |
||||||
private-owned |
5 000 |
5 |
200 |
3 |
||
community-owned |
6 400 |
7 |
300 |
5 |
||
Total of rural roads |
94 000 |
100 |
6 200 |
100 |
Note: private road: access usually controlled by the owner
community roads: either with or without limited access
If all roads within the forest, either private or community owned, are assumed to be forest roads and then compared to the corresponding figures on commercial forest, road densities of about 27 metres per hectare for Austria and 24 metres per hectare for Salzburg (Table 4) result. These figures give an indication of road densities required for the management of forests on a sustainable basis in mountainous regions of Austria.
Table 4. Road densities in commercial forest
Commercial forest |
Roads inside forest |
Road density |
|||
Political unit |
[ha] |
[km] |
[m/ha] |
||
Austria |
3 063 000 |
82 600 |
26.97 |
||
Salzburg |
239 000 |
5 700 |
23.85 |
In the province of Salzburg with its mountainous terrain and the need to open up protection forest areas, which are mostly located in steep terrain, for stand improvement purposes, well-planned road alignment and keeping slope disturbances to the absolute minimum are of highest priority. There is also a legal requirement, since every project of forest road has to be planned and supervised by a professional forest engineer and needs the approval of the Forest Authority, which will be guided by the aspects of road construction stated below:
· shortening the total length of roads and skid trails;
· avoidance of areas of wet soils and high erosion risk;
· reducing the size of cut- and fill slopes by use of excavators in steep terrain;
· use of dozers is to be restricted to easy to moderate terrain conditions;
· applying advanced drilling and blasting techniques;
· observance of minimum road standards (road gradients etc.);
· adequate compaction of road surfaces;
· adequate drainage system from road surfaces;
· erosion control by measures of slope stabilisation.
Even following these considerations, serpentine alignments are often unavoidable in mountainous terrain due to slope features, but the number of switchbacks in the route for a road must be restricted to the absolute minimum. Poor road alignment, due to a lack of co-operation among small landowners which leads to zigzag roads with too short distances between switchbacks, are hopefully all in the past (see Photos 2 and 3). They not only inflict scars on the landscape and are difficult to travel but they are also potential sources for erosion and of landslides (Sedlak, 1996).
Growing concerns on environmental issues and the fact that forest roads are unquestionably the most damaging feature of timber harvesting operations (Dykstra and Heinrich, 1996) have forced and encouraged the development of new road construction methods and blasting technologies which now are exclusively used in forest road construction in the province of Salzburg.
Photo 3. Zigzag roads with too short distances between switchbacks due to lack of co-operation between landowners unnecessarily increase the area dedicated to roads
The main features of the three selected road projects where work and time studies on environmentally sound road construction practice by excavator had been carried out, are stated in Table 5. The area opened up by each road project and the annual timber supply to the market are the key-figures on which justification of financial assistance by federal and provincial government is based.
Table 5. General description of road projects under review
Filzmoos |
Untertauern |
Golling |
||||
Project feature |
study site 1 |
study site 2 |
study site 3 |
unit |
||
Forest area |
55 |
85 |
95 |
[ha] |
||
Farmland |
--- |
--- |
--- |
[ha] |
||
Total area opened up |
55 |
85 |
95 |
[ha] |
||
Total road length |
4300 |
4000 |
2100 |
[m] |
||
Road density |
78.2 |
47.0 |
22.1 |
[m/ha] |
||
Timber volume / year |
275 |
500 |
285 |
[m³] |
||
Duration |
2 |
3 |
3 |
years |
All three road projects were handed in by road associations for approval by the authorities. The road association of each road project under review has been established by smallholders exclusively and ranged from 3 members in the political community of Untertauern, 4 members in Filzmoos to 10 members in Golling. Detailed information on the projects is given in Table 6.
Table 6. Main features of the particular road projects
Project features |
Project - Filzmoos |
Project - Untertauern |
Project - Golling |
||
Commercial forest |
35 ha |
85 ha |
10 ha |
||
Protection forest with yield |
20 ha |
--- |
85 ha |
||
Area opened up |
55 ha |
85 ha |
95 ha |
||
Range in altitude |
1050 - 1350 m |
1420 - 1600 m |
700 - 1000 m |
||
Road length |
|||||
main road |
3100 m |
2300 m |
2100 m |
||
side road(s) |
700 m + 500 m |
1500 m |
--- |
||
Bedrock material |
phyllite |
limestone formation changing with phyllite layers |
stratified layers of compact limestone |
||
Morphological and hydrological features |
moderate steep to steep terrain with wet areas |
moderate steep to steep terrain with wet areas and rock outcrops |
steep to very steep terrain with rock outcrops |
||
Streams to be crossed |
--- |
1 intermittent stream 1 perennial stream |
1 intermittent stream |
||
Fords / bridges |
--- |
2 fords with culvert |
1 ford |
||
Construction equipment |
1) excavator 2) --- 3) dump truck 4) motor grader 5) vibration roller |
1) excavator 2) --- 3) dump truck 4) motor grader 5) vibration roller |
1) excavator 2) drilling equipment 3) dump truck 4) --- 5) vibration roller |
||
Max. road gradient |
13 % |
10 % |
12 % |
||
Switchbacks/turning (outside radius) |
3 switchbacks (22 m) |
2 switchbacks (20 m) |
2 switchbacks (17 m) 1 turning (17 m) |
||
Other specifications |
local improvement of subgrade by gravel |
local improvement of subgrade by gravel |
--- |
Drainage from the road surface will be provided by a crowned road, a hillside ditch and culverts (40 cm Ø) spaced at 50 m distances. In road sections where streams, either intermittent or perennial, are to be crossed, the dimension and spacing of culverts should be adjusted to the actual need for adequate water drainage. For the road project - Golling, additional drain dips at 70 m intervals have been specified.
As an important erosion control practice, seeding of grass is considered obligatory for all three road projects. Fill slope protection will be provided by a debris cover wherever possible. Retaining structures will be built up with boulders by the excavator wherever needed for slope stabilisation alongside the road (for details see Chapters 3.2 and 3.7).
Photo 4. Fords with integrated culverts are sometime specified as they meet the requirements of normal run-off as well as of high floods (Winkler, 1992)
Table 7 provides information on alterations, adaptations and additional prescribed measures made by the approving authorities and stated in the road building licence on which the beginning of road construction work depends. All measures must be inspected by the supervising forest engineer. Disregard of prescriptions may lead to loss of governmental financial support.
Table 7. Specifications in the road building licences
Project feature |
Project - Filzmoos |
Project - Untertauern |
Project - Golling |
||
Mass transport |
on side slope > 70 % |
on side slope > 70 % |
on side slope > 80 % |
||
Fords |
with retaining structure |
with retaining structure |
--- |
||
Culverts |
inlet - outlet protection |
inlet - outlet protection |
outlet protection |
||
Alteration of road alignment |
slight alteration to circumvent wet areas |
slight alteration to avoid rock formation |
--- |
||
Other measures |
ephemeral area is to be crossed by ford |
--- |
protection of trees used by woodpecker |
Figure 1. Regular cross-section for earth and rock
The cross-section both for earth and rock recommended in the road projects is shown in Figure 1. In the road project - Filzmoos a subgrade width of 4.0 m and a running surface of 3.0 m has been specified for the two side roads. Figure 2 shows the actual cross sections found at the study sites which are derived from several measurements spaced at 30 m distances along the road centreline of the road sections where construction operations have been observed.
Figure 2. Actual cross-sections at study sites
At study site 1 and 3, the average subgrade width was considered to be in compliance with the subgrade width of the approved road projects, whereas at study site 2 the subgrade width had obviously been increased. The latter was caused by the need to store logs alongside road, not only felled during clearing of construction area but also for logs of future timber harvest. Due to terrain conditions no landing could be established for several hundred metres (Photo 5).
Photo 5. The need of log storage alongside road has led to an increase in subgrade width at study site 2 as no landing could be established for several hundred metres