3.2 TERRAIN AND SOIL
3.3 STAND AND TREES
Road surveying, construction and maintenance should be limited to the dry period whenever possible because during the rainy period not only are erosion risks and dangers higher, but costs also increase considerably. In general, we can count on about 150-180 actual working days per year. What affects the work most is the intensity of precipitation within a certain period of time rather than the yearly amount of rain, so for instance it may very well be that within a short time some 150 - 300 mm of rain may fall. Therefore, when planning roads in high rainfall areas, attention should be paid to the exposure of the road in order that the road can be dried by sunshine as quickly as possible.
In high altitudes it should be realized that due to thinner air, labour productivity is less than in the low lands and more frequent pauses are required to combat fatigue.
Road costs are heavily influenced by terrain, especially when the latter is broken and frequent gullies, creeks or small rivers occur. Careful attention should be paid to the stability of the terrain when planning and laying out the road (avoid soft and wet areas as much as possible). Very often there is a scarcity of road building material which has enough bearing capacity. Therefore, when surveying the road line, possible locations of natural gravel pits suitable for ballast material should be assessed. Very often the only suitable gravel material is found in river beds or in the vicinity of rivers. Care should be taken when extracting such material that the effect on fish stocks is minimised. Equally hard rock requires expensive blasting and crushing to be used successfully as road building material.
The volume of logs to be harvested per unit area (m3/ha) is a decisive economic factor for the road layout, design and road-net density.
In general, the roundwood volumes per hectare are higher in coniferous forests that in tropical broad-leaved forests. From the financial aspect, however, one would have to make comparisons from case to case.
If one assumes for instance a roundwood removal of 300 m3/ha and a road-net density of 15 m3/ha, road costs per m3 would only amount to the equivalent cost of 0.05 m of road length of the forest road-net, whereas a removal of only 150 m3 would result in an equivalent cost of 0.10 m.