Hydrology© is an engineering tool which provides computations for the different hydrologic methods including –Rational method, TR-55 method, Snyder method, Anderson method, USGS regression analysis and Log Pearson III methods for gaged and ungagged sites.
The current release of the software (HydrologyVA©) is based on Chapter 6 of Virginia Department of Transport (VDOT) Drainage Manual. There are seven procedures used in the Virginia Edition for determining peak discharges for drainage basins:
1. Rational method for estimating peak discharges for areas up to 200 acres;
2. The NRCS TR-55 method for areas up to 2000 acres or 3.1 square miles;
3. The Anderson Method developed by the U.S.G.S. for Northern Virginia applicable for drainage areas up to 570 square miles;
4. Snyder Method applicable for areas from 200 acres to 20 square miles;
5. USGS Rural Regression Method for areas greater than one square mile as outlined in the Tables 6.4 and 6.5 of the Drainage Manual;
6. USGS Urban Regression Method for urban watershed conditions using three-parameter or seven-parameter equation sets, and,
7. Frequency analysis using Log Pearson III method for drainage areas greater than one sq. mile, provided there is at least 10 years of continuous or synthesized flow records for 10- year discharge estimates and 25 years for 100-year discharge estimates.