Salinity Intrusion and Residual Circulation in Delaware Bay During the Drought of 1984

A three-dimensional, time-dependent numerical model is used to simulate the dynamics and thermodynamics of Delaware Bay and River and the adjacent continental shelf. The model forcing includes observed winds, observed surface heat flux, observed free surface elevation at the mouth of the Bay, observed fresh water run-off from 16 rivers and tributaries, climatological temperatures and salinities at the shelf open boundaries, and predicted tides at the shelf break. The model was started at 00:00 am January 1, 1984 and ran through the entire year.

Since the fall of 1984 was dry, the model predictions for the late autumn months are an indication of model performance in simulating droughts. The present study compares daily salinity intrusions on April 1, June 1, August 1 and October 1 of 1984 and shows substantial salinity penetration into the Bay during this period, (about 30–40 km). The strongest stratification is found in April (as much as 5–8 ppt), and the weakest is in October; this is consistent with observations.

Salinity distributions in the Bay and on the shelf are affected by such factors as the freshwater run-off, open boundary conditions and the dominant winds. During April through July, the salinity approached zero values southward of Artificial Island, while in October, the salinity penetrated all the way up to Chester, Pennsylvania which is generally consistent with observations. The study also concentrates on some aspects of the monthly mean circulation.