Initial assessment of time of travel and mixing through Gulf Island Pond and the lower Androscoggin River, Maine

Flow-stratification patterns were observed in Gulf Island Pond during time-of-travel studies in May and August 1980. The stratification patterns in this 70 million cubic-meter impoundment were due to a temperature differences between inflowing water and reservoir water. Separation was observed at temperature differences of 0.5 degrees C in May 1980 and 1.0 degrees C in August 1980. The pathway taken by inflowing water through the reservoir was governed by the temperature-related density forces acting between the two water masses. Data collected during August 1980 to define differences in dye concentrations with depth at two fixed profile points in Gulf Island Pond showed average water velocity to be seven times faster near the bottom than near the surface. A concept of mass flow was used to analyze data collected at sites downstream from Gulf Island Dam where flow varied rapidly with time. This report presents the mathematical derivation of controid traveltime, skewness, and percentage recovery of dye mass as determined from mass versus time curves. (USGS)