Most of the primary civilizations of the world emerged in or near river valleys. The construction of dams and other hydraulic structures is, therefore, one of the oldest branches of engineering (e.g. 11, 105). The earliest dams were probably built for the purposes of irrigation, flood control, and water supply. Later, water was impounded so that its subsequent controlled release could provide a source of energy, first by the use of waterwheels and later by the use of hydroelectric generators. Other purposes include the maintenance of an adequate river flow through the year for navigation, and the provision of facilities for recreation. Most modem reservoirs are designed for two or more of these purposes. Usually "the role of water storage reservoirs . . . is to impound water in periods of higher flows so that it may be released gradually during periods of lower flows" (135), but sometimes the sole purpose of the impoundment is to provide a new body of standing water for use as such; for example, for fishing or boating, or for waste-heat dissipation from a thermoelectric generating plant. The earliest dams were probably constructed by blocking the stream with earth. Such dams are still constructed. In its simplest form. an earth-fill dam is a pile of compacted earth extending across a stream with a fairly gentle slope both upstream and downstream. Similar to earth-fill dams are rock-fill dams composed of quarried rock or natural boulders or gravel with a layer of impervious material on the upstream face. A later development in dam construction was the invention of the masonry dam, probably in Spain (150). The earliest masonry dams were of the gravity type. Such dams are held in place by their own weight pressing against their foundations, and usually have a long sloping downstream toe to prevent overtipping.

High Temperature Systems

Environmental Effects of Dams and Impoundments

6 – Periphyton Responses to Temperature at Different Ecological Levels

Thermophilic bacteria: Ecology, physiology and technology

Growing algal and bacterial stromatolites composed of nearly amorphous silica occur around hot springs and geysers in Yellowstone National Park, Wyoming. Some Precambrian stromatolites may be bacterial rather than algal, which has important implications in atmospheric evolution, since bacterial photo-synthesis does not release oxygen. Conophyton stromatolites were thought to have become extinct at the end of the Precambrian, but are still growing in hot spring effluents.

https://science.sciencemag.org/content/sci/178/4059/402.full.pdf

High Temperature Systems

Citations

Environmental Effects of Dams and Impoundments

6 – Periphyton Responses to Temperature at Different Ecological Levels

Thermophilic bacteria: Ecology, physiology and technology

Siliceous Algal and Bacterial Stromatolites in Hot Spring and Geyser Effluents of Yellowstone National Park

Siliceous algal and bacterial stromatolites in hot spring and geyser effluents of Yellowstone National Park

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