BACKGROUND: The Ashland Resource Area stream survey crew has surveyed over 2000 perennial, intermittent, and dry stream reaches within the Applegate. Some of the information collected during the surveys included aspect, channel type, bedload, substrate, streambank stability, slump potential, large woody debris, and riparian vegetation. This data is used to create maps of areas of concern such as slumping, wetlands, and erosion, as well as to establish trends within the watershed.
For example, the data were analyzed to see if there was a correlation between riparian width and north facing versus south facing slopes. Observations in the field indicated that there were differences in the width of the riparian corridor between north and south facing slopes on intermittent streams within the Applegate. But were these observed differences statistically significant? Were they consistent? Did the shape of the corridor (V shaped versus U shaped) have an effect? If a significant, consistent trend could be demonstrated between north and south facing slopes, it could be helpful in determining appropriate reserve prescriptions.
FINDINGS: The stream survey data for all north and south facing intermittent streams within the middle Applegate were divided into V shaped versus U shaped reaches. Using a t-test, the hypothesis that there was a significant difference between north and south facing streams was tested for both U shaped and V shaped corridors. The results showed a significant difference in riparian width between north and south facing slopes, but only in streams with a V shape.
U shape |
V shape | |||
Aspect |
North |
South |
North |
South |
Number of streams surveyed |
3 |
5 |
5 |
18 |
Average riparian width |
14 ft |
14 ft |
24 ft |
7 ft |
t-test for significance |
p= 0.99 |
|||
APPLICATIONS: Using the stream survey data confirmed the suspicion that at least for V shaped channels, north facing streams have wider riparian corridors. This was valuable knowledge during the decision making process for riparian reserve prescriptions for the Appleseed timber sale. Every watershed has different landscape characterizations that effect the decisions made about land use. Stream survey data can be a valuable tool in determining trends within streams and riparian corridors to assist in land management decisions.
SUBMITTED BY: Karen Bolda, Ashland RA, BLM. 770-2351, kbolda@or.blm.gov