Concept of a mathematical model for prediction of major design parameters of a submersible dredger/miner
Sritama Sarkar¹, Neil Bose, Mridul Sarkar² and Dan Walker³
¹Memorial University of Newfoundland, Department of Ocean and Naval Architectural Engineering, Faculty of Engineering, St. John's, Newfoundland, Canada A1B 3X5
²Excavation & Equipment Manufacturing (P) Ltd., Calcutta, India
³Oceanic Consulting Corporation, St. John's, Newfoundland, Canada
The use of surface floating dredgers in deep inland reservoirs, shelf areas and tidal inlets is limited by several operational restrictions and mobilization problems. Deployment of small, modular, autonomous to semi-autonomous submersible dredgers/ miners with parallel operations in these areas is expected to reduce the operational and mobilization constraints. Most of the existing submersible dredgers/ miners use tracks for locomotion on submerged ground. Legged locomotion is however favored in these natural unstructured terrains. A small, modular, walking submersible dredger/ miner is designed and a prototype is constructed. Prediction of the major design parameters of such a system requires a mathematical model integrating the processes of excavation, transportation of the excavated material and locomotion processes of the vehicle while moving on submerged ground. This paper describes the designed vehicle and the overall concept of the mathematical model for the vehicle.
Back
Design of sampling program for water quality management – case study of Ennore estuary
Rajat Roy Chaudhury¹, Prince Prakash Jebakumar¹, B.K. Jena¹, Vijaya Ravichandran¹, Asokan S. Sundarrajan²
¹Coastal & Environmental Engg. Div., National Institute of Ocean Technology, Chennai 600 036
²Tamilnadu Pollution Control Board, Chennai
A Waste Load Allocation (WLA) study was conducted for wastewater discharges from the North Chennai region along the coast. The receiving water bodies are tidal backwaters, the Ennore creek and coastal water bodies between Chennai Port and Ennore Port. Objectiveof the field-sampling program was (i) to monitor point sources and receiving waters simultaneously and (ii) to calibrate a water quality model for the WLA. The dynamic nature of the receiving waters and wastewater discharges required sampling over a 48-hour period at a frequency of six hours. Higher frequency of sampling was constrained by resources and logistics.
The sampling program design was initially based on the considerations specified in the Total Maximum Daily Load (USEPA) approach and reviewed initial measurements and reconnaissance surveys. Surveys were carried out during three seasons (pre monsoon, post monsoon and fair weather). This paper highlights the design considerations based on past data, water quality issues, water quality standards, modeling requirements, logistics and resources. The results of the sampling program indicate that the goals of the sampling program were met, given the ability to identify key phenomena and water quality kinetics.
Back
Scoping - an effective tool for enhancement of EIA study
Vijaya Ravichandran and Rajat Roy Chaudhury
Coastal & Environmental Engg. Div., National Institute of Ocean Technology, Chennai-600 036
Scoping is a priority setting activity in the EIA process. It identifies environmental issues that are likely to be adversely affected by the proposed project activities and focuses the assessment on the most important (significant) issues. Given the knowledge of baseline environment and type of development, environmental parameters having impacts that are considered minor, may be sampled at lower spatial or temporal resolutions. The objective of scoping is to conduct an EIA study efficiently and effectively. This is done by judiciously allocating time and resources to baseline assessment and prediction of impacts thereby focusing the study on critical issues of concern. Scoping involves identification of (i) critical impacts for detailed study, (ii) parameters for primary data collection and (iii) issues requiring prediction.
End result of the scoping exercise may be development of Terms of Reference (TOR) for the EIA study, viz., environmental parameters requiring baseline assessment, extent of prediction of impacts, type of environmental management plans / mitigation measures required etc. If a consultant does scooping at the proposal stage, it provides a competitive advantage over other offers. Advantages of scoping are that:
- It enables integrated project planning.
- It helps to identify key issues and environmental concerns in the early project planning stage.
- It reduces time and cost-overruns from structured planning of the EIA study.
- It helps in confining the baseline study and prediction of impacts to an essential set of significant environmental parameters thereby allowing judicious allocation of time and re sources for assessing relevant environmental issues in detail.
- It reduces the likelihood of a deficient EIA.
Back
Dredging strategies for the sustenance of navigation channels in large tidal range regions: Kandla Port – a case study
U.V. Purandare, T. Nagendra, N. Ramesh and S.H. Kulkarni
Central Water and Power Research Station, PO Khdakwasla Research Station, Pune, India 411024
The development of navigation channels for ports located in large tidal range regions, generally, involves continuous maintenance dredging in the channel, often on a daily basis. The navigation channel in the approaches to Kandla Port, located in the Gulf of Kutch, on the west coast of India, is one such example, where the maintenance of the channel is carried out continuously. Unlike the ports of Mormugao and Mangalore the dredging at Kandla is required to be done on a daily basis and the total annual dredging is of the order of 4 Million m 3 . The tidal currents at Kandla are very strong due to the large tidal range of up to 7 m and therefore the flux of sediments in suspension is also very high. This results in large amount of siltation in the approach channel, due to reduction in the transport capacity in dredged channel. Problems of deterioration of channel depths arise, during disruption of maintenance dredging, due to the requirement of dry-docking of the dredger for routine maintenance. Under such circumstances, the decision about the optimum period that can be allowed for the disruption of dredging becomes very vital for sustaining navigable depths in the channel. The siltation aspects in the Sogal channel at Kandla, during various periods of break in the dredging activity, were examined based on the hydrographic surveys of the channel and the hydrodynamic model simulations using a mathematical model to decide the maximum permissible period for the disruption of dredging.
Back
Disposal of contaminated dredged sediments using Geotubes and Geocontainers
Yee Tack Weng¹ and Pradip Dutta²
¹Ten Cate Nicolon Asia, Petaling Jaya, Malaysia
²Z-Tech (India) Pvt. Ltd., Kolkatta, India
Contaminated dredged sediments emerged as an environmental issue in the 1980s. Recent development of containment and dewatering technology using geotubes and geocontainers widened the options for handling and disposal of contaminated dredged sediments. Geocontainers are used to confine sediments during dumping in open water. Geotubes are used as containment dykes to construct confined disposal facility in nearshore areas adjacent to dredging works. Geotubes are also used to contain and dewater contaminated dredged sediments to reduce quantity of material to be transported to landfill. Further economy is achieved when dewatered sediments can be left within geotubes at site, subject to eventual capping.
Back
Some recent field radiotracing studies on bedload transport in Indian Coast
Noble Jacob, U. Saravana Kumar, U.P. Kulkarni, A.S. Pendharkar, G.N. Mendhekar and S.V. Navada
Isotope Applications Division, Bhabha Atomic Research Centre, Trombay, Mumbai
This paper briefly describes some of the recent radiotracing studies carried out to understand the bedload transport characteristics under different hydrodynamic and hydro-meteorological conditions near inshore channel in Kandla port, New Kandla and near Sagar Island in the Hugli estuary, Kolkata, India. In all the studies, radioactive 46 Sc glass powder was injected on the seabed and subsequent movement was monitored using g scintillation detectors. Radiotracer study at Kandla port indicates that the tidal asymmetry, with dominating flood tides, along with the coastal geometry of the area is responsible for the bedload transport towards the landward side. The radiotracer studies conducted in Hugli estuary in a fair weather season, southwest monsoon and summer season reveal that the river discharges play a dominant role in the sediment transport dynamics of the estuary. Also, storm induced turbulence is responsible for the sediment transport during monsoon season. Thus, the studies portrait the appropriateness and usefulness of radiotracing techniques in understanding the various mechanisms responsible for sediment transport in coastal environments.
Back |
