Showing papers on "Siltation published in 1992"
TL;DR: In this article, a sensor for continuous monitoring of sedimentation, or erosion, of marine sediments, has been developed and tested, which uses the difference in the electrical conductivity of seawater and sediments.
Abstract: A sensor for continuous monitoring of sedimentation, or erosion, of marine sediments, has been developed and tested. The method uses the difference in the electrical conductivity of seawater and sediments (up to a factor of 4). The conductivity change grossly distorts the voltage field generated by a current source placed close to the interface. The sensor takes the form of a thin rod carrying ring electrodes along its length. The sensor is driven into the sediment and responds to the position of the sediment/seawater interface along the rod. One of the sensors tested had a resolution of 1·0 cm and full range of 50 cm. Sensors based on this method could be used in a wide range of sediment transport studies, including beach profile measurement.
38 citations
01 Jun 1992
TL;DR: In this article, a review of more than fifty harbor-specific data sets reveals a complex contamination and recovery history and demonstrates remarkable resilience to natural and human-induced contaminant stresses.
Abstract: : Pearl Harbor demonstrates remarkable resilience to natural and human- induced contaminant stresses. A review of more than fifty harbor-specific data sets reveals a complex contamination and recovery history. Siltation is a major contaminant pathway in Pearl Harbor. Dredging operations, which are necessary due to high siltation rates, reduce contaminant loading by periodically removing the upper harbor sediment layers. The response of test organisms during sediment toxicity and bioaccumulation studies showed negligible effects from sediment toxicity. The environmental quality at an offshore dredge disposal site for the harbor is not measurable affected. Urban runoff via storm drains and tributaries is an important nonpoint source of contaminant exposure to the Pearl Harbor ecosystem. Most contaminants experience extensive physical, chemical, and biological, modification after entering the harbor environment. Certain contaminants, including PCBS, petroleum hydrocarbons, and silver, were reported at sufficiently elevated sediment concentrations to warrant environmental concern in some harbor regions and may warrant further evaluation. The overall sediment quality in Pearl Harbor, however, is less degraded than that of many U. S. mainland coastal harbors. Further detailed study of the abundance and distribution of important marine resources in Pearl Harbor is recommended.
15 citations
Journal Article•
TL;DR: The use of cartography and air photographs of several dates establishes a rhythm of verified siltation in the last century, which reflects a loss of lagoon surface area of about 9,600 m 2 /year as discussed by the authors.
Abstract: The Obidos Lagoon, oriented northwest-southeast, developed perpendicular to the shoreline and communicates with the ocean through a narrow and shallow channel that needs constant dredging. This lagoon system was until the 18th century represented on the charts as an estuary which allowed navigation. Historic references indicate that the baymouth bar was formed during the medieval period, creating problems of inlet siltation. The use of cartography and air photographs of several dates establishes a rhythm of verified siltation in the last century, which reflects a loss of lagoon surface area of about 9,600 m 2 /year.
15 citations
TL;DR: The water level of the old hydroelectric Ringedal Reservoir in western Norway was unusually low during 1985, resulting in severe erosion and siltation, which induced major effects in the zooplankton community, with a strong reduction in occurrence of Cladocera.
Abstract: The water level of the old hydroelectric Ringedal Reservoir in western Norway was unusually low during 1985, resulting in severe erosion and siltation. The secchi disc transparency was 18 m in July 1984, decreased to 0.3 m in July 1985, and increased to 13 m in July 1986 after a rise in the water level. The abiotic changes induced major effects in the zooplankton community, with a strong reduction in occurrence of Cladocera (Holopedium gibberum andBosmina longispina). The allopatric population of brown trout,Salmo trutta, which mainly fed on zooplankton before the siltation, fed predominantly on surface insects during the summer of high siltation. The food consumption was lower than in the pre- and post-siltation years, resulting in reduced k-values, reduced number of spawners, and increased mortality of mature fish.
15 citations
01 Jan 1992
TL;DR: In this paper, the bottom sediment contained in estuaries is generally a mud and sand mixture, and it is this mixture which is entrained into the water column during periods of higher flow and redeposited during slack flow conditions.
Abstract: An understanding of sediment transport in estuaries is important to enable greater control of processes such as siltation, dredging, and possible pollution. The bottom sediment contained in estuaries is generally a mud and sand mixture, and it is this mixture which is entrained into the water column during periods of higher flow and redeposited during slack flow conditions. This report covers laboratory tests performed on a wider range of mixed mud and sand beds. It extends previous work to include wave erosion tests and erosion tests on undisturbed samples.
14 citations
01 Jan 1992
TL;DR: In this paper, the authors describe the application of a range of computer models to describe the seasonal variation of seabed bathymetry in the vicinity of Chukpyon Harbour, which is situated on the east coast of Korea.
Abstract: The present paper describes the application of a range of computer models to describe the seasonal variation of seabed bathymetry in the vicinity of Chukpyon Harbour, which is situated on the east coast of Korea. The coastal conditions at the harbour site are dominated by waves and wave-induced currents. Consequently, wave-period-average models were used to predict waves and wave-induced-currents for three wave conditions for two wave directions. A new three-dimensional wave-period-average sediment model was then used to describe particular patterns of seabed change, which were, in turn, combined to predict seasonal changes. Use was made of a variety of field data on waves, currents, and sediment transport rates to set up and calibrate the model. Comparison of model results with field data confirmed the presence of residual sediment movement towards the harbour entrance and the location of shoal zones near the west groyne and east breakwater. The model was subsequently used to study new additions to the existing structures to control nearshore siltation.
5 citations