way. There can be no doubt that if the flowing
waters of the Basin are to be put back in good condition and kept that
way under population pressures that are in prospect, flow augmentation
in some places is going to be an important tool.

In the upper estuary, however, its usefulness appears to be far more
limited. The plan proposed in the _Army Report_ of 1963, in line with a
Public Health Service approach emphasized in the 1961 Water Pollution
Control Act, was designed to provide an eventual minimum flow into the
upper estuary of 3100 cubic feet per second, or around two billion
gallons per day, for the purpose of dealing with treatment-plant
effluents and miscellaneous pollution. But more recent investigations
have raised strong doubt as to whether such augmentation could do the
job in the estuary with its huge volume of water, and its slow,
tide-baffled currents that greatly lessen its assimilative capacity.

In terms of dissolved oxygen, dilution of such a body of water for
quality improvement appears to decrease in unit effectiveness as the
volume of dilution is stepped up, which means that past a certain
minimal point of improvement it gets expensive and requires
unreasonable amounts of storage. In terms of nutrients, one authority
has calculated that about 20,000 cubic feet per second would be required
to reduce the nutrient level in the upper estuary to a point where it
would be only twice that of a normal and healthily "rich" section of the
upper Chesapeake Bay. Some augmentation below the point of diminishing
returns will undoubtedly be needed, not only for the estuary but to keep
the river alive in its gorge above Washington during periods of low
flow. But as a main tool for the metropolitan river, it will not
substitute for achievement of the best possible standard treatment
followed by advanced treatment and other techniques.

Obviously, just as in water supply, an ultimate cure for water quality
ills is going to consist of a "mix" of solutions, different techniques
being applied to the situations they are best suited to deal with, and
combinations of them being worked out where combinations are what is
indicated. Already the same kind of sophisticated mathematical models of
given bodies of water--including the Potomac--that are being used to
study solutions for water supply problems are being put to use on water
quality as well, weighing the benefits and drawbacks of various
combinations of means. And,