ho had lived along "flashy"
watercourses long enough to learn their habits tended to build their
more valuable structures back away from the parts of the flood plain
that got wet most often, leaving those parts for cropland and timber, or
sometimes for shacktown, promenades, and parks. Thus long-settled
countries and regions have often developed through trial and error a
degree of what is now called "passive flood protection," which simply
means recognizing that the flood plain is sometimes a rather perilous
place, and treating it accordingly. It was valid in past ages, and it is
still valid today.

The Potomac Basin has been inhabited by civilized men since long before
modern engineering evolved. Possibly early town-builders' wariness of
floods contributed to the fact that the problem of flood damages here,
though quite real, is somewhat less severe than in certain other
sections of the nation. At specific points of concentrated flood plain
development--Petersburg, W. Va., on the South Branch; Cumberland, Md.,
and the areas upstream from it on the North Branch; and metropolitan
Washington at the head of the estuary--figures show significant amounts
of average annual destruction by rampaging stream waters. In headwater
areas or small urban watersheds scattered throughout the Basin, there
are a number of other places where some damage takes place, whether
agricultural or structural. The total average annual damages for the
Basin, as computed in the 1963 Army _Report_, amount to about $8.6
million.

Along small streams, whether urban or rural, the same principles apply
as along large ones, and the proper protective measures are similar if
smaller in scale. Leaving the worst parts of the flood plain in fields
or parks is the usual and effective form of passive protection. Where
existing development demands structural measures, it has been common
practice to cover streams over as sewers or to confine them to
straightened concrete channels that sluice rainwater and mud away as
fast as they will flow--though often this is not fast enough, as is
shown by occasional messy and costly overflows of Four Mile Run between
Arlington and Alexandria. And the loss of pleasant brooks and creeks
through such practices is a heavy price to pay.

More and more often lately in such cases, a combination of some passive
protection with the small headwater dams that "catch the water where it
falls" and soil conservation measures to protect th