Sedimentation is identified as one of the major concerns affecting salmon survival. Sedimentation occurs naturally but the problem is further escalated due to various forestry activities, among which the presence of forestry roads is a major contributor. Forestry road areas leads to surface erosion of fine sediments. It is mainly seen that the mass movements of soil and other debris gets into streams and destroys spawning habitat. Once the sediments gets into streams, fine sediments fills the spaces between spawning gravels and limits the oxygen availability to the eggs, cause infilling of pools and as a consequence reduces the availability of cover habitats. (Moring et al, 1975).
The rapid accumulation of sediments has detrimental effects on salmon’s life cycle. The fact that the survival of eggs is dependent on a well-supplied oxygenated water through the streambed gravels, the seepage of fine sediments into spawning beds leads to suffocation of eggs. (Wickett et al, 1984). Once the eggs are hatched, the alevins needs to make its way through the gravels to the open streams and if the intra gravel passages are blocked with fine sediments, the emerging fish are trapped (Phillips, 1965). The increased level of fine sediment accumulation affects both the macroinvertebrates and primary producers. The increased levels of sediments causes clogging of gravel interstices and may decrease the flow of oxygenated water within the gravel bed. (Ziebell, 1960)..The alteration of sediment loads leads to changes in the channel morphology, affects the distribution and frequency of pool habitat and the stability of bed material. (Sullivan, 1972).
It is seen that logging roads adds to sediments in streams by the processes of erosion, unpaved surfaces, cut banks, side cast, associated gullies, landslides and debris torrents. A study was conducted to determine the relative importance of these sources, it was found that typical in a 40% clear-cut tributary basin with a road density of 2.5 km/km2, road surface erosion contributed to 49 t/km2, while cut bank was responsible for only 2 t/km2 per year (Reid et al, 1984). Thus, to control the sedimentation related impacts we must determine the sources of logging related sediment, and identify the factors controlling the rate of sediment production.