Siltation

About: Siltation is a research topic. Over the lifetime, 1420 publications have been published within this topic receiving 20983 citations.

Dynamics of discharge, sediment transport, heavy metal pollution and Sábalo (Prochilodus lineatus) catches in the lower Pilcomayo river (Bolivia)

Abstract: The Pilcomayo river is one of the few intact natural river systems left on the South American continent. The high, largely natural, sediment loads of the river have led to the development of an alluvial fan system, which is still active. The river is currently retracting due to siltation of its bed, and in the near future the river is likely to abruptly change its course. There is a large difference in discharge between the wet and dry seasons. Pollution of the transported sediments by heavy metals from the mining district of Potosi is largely prevented by dilution of the toxic mining sludges with clean sediments derived from natural erosion processes. The Sabalo (Prochilodus lineatus) is a migrating fish which is very important for commercial fishing. The Sabalo grows up in the floodplains in the lower reaches of the river and starts its upstream migration at the end of the rainy season to spawn in the Andean foothill at the beginning of the next rainy season. Pollution does not seem to affect fish catches. Sabalo catches in a given year, however, do appear to depend strongly on the mean discharge in the three preceding years. Annual discharge is strongly influenced by the El Nino–Southern Oscillation (ENSO) phenomenon. Copyright © 2002 John Wiley & Sons, Ltd.

The biota of the Hawkesbury-Nepean catchment: reconstruction and restoration

Abstract: Despite 200 years of European settlement, the Hawkesbury-Nepean catchment sustains a rich and diverse fauna. This is a consequence of extensive sandstone environments largely unsuited for development that escaped the extensive habitat modifications affecting the fauna of the grassy woodlands on the Cumberland Plain and Southern Tablelands. The most significant impacts followed the clearing and fragmentation of the vegetation for agriculture. Changed fire regimes, the naturalization of exotic plants and animals, and disease were also factors in the decline of native birds and mammals. Data on frogs and reptiles are limited, but some reptiles have declined in abundance in association with the loss of habitats. Not all native species have been adversely affected by European settlement and a number of birds have increased in abundance and extended their range within the catchment. Agricultural clearing and urban development have also affected aquatic ecosystems. The pre-European environment was apparently characterized by creek and river systems subjected to periodic floods, but with clear water, low nutrient levels, and clean sandly or rocky substrates. Increased nutrient levels, turbidity and siltation associated with urban and rural effluents, land clearing, foreshore erosion and river bed mining has reduced the extent of seagrass communities in the lower Hawkesbury and changed the substrate of rivers and the estuary. Mangrove communities have expanded. Other impacts on aquatic environments include the removal of riparian vegetation and the draining of wetlands, changes of flow regimes, dredging of channels, pollution of water from domestic, industrial and agricultural sources, changes in salinity, eutrophication of wetlands and the over-exploitation of the aquatic fauna. In freshwater creeks and rivers the native fauna has declined in abundance, while introduced species have spread throughout the catchment. In estuarine and marine environments, the fauna associated with clear water, low siltation rates, and seagrass beds has declined and species that were formerly abundant are now scarce. The native terrestrial and aquatic fauna in the catchment will continue to decline with urban expansion and better management of human activities within the catchment is urgently required. Further clearing within the catchment is unwise and existing vegetation remnants (including freshwater wetlands) should be protected from development. This is particularly important on the Cumberland Plain and Southern Tablelands where as distinctive fauna is associated with vegetation remnants and the reserve system is inadequate. Similarly provision needs to be made for minimum freshwater flows into the Hawkesbury-Nepean estuary. Nutrient removal from sewage, control of stormwater runoff, and better management of agricultural chemicals, fertilizers and mining within the catchment is necessary to restore water quality. Foreshoes should be revegetated. Most importantly, urban expansion and population growth within the catchment should be restricted.

Longshore sediment transport data: a review

Abstract: Siltation rates anticipated at harbor entrances, in navigation channels and at inlet structures as well as possible adverse effects caused by these and other coastal engineering constructions are often assessed based on considerations of longshore sediment transport rates. The ability to predict the longshore sediment transport rate is consequently of considerable importance in many coastal engineering problems. The engineering need for an ability to predict longshore sediment transport rates is evidenced by the fact that the development of empirical relationships preceeded, by decades, any attempts at rigorous analyses of the mechanics of sediment transport processes in the surf zone. A predictive relationship for longshore sediment transport rates, which enjoys considerable popularity in the United States, is the empirical relationship suggested by the U.S. Army (1973), Coastal Engineering Research Center (CERC) in their Shore Protection Manual (SPM-73).

Temporal Variation of Streamflow, Sediment Load and Their Relationship in the Yellow River Basin, China

Abstract: Variation of streamflow and sediment load in the Yellow River basin has received considerable attention due to its drastic reduction during the past several decades. This paper presents a detailed investigation on the changes of streamflow and sediment load from 1952 to 2011 using monthly observations at four gauging stations along the Yellow River. The results show significant decreasing trends for both streamflow and sediment load at all four gauging stations over the past 60 years. The wavelet transform demonstrated discontinuous periodicities from 1969 to 1973 and after 1986 due to the construction of large reservoirs and implementation of numerous soil and water conservations practices. The sediment rating curves with the power-law function was applied to investigate the relationship between discharge and sediment load. The results indicate distinct variations of the relationship between streamflow and sediment and implied significant hydro-morphological changes within different periods. The reducing sediment supply from the source region and the increased erosive power of the river are detected at Lanzhou station, while the decrease of the transport capacity at Toudaoguai is caused by severe siltation. Significant changes in the relationship between streamflow and sediment load are found at Huayuankou and Gaocun stations, which are largely induced by evident sediment income and trapping effects of large reservoirs. It is estimated that numerous reservoirs have strongly altered the regime and magnitude of streamflow and trapped large amount of sediment, leading to severe siltation and evident reduction of their total volumes. A decrease in precipitation, incoming water from the upper reaches, soil and water conservation measures as well as water consumption contribute most to the significant reduction of streamflow. The decrease of sediment load mainly resulted from various soil and water conservation measures and trapping in reservoirs from 1986 to 2011.