Showing papers on "Dredging published in 1977"

Patterns of succession in benthic infaunal communities following dredging and dredged material disposal in Monterey Bay

Abstract: : This report deals with the patterns of benthic succession in soft-bottom marine communities. The primary study objective was to elucidate and evaluate the mechanisms that control these patterns. Benthic succession is the pattern of community recovery following a perturbation. Controlled perturbations of bottom communities were effected by the dredging of locations in Moss Landing Harbor and by the disposal of dredged material in Monterey Bay, Calif. The general pattern of succession was highly dependent upon the nature of the physical environment and the structure of surrounding communities. The open coast communities of Monterey Bay are numerically dominated by small crustaceans and polychaetes. Succession was divided into an early and a late phase. The early phase was characterized by the immigration of peracarid crustaceans and the settlement of the larvae of relatively opportunistic species of polychaetes. The latter have relatively short generation times, small size, low fecundity and high larval availability (frequency and abundance of larve in the water). These opportunistic are uncommon in the natural, undisturbed bottom community. The later phase of succession was characterized by the gradual reestablishment of the less mobile crustaceans and less opportunistic polychaetes that inhabited the areas prior to the experimental distrubances. It was concluded that the management of benthic marine resources and dredging operations should involve an analysis of the natural distrubance regime at a potential dredging or disposal site and its relation to the associated bottom communities.

Impact of Fluid Mud Dredged Material on Benthic Communities of the Tidal James River, Virginia

Abstract: : The unconfined open-water disposal resulting from the maintenance dredging of the Jordan Point - Windmill Point channel had an acute impact on the macrobenthic community. The fluid mud produced from the disposal operation probably had both physical and physiological effects on the fauna. Responses varied by species. Insects were the most sensitive and oligochaetes the least affected. Due to the resilience and opportunistic nature of the fauna the detectable impacts lasted less than 3 months. Fluid mud produced from disposal of fine-grained dredged material has properties and effects different than natural sediments. Its low density, instability and low oxygen concentration present severe problems of support, respiration and feeding of benthic organisms. (Author)

Dredging and spoil disposal-major geologic processes in san diego bay, california

Abstract: San Diego Bay is a crescent-shaped, well-mixed estuary 22.5 km long, and initially about 55 km 2 in area, with depths generally less than 4.5 m except for a 7.5-20 m deep channel. The present bay volume is roughly 230 × 10 6 m 3 . Since the early 1900's, dredging and use of spoil disposal as fill have reworked and shifted 100 to 140 × 10 6 m 3 of sediment, with a resulting 27% reduction in the bay's water area and an approximate doubling in depth of 55% of the original water area. Only 17 to 18% of the original area remains undisturbed by dredging or fill. Since the bay reached its approximate present configuration in Holocene time, the only significant sediment source has been river/stream deposition which delivered an estimated 0.8 to 1.1 × 10 6 m 3 annually, until diversion and damming of principal tributaries between 1875 and 1919 reduced sedimentation by more than 80%. For the 30 year period of maximum dredging (1940-1970), the average dredging rate was 3 to 6 times the original sedimentation rate, and roughly 17 to 34 times the sharply reduced present sedimentation rate. Thus, dredging and spoil disposal as geologic processes are substantially more important than all other erosional and depositional processes presently operating in San Diego Bay.

Changes in an urban water resource, an example from Sydney, Australia

Abstract: This paper examines present and future resource utilization in the tidal section of the Georges River in the southern part of Sydney. Over the last 30 years, the physical characteristics of the river have changed as a result of urbanization, changed hydrologic regime and sand dredging. Urbanization has resulted in an increase in population from 190,000 in 1947 to 550,000. This has resulted in an increase in runoff, sediment input to the river and waste disposal. The change in hydrologic regime has resulted in a substantial increase in the magnitude and frequency of flooding which has increased erosion. Sand dredging has increased the channel capacity, enlarged the tidal prism and increased water turbidity. It has also resulted in extensive bank erosion in the upper part of the river and extensive deposition lower down as tailings are deposited. Although most of these changes have resulted in the deterioration of environmental quality, use of the river for recreation and as an urban amenity has increased.

Dredge Disposal Study. San Francisco Bay and Estuary. Main Report.

Abstract: : The report presents the results of a five year, interdisciplinary study of the impacts associated with dredging operations with open water disposal in San Francisco Bay and the ocean and evaluates alternative disposal methods including land disposal and marsh development. (Author)

Investigation of Subaqueous Borrow Pits as Potential Sites for Dredged Material Disposal.

Abstract: : Disposition of dredged material has become a problem of such proportions that all potential solutions must be explored. The present study was conducted to survey existing knowledge of, inventory, describe, and evaluate the potential for using subaqueous pits, holes, or depressions as dredged material disposal sites. The scope was limited to investigating the estuaries, bays, rivers, and continental shelf areas of the Atlantic, Gulf, Pacific, and Great Lakes coasts of the United States. Included were all subaqueous depressions whether caused by dredging or extraction activities or by natural erosional events. The author concludes that the potential for having or creating man-made subaqueous disposal sites will depend upon demand and supply of the products excavated. Demand for construction aggregate in the vicinity of large coastal metropolitan areas and for shell as a source of aggregate or feed supplement. Adequate supplies for beach replenishment and construction aggregate are presently known or can be reasonably hypothesized, with economic constraints being the only hindrance to widespread usage. Conversely, shell supplies are limited, dredging areas are being curtailed, and the resulting pits fill rapidly. Thus, there is little potential, for shell dredging to leave extensive pits.

Zooplankton and dredging: research perspectives from a critical review

Abstract: Studies on the responses of zooplankton to dredging are summarized and discussed. Design criteria for studies intended for impact assessment require careful consideration of sampling due to the highly variable spatial and temporal distributions of zooplankton. It is suggested that ocean dominated systems present different research requirements than those estuarine regions which have endemic zooplankton populations.

Characteristics of dredged bottom sediments

Abstract: Certain physical and bulk chemical characteristics of bottom sediments that are candidates for dredging are summarized for approx. 50 locations throughout the United States. According to empirical criteria that were used for the past several years, most of these sediments would be termed polluted. Based on the results of a bivariate regression analysis among the reported parameters, some plausible correlations were identified between different metals and between metals and certain fractions of organic material. None of the parameters were highly correlated with the mass of submicron particles in a dredged material. However, additional site-specific data are needed to advance broader and more definitive conclusions regarding the water-quality impact that might occur during dredging and disposal operations.

Trash collect and sludge dredge boat

Abstract: PURPOSE:A dredge boat having trash collect apparatus and sludge dredge apparatus separately; dredge efficiency is improved by sludge dredging while trash collecting.