Boise River Cross Sections
Conducted in cooperation with Federal Emergency Management Agency
Methods
Between October 1997 and December 1998, U.S. Geological Survey scientists collected stream channel cross-section data and documented elevation reference marks established for horizontal and vertical control. The total river length studied was approximately 32.5 miles, which included 26 miles of the Boise River main channel and an additional 6.5 mile reach around the south side of Eagle Island (South Channel of Eagle Island). During the study, the following tasks were completed:
- Conducted field reconnaissance and surveys of the channel and adjacent floodplain.
- Identified existing elevation reference marks (ERMs) and, where necessary, established new ones.
- Determined Manning's roughness coefficients (n) for each cross section.
- Developed a 2-foot contour map of the river channel and flood-plain area.
- Determined water-surface elevations for the 10-, 50-, 100-, and 500-year floods using the surface-water computer model using the Hydrologic Engineering Centers River Analysis System (HEC-RAS) model. No analysis was done to determine the flood discharge values; the U.S. Army Corps of Engineers (1978) values were used.
- Delineated the calculated floodplain and floodway extents on the 2-foot contour map developed in task 4.
- Prepared and submitted final maps and reports to FEMA.
