Vertical sediment distribution

So far, various calculation models for the vertical distribution of suspended sediment concentration have been produced by several investigators from different theories. The limitations of all these models imply that it is possible to find a more reasonable model, for which each previous model can be included as special case. The formulation of a reasonable general model is the purpose of this paper.

Stratification by solid particle suspensions

Turbulence was generated by an oscillating grid above a bed of sediment of spherical glass beads. As expected, part of the sediment was lifted up by the grid action and a suspension layer of depth D formed above the grid. This depth was found remaining independent of grid action but varying with the sediment layer depth when the grid action was kept constant. Volume concentration measurements show the existence of only weak concentration gradients over the layer depth with a rapid fall off in concentration at the outer edge. The theoretical analysis based on a concentration flux model is in good qualitative agreement with observations.

Coastal engineering investigation at Jupiter Inlet, Florida

A fixed-bed hydraulic model of Jupiter Inlet, Florida, was constructed for the purpose of testing measures designed to remedy problems of sediment erosion and deposition in the inlet area. Both tide-induced flows as well as waves were simulated in the model which was built on an undistorted scale of 1:49. Model verification was based on prototype measurements of waves, tides and currents. Results have been interpreted in terms of the influence of various proposed remedial schemes on flow velocity magnitude, distribution and wave height at various locations within the study area. A stability parameter has been utilized for evaluating the degree of sediment erosion or deposition at a given location. Various structural solutions were examined in the model. It is proposed that, in the initial phase of solution implementation, sediment removal/nourishment methods be used primarily to mitigate the existing problems. New structures, as per model test results, should be installed under subsequent phases, only if sediment management procedures do not prove to be adequate. The currently followed procedure of periodic sand trap dredging may be extended to include the new dredging/nourishment requirements. (PDF contains 245 pages.)

Sediment budget: principals and applications

The framework of sediment budget concepts provides a formalized procedure to account for the various components of sediment flux and the changes of volume that occur within a given region. Sediment budget methodology can be useful in a number of coastal engineering and research applications, including: inferring the amount of onshore sediment transport for a nearshore system that contains an "excess of sediment", determining sediment deficits to downdrift beaches as a result of engineering works at navigational entrances, evaluating the performance of a beach nourishment project, inferring the distribution of longshore sediment transport across the surf zone, etc. This chapter reviews briefly the governing equations for sediment budget calculations, considers various measurement and other bases for determining the sediment flux components necessary to apply the sediment budget concept and finally for illustration purposes, applies the sediment budget concept to several examples. (PDF contains 52 pages.)

Use of Sediment Bioassays to Verify Efficacy of Caulerpa taxifolia Eradication Treatments

Infestations of the marine macrophytic alga Caulerpa taxifolia were discovered in Agua Hedionda Lagoon, California in 2000. Rapid response actions included containment under pvc tarps coupled with injection of liquid sodium hypochlorite. To assess the efficacy of these treatments, replicated sediment cores were removed from representative treated sites and transferred to grow-out facilities. Similar cores from uninfested (control) sediments were removed, inoculated with viable explants of C. taxifolia and placed in grow-out facilities. Results from two sampling periods (1 year, 2 years post-treatment) showed that no viable C. taxifolia emerged in cores, and that inoculated “control” sediments supported normal growth. Eelgrass ( Zostera marina L.) seedlings emerged from native seed-banks in “treated” cores, which also supported growth of some invertebrates (annelid worms and hydroids). This study provided essential verification of C. taxifolia eradication efforts, and demonstrates the feasibility of incorporating quality control/quality assurance components in rapid response actions. Results of this study also suggest that seeds of eelgrass are viable for at least two years. (PDF has 9 pages.)

Influence of Sediment Nutrients on Growth of Emergent Hygrophila

Hygrophila ( Hygrophila polysperma (Roxb.) T. Anderson) is a plants which forms serious aquatic weed problems. Both submerged and emergent growth forms occur. Nutritional studies with a controlled release fertilizer and sediments collected from hygrophila-infested areas were conducted with the emergent growth habit to provide insights into growth of this introduced plant. Plant dry weights for experimental 16- week culture periods with low average temperatures were associated with low amounts of hygrophila biomass as compared to culture periods with high average temperatures. Hygrophila cultured in sand rooting media with the controlled release fertilizer produced as much as 20 times more dry weight than plants cultured in sediments only. First-degree linear regression statistics showed hygrophila dry weights were highly related to ammonia nitrogen, magnesium, sodium, and pH values in the sediments. These findings show the close relationship of the emergent growth habit of hygrophila to sediment nutrients. Analyses for certain sediment characteristics may provide an indication of the potential growth that may be expected for weed infestations of this plant. Hygrophila grows year round in south Florida; however, visual observations of canals and other bodies of water indicate that lower amounts of hygrophila plants occur during the cooler months of year than during the summer season. These findings show the seasonal growth of emergent hygrophila occurs with biomass dependent on both sediment nutrients and temperature.