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Showing papers on "Siltation published in 1976"


Journal ArticleDOI
TL;DR: The environmental effects of water impoundment vary greatly with the characteristics of the region as well as the type of reservoir to be constructed, so decisions regarding the development or non-development of water resources must be based on sound investigation of both the long-and short-term effects of reservoir construction and operation.
Abstract: Recognition of the potentially harmful effects of water development in the tropics had led to increasing efforts to assess the environmental impact of such projects prior to construction. Decisions regarding the development or non-development of water resources must be based on sound investigation of both the long-and short-term effects of reservoir construction and operation. The environmental effects of water impoundment vary greatly with the characteristics of the region as well as the type of reservoir to be constructed (area and depth of reservoir, ratio of water inflow to storage). Of major concern are the reduction of reservoir capacity as sediments accumulate behind the dam and the loss of these sediments to downstream agriculture and fisheries. The potential impact of altered flow regimes, siltation, reduction in beach formation and nutrient enrichment at the mouths of rivers, and the possibility of saltwater encroachment should receive careful stdy. A thorough description of the plants and animals to be affected by inundation should be made to determine the possible loss of rare or key organisms as well as the potential development of "nuisance species". Included in this survey should be a detailed study of existing fish and the potential for commercial fishery development in the proposed reservoir. Consideration should be given to vegetation removal in the reservoir basin prior to inundation, since decaying vegetation can result in deoxygenation, formation of hydrogen sulfide, possible development of suitable habitats for undesirable species and snagging of fish nets. Sanitation and land use practices as well as erosion in the watershed surrounding the reservoir must be controlled to prevent accelerated eutrophication caused by increased nutrient loading. Inundation in tropical areas can have serious sociological and human health implications including the increase of diseases, e.g., malaria, schistosomiasis, onchocerciasis, and dysentery, and the probable resettlement and alteration of land use practices. Census information and surveys concerning land use, housing and health standards and the social and economic structure of the community to be affected must be evaluated in order to anticipate and avoid potential problems. The archaeologic, historic, scenic and recreational value of the site to be inundated must also be considered. Studies of the EL Cajon site on the Sula River in Honduras and the Purari River Project in Papua, New Guinea, are utilized as examples in this report.

17 citations


Journal ArticleDOI
29 Jan 1976
TL;DR: In this paper, the authors proposed a sandtrap-based approach channel sandtrap design, which is governed by a number of factors such as the extent over which a major part of the drift takes place, quantity of material transported, size distribution of sediments, velocity of currents, mode of dredging etc.
Abstract: Siltation in harbours and their approach channels is one of the major problems connected with the development of harbours. The economics of harbours are directly related to their annual maintenance dredging, and as such a proper assessment of the quantity of siltation and provision of adequate measures for the maintenance of depths would form an important part of planning the development programmes. Siltation could occur due to various reasons viz. deposition of littoral drift which is interrupted by the approach channel, deposition of sediments brought into suspension by wave action (including during storm/cyclone) Whenever the alongshore drift is large, wave action obviously is quite substantial which renders the maintenance of depths during this period by dredging difficult. In such cases it would be necessary to make adequate provision to ensure that the depths are not deteriorated to any substantial extent by the movement of the drift. One of the common means for achieving this is the provision of sandtraps on the updrlft side of the approach channel which would 'store' the drift material temporarily and from where the material could be dredged at convenience. The design of the sandtrap would be governed by a number of factors such as the extent over which a major part of the drift takes place, quantity of material transported, size distribution of sediments, velocity of currents, mode of dredging etc. Waves of moderate to high intensity occurs along the eastern coast of India from south and south west direction during south west monsoon period from May to September and from North Easterly direction during North East monsoon beginning from November. In view of this climate the direction of drift along the shore changes with Mason. The quantities of drift during these periods are also different owing to the magnitudeand periods of wave action which differs between the two seasons. The net drift along this coast varies from 0»60 million m3 at Madras on the south which increases progressively to 1,00 million m3 at Paradip further North (Fig, 1),

8 citations


Journal ArticleDOI
TL;DR: A few states have already enacted legislation posing land use-environmental restrictions, such as Illinois, Vermont, Hawaii, Colorado, Maine, Massachusetts and New York as mentioned in this paper, which is based on soil erosion and sedimentation.
Abstract: Environmental and resource quality recently have become special public concerns. A few states have already enacted legislation posing land use-environmental restrictions. Vermont, Hawaii, Colorado, Maine, Massachusetts and New York, passed land use laws. Illinois formed a Pollution Control Board to quantify nutrients and sediment polluting streams and suggest action. In 1971, the Iowa Legislature passed the “Conservancy District Act,” creating soil conservancy districts “to preserve and protect public interest in soil and water resources for future generations.” Legislation centers on soil erosion and sedimentation. Erosion is declared a nuisance if it results in siltation damage. The law sets allowable soil loss limits on land at one to five tons per acre per year, depending on soil type.

3 citations


Journal ArticleDOI
TL;DR: In this article, a series of unexpected potential impacts on the environment, wildlife, and human health and safety in the arctic tundra and subarctic taiga regions of the world has been discussed.
Abstract: Rapid development for the exploration and extraction of mineral and petroleum resources in the cold-dominated arctic tundra and subarctic taiga regions of the world has resulted in a series of unexpected potential impacts on the environment, wildlife, and human health and safety.Surface transportation, especially over low wet-tundra areas in summer, causes long-term changes in vegetation through reduction of insulation to the underlying permafrost. The number of passes over the same track, ground pressure of the vehicle, and speed of travel, affect the degree of degradation. For permanent roads, gravel removed from adjacent stream-beds or hillsides and laid directly on the tundra mat, has provided the most suitable road-bed. These roads, and the removal of gravel, however cause aesthetic and practical problems such as spreading of dust, impoundment of water, behavioural barricading of animals, alteration of river channels, and siltation of streams.Anadromous fishes constitute a major food resource; alteration of stream channels or siltation of rivers can affect their movement and reproductive success. Oil-spills in aquatic systems, especially in rivers, are harder to control and clean up than terrestrial ones. Recovery of ponds in which oil has been spilled takes several years. The oil-rich outer-continental shelves in the Beaufort, Chukchi, and Bering Seas, now under exploration for oil, are especially sensitive, as they are highly productive and contain unique populations of marine mammals and birds.Human habitation of the Arctic requires transport of food, fuel, and construction materials for lodging, and disposal of refuse and human wastes which, due to the permafrost-underlain vegetative mat, is difficult in arctic areas. Heating by fossil fuels results in ice-fogs in winter and accumulation of atmospheric pollutants at ground-level during thermal inversions at all seasons.Perhaps the greatest impact on arctic ecosystems is simply the increased intervention of the human population. Where native people were previously only sparsely settled or nomadic in the tundra, and on coasts where they tended to congregate, now the economic need for resources has resulted in increased pressure overall which will result in decreasing habitats for wildlife, destruction of wilderness areas, and increased access to humans for further exploration and recreation.

2 citations