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Show Sedimentation Another major pollutant of our streams is sedi- ment. Natural land erosion has been aggravated tremendously by bad farming and other kinds of faulty land usage. Sediment combined with other wastes pro- duced by civilization can change a normal life- giving stream or lake into sick water. Suspended matter cuts down the light entering the water on which plants depend for photosynthesis and stim- ulation of growth and the manufacture of oxygen. It affects the nature of all the plants and animals living in or on the water which in turn affects those that live upon them. Mud and sludge blanket spawning beds and destroy fish and fish-food organisms such as the larvae of May flies, dragonflies, damsel flies, stone flies, hell- grammites, and water animals such as shrimp, crayfish, clams, oysters, snails, and water beetles. Green algae and diatoms are replaced by un- healthy fungus growth and tubifex worms. Slime and aquatic vermin take over, and the water becomes unfit for fish, waterfowl, wild birds, and animals. The entire ecological bal- ance or natural beneficial interrelationship is upset. The loss of the healthy relationship between life and its environment is only one direct con- sequence of sediment and other pollution. All other benefits arising from the development of water resources are also affected. In respect to flood control, deposits of sediment and other pollutive substances raise streambeds, divert flows, and impair the usefulness of works constructed to reduce flood damage. In domestic, municipal, and industrial water supply, pollution not only reduces the usefulness of reservoirs and other costly construction but may make the water itself unsuitable for use. In irrigation, it may make the irrigating water dangerous to public health, and silt up dams and canals. In navigation, it chokes channels and damages navigation structures, shipping, and water-front buildings. In production of hydroelectric power, it dam- ages turbines and other equipment and reduces capacity. It greatly shortens the life of con- densers in steam plants. It shortens the life of all storage reservoirs, whatever their purpose. Pollution Abatement and Multiple Use In the development of water resources in a river system through building multiple-purpose dams for flood control, power production, irriga- tion, public water supply, and other uses, what are some of the public health and pollutional factors to be considered? By changing a flowing stream into an arm of a reservoir, the self-purification capacity of the stream may be altered sufficiently to aggravate pollution problems of towns and industries along the reservoir shore line. Waste discharge may be backed up into waterworks intakes. Heavy growth of algae, imparting obnoxious tastes and odors to the water, may also result. The recrea- tional development of the reservoir area would be impaired. Reservoir site-clearing has water quality impli- cations that require attention. Also, when public water supply is to be developed, special safe- guards have to be taken into account. Dams should be designed to allow a fluctuation in the reservoir level that will break the life cycle of the anopheles mosquito. Reservoir water quality varies according to depth, too-physically, chemically, and biologi- cally. This should be considered in release of the water for downstream use, including that for dilution of wastes. The most important pollution control function of a dam is its regulation of flow for downstream dilution. Waste treatment below the dam will be based on this flow. Also, the flow will affect the classification of the stream in conformance with present and prospective uses. Knowledge of reservoir operation makes possible fullest use of the stream's self-purification capacity, re- flected in lower treatment costs. These factors have not received the consideration that must be given them in planning multiple-purpose projects. 190 |
