The Chief of the Forest Service declared a
moratorium on National Forest road construction until the impacts of existing
roads is made acceptable. The Forest Service’s National Resource Agenda
advocates the removal of several hundred miles of poorly constructed or
maintained roads in the next 3-5 years (250+ miles on the Lolo National Forest
alone). Yet, data on the effects of
road removal is often viewed as inadequate.
Current techniques for evaluating the effectiveness of road removal/recontouring
are based on empirical studies and basic soil erosion properties extrapolated to
forested environments.
The O’Brien Creek Watershed
restoration project offers an opportunity to monitor the effects of road
recontouring on sediment production and may be used to establish evaluation
criteria for similar locations. This
study compared sediment yield from existing Forest Service roads, newly
recontoured roads, one-year revegetated-recontoured roads and
natural/undisturbed sites. Two
geologic formations with associated soil types were selected for sampling--Mount
Shield’s formation, and Bonner formation.
Two slope categories were sampled for each soil type: <45% slope and
>45% slope. For all treatments, sediment runoff samples were collected using
a rainfall simulator to generate rain, with five samplings over 2 days per site.
Sample analysis determined percent infiltration, water and sediment
yield, silt and clay content, and
largest particle size removed. Hydrometer
and sieve analyses determined particle size distribution.
Soil bulk density and organic matter content
were determined at each site. Statistical analyses are in progress.
Some trends have been noted based on preliminary data.