The subject of floods is fraught with more drama than that of water shortages, for a flood can be not only a hardship but a catastrophe. For this reason, accounts of floods tend sometimes toward exaggeration, and appeals and proposals for protection against flood threats often take on the highpitched tones of impending disaster. The subject badly needs sober public understanding, despite the fact that for decades a good many knowledgeable scientists and engineers and planners have been laying out their conclusions for general perusal.
Rivers are supposed to run out of their banks occasionally. Topographically, stream flood plains—the expanses of flat bottomland that have been deposited over long periods of geological time by the streams they border—are similar to what legal terminology calls "attractive nuisances." Men have always known that they were dangerous and yet have always utilized them to some degree, because they contain the best farm land, are convenient to water, and are easier places in which to build houses and factories and roads than are the safer hills and uplands.
In times before engineering technology was able to erect such effective control structures as today, populations who had lived along "flashy" watercourses long enough to learn their habits tended to build their more valuable structures back away from the parts of the flood plain that got wet most often, leaving those parts for cropland and timber, or sometimes for shacktown, promenades, and parks. Thus long-settled countries and regions have often developed through trial and error a degree of what is now called "passive flood protection," which simply means recognizing that the flood plain is sometimes a rather perilous place, and treating it accordingly. It was valid in past ages, and it is still valid today.
The Potomac Basin has been inhabited by civilized men since long before modern engineering evolved. Possibly early town-builders' wariness of floods contributed to the fact that the problem of flood damages here, though quite real, is somewhat less severe than in certain other sections of the nation. At specific points of concentrated flood plain development—Petersburg, W. Va., on the South Branch; Cumberland, Md., and the areas upstream from it on the North Branch; and metropolitan Washington at the head of the estuary—figures show significant amounts of average annual destruction by rampaging stream waters. In headwater areas or small urban watersheds scattered throughout the Basin, there are a number of other places where some damage takes place, whether agricultural or structural. The total average annual damages for the Basin, as computed in the 1963 Army Report, amount to about $8.6 million.
Along small streams, whether urban or rural, the same principles apply as along large ones, and the proper protective measures are similar if smaller in scale. Leaving the worst parts of the flood plain in fields or parks is the usual and effective form of passive protection. Where existing development demands structural measures, it has been common practice to cover streams over as sewers or to confine them to straightened concrete channels that sluice rainwater and mud away as fast as they will flow—though often this is not fast enough, as is shown by occasional messy and costly overflows of Four Mile Run between Arlington and Alexandria. And the loss of pleasant brooks and creeks through such practices is a heavy price to pay.
More and more often lately in such cases, a combination of some passive protection with the small headwater dams that "catch the water where it falls" and soil conservation measures to protect the watershed lands above the reservoirs, has proved to be a better solution. This is what has been done in the Rock Creek watershed in the District of Columbia and Montgomery County, Md., and its value was shown during the heavy rains of September 1966. Here stream valley parks have given passive protection for a long tune, though the popularity and heavy use of the parks have caused a big investment in picnic areas, playgrounds, and other facilities, which themselves have often suffered expensive flood damages. As a result of long effort by a watershed association, two S. C. S. dams had been finished shortly before the September flood at the only useful sites on the creek's upper branches that rapidly spreading residential development had left available. They kept runoff from the big sudden rains entirely in hand in Maryland and reduced damage in the Federal park in the District to a point far below what it would have been without them.
Ideally, of course, such planning should be done before heavy development, and a pilot urban watershed program of this sort is being undertaken in the Pohick Creek basin on the metropolitan fringe in Fairfax County, Virginia. With freedom to locate necessary structures in the right places and to protect them against silt and ruinous runoff by requiring good land treatment and a sensible distribution of buildings, pavements, and wooded or grassy open space, planners there ought to get good flood protection while preserving a pretty valley and stream for the people who will be living in the neighborhood. From any number of standpoints, this is vastly preferable to the more usual traditional procedure of letting growth run wild and then trying to cope with trouble when it comes up.
The headwater dams are equally effective in reducing flood damages in small rural watersheds where losses warrant their installation. But even on a massive scale of installation they have little influence on downstream flooding along the main rivers. In such places—at Cumberland, Petersburg, and the Washington metropolis, and at certain other river towns where less damage occurs—other measures are going to have to be selected and applied in each individual case according to costs and benefits, physical possibilities, and the best interests of the region.
Cumberland and the lesser damage centers on the North Branch are scheduled for the classic engineering solution of big dams upstream. The existing Savage River reservoir, finished in 1950, has cut down flooding notably in that area, and a dam at Bloomington above Westernport, already authorized by Congress, will relieve it still more, as well as fitting into the complex clean-up task along the North Branch and furnishing water for local and Washington use.
The 1963 plan proposed similar protection for metropolitan Washington and for Petersburg, West Virginia, in the form of major reservoirs at Seneca and Royal Glen. Physically and culturally, there is very little similarity between the two communities, but their flood situations and the potential effects of the proposed protective structures have a certain kinship.