G. Udhaba Dora

Variations in Tidal Constituents along the Nearshore Waters of Karnataka, West Coast of India

Abstract The characteristics of tidal constituents along the nearshore waters of Karnataka, west coast of India, are described. These are based on the sea level data measured at three locations by the Valeport wave and tide gauge during the presummer monsoon period. The objective of the study is to identify the tidal and nontidal variations along the coast. Analysis shows that astronomical tides are responsible for most of the observed sea level variability along the Karnataka coast. Ninety-seven percent of the variation in measured sea level at Honnavar and Malpe and 96% of the sea level variation at Kundapur was due to tide. The observed nontidal sea levels were related to local wind forcing. The study shows that when the wind from the south was strong, a rise in sea level was observed, and when the wind from the north was strong, a fall in sea level was observed. Correlation between the alongshore component of wind and nontidal sea level was 0.54 at Malpe and 0.48 at Honnavar. The nontidal sea level variation was found to vary according to the significant wave height. High residuals of sea level were found during high waves. Amplification of shallow-water constituents were relatively high compared with other constituents from south to north along the study area.

Textural characteristics of foreshore sediments along Karnataka shoreline, west coast of India

Grain character analysis of beach sediments along three selected beaches (Pavinkurve, Kundapura and Padukare) of Karnataka coast, west coast of India is carried out in the present study. The objective was to identify the textural behavior of beach sediments during an annual cycle from March 2008 to February 2009. Grain characteristics such as central tendency, sorting, kurtosis and skewness were estimated using GRADISTAT and discussed. The maximum (62%) sediment samples were medium sand with unimodal and bimodal characters at all the three beaches. The median values varied in between -0.04? and 2.74? with an average value of 1.61?. The beaches were characterized as well sorted, moderately well sorted and moderately sorted sediment environments. Sediments were identified as fine skewed to coarse skewed with platykurtic, mesokurtic and leptokurtic characters. Grain characteristics varied spatially and temporally along with beach orientation, foreshore slope and wave action. A negative correlation between mean and sorting is identified for maximum number samples along the study region but not very significant. The study shows that the sedimentary environment at Kundapura were influenced by relatively high wave action compared to Padukare and Pavinkurve beach and the beaches were under erosion or non-deposition with strong winnowing process.

Near shore waves, long-shore currents and sediment transport along micro-tidal beaches, central west coast of India

Abstract Coastlines are undergoing constant geomorphologic changes with respect to the incident wave climate. Based on waves measured at 9 m water depth, simulation of near shore wave transformation is done using REFDIF-1 numerical model and the near shore breaker parameters are estimated at two micro-tidal beaches along central west coast of India. Model results are validated with measured values. From the breaker parameters, long-shore current and long-shore sediment transport rates (LSTR) are computed by using semi-empirical equations. Estimated long-shore current and LSTR are showing dramatic variations with respect to seasons. Predominant direction of LSTR is observed towards north since the approach waves are from south-west direction during pre-monsoon and post monsoon. During monsoon season, waves are from west south-west and resulted in southerly transport. The estimated annual net and gross LSTR by Cambridge Environmental Research Consultants (CERC) at two locations are in the same order whereas LSTR estimated by Walton & Bruno and Kamphuis equations are showing different estimations because of difference in surf-zone width and foreshore slope between the two locations. For micro-tidal beaches with length less than 6 km, Kamphuis equation is giving agreeable estimation of LSTR. Sensitivity analysis of LSTR estimate shows that coastal inclination is the prominent factor in determining LSTR than incident wave angle.

Nearshore Currents along the Karnataka Coast, West Coast of India

Measured current data at 7 locations and tide data at 3 locations during the pre-summer monsoon period along the west coast of India is used in the study. The surface currents during March showed a predominant northward trend and during April it was towards south. Estimated tidal currents were upto 25 cm s−1 with an average value of 8 cm s−1. Current tidal form number varied from 0.56 to 1 at different locations indicating currents are mixed. M2 and S2 tidal current constituents rotated clock wise at all location. Near surface, the alongshore current was 2.6 to 5.9% of the alongshore wind and near bottom it was 1.9 to 3.6% of the alongshore wind.

Hindcast of breaking waves and its impact at an island sheltered coast, Karwar

Variability in the characteristics of depth-induced wave breakers along a non-uniform coastal topography and its impact on the morpho-sedimentary processes is examined at the island sheltered wave-dominated micro-tidal coast, Karwar, west coast of India. Waves are simulated using the coupled wind wave model, SWAN nested in WAVEWATCH III, forced by the reanalysis winds from different sources (NCEP/NCAR, ECMWF, and NCEP/CFSR). Impact of the wave breakers is evaluated through mean longshore current and sediment transport for various wave energy conditions across different coastal morphology. Study revealed that the NCEP/CFSR wind is comparatively reasonable in simulation of nearshore waves using the SWAN model nested by 2D wave spectra generated from WAVEWATCH III. The Galvin formula for estimating mean longshore current using the crest wave period and the Kamphuis approximation for longshore sediment transport is observed realistically at the sheltered coastal environment while the coast interacts with spilling and plunging breakers.