Showing papers on "Siltation published in 1994"

Recent floods in Bangladesh: Possible causes and solutions

Abstract: In recent years the frequency of abnormal floods in Bangladesh has increased substantially, causing serious damage to lives and property. The most crucial questions that need to be addressed are: what really causes the havoc-creating floods and is there any solution to the problem? The heavy monsoon downpour and synchronization of flood-peaks of the major rivers are generally considered to be the main causes of the floods. Some underlying factors also deserve serious consideration as possible contributors to the recent floods: change in the base level of the rivers due to local sea level rise and subsidence, inadequate sediment accumulation on flood plains, a possible increase in the watershed area due to seismic and neotectonic activities in the region, river bed aggradation due to siltation and damming of rivers, soil erosion due to unwise tilling practices, deforestation in the upstream region, and excessive development and population growth. Without regional cooperation among the co-riparian nations any major interbasin flood control activity is considered to be almost impossible. However, among other proposals in this paper, extensive annual dredging of the rivers, channels and creeks, and reoccupation of the abandoned channels in Bangladesh through re-excavations could still increase the water carrying capacity of the rivers. Land elevations could be increased if the dredged or excavated materials are dispersed on the flood plains, which would in turn reduce the severity of floods. Language: en

The Historical and Current Status of Freshwater Fish in New South Wales

Abstract: Examples are given of a number of New South Wales freshwater fish species which have declined in abundance since last century. Reasons for the declines include river regulation, changes to riparian vegetation, erosion and siltation. The effects of alien species on the stocks of native fish are also discussed together with possible remedial measures to restore both habitat and fish communities.

Current vegetation characteristics within tree-kill zones of F- and H-Areas

Abstract: Vegetation of two wetland areas previously adversely affected by outcropping groundwater was characterized to evaluate the type and extent of revegetation. When the damage first became evident in the late 1970s and early 1980s the areas were examined and described to try to establish the cause of the extensive tree mortality. The F- and H-Area seepage basins above the wetland areas received waste products from the separation areas beginning in 1955. The operation, estimated loading, and current status of the basins were summarized by Killian et al. Analysis of soil and water at the affected seeplines where the tree-kill was occurring confirmed that the surface water was strongly influenced by constituents of the F- and H-Area seepage basins. While no single cause of the forest mortality was defined, alterations in the hydrology and siltation patterns, pH changes, increased conductivity, and increased levels of sodium, nitrogen compounds, and aluminum were believed to be interacting to cause the mortality.

Regularities of siltation of reservoirs and ponds

Abstract: This paper describes a mathematical model for siltation of reservoirs and ponds. It is shown from the model that small reservoirs and ponds, to a considerable extent lose a capacity as a result of accumulation of biomass and deposition of sediments from reworking of banks. But these deposits affect the increase of the current velocities and the transporting capacity of the flow, just as the deposition of ordinary river sediments. An analysis was performed on the settling pond of the Shaarikhan hydrostation and the headrace canal of the Perepadnaya hydrostation.