Terraqua Methods Used
to Analyze Road Density and Road-Stream Crossings
Roads
in the Battle Creek Watershed
From: Terraqua,
Inc. 2004. Battle Creek Watershed Assessment :Characterization of stream
conditions and an investigation of sediment source factors in 2001 and 2002.
Performed under contract to the Battle Creek Watershed Conservancy, Manton,
CA. Funds from the Anadromous Fisheries Restoration Program and U.S. Fish
and Wildlife Service under Agreement DCN: 11330-1-J113.
From Page 17 in the Battle
Creek WA:
Road Density -
Road information used for sediment source analysis on lands owned by Sierra
Pacific Industries (SPI), the U.S. Forest Service (USFS), and the National
Park Service were derived using data provided by each of these landowners.
Road information obtained from USGS was used on lands owned by other parties.
Data from these four sources were merged to form one road data layer. Mapping
data for roads in Battle Creek are incomplete and inconsistent across ownership
which may be a source of error in estimating road-related sediment source
factors. For example, USGS roads represent data mapped when the last topographic
map series was generated and are outdated. Many roads on National Forest lands
are not included in National Forest maps while other roads, since abandoned,
remain on their map. SPI road maps are much more accurate. None-the-less,
even the most detailed road data provided by SPI seems to consider only main
hauls roads and does not include spur and temporary roads, skid trails and
landings which might also be sources of sediment. Road densities were derived
by dividing the linear miles of road by the area of the watershed in square
miles and are expressed in units of miles per square mile (mi./sq. mi.).
Near-Stream Road Density
- Road data used in this analysis are described above in "Road Density."
Road densities were also calculated for "near-stream" subsets of
each site specific watershed which were created to approximate riparian areas.
The "near-stream" area was defined as all area within 100 meters
of the stream on both sides of the channel. The length of only those segments
of roads within this 200 meter-wide zone were divided by the "near-stream"
portion of the site-specific watershed to derive near-stream road densities.
Near-stream road densities are expressed in units of miles of near-stream
roads per square mile of near-stream watershed area.
Road-Stream Crossing
Frequency - Road data used in this analysis are described above in "Road
Density." The number of intersections of roads and streams were summed
and divided by the number of stream miles. The frequency of road-stream crossings
was expressed in units of the number of crossings per stream mile.
