Department of Civil
and Environmental
Engineering
Title:
Coastal Processes and Environmental
Modelling: A Few Case Studies Along The
West Coast of India
Speaker:
Professor P. Vethamony
National Institute of Oceanography, Goa, India
Scientist-G, Professor of AcSIR &
Head of Division, Coastal Processes & Environmental
Modelling
Organizers:
Department of Civil & Environmental Engineering
(CEE)
Tropical Marine Science Institute (TMSI)
Target Audience:
All are welcome. Admission is free.
Date:
Tuesday, 04 October 2011
Time:
3.00 pm - 4.00 pm
Venue:
Seminar Room EA-06-03
Faculty of Engineering, NUS
General Enquiry:
Mr. Yong Tat Fah
Tel: 65162149
Contact Person:
Email: ceeytf@nus.edu.sg
Dr. Madhusoodanan M. Sukumarannair
Tel: 96135730
Email: madhu@nus.edu.sg
Synopsis:
Winds, waves, tides and currents are the driving forces which are primarily responsible for the
processes related to sediment transport, oil spill movement, larval transport, residency period
and transport of pollutants and waste assimilative capacity of coastal waters. In this talk, I
would like to bring out a few salient features / examples from our recent work which explain
how does hydrodynamics play the major role of regulating coastal processes along the west
coast of India. Impact on the coastal region due to expected anthropogenic pressures can be
predicted through environmental modelling, and subsequently controlled by suitable remedial
measures. In this context, we have conducted a few numerical experiments in order to study
the following coastal environmental problems: (i) in an eco-sensitive area such as Gulf of
Kachchh (GoK), west coast of India, where, southern coast of GoK is declared as Marine
National Park and Marine Sanctuary, and a dynamic barrier and topographical eddies are
present, how do we compute diffusion and dispersion characteristics of effluents released in
the GOK, and estimate residency period of the effluents released at different locations in the
Gulf, (ii) in an estuarine coastal region such as Goa, which is identified as a global tourist
destination, how do we generate possible spill trajectories for various oceanographic and
environmental conditions when an accidental oil spill occurs, and estimate the arrival time of
the spill at designated sensitive points and (iii) in a Backwater region such as Kochi, what
would be the assimilative capacity of the water body in terms of Dissolved Oxygen (DO) and
Biochemical Oxygen Demand (BOD) for known quantities of treated wastes which are
released in an offshore location, and how an offshore location can be used an alternate to
Backwater for the discharge.
The Gulf of Kachchh (GoK), a semi-enclosed basin situated on the northwestern coast of
India, is approximately 170 km long and 75 km wide at the mouth. It is a macro-tidal regime,
where high water levels (upto 7.2 m) and high salinities (upto 45 psu) are observed at the
upstream. Though GoK is considered as a well-mixed system, the study reveals that only the
central Gulf is well mixed. Vertical gradients in temperature and salinity fields are noticed in
the eastern Gulf, where a cold and high saline tongue is observed in the subsurface layers. The
model simulated temperature and salinity fields exhibit semidiurnal oscillations similar to that
of field observations. Model results show warm, less saline waters advecting from the east
during ebb, forming a transition zone, which oscillates with tides. A high salinity tongue is
seen in the bottom layer, indicating a westward flowing bottom current. The hydrodynamic
modelling along the Sikka-Mundra section revealed the presence of a dynamic barrier that
divides the Gulf into two distinct dynamic systems. Numerical results show that particles
follow the eddy system present in the Gulf. It is possible that these eddies could effectively
decrease the flushing of the effluents from the inner Gulf, and thus increase the residence time
of the waste material. Measurements, modelling and BOD load assimilation in the GoK
suggest that DO can be used as a target indicator in determining the use of Gulf waters. Fish
larval transport scenarios in the Gulf of Kachchh were simulated to study the retention and
dispersal of fish larvae for a wide range of hydrodynamic conditions. Fish larvae were treated
as neutrally buoyant particles with definite mass and were released from the pre-decided
spawning sites based on a field survey. The larval dispersion was prominent for all the three
seasons at ecologically significant sites, rich in mangroves or reefs.
Mandovi and Zuari are the two major estuarine systems along the Goa coast. The maximum
tidal elevation inside the estuary is of the order of 2.0 m. The flow pattern in the entire estuary
reveals that in general, water flows into the estuary from the north, and when water from
south flows northward, it takes a cyclonic reversal and flows again southwards without
entering the estuary. The results show that DO concentrations within the estuary do not go
below 3 mg/l either due to STP discharge or Baina discharge, but there is an increase in BOD
and marginal variation in DO during ebb flow. This may be the result of retrieval of water
from upstream of the estuary, which carries the non-point source pollutants into the estuary.
The hydrodynamic results indicate that the pollutant transport is towards south along the
coast, and therefore, it rarely alters the water characteristics of the estuary. In general, fair
weather with weak winds prevails along the west coast of India in March, and therefore, the
oil spill that occurred in March 2005 would have moved slowly. However, in this event,
stronger winds forced the spill to move away from the coast as well as the estuary. The spill
features and the observed trajectory are in good agreement with the model simulations. As the
economy of Goa depends on tourism to a large extent, it is very essential to have pre-validated
trajectories of spill scenarios for effective implementation of containment.
The Kochi backwaters, along the west coast of India are connected to the Arabian Sea through
a narrow opening at Kochi. At present, an amount of ≈ 0.5×106 m3/d industrial effluents
along with urban sewage released directly into the estuary form a major source of pollution in
the region. Excessive organic waste has already polluted the backwaters, resulting in
ecological degradation and fish mortality. As an alternate step to mitigate the situation, an
offshore outfall is suggested following model simulation based on measurements of
hydrodynamics and water quality data collected over a period of 7 years. The assimilative
capacity of waters off Kochi is estimated as 8.8 m3/s of discharge with a BOD of 50mg/l. The
model results indicate that offshore waters could be used as an alternative to the Kochi
backwaters for waste disposal without polluting the coastal sea off Kochi.
Profile of Professor P. Vethamony
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Received PhD from IIT Bombay in Hydraulics after Masters in Oceanography;
working at the National Institute of Oceanography, Goa, India since 1980; at present
as Scientist‐G, Professor of AcSIR and Head of the Division dealing with Coastal
Processes and Environmental Modelling.
Guiding 7 students for PhD work (3 awarded) and several students for project
dissertations. Given invited talks at several Academic institutes, Research
organizations, Universities, Engg. colleges, Industrial establishments, Govt. agencies
and International conferences.
Member of several national and international committees; Reviewed papers for 15
international journals and several conferences; visited 20 countries on various
scientific assignments; established collaborations with 4 international organizations
including NUS.
Carried out 10 long‐term R&D projects and more than 100 consultancy projects for
Govt. and industries; Published 47 papers in peer‐reviewed journals and books, 46 in
conference proceedings/abstracts; prepared 106 scientific and consultancy reports.
Visitors may park their cars at the Cash-Card operated Car park 2A opposite Engineering
Block E3A.
EA-06-03