HISTORY. GEOLOGY. AND DEMOGRAPHICS 
by 
Dr. Robert B. Biggs, University of Delaware 
and 
Dr. Grace S. Brush, Johns Hopkins University 
Dr. Biggs: I would like to start with a simple declara¬ 
tive sentence to try to get your attention, that is, "The 
Chesapeake Bay is very small." 
The Chesapeake and its tributaries represent only 7 per¬ 
cent of the 64,000 square mile watershed that's illustrated in 
Figure 1. The principal watersheds are the Susquehanna Basin 
and the Potomac Basin. Smaller basins include the Rappahannock, 
York, and the James River Basins. 
The Chesapeake is small. Its average depth is only 8 
meters. The volume of water contained in the Chesapeake and its 
tributaries is fifteen cubic miles. That volume is so small 
that most of the physical processes that occur in the Chesapeake 
Bay, although not necessarily the most important ones, are a 
function of what happens on the continental shelf off the Mouth 
of the Bay. Except for a small area at river mouths where they 
discharge into the open waters of the Bay, the Chesapeake's ele¬ 
vations and major current structures are controlled by what 
happens on the continental shelf. 
From a regional geologic perspective the Chesapeake Bay lies 
in the Atlantic Coastal Plain and is bordered in the inland by a 
fall line where the Coastal Plain laps up against the peidmont. 
The Chesapeake is small. It's so small that if you look at 
a cross-section of the Chesapeake representing only the uncon¬ 
solidated sediments, you can't see the Chesapeake Bay in the 
cross-section. Its maximum depth of 175 feet doesn't even show 
in the thickness of a line. 
The Chesapeake is large. It has 18 trillion gallons of 
water in it. If you were to build a process plant to try to 
extract something from the water of the Chesapeake Bay and you 
shut off all the river systems so that all you had to do was 
pump out that 18 trillion gallons, you could pump a million 
gallons a day and it would take 15 years to empty the Chesa¬ 
peake. It's a very large body of water. 
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