An analysis of beach profile changes subsequent to the Colombo Harbor Expansion Project,Sri Lanka

Man-made coastal structures directly affect sediment balance and sediment dynamics on the surrounding beaches. The Colombo Harbor Expansion Project has created about 5-km-long breakwater nearly perpendicular to the beach. The present study is focused on quantitatively and qualitatively analyzing the effect of the Colombo Harbor Expansion Project on economically important beaches in and around Colombo city area. In this study, the authors measured monthly variations of beach width, beach profile and the mean grain-size of the sediments at mean sea level for complete annual monsoon cycle. Data were analyzed to establish site-specific erosion vulnerability. Monitoring results show that cumulative beach erosion has increased after the construction of the breakwater (rate = 0.7 m/year from May 2000 to April 2011 and rate = 28.2 m/year from April 2011 to June 2012). In addition, the cumulative and site-specific sand accretion and erosion patterns have a clear relationship with the monsoon seasonality. Beaches were narrower during the stormy southwestern monsoon, whereas beaches were wider during fair weather of northeast monsoon and inter-monsoon periods. In contrast, the constructed breakwater obstructs natural longshore sediment dynamics. For example, a significant amount of sediments from the Kelani-Ganga River were buried in the Colombo Harbor due to alteration of prominent longshore sediments transportation on the western coast of Sri Lanka. Therefore, this study shows enhancement of coastal erosion in the studied southern beaches due to a lack of sediment deposition.     

Plasma disks around compact objects with self-consistent electromagnetic fields

We present a general formalism for discussing the structure and dynamics of plasma disks, around slowly rotating compact objects, having finite viscosity and conductivity. As a test case we consider the situation for the case when the central object is non-rotating and the plasma is with infinite conductivity and show the existence of equilibrium solution for a self-consistent velocity distribution.     

Major ion chemistry and identification of hydrogeochemical processes controlling groundwater in and around Neyveli Lignite Mines, Tamil Nadu, South India

Groundwater geochemistry was studied in and around the Neyveli lignite mining region of Tamil Nadu, India. Representative groundwater samples (168) were collected from bore wells during June 2004, October 2004, January 2005, and March 2005 to broadly cover seasonal variation. Higher electrical conductivity values were observed in the southeastern and southwestern part of the study area. During the southwest monsoon (June) and postmonsoon (January) seasons, bicarbonate?+?chloride dominated the anions, with few representations for sulphate. Sodium?+?potassium were the dominant cations in all the seasons except in summer (March). The data reveals that the region is a complex hydrogeochemical system with proportional interplay of ions from leaching of ions, ion exchange, agricultural return flow, and stagnant waters. The influence of mine waters and weathering of minerals varies according to the season and spatial distribution of the sources. The water quality can be used for drinking and irrigation, except in a few locations.     

Simulated changes in the atmospheric water balance over South Asia in the eight IPCC AR4 coupled climate models

This paper evaluates the performance of eight state-of-art IPCC-AR4 coupled atmosphere-ocean general circulation models in their representation of regional characteristics of atmospheric water balance over South Asia. The results presented here are the regional climate change scenarios of atmospheric water balance components, precipitation, moisture convergence and evaporation (P, C and E) up to the end of the twenty-second century based on IPCC AR4 modelling experiments conducted for (A1B) future greenhouse gas emission scenario. The AOGCMs, despite their relatively coarse resolution, have shown a reasonable skill in depicting the hydrological cycle over the South Asian region. However, considerable biases do exist with reference to the observed atmospheric water balance and also inter-model differences. The monsoon rainfall and atmospheric water balance changes under A1B scenario are discussed in detail. Spatial patterns of rainfall change projections indicate maximum increase over northwest India in most of the models, but changes in the atmospheric water balance are generally widespread over South Asia. While the scenarios presented in this study are indicative of the expected range of rainfall and water balance changes, it must be noted that the quantitative estimates still have large uncertainties associated with them.     

Tidal effects on groundwater dynamics in shallow coastal aquifers—southeast coast of Tamilnadu,India

Tides play a significant role in the coastal environment; the mangroves, back waters, creeks, and the coastal groundwater interface. Tidal range has been calculated by using TIDECAL software. This study attempts to find the relation between water table condition and tides in the shallow coastal aquifers. The study was conducted by selecting 12 open wells along the coast of the southern part of Cuddalore to the northern part of Nagapattinam district of Tamilnadu. Observations were made in situ for water table fluctuation, dissolved oxygen (DO), and electrical conductivity (EC) for 24 h during full moon (FM) and new moon (NM) of every 2 h. The present study shows the relationship between tidal variations with respect to water table fluctuations and helps to understand the behavior of DO and EC. An interpolation technique, inverse distance weighted (IDW) method was used to obtain the spatial distribution map. The temporal and the spatial relationships between water table fluctuation, EC, and DO were also used in order to understand the coastal ecosystem in the natural environment.     

Monsoon-Driven Geomorphological Changes Along the West Coast of Sri Lanka: A Combined Approach Utilizing ‘CoastSat’ and Google Earth Engine

Ocean Science Journal - Long-term field monitoring of shoreline changes is time-consuming, expensive, and labor-intensive. Instead, satellite images can be used as an alternative method to collect...     

Magnetic field configuration of active region NOAA 6555 at the time of a long-duration flare on 23 March 1991 – An Exception to Standard Flare Reconnection Model

The high-resolution H images observed during the decay phase of a long-duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long-duration flare was observed in the region of low magnetic shear at the photosphere. The H loops activity started soon after the maximum phase of the flare. There were a few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45° to the east-west axis. Gradually, an increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H loops. The height of the H loops were derived by comparing them with the computed field lines. From the temporal evolution of the H loop activity, we derive the negative rate of appearance of H features as a function of height. It is found that the field lines oriented along one of the neutral lines were sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long-duration flare.