Showing papers on "Dredging published in 1970"

Eutrophication Modelling Of A TidallyInfluenced Mangrove Area In Bali Subject ToMajor Dredging And Reclamation Activities

Abstract: A large fashionable tourist resort area is under construction at Benoa Bay, Bali. The location is an island called Turtle Island, which is an enlargement of the existing Serangan Island. Extensive dredging operations of surrounding sea bed are needed for land reclamation, resulting in a general change in current pattern and water exchange for the Benoa Bay and the strait between the coast and Turtle Island. Prediction of the water quality before and after construction was accomplished in order to find the preferable of three layouts from an environmental point of view. The existing Serangan Island is relatively small, with no tourism and inhabited by a small number of local people. The shallow waters around the island are covered by benthic vegetation. A coral reef to the east of Serangan Island forms a border to the ocean. The water quality in terms of benthic vegetation, concentrations of phytoplankton, nutrients, dissolved oxygen and water turbidity was modelled using the MIKE 21 eutrophication model. The water quality was predicted to improve in the strait between the coast and the island due to increased flushing of the dredged channels. On the other hand, the improved flushing resulted in a larger spreading of the nutrients and deterioration of the -water quality north and south of the proposed construction site. Lagoons proposed for leisure crafts also showed a deterioration of the water quality. For a lagoon close to a conservation area of the reef a large decrease in submerged vegetation was predicted. One layout was finally recommended as the optimal combining the various modelling results and results of other related studies.

Measured Environmental Impacts Of Dredging Operations

Abstract: Recent dredging operations in the port of Auckland, New Zealand were preceded by detailed environmental impact assessments. One operation was completed in 1992 for the removal of 270,000m3 of marine mud from the commercial port basins using a trailer suction dredger. Another operation was completed in 1993 for the removal of lO^OOOm^ of marine mud from a small enclosed boat harbour using a clam shell dredger. As part of the approval process, a compliance water quality monitoring programme for turbidity and suspended solids released by the dredger was conducted during both dredging operations. This included intense monitoring during a full tidal cycle and weekly up current and down current monitoring. The results of both compliance monitoring programmes concluded that the environmental impact of the dredging operations was minimal.

Study of durban harbor silting amd beach erosion

Abstract: miles of coastline, including the major area of the port limits and the inner harbor, was constructed to study combined wave, tide and wind action on transport of sand along the coast. The effects of three predominant conditions of swell and wind-waves on the state of the ocean front beaches were studied by observing relative changes in shoreline contours. Fluorescentdyed sand tracers were also used in the model. The accumulation and dredging of sand near the harbor entrance was reproduced in the model and various dredging and storage proposals were carried out to scale on the model. The model study enabled the cause of beach erosion to be attributed to the existence of an offshore shoal produced by the localized dumping of sand dredged from the harbor approaches. This shoal caused selective wave action along the coastline, which was reproduced to scale in the model. It was found that wind and tidal action had a major effect on the redistribution of sand on the beaches as modeled but a minor effect on the permanence of the harbor entrance channel. Apart from the interaction of dredged sand at times being fed to the beaches, the problem of beach erosion could be studied independently of that of harbor silting on the same model. Sand was fed to maintain a state of equilibrium on the southern aooroach beach to the harbor to simulate the littoral sunply. The northern beach downdrift of the harbor entrance, where the erosion problem existed, was found to be essentially starved of littoral supply, due to maintenance of the harbor entrance by dredging and offshore dunroing. The requirements of the model study also gave rise to a program of field data collection on the governing environmental factors, which in itself aided considerably to the diagnosis of the causes of the state of unbalance in the shoreline. The model study led to several proposed remedial schemes, certain of which have been adopted since completion of the model study. The model study was conducted by the South African Council for Scientific and Industrial Research, for the South African Railways and the City Council of Durban.