Project Summary:

Safe, efficient, and environmentally sensitive design of roads, bridges, culverts, dams and other infrastructure in the riverine environment requires estimates of the magnitude of floods at 5-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals. Often, flood frequency estimates are determined from historical peak-streamflow data collected at USGS streamgages. However, it is impractical to gage all streams in New Hampshire and often the streamflow data required for flood-frequency analyses is not available. In such instances, techniques are commonly applied to estimate flood frequency and magnitude based on data collected on gaged streams in a similar hydrologic region—a technique referred to as regionalization.

Regionalization involves finding statistical relations between flood frequency data determined at multiple gages in a region and the physical and climatic characteristics of the watershed upstream of the gages using regression techniques. The result is a set of regression equations for estimating flood frequency and magnitude that may use several explanatory variables, including, but not limited to drainage area, basin slope, channel slope, elevation, areal percentage of waterbodies or wetlands, or rainfall characteristics.

The USGS, in cooperation with the New Hampshire Department of Transportation, is developing equations for estimating flow frequency. The equations will be incorporated into StreamStats. StreamStats is a web-based tool that will allow users choose locations on an interactive map, obtain the basin and climatic characteristics that are required by the regression equations, and solve the equations.

This study will be conducted in 2007 and 2008 with the final report and StreamStats application to be completed in 2009.