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PREDICTING SEDIMENT FROM FOREST ROADS
SYSTEMS IN THE SOUTH
Dr. George Ice, NCASI
On May 21 and 22, 2003, in Nacogdoches, TX, NCASI
sponsored a workshop on predicting sediment from forest
road systems in the South. Other sponsors were Arthur Temple
College of Forestry, Stephen F. Austin State University (SFASU);
Temple Inland Corporation; Weyerhaeuser Company; and Water
Resources Working Group of the Society of American Foresters.
Forest roads represent an important investment to forest managers,
facilitating various management activities. There also are
concerns that roads represent a significant environmental
risk to watersheds. The purpose for this workshop was to bring
road researchers and road practitioners together to discuss
sediment and roads. The workshop focus was on southern forest
conditions and the unique challenges for forest managers in
this region. The workshop capitalized on the ongoing research
at watersheds near Alto, Texas.
A total of 80 participants from 15 different states converged
on Nacogdoches for the workshop. Dr. R. Scott Beasley of SFASU
and Dr. George Ice of NCASI welcomed the participants and
outlined the purpose for this workshop. Dr. Charlie Luce,
USDA Forest Service, provided an overview of road erosion
mechanics, noting that although conditions vary between regions,
the physics of road erosion remain the same. Regional differences
in road erosion should be reconciled by understanding the
underlying processes of road erosion and sediment delivery.
Dr. Walt Megahan, formerly with NCASI, and Kathy Dubé, with
Watershed GeoDynamics, then presented a history and introduction
to the road sediment model SEDMODL2. This model is based on
the USDA Forest Service R1-R4 sediment model and the road
sediment portion of the state of Washington's Watershed Analysis.
Boise Cascade Corporation developed it into a GIS-based model,
and with further development, it is now available from NCASI
(http://www.ncasi.org/forestry/research/watershed.stm). With
support from SFASU and Temple Inland, this model was applied
by Dubé to a road network covering the research watersheds
near Alto, Texas. One highlight of the meeting was an animated
slide developed by P. R. Blackwell of SFASU showing a virtual
fly-over of the Alto Watersheds with estimated erosion from
different road segments depicted. The slide was developed
using GIS and SEDMODL2 outputs. This type of application allows
managers to identify the road segments contributing the most
to sediment runoff. It can also provide some estimates of
the relative importance of roads to the overall sediment budget.
Dr. Mark Riedel, USDA Forest Service, gave a fascinating
presentation on data resolution and model accuracy in simulating
sediment losses from forest roads. He noted the paucity of
sediment data to support model development and that digital
elevation model (DEM) resolution limits may impede progress
in predicting delivery of sediment to streams from roads.
Dr. Ge Sun, North Carolina State University, discussed the
application of the Universal Soil Loss Equation and GIS technology
to modeling erosion for forest roads in the South using the
GATES (GIS Assessment for Transport of Eroded Sediment) model.
Model estimates of sediment generation were comparable to
outputs measured for a stream in Nantahala National Forest,
North Carolina. Dr. Don Turton, Oklahoma State University,
provided a history lesson about past research on forest road
erosion in the Ouachita Mountains and updated the participants
about an ongoing research project. Dr. Dan Marion, USDA Forest
Service, described work by his group to assess the effectiveness
of forest road BMPs in southern highland forest conditions.
This project involves mapping of entire road networks in five
watersheds, locating road features such as road type, culverts
(including size and presence of scouring below culverts),
and stream crossings. Mark Riedel returned to describe modeling
to predict possible cumulative effects from forest roads on
stream sedimentation using GEOWEPP. This is a spatially explicit,
process-based application of the WEPP (Water Erosion Prediction
Project) model.
The workshop session concluded with three papers describing
BMP effectiveness, albeit, for very different circumstances.
Dr. Devendra Amatya, USDA Forest Service, presented research
from colleagues at North Carolina University on erosion control
options for roads located on the very flat Coastal Plain of
North Carolina. The results of the road-scale portion of the
study showed that a graveled road surface can reduce the total
loss of sediment from roads to an average of 39% that of a
nongraveled, noncontinuous bermed standard graded soil road
surface; a grassed strip on the edge of the driving surface
can reduce total sediment loss to an average of 44% that of
a nongrassed, noncontinuous bermed standard graded soil road
surface; and a continuous berm maintained along the edge of
road surface can reduce total sediment loss to an average
of 1% that of a non-graveled, non-continuous bermed standard
graded soil road surface. Johnny McFero Grace III, USDA Forest
Service, described ongoing research in Tuskegee National Forest,
Alabama, to test the effectiveness of four treatments for
reducing sediment delivery from roads. These treatments include
vegetation trapping, rip-rap, sediment fences, and settling
or detention ponds. Dr. Steven Taylor, Auburn University,
discussed research on erosion from installation and operation
of stream crossings. With proper stream crossing structures
and installation, much more sediment can be generated from
road approaches than by the stream crossing itself.
In the evening Dr. Ice provided a review of efforts to define
road sediment control options in the South and some personal
"challenges" he has faced in road research. Dr. Ice then led
the group in a discussion about information and research needs.
A list of information needs and questions generated at the
road workshop is available at http://fri.sfasu.edu/pages/projects/alto/html/proposal.html.
The following day the group was hosted to a tour of the Alto
Watersheds. Dr. Scott Beasley described the small watershed
studies near Alto and Matt McBroom, a PhD student at SFASU,
described road sediment research. Kathy Dubé gave a presentation
on field observations for application to road sediment prediction
models. Dr. Walt Megahan described problems that create additional
road sediment and opportunities to trap road sediment before
it reaches a stream. The workshop was characterized by strong
interactions between participants and speakers. Forest road
managers challenged the researchers to make their information
useable and to realistically address road sediment questions.
PowerPoint presentations by all the speakers are available
online at http://fri.sfasu.edu/pages/projects/alto/html/forest_roads_03l.html
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