Case Study: Connecticut River PMP/PMF

Upper Connecticut River Site-Specific PMP/PMF Study

TransCanada Hydro Northeast (Connecticut River watershed in NH/VT)


Gomez and Sullivan developed site-specific PMP values and PMF for three sites on the portion of the Connecticut River, with a total project drainage area of approximately 3,400 square miles. PMP tasks included evaluation of historic storms, storm maximization and transposition, adjustments for topographic barriers and within basin orographic effects, and development of site-specific PMP envelope curves. GIS was used to evaluate the impact of topographic barriers in diminishing the moisture carried by the studied historic extreme storms transposed to the basin, as well as to determine factors such as the maximum dewpoint at the storm source, which affects the development of the storm. PMF tasks included development of a HEC-HMS hydrologic model, calibration to large storm events, evaluation of loss rate parameters, unit hydrograph and routing parameters, initial reservoir conditions, gate operating conditions and evaluation/development of updated discharge rating curves. GIS was utilized to delineate sub-basins and make initial estimates of basin unit hydrograph parameters. Both warm season and rain-on-snow PMF type events were evaluated, the latter of which was found to be the controlling event for these projects. Calibration of historic rain-on-snow events included evaluation of temperature, wind, rainfall, solar radiation, and basin cover parameters.