Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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Maryland’s colonial ports of Joppa Town and Elk Ridge, located on
opposite sides of Baltimore, were abandoned after they could no longer
accommodate ocean-going vessels. Established by an act of the Maryland
legislature in 1707, Joppa Town rapidly grew to become the most important
seaport in the colony. The largest oceangoing merchant ships loaded
at its wharf until clearing of the uplands started a cycle of erosion that
began filling in the bay. By 1768, the county seat was moved to Baltimore
where the harbor was unaffected by sedimentation. In the 1940s the remnants
of the old wharf stood behind a hundred feet of tree-covered land
that extended out past where tall ships once anchored.
The head of Chesapeake Bay shoaled by at least two and a half feet
between 1846 and 1938 with deposition of dirt from the surrounding farmlands.
The bay also filled with sediment at the head of navigation on the
Potomac. A decade after Georgetown was established in 1751, the town
built a public wharf extending sixty feet out into deep water. In 1755 a
British fleet of heavy warships moored in the river above Georgetown but
by 1804 sediment had filled in the main shipping channel.
Arguments over the cause complicated decades of congressional debate
over what to do about silting up of the Potomac. By 1837 the river was less
than three feet deep above Long Bridge; some blamed construction of the
bridge while others blamed the Georgetown causeway. Leading a survey of
bridges across the Potomac in 1857, engineer Alfred Rives recognized the
true cause as rapid erosion from the extensively plowed hillsides of the surrounding
country. Today the Lincoln Memorial sits on ground where ships
sailed in the eighteenth century, and Indian missionary Father Andrew
White’s 1634 description of a crystal-clear Potomac River reads like fiction.
“This is the sweetest and greatest river I have seene, so that the Thames is
but a little finger to it. There are noe marshes or swampes about it, but
solid firme ground. ...The soyle ...is excellent ...commonly a blacke
mould above, and a foot within ground of a readish colour. ...It abounds
with delicate springs which are our best drinke.” 28
Sedimentation rates in the Furnace Bay tributary of Chesapeake Bay, just
east of the mouth of the Susquehanna River increased almost twentyfold
after European settlement. At Otter Point Creek, Maryland, the sedimentation
rate in a tidal freshwater delta in upper Chesapeake Bay increased by
a factor of six after 1730, and then again by another factor of six by the mid-
1800s. The rate of sediment accumulation in a bog at Flat Laurel Gap in the
Blue Ridge Mountains of North Carolina remained relatively steady for
w estward hoe