[Show abstract][Hide abstract] ABSTRACT: Longterm current measurements for a period of 14 months were taken up by National Institute of Oceanography, Goa, India at high current regime in Gulf of Khambhat. The measurement was intended at seabed for obtaining vector averaged current speed and direction on the sea surface and at a fixed five layers. The company supplied frame was not suitable to use at the proposed measurement location, owing to random oscillation in the seabed, strong currents and high concentration of sediments in the water column. The authors have designed a special frame to withstand for above problems and the measurements were carried out successfully for such harsh environment, first time in India. The details of the design and the measurement techniques are described in the paper.
[Show abstract][Hide abstract] ABSTRACT: Measurements of the longshore sediment transport rate (LSTR) along the surf zone at a 4-km-long beach on the central west coast of India were made over a 4-month period. During the study, both the lateral and vertical distributions of the sediment transport rate were measured with traps deployed on a line spanning the surf zone. Sediment transport in the swash zone was not considered in the present study. The longshore current was measured at each trap location. The breaking wave parameters were calculated from a directional wave buoy at 16-m water depth. The measured values were compared with those calculated from three selected empirical formulas. The standard coefficient values in the empirical formulas were used without calibration to the data sets. The measured average gross transport was 726 m3/day and that calculated were 1108, 1017, and 781 m3/day based on CERC, Walton and Bruno, and Van Rijn formula. During the data collection 69% of the time, the transport was direct towards north, and in the remaining period, it was direct towards south. The correlation coefficient between the longshore sediment transport rates measured and those calculated by CERC, Walton and Bruno, and Van Rijn formula were 0.38, 0.71, and 0.74, respectively. The average RMS error between the measured and the calculated longshore sediment transport rate based on CERC, Walton and Bruno, and Van Rijn formula were 0.91, 0.57, and 0.47.
No preview · Article · Apr 2003 · Coastal Engineering
[Show abstract][Hide abstract] ABSTRACT: Numerous theoretical and field studies have been carried out to quantify the volume and direction of littoral sediment transport along the Indian coast. Nevertheless, very little effort has been made to identify the sources for the littoral transport, which feed to the nearshore transport mechanism and on sinks, wherein the continuous movement of the littoral sediment breaks and deposits over a considerable period of time. Rivers are the major source for the littoral drift and the annual discharge of sediments to sea along the Indian coast is about 1.2 × 10<sup>12</sup> kg. The construction of inland dams, irrigation barrages, have considerably reduced the sediment load brought to the sea. Due to the fall in the influx of sediments and concentration of wave energy, many coastal segments experience erosion. In order to identify the extent of the significance of the major sinks for the sediment deposition along the Indian coast, a study was undertaken to evaluate the long-term sediment deposition in Gulf of Kachchh, Gulf of Khambhat, Gulf of Mannar, Palk Bay and Sandheads. The study shows an average yearly deposition of sediments to a thickness of 0.025 m at Gulf of Kachchh, 0.03 m at Gulf of Khambhat, 0.01 m at Gulf of Mannar, 0.006 m at Palk Bay and 0.003 m at Sandheads. The depositional features identified in the present study have been noticed as occurrences of spits, shoals and the progradation of coastline.
[Show abstract][Hide abstract] ABSTRACT: The accurate assessment of longshore sediment transport pattern along Nagapattinam-Poompuhar, Tamil Nadu, India coastline bears significance due to the historical erosion and its geographical location adjoining the sheltered Palk Bay. Directional waves were measured off Nagapattinam coastline for one year to estimate the longshore sediment transport rate. It shows that the transport rate is relatively high about 0.1 x 10 sup(6) m sup(3)/month in November and December and is low showing less than 0.03 x 10 sup(6) m sup(3)/month in March, April and July. Though the annual gross transport is found to be 0.6 x 10 sup(6) m sup(3)/year, the annual net transport is very low showing less than 0.006 x 10 sup(3)/year (towards north), indicating the coastline tends to be a nodal drift regime. The temporary rise in wave activities during the cyclonic days often increases the southerly drift, which partly gets deposited in the Palk Bay and causes deficit for the northerly drift
No preview · Article · Mar 2001 · Journal of Coastal Research
[Show abstract][Hide abstract] ABSTRACT: The objective of the study was to estimate longshore current and sediment transport from measured wave data and from the observations on the littoral environment. A directional wave rider buoy was deployed at 12m water depth, 11 km off Kannirajapuram. Wave data at 3 hourly intervals from March 1997 to Februayr 1998 were recorded. The first wave direction corresponding to the peak of the spectrum and second wave direction corresponding to the secondary peak were estimated since wave spectrum at this location was mainly double peak spectrum. Daily observations on surf zone width and longshore currents were carried out at Kannirajapuram beach during March 1997 to February 1998. The longshore currents and sediment transport were estimated considering first and second breaker angles and resultant was estimated considering the ratio of the first and second spectral energy peaks. Comparison of measured and computed longshore current shows that currents can be reasonably well estimated based on Galvin's equation and sediment transport based on Walton's equation
Full-text · Article · Mar 2000 · Journal of Coastal Research
[Show abstract][Hide abstract] ABSTRACT: This paper describes wave directional spreading in shallow water. Waves were measured for a period of 2 months using the Datawell directional waverider buoy at 15 m water depth on the east coast of India in the Bay of Bengal. The study also showed that in shallow water wave directional spreading was narrowest at peak frequency and widened towards lower and higher frequencies. The wind direction was found to deviate from the wave direction during most of the time. The unidirectional spectrum was found to be satisfactorily represented by Scott spectra.
[Show abstract][Hide abstract] ABSTRACT: Vainguinim Beach is a small and narrow pocket beach located on the rocky coast of Dona Paula Bay, at the estuarine front of the Zuari River in Goa, India. The beach has been widely used for recreation and swimming by a large number of tourists. The beach sediments consist primarily shell fragments and quartz, with heavy mineral composed of ilmenits, magnetite and manganese. The black stain of the fine-grained heavy minerals deposited on the beach face reduces the aesthetics of the beach. This paper summarises the various studies undertaken to identify the sediment processes and the possible measures to improve the usability of the beach
[Show abstract][Hide abstract] ABSTRACT: Goa has a 125-km-long coastline of which two-thirds consists of beautiful sandy beaches. There are mainly 17 beaches having significant importance of tourism. Sporadically, surf drownings have been reported at a few stretches of the beach. Longshore currents were measured at 2-week intervals from November 1993 to October 1994 along these beaches to identify the zones of strong longshore currents and rip currents. Entire beaches were found to be unsafe for swimming during the southwest monsoon season. Parts of stations 5 and 6 in Harmal Beach, 16 at Vagator Beach, 51-54 at Miramar Beach, 75 and 76 at Valsao Beach, 84 at Majorda Beach, and 116 at Palolem Beach are observed to have the risk of permanent rip current zones; and they are unsafe places for swimming all through the year. Parts of Colva, Banaulim, and Agonda beaches, which are suitable for surf swimming, are identified
No preview · Article · Nov 1997 · Journal of Waterway Port Coastal and Ocean Engineering
[Show abstract][Hide abstract] ABSTRACT: Longshore sediment transport characteristics of the Kerala Coast have been examined to delineate various physical processes affecting the different coastal environments. Monthly averages of the daily LEO (Littoral Environmental Observation) data for one year made at each station have been used for this study. Monthly longshore sediment transport rates showed high variability in the sediment transport mechanism.
Preview · Article · Jan 1997 · Indian Journal of Geo-Marine Sciences
[Show abstract][Hide abstract] ABSTRACT: Numerical wave refraction study for the Kerala Coast has been carried out for waves representing southwest monsoon (June-September), northest monsoon (October-February) and fair weather period (February-May). Distribution of wave heights vary significantly from place to place due to wave refraction and shoaling. The covergence and divergence of wave energy induce non-uniform distribution of wave heights during the monsoon period. Ezhimala promontory causes waves to refract considerably along the coastline of Cannanore, Badagara and Mahe during October to February, whereas the headland at Thankasseri induces divergence of wave energy along Quilon and Varkallai. Vypin experiences convergence of wave energy almost throughout the year.
Preview · Article · Jan 1997 · Indian Journal of Geo-Marine Sciences
[Show abstract][Hide abstract] ABSTRACT: Maintenance dredging has been carried out along the navigational channel at Kavaratii Island and dredge spoil is disposed in the open sea. This paper describes the movement of sediment plume while dredging and disposal. The study indicates that for the present disposal location, the sediment plume settles down before reaching 50 m waterdepth, whereas shifting the disposal location to a distance of 1000 m from the reef, would cause the sediments to settle down before 200 m water depth. The study confirms that there is no settlement of dredge spoil in the lagoon bed or on the reef.
[Show abstract][Hide abstract] ABSTRACT: Mean grain size distribution under different environmental conditions along the coast of Kerala showed considerable spatial variation (0.14-0.96 mm). Standard deviation values indicated a very well sorted class along all the beaches with a lowest value of 0.48 phi. Difference in standard deviation values between the stations were significant in all the stations. Samples were nearly symmetrical to negatively skewed with most of the values clustered at -0.01 to -0.10.
Preview · Article · Jan 1996 · Indian Journal of Geo-Marine Sciences
[Show abstract][Hide abstract] ABSTRACT: Estimation of breaker angle in a littoral environmental observation (LEO)program is still based on a visual method and therefore is subjective. Breaker angles thus measured generally vary from person to person. In the absence of a sophisticated wave-direction recording instrument, a simple and practical method has been evolved based on the time lapse between the wave breaking progressively at two points along the crest parallel to the shoreline. This method removes to a greater extent the subjectivity in observation, thereby making it a more reliable practical procedure. The method can be readily adopted for field observation by coastal engineers.
No preview · Article · May 1994 · Journal of Waterway Port Coastal and Ocean Engineering
[Show abstract][Hide abstract] ABSTRACT: Beaches after being subjected to erosional phase during southwest monsoon season, were found to regain their profiles by January or February. The erosion observed at the river mouths can be attributed to the readjustment of the river mouths during monsoon season when the river flow was highest. Longshore currents were stronger in June, and relatively low and steady during the rest of the year. -from Authors
No preview · Article · Jan 1994 · Indian Journal of Geo-Marine Sciences
[Show abstract][Hide abstract] ABSTRACT: Shows seasonal changes without annual net erosion. The beaches are stable and regain the maximum profiles during February to April. Distribution of longshore current direction is not uniform along the study region indicating the presence of variable littoral transport environment. -from Authors
[Show abstract][Hide abstract] ABSTRACT: Estimation of the breaker angle in the littoral environmental observation (LEO) programme is still based on visual methods and therefore is subjective in nature. In the absence of a wave direction recording instrument, a simple device called the wave vane as described here has been developed to measure the breaking wave angle. The changes in the horizontal component of the orbital velocity under a progressive wave govern the operation of the wave vane. The wave vane consists of a pair of fins, one responding to the velocity in the direction of wave propagation below the wave crest, and the other to the velocity in the direction opposite to wave propagation below the wave trough. This results in wave vane orienting itself in the direction of the wave orthogonal. The performance of the wave vane was evaluated using the instrumentally recorded wave directional data as well as the visually observed data. The wave vane was found to give the wave directional information fairly accurate for the open coast where the influence of tidal currents was negligible.
No preview · Article · Jul 1993 · Coastal Engineering
[Show abstract][Hide abstract] ABSTRACT: Ten day records of Aanderaa current meters (24 Dec 1981 to 2 Jan. 1982) at four depths, viz. 30, 45, 60 and 75 m at Bombay High (19˚24.5'N, 71˚2.5'E) off the west coast of India, in a water depth of 80 m have been subjected to spectral, cross-spectral, rotary spectral, harmonic analysis, and low pass filtering in the frequency domain. It was found that at semidiurnal and diurnal frequencies the currents were predominantly barotropic. At all depths the tidal ellipses corresponding to the semidiurnal and diurnal tides were oriented roughly perpendicular to the shelf-break while the mean currents were northwestwards along the shelf-break. During the observation period, the mixed layer (-50 m) remained isothermal while a steady rise in temperature (~2˚C) with time was noticed in the cooler bottom layer.
[Show abstract][Hide abstract] ABSTRACT: The longshore current velocity varied between 0.1 and 0.33 m.sec/1. The longshore current direction was predominantly southward at Ratnagiri, Ambolgarh (Maharashtra, India), whereas it was variable at Vengurla during the study period. Based on the field measurements, the estimated longshore sediment transport rates at Ratnagiri, Ambolgarh and Vengurla were 1.19 x 10 super(5), 1.9 x 10 super(5) and 0.53 x 10 super(5) m super(3) y/1 respectively and the direction was southward. Significance of field measurement is emphasized here, in view of the large variation in the computed longshore sediment transport rates reported in earlier studies