Recognition of the river as the dominant force in forming basins may be traced back to John Playfair in 1802. In contrast to the leading opinions, Playfair observed that rivers were proportional to valley size and tributaries were accordant, neither of which would be likely unless rivers had created the basins, rather than the other way around. Now known as Playfair's law, his observation has led to extensive efforts to quantify river basin characteristics.
In 1945, R. E. Horton developed the concept of stream order, and Arthur Strahler further elaborated on the subject. The smallest tributaries are labeled "1," and when two first order streams converge, they form a second order stream ("2"), and so forth. The ratio of lower order to higher order streams remains remarkably consistent throughout a given basin. Uniformity is the important factor in all of these because it demonstrates that drainage network characteristics are quantitatively consistent.
Renowned geomorphologist William Morris Davis, noted in Water, Earth, and Man (1969) that "the river is like the veins of a leaf; broadly viewed, it is like the entire leaf." There is, however, one critical difference. In the leaf, the flow of water and nutrients is primarily from larger to smaller veins. However, in river basins all matter, good and bad, flows downstream. That is why when urban water systems use rivers, their intakes are located upstream and drainage outlets downstream. Groundwater pollution follows this same downward pathway, though at a far slower pace; it is one of our most serious problems.
The river basin, as part of the hydrologic cycle , is increasingly a technological and social system. For the United States, an estimated 10% of the national wealth is devoted to structures involving the movement of water, including dams , irrigation systems, water supply networks, and sewers, with increasingly sophisticated controls.
The importance of river basins is well illustrated by the Tennessee Valley Authority (TVA) project. Launched by the Roosevelt Administration in 1933, it was a massive economic and social effort aimed at the chronic problems of depleted soils, rampant soil erosion , recurrent flooding , and economic desolation. Industrial demand for electricity has subsequently grown so large that hydroelectric power, the initial source, now supplies less than 20% of TVA demand.
[Nathan H. Meleen ]
Chorley, R. J., ed. Water, Earth, and Man: A Synthesis of Hydrology, Geomorphology, and Socio-economic Geography. London: Methuen, 1969.
Gore, J. A., ed. The Restoration of Rivers and Streams. Boston: Butterworth, 1985.
Morisawa, M. Streams: Their Dynamics and Morphology. New York: McGraw-Hill, 1968.
Petulla, J. M. American Environmental History: The Exploitation and Conservation of Natural Resources. San Francisco: Boyd & Fraser, 1977.