Journal of Coastal Research, Special Issue 39, 2004 Journal of Coastal Research SI 39 pg - pg ICS 2004 (Proccedings) Brazil ISSN 0749-0208 HYDRODYNAMIC MODELLING OF A MARINE HABITAT OF WEST COAST OF INDIA, FOR ECOSYSTEM MANAGEMENT R. S. Kankara†, B. R. Subramanian†, V. Sampath† and S. Ramachandran‡ † ICMAM-Project Directorate, Dept. of Ocean Development, NIOT campus, Pallikaranai, Chennai -601302, INDIA email kankara@icmam.tn.nic.in brs@niot.res.in sampath@niot.res.in ‡ Institute for Ocean Management, Koodal Building, Anna University Chennai -600 025, INDIA Email ; chandran@annauniv.edu ABSTRACT KANKARA, R.S.; SUBRAMANIAN, B.R.; SAMPATH, V; and RAMACHANDRAN, S 2003, Hydrodynamic Modelling of a Marine Habitat for Ecosystem Management. Journal of Coastal Research, SI 39 (Proceedings of the 8th International Coastal Symposium), pg – pg. Itajaí, SC – Brazil, ISSN 0749-0208 Management of coastal and marine areas by maintaining the balance between the developmental activities and protection of marine environment is a challenging task for coastal managers and requires a complete understanding of the technical aspects of the system. An ecologically rich marine habitat, Gulf of Kachchh (Gulf), has a vide variety of uses activities such as extensive salt farming along the coast, brine release from salt farms, maintenance dredging by ports and disposal of dredged material, release of hot water from thermal power plants, navigation, etc influence the mixing pattern in Gulf. A two-dimensional hydrodynamic model MIKE-21 with rectangular grid resolution of 450 m * 450 m, was applied to understand the circulation pattern in Gulf of Kachchh. The model was calibrated with tide and current at predetermined locations. The model predictions show good agreement with the measured data of tide and current pattern. Harmonic analysis of major tidal constituents for measured data and model computed output was carried out. The amplitudes and phases of tidal constituents at 4 locations were compared to create a database of tidal constituents at strategic locations in Gulf for a predictive model. Analysis of residual currents obtained from 30-day simulations revealed the formation of several eddies in outer Gulf. Presence of these eddies and the magnitudes of residual currents indicate the mixing capacity of central and outer Gulf. The results strengthen and extend the understanding of the circulation and mixing pattern to manage the habitat. ADDITIONAL INDEX WORDS: Tide, Harmonic, Calibration, Circulation, residual, mixing OVERVIEW OF GULF OF KACHCHH HABITAT Gulf of Kachchh (Gulf), a large macro-tidal water-body located in West Coast of India, occupies an area of 7350 km 2 and has a width of 70 km at the entrance near Okha and a length of 145 km from Okha to Navlakhi an east-west alignment. The depths, which are about 55 m at the entrance of Gulf, reduce to less than 10 m in inner Gulf, consists irregular bottom topography, several shoals and islands (Figure-1). The Gulf abounds in marine wealth with 37 ecologically rich island, coral reef patches, mangroves, about 1500 km 2 mudflats, sandy & rocky beaches. The southern coast of Gulf from Okha to Jodia covering 458 sq. km has been declared as Marine sanctuary and 163 sq. km as Marine National Park. The high range of tidal fluctuations submerges the tidal flat area comprising a network of creeks, which is about 20% of its total area. The hinterland of the Gulf is producing about 52,43,200 tonnes (as on 1997) of salt from 540 sq. km salt works area spread around the Gulf, which is 28 % of the nation's supply. In an estimate, 9.4 million m 3 (Kilolitres) bittern of 300 ppt salinity is being released every year. The high salinity (>40 ppt) has been reported in inner parts of Gulf than at outer and central Gulf, where it is about 37 ppt. The available salinity data suggest that the Gulf water is vertically well mixed. The average rainfall in the region is ~50 cm/year and evaporation rate is estimated to be ~1.5