Among the many things that affect water quality is impoundment. Water quality may be improved or degraded by impoundment. This article discusses some of the more significant beneficial and detrimental effects of impoundment and the principal factors causing changes in water quality. Important beneficial effects of impoundment on water quality include: reduction of turbidity, silica, color (in certain reservoirs), and coliform bacteria; evening out of sharp variations in dissolved minerals, hardness, pH, and alkalinity; reductions in temperature, which sometimes benefit fish life; entrapment of sediment; and, storage of water for release in dry periods for the dilution of polluted waters. In addition to benefits, impoundment also has certain undesirable effects, including: increased growth of algae, which may give rise to tastes and odors; reduction in dissolved oxygen in the deeper parts of the reservoirs; increase in carbon dioxide and frequently iron, manganese, and alkalinity, especially near the bottom; increases in dissolved solids and hardness as a result of evaporation and dissolution of rock materials; and, reductions in temperature, which, although sometimes beneficial, may also be detrimental to fish life.
15. Well 717 ft. deep, Snffolk, Va. 16. Well 305 ft. deep, part of public supply, Fairfax, Va.; Wissahickon schist 17. Well 78 ft. deep, Cedarville, Va.: Beekmantown limestone t Contained free acid equivalent to 8 ppm. H2S04.
The measurement of the loads of suspended matter carried past 34 gaging‐stations located on streams in eight regional projects of the Soil Conservation Service has required greater precision in the measurement of discharge and a more intensive program for the collection of samples of suspended matter than has been found necessary by the Geological Survey in making similar measurements on the larger streams on which measurements have been made in the past. It was found early in the work that much the greater part of the annual load of suspended matter was carried in a relatively few days of high water for almost all the streams on which measurements were made. In order that these loads might be determined with reasonable accuracy it was found necessary to collect samples every hour and occasionally every half‐hour on rising and rapidly changing stages during floods. Some floods occurring at night were missed in part or entirely because the resident observer did not realize that a flood was in progress. Twenty‐four‐hour sampling programs, together with the aid of electric‐alarm systems at some stations, have made possible the collection of an adequate number of samples during most floods.
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