The key discoveries came early for Don Pritchard. In 1950 and 1951, the young oceanographer and his new staff motored down to the southern Bay in their research vessel, a converted yacht called the Joanbar, and mounted a series of now-famous research expeditions along the James River in Virginia. They brought with them a collection of new tools, some adapted from deep-water oceanography, some created de novo back in their workshop.

At station after station, they took current, temperature and salinity measurements at multiple depths. The surface water, they found, was river water moving seaward. And down below the fresh water they found seawater sliding in the opposite direction. Colder, saltier, denser, the seawater was flowing up river.

After the measurements came the mathematics. From all his data points, so painstakingly acquired, Pritchard worked out the basic equations of motion that described the circulation of the James River, then scaled his equations to explain the estuarine circulation for the entire Chesapeake Bay. He quickly published a seminal monograph on "Estuarine Hydrography" that revolutionized thinking about the Chesapeake and estuaries around the world.

It was a fundamental paradigm, a turning point for Bay science, according to M. Gordon "Reds" Wolman of Johns Hopkins University. "In terms of understanding how the Bay works," he said, "Don Pritchard's physical model was absolutely essential." It changed thinking about the Bay more than any other single piece of research, according to Gene Cronin, the man who followed Reginald Truitt as a long-time director of the Chesapeake Biological Laboratory.

What Pritchard had described accurately for the first time was the basic two-layer flow that dominates water movement throughout the tidal Chesapeake and its tributaries. It's a steady-state model, the idealized underlying pattern for a system that never stays stable long. Complicating the interplay between fresh water and salty water are forces like winds, tides, river discharges, the topography of the Bay and the rotation of the earth.

Figuring out the physics of all these forces would keep Pritchard busy for decades and leave plenty of work for the oceanographers who followed him. Out of that early model they would derive an assemblage of estuarine features ranging from turbidity maxima to plume fronts, upwelling fronts, lee waves, eddies, vertical mixing, stratification and anoxic zones.

Betting on Pritchard had paid off, not just for the state labs that put up the money, but for all those fishery biologists studying the Bay. They could start to work now on figuring out how that two-layer flow was responsible for moving around and mixing nutrients and plankton and early-stage larvae for blue crabs and oysters and finfish.

As first in the field, the young oceanographer had nailed the essential physical feature of nearly all estuaries. And set the paradigm that would keep oceanographers busy in the Chesapeake for the rest of the century.

The pipe smoking Don Pritchard got his introduction to oceanography working out sea swell forecasts for the Normandy Invasion of World War II. The first oceanographer to study the physics of the Chesapeake Bay, he discoverd the two-layer flow pattern that underles water circulation throughout the Bay. Photographs by Don Prichard.

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