watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
Figure 21. Erosion Sensitivity Ranking
Runoff Response Sensitivity
The runoff response sensitivity was identified to show the relative ability of a subwatershed to produce
rapid runoff following a storm event. This sensitivity is also based on inherent characteristics of the
geology, soils, and basin characteristics (topography) of a watershed. Many of the factors included in this
sensitivity are the same as those included in the erosion sensitivity described above, and the extent of this
data was limited to lands within the GMUG boundary. Basin characteristics were calculated for entire
subwatersheds both on and off the Forest. Factors that contribute to the flashiness of a given
subwatershed include:
1. Time of Concentration, a function of basin length (defined as the greatest distance from the
watershed pour point to a point on the watershed divide which roughly follows the main
drainage) and basin relief (the difference in elevation between basin pour point and highest point
on the watershed boundary). Time of Concentration was considered to be a stressor.
2. Stream Density – total miles of perennial and intermittent streams per square miles of
subwatershed. This factor characterizes the degree of dissection and network transport capacity
for both runoff and sediment. The higher the stream density, the larger the amount of runoff that
may be moved through a subwatershed. Stream density was considered to be a stressor.
3. Basin Ruggedness, a function of drainage density, basin relief and basin area.
4. Rainfall Intensity Factor – weighted average for each subwatershed. The rainfall intensity factor
was derived from the RUSLE R factor from PRISM data (obtained from Oregon State
University). When other factors remain constant, soil loss is directly proportional to a rainfall
93 Assessing the Vulnerability of Watersheds to Climate Change