A COMPUTER MODEL IS A MASTER MIMIC: it takes what nature does in all its complexity and tries to reproduce a believable version of it using mathematical equations. By the early 1980s, estuarine scientists and programmers were already developing the first computer models of the Chesapeake Bay. These models have become invaluable tools to inform key decisions in the ongoing federal-state partnership to clean up the largest estuary in the nation.

But as Chesapeake scientists and policy makers were saying hello to the new computer tools, they were waving a fond farewell to a very different kind of model: a physical mini-replica of the estuary called the Chesapeake Bay Hydraulic Model.

This Lilliputian estuary was not built with transistors and wires; instead it was a three-dimensional scale model made of concrete. The model covered nine acres within a 14-acre, metal-sheathed building in Matapeake, Maryland, just south of the Bay Bridge on the Eastern Shore. This scientifically designed tool, the largest indoor model of its kind ever built, was bigger than a city block — 1,050 feet long and 650 feet wide. Its depth ranged from mere inches in the shallows to about two feet in the deepest part of the Chesapeake's mainstem. When full, the model contained 450,000 gallons of water — enough to fill most of an Olympic swimming pool.

The press dubbed it the "Matapeake monster." To scientists, it was a test bed for asking "what if" questions about the Chesapeake Bay.

In 1965, Congress authorized the Chesapeake Bay Hydraulic Model in part to support a comprehensive study of the estuary. The research topics would include water use, navigation, flood control, water pollution, and beach erosion. Despite the efforts of project boosters, budget cuts and redesigns delayed construction, which was not completed until 1976 at a cost of $15 million.

This model Bay was controlled by dozens of scientists and technicians working for the U.S. Army Corps of Engineers. By pumping artificially salted water into the model's mouth and flowing fresh water into its rivers, the operators could simulate the estuary's tidal cycle.

Research using the newly completed Matapeake monster kicked off in 1978 with a study to determine if deepening Baltimore Harbor would affect Bay salinity levels enough to harm the estuary's living resources. The research showed that dredging posed no threat, so the project went ahead.

But the Matapeake monster was heading for a showdown with the computer age. With every computing advance, the physical model became incrementally more obsolete. Legislators also balked at the high cost of running the model facility: $4,000 per day in 1980 dollars. Support ebbed for the facility, and it was finally shuttered in 1984.

For all its physical grandeur, the Chesapeake Bay Hydraulic Model may seem crude compared with the computer models that guide the ongoing cleanup of the Bay. Unlike these digital simulations, the physical model was limited in its ability to mimic the biology of the living Bay.

"Going back and comparing the current technology of computer models to the huge, cumbersome physical models helps us appreciate how powerful computer models are today," says Christine Keiner, a historian of science at the Rochester Institute of Technology who has written a comprehensive history of the Matapeake model project. Looking at this history, she says, shows "how fast the technology of computing has evolved over the past 40 years."