Showing papers on "Dredging published in 1979"

Dredging: A Handbook for Engineers

Abstract: The second edition of this highly successful book, which covers all aspects of modern dredging including operating methods, outputs, costs, contracts and environmental impact, has been fully updated and expanded. New material on site investigation, project implementation, and environmental aspects of dredging bring the book up-to-date. It instructs the reader in the planning and implementation of dredging projects, gives methods of estimating costs and gives a complete technical treatment of dredging. Illustrations and in-depth descriptions make this book accessible and easy-to-use.

Deposit and mobility of cadmium in a marsh-cove ecosystem and the relation to cadmium concentration in biota.

Abstract: The study reported here presents the results of an investigation of a marsh-cove ecosystem heavily contaminated by cadmium. The most contaminated aquatic sediments were dredged in 1972-73, but the resuspension of the sediments and recycle of water from the dredge spoil resulted in reestablishment of a large contaminated sediment bed with concentrations very similar to those observed before dredging. The stability of the sediment concentrations and shallow depth of the cadmium in the sediments indicate that the deposit is relatively stable in agreement with the expectations based on the water chemistry of the system. Uptake does occur in both marsh and aquatic plants and all species of animals tested. Significantly elevated concentrations are observed compared to noncontaminated areas; however, edible portions of most fish do not appear to present a hazard. Crabs appear to present the most likely source of a hazard to humans. This potential hazard is still under investigation. The dredging removed about 5.5 MT of cadmium, about one-fourth of that originally estimated to be present, but twice that amount is found to be in the cove sediments 3 to 4 years after dredging. No appreciable improvement in the ecosystem has been made, and more careful consideration should be given to the need for decontamination and the method of removal of contaminated aquatic sediments in any future case.

A method of dredging and dredging implement

Abstract: When sucking ground material through a lying, elongated suction slot movedver the ground, the water stream for suctioning this ground material is adjusted in dependence upon the types of ground material to be fluidized

The littoral sediment budget between Selsey Bill and Gilkicker Point, and its relevance to coast protection works on Hayling Island

Abstract: Summary The sediment distribution pattern on the beach and near-shore seabed has been established with the aid of a sampling programme and diving inspection. The littoral sediment budget has been established and quantified for the coastal unit, and a method of estimating historical rates of littoral drift from coastal changes has been developed. The effect of sediment reservoirs in regulating the budget, and the effect of dredging has also been considered. Neither groynes nor seawalls have entirely succeeded in preventing erosion on Hayling Island, where the basic problem is a reducing feed of beach material to maintain the littoral drift. Beach replenishment proposals conclude the paper.

Prediction of pollutant release resulting from dredging

Abstract: Dredging of sediment from harbors and waterways is necessary to establish and main tain navigational depths. The dredged sedi ments primarily consist of soil particles and organic matter and are generally considered to be sinks of diverse chemical pollutants. Be cause the sediment has adsorbed pollutional materials on its surface or has incorporated them by exchange reactions within the crystal lattices of its atomic structure, these materials could be rereleased when the sediment is re suspended by dredging. The National Environmental Policy Act of 1969 requires detailed statements of the en vironmental impact of proposed new naviga tion projects and projects requiring mainte nance dredging; the River and Harbor Act of 1970 authorizes a "comprehensive program of research, study, and experimentation relating to dredged spoil." As a result of this legisla tion, the U. S. Army Corps of Engineers and the

Developing management guidelines for oil and gas activities: The louisiana experience

Abstract: Preliminary management guidelines have been derived for oil and gas activities in coastal Louisiana. Derivation of these guidelines was done in terms of the natural function of the coastal ecosystem; this means that all economic activities should be designed to complement natural function as much as possible. The guidelines range in scope from very specific, almost performance standards, to very general admonitions. For example, we have suggested that spoil banks, produced as a result of dredging, should not be higher than the height of the daily tide or roughly 15 cm in coastal Louisiana, and at the other extreme, we have suggested that all dredging should be done with great care during wildlife migrations, spawning, and nesting times.

Savannah Harbor Investigation and Model Study; Volume IV. Reanalysis of Freshwater Control Plan. Numerical Model Study.

Abstract: : An extensive series of physical model investigations was conducted during the late 1950's and early 1960's to develop plans for reducing maintenance dredging costs for Savannah Harbor The plan developed involved dredging a sediment basin at the lower end of Back River, construction of a tide gate in Back River, dredging a connecting canal between Back River and Middle River, and channel improvements in the upstream portion of Back River As the plan was being implemented, questions arose that required a reanalysis of the impact of the plan on salinities in Little Back River Numerical models, flow and salinity, were developed and applied to the channel network above Fort Jackson to estimate salinity levels at the location of the freshwater intake for the wildlife refuge adjacent to Little Back River Computations for preproject conditions and with the plan fully implemented indicted relatively small salinity increases at the location of the intake The computations also indicated that should these small increases prove detrimental, further improvements in the back channels could increase the freshwater inflow to the back channels Appendices A and B of the report discuss the hydrodynamic and salinity models, respectively, used in the investigation (Author)

Semi-submersible dredge

Abstract: Up to the present time open sea sand delivery operations have been carried out by trailing suction hopper dredges and stationary suction dredges under favorable weather and wave conditions. When working in exposed areas under unfavorable conditions, these types of dredges have a low operational efficiency. A new type of dredge has been developed which provides a solution to the problems attendant to stationary dredging operations in open sea and which has a semi-submersible hull. This paper deals with a design developed for a Semi-Submersible Dredge (SSD) destined for operations in southern areas of the North Sea, and in which areas it can operate for 95% of the year. The SSD offers the opportunity to supply sand to coastal areas from the open sea under circumstances in which conventional dredging equipment is unable to operate.

Diagnosis of Chronic Impacts of Estuarine Dredging

Abstract: A method for identifying environmental impacts to estuaiine sediments has been developed and applied to Coos Bay, Oregon. This approach is directed towards early phases of environmental impact assessment and appears to be effective for promoting truly interdisciplinary efforts. Physical, chemical and biological characteristics are sketched on a two-dimensional plot of organic content of the sediment (OCS) versus rate of sediment turnover (RST). These plots are overlay ed to given common characteristics. Movements of stations on the plane are identified as chronic impacts. INTRODUCTION The assessment of chronic environmental impacts in estuaries is difficult and often poorly understood; as such, most assessments have focused on short-term acute alterations. To overcome some of these difficulties, a general assessment approach for dredging-related impacts has been developed. This approach provides a simplified, but practical methodology for impact assessment; it can be used to predict general alterations of the chemical, biological and physical characteristics of the top 20 cm of estuarine sediments. The data summarized herein that illustrate the use of this approach were obtained from an interdisciplinary research study of Coos Bay, Oregon [1]. 2S9 © 1980, Baywood Publishing Co., Inc. doi: 10.2190/3H02-G5E1-GXRA-BLPK http://baywood.com 290 / D.A.BELLA AND K.J. WILLIAMSON A DIAGNOSTIC APPROACH The Need for a Diagnostic Approach Interdisciplinary impact assessment is widely recognized as an essential activity to aid society in coping with its expanding technological capacity to impact ecological systems. However, it appears that truly interdisciplinary efforts often tend to fail in that their actual accomplishments fall far short of their ambitions [2, 3] . Many of these failures seem to result from a lack of identification of a useful conceptual framework during the initial phases of the assessment. This early phase of an assessment study is required before information needs are identified and data collection undertaken. It should proceed concurrently with impact identification. The technical literature provides little information about this early phase of projects because such publications typically present only the end results. In general, the end results of studies tend to be more precise and detailed than the earlier conceptual frameworks that lead to the successful results. The initial phases often involve disagreement, disorder, accidents, conflicts, failures, mistakes and much imprecise or \"fuzzy\" thinking, particularly in the case of interdisciplinary efforts. These early phases are important because they can lead to the identification of important questions, tasks and unifying conceptual frameworks. Too often, however, interdisciplinary impact studies try to establish the order associated with the end product too soon. The imposition of such order at the beginning of the project may result in the project being based on a conceptual framework that is inappropriate for the problem being studied. Diagnosis Applied to Environmental Assessment The term \"diagnosis\" is used herein to imply an early process of information gathering and decision making. Consider a visit to a family doctor. The doctor reviews the records, asks a few questions and proceeds with an examination that typically includes a few simple measurements. The data collected may be unsophisticated; yet based on this brief assessment, the doctor usually arrives at a reasonable decision. In comparison, environmental scientists and engineers often appear to be confused and lost when asked to \"diagnose\" the impacts within an ecological system. It appears that the doctor's initial diagnostic approach involves the collection of a set of information, much of which is general and imprecise ; the assemblage of this information into general patterns that correspond to a diagnostic condition (such as \"flu\"); and speculation as to the nature of the condition and its seriousness, causes, unrecognized symptoms, and possible remedies. Based on this initial diagnosis, the doctor can call for more tests, dismiss the problem as not serious, recommend a remedy, or seek help from a specialist. It appears that impact assessments call for a similar diagnostic approach. CHRONIC IMPACTS OF ESTUARINE DREDGING / 291 Such an approach would provide an important and possibly essential direction to a study so that important questions can be asked, information needs identified, potential problems assessed, possible causes described and possible remedies suggested. Such a diagnostic paradigm will not, however, define precise answers or eliminate the need for detailed disciplinary work. Similar to the doctor's diagnostic paradigm, the environmental diagnosis would deal with a set of information, much of which is imprecise; identify some patterns within this information; and associate such patterns with conditions for which causes, symptoms and remedies can be initially identified. Another important characteristic of such a diagnostic paradigm would be its ability to accommodate a wide range of disciplinary views particularly during the early phases of an environmental impact assessment. The approach presented herein is concerned with the chronic impact of dredging; as such, focus is directed toward the sediments of estuaries. In general, impacts in the water column tend to be more acute than those associated with the sediments. Two sediment characteristics receive particular attention: the organic content of the sediments (OCS) and the rate of sediment turnover (RST). OCS relates to the organic matter present as mg organics/mg sediment. RST relates the frequency of disruption or hydraulic flushing of the sediments; its units are 1/time. This frequency is estimated from the frequency of the disrupting mechanism (e.g., storms, tides, bioturbation, ship traffic, sedimentation). It is not necessary to precisely define or measure these characteristics. Remember, a doctor does not have a flu meter or flu units; rather, the illness, flu, is identified through general patterns of symptoms and behaviors. So it is with OCS and RST. The general approach involves a diagnostic plane with OCS and RST as the axes. A variety of physical, chemical and biological characteristics (symptoms) are described on this plane. Each location or station on the OCS-RST diagnostic plane is characterized by a particular pattern or set of physical, chemical and biological \"symptoms.\" Thus, one can \"diagnose\" the location of an estuarine sediment on the OCS-RST plane by examining such patterns of symptoms. Natural estuarine sediments tend to fall within certain regions of the OCS-RST plane and normal patterns of symptoms or system characteristics can be expected. Dredging and other human activities tend to force an estuarine sediment out of the natural OCS-RST region and, as a result, new patterns of symptoms result. The impact of such dredging is estimated as the shift away from normal patterns to the new or abnormal patterns. The System Patterns Some general patterns of system characteristics as related to OCS and RST are shown in Figure 1 ; these patterns are generalized results of more detailed studies [1]. A variety of different approaches were used to obtain these patterns. As an >I 0. 0 5. 010 .0 1. 05. 0 <1 .0 V ol at ile S ol id s (p e rc e n t) B a. T ur no ve r fr eq ue nc y * O Ï ki 0.