LAUSR

The Norwalk Harbor is the estuarine portion of the Norwalk River, which connects to Long Island Sound. Like many embayments, this macrotidal harbor experiences higher summer water temperatures than waters farther offshore, which contribute to water quality problems. The summer season is characterized by surface heating, strong tides (as in all seasons), weak winds, and low river discharge. To determine the relative importance of exchange with offshore waters in regulating the harbor temperature, a control volume approach is used to make a summer temperature budget for the harbor based on observations. Time series of harbor temperature, surface heat flux, and Norwalk River inflow are constrained with measurements of water temperatures, atmospheric conditions, and river discharge. The impact of offshore exchange is inferred as the residual after the real temperature change in the harbor, and all other sources of temperature change are constrained. The analysis indicates that, in the summer, the impact of offshore exchange is comparable to the impact of the surface heat flux and far greater than the impact of the river. Consequently, the harbor is much cooler during summer than it would be if it was not connected to Long Island Sound. The methods applied here are applicable to any relatively small, semi-enclosed body of water and do not require the use of models or velocity observations. It is likely that many other embayments have an appreciable degree of thermal buffering via exchange with offshore waters.