ed at large
reservoirs. But the scale is smaller; they tend to be less imposing and
pre-emptive of good land than big river dams, "catch the water where it
falls" to hold it for local use and to alleviate local flooding, and are
backed up by erosion control practices in a program that has proved to
be one of the best available stimulants to good land use. For these
reasons they have appeal for many rural people and conservationists.

* * * * *

However, the conclusion which some of their supporters have reached is
that if only enough of the small dams could be built throughout the
headwater areas of a river basin, they would eliminate the need for most
other forms of water management, leveling out flood and drought flows
and holding a great aggregate amount of water on tap for use anywhere
down the line. At times in the past, the controversy between supporters
of big dams and supporters of little dams achieved the proportions of a
bloodless war, but after a good many years of testing and observation
it is now generally agreed by hydrologists that both have their place
and that the most appropriate focus for the small dams' functioning is
local.

At any rate, they are not an answer for Washington's problems. Even if
enough of them were installed specifically to provide the storage volume
needed for metropolitan use, the question of operation--ensuring and
coordinating releases from a large number of places at varying long
distance upstream from the point of intended use, in such a way as to
make the required volumes of water arrive at the right time, without
waste--would be very difficult even with much more sophisticated and
expensive design than these structures customarily have. Without it the
problem would be insuperable.

* * * * *

Thus, for metropolitan Washington's water in the near reaches of the
future, some reservoir storage is indicated with fewer ecological,
recreational, and scenic drawbacks than a Potomac main stem dam, and
more efficiency for massive supply than the small headwater structures.
Since the Potomac river system is a unit, with the metropolis at the
downstream end of its non-tidal part, water stored anywhere in the upper
Basin can be released for use there. This gives much freedom of choice
in the selection of sites for reservoirs and in the combination of
releases from various places to make up an adequate total supply, though