USING HISTORIC CLIMATOLOGICAL DATA TO DETERMINE THE HYDROLOGIC SEASONS IN A SMALL WATERSHED

We are in the process of creating a comprehensive numerical model of the seasonal hydrogeochemical dynamics of the Belgrade Lakes Watershed in Central Maine. Understanding hydrologic seasons is critical to watershed modeling because changes in the seasons define the dynamics of the inputs and outputs to the system. Since seasons are so pronounced in Maine, annual averages of climatological parameters would inadequately represent the hydrological dynamics of the system. We have evaluated historic climatological data and defined six distinct hydrologic seasons for the Belgrade Lakes Watershed.

Daily mean temperature, precipitation, snowfall, and snow depth from a 25-year period (1975-1999) were analyzed. Potential evapotranspiration was calculated using Mather's equation and snow storage and melt was examined. Runoff from the watershed was determined by constructing a unit hydrograph for the Messalonskee Stream, the outflow of the Belgrade Lakes Watershed, using gauged streams in the area. Six hydrologic seasons were determined and include: a cold season where the ground is mostly covered in snow (Dec-Feb); a rapid snowmelt season (March); an ice out season (April); a growing season (May-June); a hot, high potential evapotranspiration season (July-Aug); a rainy season (Sept-Oct); and a short cold season without snow cover (Nov).

The methods by which these seasons were defined and the application of these seasons to the numerical model of the Belgrade Lakes Watershed will be presented.