Each of the first five methods listed above are appropriate to use for different design conditions and none of the methods will cover all situations. The first step in performing a hydrologic analysis is to determine which method is most appropriate. Generally there is no need to select more than one method.
1. Rational Method:
This method is used when peak discharges for small basins must be determined. It is a fairly simple and accurate method especially when the basin is primarily impervious. The rational method is appropriate for culvert design, pavement drainage design, storm drain design, and some stormwater facility designs.
2. SBUH Method:
This method is used when peak discharges and runoff volumes for small basins must be determined. This method is not complicated but requires a computer due to its computationally intensive nature. The SBUH method is required for many stormwater facility designs and can also be used for culvert design, pavement drainage design, and storm drain design.
3. Published Flow Records:
This method is used when peak discharges for large basins must be determined. This is more of a collection of data rather than a predictive analysis like the other methods listed. Some agencies (primarily the USGS) gather streamflow data on a regular basis. This collected data can be used to predict flood flows for the river and is typically more accurate than calculated flows. Published flow records are most appropriate for culvert and bridge design.
4. USGS Regression Equations:
This method is used when peak discharges for medium to large basins must be determined. It is a set of regression equations that were developed using data from streamflow gaging stations. The regression equations are very simple to use but lack the accuracy of published flow records. USGS regression equations are appropriate for culvert and bridge design.
5. Flood Reports:
This method is used when peak discharges for medium to large basins must be determined. It is basically using results from an analysis that has been conducted by another agency. Often these values are very accurate since they were developed from an in-depth analysis. Flood report data are appropriate for culvert and bridge design.
