Timber harvesting and flooding

Excerpt

RELATIONSHIPS between timber harvesting and changes in stream channel stability have received a great deal of attention in the past decade. According to one philosophy, removal of vegetation reduces interception and evapotranspiration, resulting in higher flows. Higher flows exert more energy on the stream channel system, which accelerates channel degradation. A number of models have been developed to predict the percentage of a watershed that can be harvested without altering channel stability.

A second philosophy suggests that accelerated channel degradation depends upon major wet-mantle floods, which result from storms that occur after the soil mantle becomes saturated. Because soils are saturated regardless of the presence or absence of vegetation, these floods are unaffected by timber removal. According to this philosophy, channel systems have evolved to withstand normal fluctuations in energy levels. Although timber removal may increase annual and seasonal flows, even increased flows during a normal year are not sufficient to break down a channel's armour layer and initiate movement of the channel substrate.

Both philosophies have merit, but which is dominant depends upon a region's climate, soil type, and topography. Each philosophy was considered during an evaluation of flooding in the Cabin Creek watershed, which …