Indian Journal of Geo-Marine Sciences Vol. 43 (7), July 2014, pp. 1272-1280 Field measurements and numerical modeling of nearshore processes at an open coast port on the east coast of India P. Mishra1*, U. K. Pradhan1, U. S. Panda1, S. K. Patra2, M. V. RamanaMurthy2, B. Seth3 & P. K. Mohanty3 1ICMAM - Project Directorate, NIOT Campus, Pallikaranai, Chennai-600 100, India 2National Institute of Ocean Technology, Velachery-Tambaram Road, Pallikaranai, Chennai-600 100, India 3Department of Marine Sciences, Berhampur University, Berhampur 760 007 *[E-mail: [email protected]] Received 19 August 2013; revised 30 October 2013 Port development and associated constructions such as groins, jetties, breakwaters along the shore front alter the coastal environment considerably. Gopalpur (19°18′13″ N : 84°57′ 52″ E), a seasonal port along east coast of India is under phases of development to an all weather open coast port and has a significant impact on the coast. Field data collected on beach morphology, waves, tides and currents at seasonal and annual basis for two years are analyzed. Numerical modeling of hydrodynamic, wave, sediment transport and shoreline evolution using DHI-Mike models are carried out. Present study describes the field data, the hydrodynamics, wave induced sediment transport and the nearshore circulation pattern suggesting an appropriate management plan. [Keywords: Coastal processes, Modeling, Hydrodynamics, LITPACK, SLM Plan, Gopalpur] Introduction development for converting it to a major open-coast Interactions among the coastal process parameters port. The construction activity along the shorefront (waves, tides, currents, etc), longshore sediment and has changed the shoreline significantly in the last two shoreline are very complicated and embrace abroad decades10,13,14. In the year, 2008, the Ministry of Earth spectrum of nearshore dynamics1-3. Port development Sciences, Government of India conceived a program and associated marine structures such as groins, to assess the impact of the port on the coastline. Field seawall, breakwaters, jetties interfere with littoral drift measurements on waves, tides, currents and beach and affect the coastline tremendously4-7; a plethora of geomorphology at spatio-temporal scales are papers has been written on shoreline process and made13,15. Numerical modeling of hydrodynamic, influence of marine structures purporting to stabilize wave and sediment transport using Mike 21 modules the shoreline have been distinctly unsuccessful in are carried out. The shoreline was simulated and coming to grips with the situation8. Examples along predicted using one dimensional LITPACK model. Indian coasts indicate that hard engineering solutions This paper describes the field data, the such as concrete protection measures designed to hydrodynamics, wave induced sediment transport and trap the sediment for building a protective beach, the circulation pattern suggesting an appropriate preventing erosion of beaches or sedimentation management plan. of inlet invariably fails and initiates various Materials and Methods irreversible situations by altering the coastal geomorphology e.g., accumulation of sediment, Study Area progression of coast on up-drift side whereas erosion Gopalpur Port (19°18'14"N and 84°57'52"E) 9-13 and recession of the shoreline on down-drift side . is located along the south Odisha, east coast of In such cases, field data and numerical modeling of India (Fig. 1). The coast is primarily depositional the nearshore environment is essential to understand in nature backed by parallel ridges of sand dunes the spatio-temporal variations for resolving coastal 1 (~ 10-12 m height), rich in rare earth minerals. zone problems . The coastline is oriented 48° E to true north. The Gopalpur, a seasonal minor port along the east wind and wave climate follow seasonal patterns coast of India is undergoing phases of infrastructural prevail in Bay of Bengal viz., southwest (SW) MISHRA et al.: FIELD MEASUREMENTS AND NUMERICAL MODELING 1273 monsoon (June to September), northeast (NE) RCM 9 current meter at ~18 m depth and installation monsoon (October to December) and non monsoon or of tide gauge in the port for one year (June 2008- fair weather period (January to May). The climate is May 2009). Seasonal measurements of water levels semi-arid with an average rainfall of 1210 mm. and current extending over 3 weeks representing post Monsoon depressions formed over the Bay of Bengal monsoon (December' 08-January' 09), southwest during May to September contribute significantly to monsoon (May' 09) and northeast monsoon (November' the annual rainfal16; however, cyclonic storms during 09) were carried out at 8 and 18 m depths at Gopalpur northeast monsoon months often cross the coast and beach (GPL-8, GPL-18), Gopalpur Port (PORT-8, trigger temporary coastal erosion10. PORT-18), and Rushikulya (RUS-8, RUS-18) (Fig. Huge amount of littoral drift i.e., 1106 m3/yr 1). Monthly shoreline (berm position) mapping and moves along this coast17. Based on LEO data, a beach profiles are measured during May 2008 to northerly drift of 0.96106 m3/yr and 0.26106 m3/yr March 2011 for 30 kilometers of the coastline using of southerly is reported17; another study10, whereas, ArcPad DGPS and SR 1200 real-time kinematic 10estimated 1.1106 m3/yr and 0.51106 m3/yr GPS with position accuracy of ± 1 cm and ± elevation respectively. accuracy of 2 cm (Leica Geosystems, Switzerland). The port is under major renovation since 2007, the Bathymetry measurements were made using single port was constructed initially in 1987 by excavating beam ecosounder (ODAM Hydrotrac, USA) interfacing the backshore and connecting it through a 250 m wide DGPS to HYPACK 4.0 software. C-map and the channel. Two shore perpendicular groins of 530 m observed bathymetry was combined and interpolated long on south side and a 370 m north on both sides of for preparation of the final bathymetry map. The the channel are constructed during 2007 to 2010 to standard protocols are followed for setting up the instruments, measurements and data retrieval and maintain 250 m wide entrance channel from siltation. 13,15 A southern breakwater (2.6 km long) is under analysis . The absolutedata sets were utilized for construction since 2012 onwards at 2.3 km south of model set up, validation and analysis. south-groin as a part the proposed harbor. A series of Result and Discussion 10 groins are being constructed on the north of north- groin in an attempt to arrest the eroding north coast. Waves The Gopalpur tourist beach is located 6 km south and For a better clarity, the wave data were presented a major Olive ridley turtle rookery is formed north of under two broad seasons i.e., SW (May-September) Rushikulya estuary, 16 km north of the port (Fig. 1). and NE (October-April) monsoons.The Gopalpur Data coast is exposed to waves approaching predominantly Extensive field campaigns were carried out from from SSE, SE and S directions. Nearly 84% of waves May 2008 to March 2011 includes deployment of a reach the coast between 135-180° (southeast-south), Datawell directional wave rider buoy at ~22 m, a 14% waves from 180-225° (south-southwest) and the rest 2% are from 90-135° (east-southeast). Annually, the significant wave height (Hs) ranged from 0.26 to 3.29 m with an average of 1.06 m. During the SW monsoon, Hs ranged from 0.4 to 3.29 m with an average of 1.29 m; the NE monsoon values are from 0.26 to 2.18 m with a mean value of 0.71 m. The percentage distribution of significant wave height shows that nearly 37% of waves have heights of 0.5-1.0 m, 30% of waves have heights of 1.0 to 1.5 m and only 3% of waves exceed 2.0 m height. Seasonal distribution of wave indicates that during SW monsoon, 80% of waves are between 1.2 - 2.0 m and about 10% of waves are between 2.0 -3.0 m (Fig. 2a). During NE monsoon 92% of the waves are between 0.5 -1.0 m; whereas December, January and Fig. 1. Map of the Study area showing data collection points. February months, nearly 94% of waves are between 1274 INDIAN J MAR SCI , VOL . 43 , NO. 7, JULY 2014 0.2-0.8m. Hs exceeding 2m was observed mostly and minimum water level variations of 1.32m during July and August consistent with high wind and and -1.08m were recorded on 2nd August, 2008 and cyclonic conditions in the Bay of Bengal. The 12th February 2009 respectively with respect to mean maximum wave height (Hmax) of 5.22m and 5.37m sea level (MSL). However, the maximum and was recorded during SW monsoon months (29th July minimum astronomical tidal component of 1.1 m and 11th August 2008). Hmax exceeded 4m during and - 0.99 m was observed on 15th October, 2008 September, November 2008 and May 2009 and 4th June 2008 respectively. in consistent with cyclonic storms events i.e., The main lunar semi-diurnal (M2) is most dominant No2 during 16-18 September 2008, KhaiMuk on constituents (53%) followed by the solar semi-diurnal 14 -16 November 2008 and Aila on 24-26 May 2009 constituent (S2) being the second dominant (26%). in Bay of Bengal. Tidal form number (F) was calculated to be 0.246 Peak wave period (Tp) ranged from 2.2 to (< 0.25) describing that the tide for the coast are semi- 28.5 seconds with an average of 11.2 seconds. Peak diurnal (Table 2). period with more than 12 seconds occurs nearly 42%; Tidal range is mostly within 2m for Gopalpur 21% is shared by 10-12 seconds and about 37% is less coast and classified as micro-tidal or lowermeso-tidal 21, 22 than 10 seconds.