Also, increasingly, bad land use involves the ways in which great machines adapt the landscape to hundreds of sophisticated purposes. The massive eatings of powered blades and scoops to get at coal and other minerals on the steep slopes of the North Branch watershed and elsewhere, add heavily to sedimentation. So do broad rights-of-way gashed out of the countryside and left bare under storms in the months before highway construction is done, and secondary roads that even when finished may be left for years or forever with denuded clay shoulders and ditches and banks that wash with every rain. And so, most particularly, do the great polygons of rolling land around the Basin's town and cities that are stripped naked by bulldozers and left sitting in that condition for long periods, while they await the erection of buildings and blocks of homes. This is occurring throughout the Basin, but most notably around Washington, where the highest erosion rates of all are found. We will take a look at its details and the reasons for it a little further along in this chapter when we examine the estuary's situation.
Except for the acid parts of the North Branch, the upper Basin's waters in most places, most of the time, can still serve the "practical" purposes to which they are put—irrigation, industrial uses, municipal supply after purification, and even the absorption and digestion of effluents from adequate, well-run treatment plants. Most of the streams are usually good to look at, especially in conjunction with the superb rural landscapes against backgrounds of wooded mountains that are characteristic. They furnish much pleasure to fishermen, hunters, boatmen, swimmers, picnickers, and other folk, though in some places it is an open question, as we have seen, whether or not contact with the water is prudent. And almost everywhere, aging locals can recall a time when their stream was a happier amenity than now—when it held more fish, ran clearer over stones and gravel not coated with weeds and green slime, did not have the smell it presently emanates, was colder and more copious....
Their nostalgia probably does not play them false, even though conditions in many places are better now than in the intermediate past, after modern times had settled in, but before INCOPOT and the Soil Conservation Service and such influences had begun to push for reform of the casual, anciently human ways of doing things in which present human populations can no longer afford to indulge themselves. Some of the gains that have been made are being cancelled out by growth and new types of pollution, however, and in general the flowing Potomac river system is teetering at the brink of bad trouble. It needs help.
If the flowing upper Potomac had any lingering oxygen deficiency in its lower stretches—though it seems usually not to—it would tend to rectify the lack in its turbulent eighteen-miles descent across the Fall Line, a superb natural "treatment plant." Normally it arrives at Washington charged with oxygen, but does bring down with it the part of its nutrient load that has not fertilized upstream weeds and algae, periodic waves of bacterial concentration, and a great deal of debris and silt in season.
In the broadening, slowing upper estuary, its sluggish currents confused by the twice-daily surge and ebb of tides, these materials from above are stirred in with an array of specifically metropolitan pollutants—with more silt off of the outraged urban watershed, with junk and debris of a thousand sorts, with decaying substances and bacteria from many sources, and with vast new quantities of nitrogen and phosphorus. The consequence is a weighty and sometimes spectacular pollution problem directly adjacent to the proud national capital. It is at its vivid and aromatic worst in summer, when the most Americans come there fondly to view the city and the Potomac, and when locals who want to boat and fish and swim and do the other things one does on water would make most use of the river—indeed, do make use of it in spite of everything.
Like the meek, the upper estuary inherits the earth, or at least that part of the Basin's earth that is washed downriver as silt. There are enough fine suspended sediment particles in the water of the metropolitan river to make it drably opaque most of the time, even during relatively dry spells, when heavy sand and gravel dredging helps to keep it stirred up. As the current loses force and washes back and forth with the tides, the particles settle out slowly into smothering, continually renewed blankets on the bottom, and over two centuries have accreted into great mudbanks and shoals. Channel dredging to maintain navigation has been going on since the early 19th century, about 180,000 cubic yards being presently removed each year. The dumping of the dredged materials on the marshes and long low shores has built up wide, flat, new flood plain areas around the city over the years, including the sites of Washington National Airport, Anacostia and Bolling Air Fields, and East and West Potomac Parks.
Such channel dredging has little effect on the gradual shoaling of this whole part of the river in general. Miles of formerly navigable water downstream from Memorial Bridge are now only one to four feet deep and useless for either pleasure or commercial craft. It has been estimated that present rates of deposition will within fifty years fill in the upper estuary completely to a mile or so below Alexandria, except for a river channel. The same process is at work in the tributary creek-bays that give onto the estuary, some of which have silted so heavily since Colonial Days that formerly thriving ports—among them Bladensburg, Dumfries, and Port Tobacco—are now distant from the water.
The bulk of estuarial silt comes down the main river from the upper Basin. But a heavy increment is added in the metropolitan area. Modern mechanized development of the city's hilly environs on a huge scale, continuing year by year with few thoughtful rules to guide it heretofore, has brought about erosion that on individual patches of bared land may reach a temporary rate of 50,000 tons per square mile per year, and even average rates in this area are far in excess of anything else in the Basin.
