We had to examine the reasons for this rather closely last year in a study of Rock Creek's ailments, whose findings we published in a report called The Creek and the City. This much-admired metropolitan stream has been relatively well protected, with the parks along its wooded valley and an upper watershed that until quite recently remained essentially rural. But as development has proceeded in standard and careless ways—the wholesale stripping and scarification of big tracts of rolling, fine-textured land, the long naked wait for development—the creek has come to be muddy and ugly almost all the time and has been spewing an estimated 100,000 tons of sediment a year into the estuary, with frequent floods.
To help save the creek and its parks and to stimulate a better kind of development of the rest of its basin, citizens formed a watershed association under Soil Conservation Service auspices and brought about the construction of two small upstream reservoirs to control flooding—with results noted in the preceding chapter—and to collect silt. They sought to promote better land use as well, for the reservoirs' effectiveness is obviously dependent on their not filling up quickly with an excess of sediment. Better land use around a city depends on zoning and other legal devices to regulate the density and distribution of construction, and on controls over the way land is shaped, and a sharp conflict developed between the watershed's defenders and the Council of Montgomery County, Maryland, in office at that time, whose rezonings in favor of standard massive suburbanization and whose failure to enact sediment-control ordinances threatened the whole effort. Rock Creek has many friends, and their subsequent fight for its salvation has had good effect, though much remains to be done.
However, Rock Creek is only one of many metropolitan streams that need protection, both for their own sake and for that of the estuary. Some are getting it—in the preceding chapter we noted the happy example of Pohick Creek in Virginia, where whole watershed planning is being accomplished almost from scratch, before development. But many more are being ruined by the steady advance of standard urban sprawl.
Thus the main cause of urban silt is faulty or nonexistent or powerless land planning, and the problem merges with the whole question of landscape preservation. The ecological principles involved in good practical land planning—the distribution of uses based on what land and water can take without being degraded and causing silt, flooding, and downstream pollution—are the same basic principles that lead to scenic beauty and a decent human environment. This is a subject we will explore in more detail when we arrive at considering the landscape as a whole, but for now it may be worthwhile to note that insofar as urban erosion and silt stem from decisions of political agencies inclined to subjugate well-known good land use principles to speculative pressures, expediency, and other things, their origin is political and economic.
Organic materials are pervasive enough in the upper estuary that during periods of even normal flow their decay pulls oxygen levels down. Under usual conditions this B.O.D. grows worse and worse downstream and reaches a peak in the neighborhood of Mount Vernon, though its effects continue to be felt below. Fish kills among the rugged resident species that predominate in these reaches of the river are not uncommon, the shoreline windrows of deceased carp and perch periodically adding their essence to what metropolitans have come to accept as the Potomac's normal summer smell. And along with the organic materials are heavy concentrations of bacteria.
The organic and bacterial load enters the estuary from many sources, most of them local, for only a little of this material comes down from the upper river. A significant amount of it issues from the network of small urban watercourses like Rock Creek. Many of these were covered over as storm sewers or troughed in concrete long ago, but they continue to serve their age-old function of draining the lands they traverse, even if through cast-iron gratings.
A good bit of the organic load in these tributaries consists of raw human waste, incongruous and particularly obnoxious around a modern city. The bulk of it is released in periodic surges when local rainstorms overload the old-fashioned combined sewer systems of the District of Columbia and Alexandria. In dry weather these systems send both collected sanitary wastes and street drainage down to the cities' respective treatment plants, but during storms when street drainage is heavy the sewers' capacity is exceeded and overflow gates gush mixed stormwater and sewage out into the streams, which carry it to the estuary.
In the suburbs, more modern separate storm and sanitary sewers are the rule, but they too have some problems of a kind we noted in relation to the upper river. Investigations on Rock Creek revealed steady dribbles of raw sewage entering the creek or its tributaries from a large number of storm-sewer outfalls and other places. Partly these flow from malfunctioning individual septic systems in outlying areas, surreptitious connections of house sanitary sewers to the storm system, breaks and leaks in sanitary sewers, and such things. Partly too they seem to come from the fact that some sanitary sewers are having to carry more sewage than they were designed to handle, so that their overflow valves leak more or less constantly into the storm sewer system. The capacity of sewage collection systems is related to planning. If a pipe is laid down to a fringe area where county zoning maps indicate only limited development is going to be permitted, its size is gauged to that kind of development. But if the zoning is changed later and three times as many houses are hooked up to the line as were originally envisioned, trouble results. Rock Creek is heavily affected by such sewage, and the chances are that the situation is much worse on many other urban drainways, for their longstanding degradation or sheer disappearance from view has lost them the alert defenders who watch over Rock Creek in its pleasant valley.