Showing papers on "Siltation published in 1989"

Land degradation, soil conservation and the sediment load of the Yellow River, China: Review and assessment

Abstract: Ninety per cent of the sediment load of the Yellow River, the world's muddiest river, comes from the loess plateau region in the middle course of the river. Control of this sediment supply is essential to avoid the danger of flooding in the lower reaches on the South China Plain. Since 1971, sediment loads entering the lower reaches have decreased, by 20 per cent as a result of lower precipitation, and by 27 per cent through soil conservation works and reservoir construction. Reductions in erosion can be obtained by restraining the formation of overland flow through promotion of an effective vegetation cover and elimination of the soil surface cover to encourage infiltration. Reservoir operation is a key to control of sediment movement through tributaries and along the main river. Water demands often conflict with sediment control, and, as a consequence, reservoir operation systems have changed several times in the past decade. The possibility of a further reduction in the sediment load of the Yellow River exists, but much depends on how rapidly control of grazing and deforestation leads to the establishment of plant cover on the loess plateau.

Density currents and siltation - with particular reference to Cochin -

Abstract: In an estuary, the confluence of fresh water of upland rivers with salt water from the sea gives rise to a complex regime of flow pattern due to the difference in densities of the two liquids of about 2.5%. Vhen the estuary is stratified, the heavier salt water which dives underneath the lighter fresh water extends as a long wedge far into the upstream. The amount of saline water brought in by the density current into an estuary can be much larger than the tidal filling, when the freshet dis charges are high compared to the tidal prism. Density currents play a major role in the hydrodynamics of a harbour basin located at the mouth of an estuary The Port of Cochin on the west coast of India is located inside a natural lagoon with a large monsoon discharge passing through its channels. The saline water which enters the deep navigation channels brings in a large amount of silt from the sea resulting in heavy siltation. This thesis deals with the density currents at Cochin and presents the results of a desk study made with the objectives 1. to analyse the hydrodynamics of density currents in general with particular reference to the local situation. 2. to derive the siltation pattern from it and make a first order estimate and 3.to suggest solutions and make recommendations for furhter study.

Prediction of Siltation at a Point

Abstract: This paper describes a zero-dimensional mathematical model which predicts siltation at a point on a cohesive sediment bed. The processes of erosion, deposition and consolidation are modelled over a period of many tides. The model uses several parameters to define the sediment properties at the application point: examples are given of these relationships, which have been derived from field and laboratory experiments. An application of the model in the approach channel to a UK port is presented.

The reduction of erosion by pre-formed systems. proceedings of a symposium on soil erosion and its control, regents college, regent's park, london, april 21, 1989

Abstract: This paper describes the basic types of pre-formed control systems and suggests the various erosion mechanisms against which each is most effective. Five main types of system are discussed: (a) vertical silt fences; (b) over-soil mats; (C) in-soil mats; (d) discrete inclusions of elements such as continuous filament, staple filament or mesh element reinforcement into the soil in the form of an intimate mixture; and (e) wind fences. Particular attention is given to a particular type of vertical silt fence, the siltation fence, used for the control of extreme erosion conditions on bare slopes. The design principles of two alternative layouts (total and partial retention methods) are described briefly, and design equations are provided which assist in the first approximate assessment of the necessary quantity of geotextile required and its dimensions in any particular system. For the covering abstract of the conference see IRRD 824252.