Showing papers on "Siltation published in 1988"

The effects of siltation on recruitment of spiny lobsters, panulirus argus

Abstract: Several surveys in the Florida Keys indicated fewer juvenile spiny lobsters, Panullrus argus, in an area where their primary habitat, stands of benthic algae Laurencia spp., was heavily silted as compared with similar, less silted habitat. We tested several hypotheses explaining this relationship: 1) planktonic postlarvallobster abundances are lower in the silted area, 2) siltation of algae impedes postlarval settlement or subsequent juvenile habitat selection, or 3) siltation increases mortality at the time of metamorphosis. We also compared the time-to-metamorphosis for settling pueruli within silted and nonsilted algae, analyzed the physical character of algal silt in low-silt and h,gh-sllt regions and measured the abundances ofepifauna constituting prey ofjuvenile spiny lobsters. Plank­ tonic postlarval abundances were substantially higher in the high-silt area thus rejecting hypothe­ sis 1. Likewise, results from laboratory experiments testing the effect of algal siltation on postlarval time-to-metamorphosis and early postsettlement survival showed no short-term Increase in mortal­ ity. Limited postlarval settlement and avoidance of silted alga: habitats by juveniles, as determined in substrate choice experiments, probably accounts for the paucity ofyoung spiny lobsters in heavily silted localities. In addition, although juvenile spiny lobsters are nonselective predators, lower prey availability in silted algae probably promotes transciency which, in tum, causes increased mortality by predation while juveniles are exposed. Large-scale siltation exacerbated by human activity must be viewed as potentially deleterious to spiny lobster recruitment.

A two-dimensional model of the movement of fluid mud in a high energy turbid estuary

Abstract: The movement of fluid mud has been cited as the most likely cause of rapid siltation in the majority of the ports in the world located in muddy estuaries. In the past, it has been very difficult to predict or quantify this extra siltation, which may in some cases double the annual and maintenance dredging bill for a new port extension. The new model simulated the interchange of mud between the suspended mud, fluid mud and settled mud phases. The new modelling method was used to set up a pilot model of mud transport in the Severn Estuary.

The Use of Natural Stream Characteristics for Stream Rehabilitation Works Below the Manitoba Escarpment

Abstract: Drainage improvement of watersheds draining from the Manitoba escarpment has been based on channel designs which result in nearly straight canals with uniform gradients and trapezoidal cross-sections. These conditions are often associated with environmental degradation, such as loss of fish spawning and rearing habitat, increased erosion and siltation, and changes in water conveyance patterns that can cause property damage. In mobile bed streams, the geometry of the "natural" stream channel in profile and in cross section is determined by the geology of the basin, the extent of the tributary drainage area, and the position of a stream reach in the hierarchical order of the drainage network. Regional stream channel characteristics can be determined from channel surveys in sample reaches that are selected throughout the basin. Selected aspects of the "natural" stream geometry can then be mimicked in rehabilitation schemes that enhance or create physical stream characteristics in the uniform drainage canals ...

Sediments and bionomic mapping on soft bottoms in the south-western lagoon of new caledonia.

Abstract: The south-western lagoon of New Caledonia covers an area of 5 550 sq.km. composed largely of soft bottoms. As part of the identification of the Soft bottom biotopes of-the New Caledonian lagoons that is being carried out, a study of the distribution of sediments arid communities tias also been undertaken. Sampling has been done with a 2 nautical miles grid, using a dredge for the benthos and a grab for the sediments. Mapping of the muds and a multivariate analysis have made it possible to define the sedimentological structure of these bottoms. A qualitative inventory of the benthic macrofauna communities has been drawn up in respect of the mairi zoological groups. Mud distribution is governed by the morphology of the shore, bathymetry arid hydrodynamics. Sediments are divided according to two gradients, one relating to gpin size, the other to siltation, which reflect a twofold influence, from the land and from the reef. One of the main factors affecting the distribution of benthic communities is the mud content of the sediment, which influences ttie wealth of species arid the composition of the fauna. For herbivorous species however, this relationship is indirect, for their distribution is primarily a ssociated with the presence of vegetative cover, which itself is dependent on the nature and the texture of the sediment. Examples of species distribution concerning the Strombidae and Cerithiidae molluscs are described.

Reservoir Sedimentation: Impact, Extent, and Mitigation

Abstract: Storage reservoirs play an important role in water resources development throughout the world. The one problem with reservoirs that is universal is the continual reduction in usable capacity caused by siltation. This book reviews the world picture of erosion and sediment yield, the large variations that exist, and the physical phenomena related to reservoir siltation. The book is in the Technical Paper series of The World Bank (Technical Paper 71) and is not a formal publication. Rather, it is intended to be circulated to encourage discussion and comment and to communicate results quickly. The book is reproduced from typescript, but this does not detract from the value of the contents as a useful text for hydrologrsts, engineers, and soil conservationists in developing countries.

Effects of Eroding Glacial Silt on the Benthic Insects of Silver Creek, Portage County, Ohio

Abstract: Between March and November 1984, Silver Creek, a small tributary of the Mahoning River in northeastern Ohio, eroded into and through a small lacustrine deposit of glacial silt. During this erosional/ siltation episode, the stream was very turbid and siltation was observed at least 5 km below the source of silt. Only a few individuals of the caddisfly, Neophylax, the mayflies, Isonychia and Stenonema, and the snipe fly, Atherix variegata, were collected within the silted region. Siltation abated during the winter 198485; by late March 1985, substantial recolonization of the previously silted area was observed. The most abundant "pioneer" insects were chironomids, (Larsia, Orthocladius, Microtendipes, and Stictocbironomus), black flies, (Simulidae), craneflies, (Antocha), horseflies, (Tabanidae), and caddisflies, {Hydropsyche and Neophylax). By late May 1985, recolonization of once silted areas was well advanced as indicated by a high degree of similarity in species composition and numbers of taxa between areas that were recently silted and never silted. Recolonization probably occurred mostly from downstream drift because species composition of undamaged upstream areas and of recolonized areas was very similar, and because recolonization occurred over winter when aerial/oviposition routes would have been minimal. OHIO J. SCI. 88 (4): 154-159, 1988

Construction through delicate ecosystems

Abstract: In 1984, the Nova Scotia government proposed to build a section of provincial highway 107 across a salt marsh at chezzetcook. Salt marshes were identified by several agencies as being sensitive to any construction, especially a roadway which would have the potential of even greater effects from deicing chemicals or accidental spills. The department established a series of testing procedures which would be used to judge the effects of the construction. Parameters to be measured included water chemistry, chlorophyll, bacteria, vegetation, benthos, fish, clams, birds, foraminifera and sedimentology. In order to protect the salt marsh, extraordinary construction techniques had to be implemented to reduce siltation at any other injurious site. Special lagoons were constructed to collect any runoff and the entire construction site was protected by silt fences. Department technicians continuously monitored water chemistry, expecially the ph of runoff waters. Detailed monitoring of the suspended solids in all runoff waters was done using a special sampling device, the van dorn sampler. (a)

The Use of Silt-Trap Dams in Xingzi River Basin

Abstract: THIS paper describes a kind of gully reclamation practices in the Xingzi River Basin of Loess Plateau of China, where the rates of soil erosion and sediment yield both are very high. Recently, a number of silt-trap dams have been built and formed a dam system in small catchments to control flood and sediment. The design, construction and use of silt-trap dams were studied to provide a useful reference for a comprehensive basin reclamation project. Two kinds of damming techniques — Chinese sluicing siltation and sluicing siltation by means of a monitor —• are the most effective. Effects of decreased flooding and sedimentation, and increased grain yield as well as a cost on various damming methods were also discussed..

The rehabilitation of an irrigation system along the Yellow River

Abstract: The People's Victory Irrigation System which diverts water from the Yellow River of China covers a total irrigable area of 59 000 ha The system encountered some serious problems in the first decade of its operation — salinity and waterlogging of irrigated land, siltation of irrigation and drainage channels, as well as a low efficiency of water use This paper describes a series of structural and functional measures which have been adopted in the past 24 years for the rehabilitation of the system, including: improvement of the existing drainage system and construction of new drainage system on agricultural land, conjunctive use of surface and groundwater supplies, a comprehensive programme to reduce the levels of siltation as well as the implementation of improved water management practices A model for the optimal operation of the system by using system analysis theory as an aid in reducing the operation and maintenance (O & M) costs has been developed in recent years The results are that the soil salinity has been controlled and the agricultural production has increased whilst the efficiency of water use has improved and the siltation levels reduced Experience gained on this system has been successfully used in developing and managing other irrigation projects along the lower reaches of the Yellow River The proposed procedure of solving the said optimal model has also embodied some benefits from reducing O & M costs in operation

Middle Fork Holston River watershed biological assessment, summers of 1986 and 1987

Abstract: Fish and macroinvertebrates were collected to obtain a qualitative and quantitative determination relating the impacts of land use activities on aquatic fauna and water quality in watersheds of the Middle Fork Holston River. Samples were compared to historical data, used for calculating an Index of Biological Integrity (IBI), and examined for diversity and abundance of macroinvertebrates. Most IBI's determined for subwatersheds of the Middle Fork Holston River (MFHR) supported land use inventories and soil loss estimates previously completed by TVA in 1985. These inventories targeted streams likely to be impacted by siltation, agricultural runoff, and other nonpoint pollution sources. Findings indicated that siltation and enrichment had increased in the mainstream of MFHR since 1969. Several sites exhibited characteristics implying additional forms of pollution which were impacting the fauna. Benthic macroinvertebrate samples were helpful in documenting degradation but did not always support IBI's and land use inventory and soil loss estimates. Macroinvertebrate fauna are typically more resilient and recover faster than fish fauna, offering a partial explanation for this phenomenon. 6 refs., 3 figs., 12 tabs.

Estimation of siltation of the Tereblya-Rika hydroelectric station reservoir

Abstract: An estimation of the suspended-load discharge with the use of the existing data of hydrological yearbooks was not very reliable, since it gave quite underestimated results of the calculation in comparison with the actual volumes of siltation of the reservoir.