Abstract
Estimating Stream Gradient Using NHD Stream Lines and DEM Data
Track: Water Resources
Author
Gradient has a dominant influence on channel morphology and strongly affects biophysical processes in streams. Many approaches have been used to quantify stream gradient from maps and DEMs, but no approach is universally accepted. Here, we investigate the best method for computing stream gradient using NHD stream lines and DEM data. The results will be used as part of a larger effort to map streambed grain size for assessing basin-scale availability of salmon spawning habitat.
We examined numerous approaches and data treatments, such as cell-by-cell raster processing, DEM drainage enforcement, and equal interval spacing. Results showed that gradient was best predicted from a variable interval spacing that approximated the underlying contour spacing of 1:24,000 scale maps, using four slope classes associated with different reach-scale channel types. Furthermore, in low-gradient mainstem reaches, computing slope over longer intervals was most accurate, whereas shorter intervals were more accurate for gradients in steeper reaches.
David Nagel
U.S. Forest Service Research
322 E. Front St.
Suite 401
Boise, Idaho 83706
United States
Phone: 208-426-0795
E-mail: dnagel@fs.fed.us
John Buffington
U.S Forest Service
322 E. Front St., Suite 401
Boise, Idaho 83702
United States
Phone: 208-373-4340
E-mail: jbuffington@fs.fed.us
Daniel Isaak
U.S. Forest Service
322 E. Front St., Suite 401
Boise, Idaho 83702
United States
Phone: 208-373-4340
E-mail: disaak@fs.fed.us