The sad situation of the smaller and much less industrialized Monocacy in the same summer underscores the point. The Monocacy flows through similar farming country and passes by a few towns. The largest of these is Frederick, Maryland, for whose approximately 40,000 people the little river furnishes water and a conduit to carry away the effluent from their average-to-good secondary plant. At times during that dry summer practically the entire flow of the river below Frederick consisted of effluent, with effects on stream life, esthetics, and the general surroundings that are not hard to imagine.
Another good example of a place where, under present conditions, augmentation could sometimes be used beneficially is at Great Falls and in the Potomac gorge below. Heavy public expenditure has protected the shore in much of this neighborhood and provided pleasant recreation areas whose main scenic focus is the violent magnificence of the river in its plunge. But the magnificence becomes a rather drab joke in dry summers when metropolitan withdrawals of water above that point shrink the river to a semblance of normal flow.
Low Flow Augmentation
The North Branch and some smaller Basin streams also need this same kind of help and most will continue to need it even when the best economically feasible treatment of all collectable wastes entering them is ensured. It can be provided out of reservoirs, large or small, whose need for other purposes as well will keep the cost of dilution within reason. A future possibility, if research presently going on in the Basin verifies it and shows ways of putting it to use, is to employ ground water in the same 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, just as in water supply, ultimate "hard" technology is undoubtedly going to make better solutions possible, while a strong and meaningful start is possible with the technology that is on hand.
Silt is a truly Basinwide problem. The individual tiny grains of soil that mass to sully and choke the estuary may have originated anywhere in the thousands of square miles of drainage above. They constitute an economic loss at their points of origin as well as a trouble all along their downstream course of migration.