Engineering Field Handbook, Chapter 2
VERSION: 1.1.0.01, March, 2003
OPERATING SYSTEM: Windows
DESCRIPTION: EFH2 Hydrology
Peak discharge is determined by procedures in Engineering Field Handbook Chapter 2. Required information includes watershed characteristics (drainage area, curve number, hydraulic length, watershed slope) and rainfall amount and distribution.
1.) Watershed is accurately represented by a single runoff curve number between 40 and 98.
2.) Watershed area is between 1 and 2,000 acres.
3.) Watershed hydraulic length is between 200 and 26,000 feet.
4.) Average watershed slope is between 0.5 and 64%.
5.) No valley or reservoir routing is required.
6.) Urban land use within the watershed does not exceed 10%.
Software comes with rainfall data for Nebraska counties. Illinois users can download county.il file and place in the EFH2 directory (default install subdirectory is C:\Program Files\USDA\EFH2). Illinois users will then have access to 1-year through 100-year 24-hour duration rainfall for each county (Illinois State Water Survey Bulletin 70 data).