d damage. Existing
damages in the whole urban area are estimated to average $1.4 million
each year. The most damaging flood in the metropolis' history occurred
in March of 1936, and if a flood of the same dimensions were to strike
today, it would cause estimated damages of about $21 million.

These are not small figures, though if they are considered in the light
of the area's population and extent and the total value of construction
there, they seem less formidable. Obviously the threat of damages of
this magnitude must be dealt with, but just as obviously as at
Petersburg, the manner chosen for dealing with them should not be
allowed to stimulate unwise flood plain construction that would lead to
still greater longterm damages.

The Seneca reservoir as proposed in 1963 provided floodwater storage
calculated to reduce metropolitan damages by 46 percent. This is a
significant though not startling amount of reduction, and it constitutes
the most economical one-shot measure of protection that could be
attained. However, if the construction of Seneca is precluded for the
time being or for good, that measure is not available. Second-best, by
Army calculations, would be a combination of several large multipurpose
reservoirs on main tributaries farther upstream. But quite aside from
other considerations of desirability, these could only be justified
economically if a great part of their stored water were destined to
furnish massive flow augmentation to ease pollution in the upper
estuary. As will be noted in the following chapter, recent studies have
raised doubt that such augmentation would be likely to help the estuary
nearly as much as had been thought and it is no longer being considered
a primary tool for that purpose.

This leaves passive devices and local protection works as the main
available instruments for coping with floods at the metropolis. They
will probably be most effective if applied in a carefully selected
combination of means, with levees and other protective works installed
where feasible and desirable, and backed up in other areas by zoning,
flood warning systems, and good design including flood-proofing,
elevated structures, and similar devices. Some of these principles of
design are already being incorporated in new buildings and renewal
projects, but the task of planning and locating such things as levees
usefully on a flood plain containing a good part of "monumental
Washington," the beauty of whic